Platelet-activating factor mediates angiotensin II-induced proteinuria in isolated perfused rat kidney

Isolated kidney preparations (IPK) from male Sprague Dawley rats perfused at constant pressure were used to evaluate the effect of angiotensin II (AII) and platelet-activating factor (PAF) on renal function and urinary protein excretion. Compared with basal, intrarenal infusion of AII at 8 ng/min caused a progressive increase in protein excretion (11 +/- 6 versus 73 +/- 21 micrograms/min) in parallel with a decline in renal perfusate flow (RPF) (29 +/- 3 versus 18 +/- 3 ml/min). Addition to the perfusate of PAF at 50 nM final concentration also induced proteinuria (9 +/- 4 versus 55 +/- 14 micrograms/min) but did not change RPF (29 +/- 3 versus 30 +/- 3 ml/min). Preexposure of isolated kidneys to the PAF receptor antagonist WEB 2086 prevented the increase in urinary protein excretion induced by AII infusion (basal: 13 +/- 6; post-AII: 12 +/- 7 micrograms/min) but failed to prevent the vasoactive effect of AII (RPF, basal: 30 +/- 2; post-AII: 21 +/- 3 ml/min). In additional experiments, dexamethasone reduced the proteinuric effect of PAF remarkably. These results indicate that in isolated kidney preparation: (1) AII infusion induced proteinuria and decreased RPF; and (2) the effect of AII in enhancing urinary protein excretion was completely prevented by a specific PAF receptor antagonist, which, however, did not influence the AII-induced fall in RPF. It is suggested that PAF plays a major role in AII-induced changes in the permselective function of the glomerular capillary barrier.     

Effects of prostaglandins and nitric oxide on the renal effects of angiotensin II in the anaesthetized rat

1. The potential influences of nitric oxide (NO) and prostaglandins on the renal effects of angiotensin II (Ang II) have been investigated in the captopril-treated anaesthetized rat by examining the effect of indomethacin or the NO synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), on the renal responses obtained during infusion of Ang II directly into the renal circulation. 2. Intrarenal artery (i.r.a.) infusion of Ang II (1-30 ng kg(-1) min(-1)) elicited a dose-dependent decrease in renal vascular conductance (RVC; -38+/-3% at 30 ng kg(-1) min(-1); P < 0.01) and increase in filtration fraction (FF; +49+/-8%; P < 0.05) in the absence of any change in carotid mean arterial blood pressure (MBP). Urine output (Uv), absolute (UNaV) and fractional sodium excretion (FENa), and glomerular filtration rate (GFR) were unchanged during infusion of Ang II 1-30 ng kg(-1) min(-1) (+6+/-17%, +11+/-17%, +22+/-23%, and -5+/-9%, respectively, at 30 ng kg(-1) min(-1)). At higher doses, Ang II (100 and 300 ng kg(-1) min(-1)) induced further decreases in RVC, but with associated increases in MBP, Uv and UNaV. 3. Pretreatment with indomethacin (10 mg kg(-1) i.v.) had no significant effect on basal renal function, or on the Ang II-induced reduction in RVC (-25+/-7% vs -38+/-3% at Ang II 30 ng kg(-1) min(-1)). In the presence of indomethacin, Ang II tended to cause a dose-dependent decrease in GFR (-38+/-10% at 30 ng kg(-1) min(-1)); however, this effect was not statistically significant (P=0.078) when evaluated over the dose range of 1-30 ng kg(-1) min(-1), and was not accompanied by any significant changes in Uv, UNaV or FENa (-21+/-12%, -18+/-16% and +36+/-38%, respectively). 4. Pretreatment with L-NAME (10 microg kg(-1) min(-1) i.v.) tended to reduce basal RVC (control -11.8+/-1.4, +L-NAME -7.9+/-1.8 ml min(-1) mmHg(-1) x 10(-2)), and significantly increased basal FF (control +15.9+/-0.8, +L-NAME +31.0+/-3.7%). In the presence of L-NAME, renal vasoconstrictor responses to Ang II were not significantly modified (-38+/-3% vs -35+/-13% at 30 ng kg(-1) min(-1)), but Ang II now induced dose-dependent decreases in GFR, Uv and UNaV (-51+/-11%, -41+/-14% and -31+/-17%, respectively, at an infusion rate of Ang II, 30 ng kg(-1) min(-1)). When evaluated over the range of 1-30 ng kg(-1) min(-1), the effect of Ang II on GFR and Uv were statistically significant (P < 0.05), but on UNaV did not quite achieve statistical significance (P=0.066). However, there was no associated change in FENa observed, suggesting a non-tubular site of interaction between Ang II and NO. 5. In contrast to its effects after pretreatment with L-NAME alone, Ang II (1-30 ng kg(-1) min(-1)) failed to reduce renal vascular conductance in rats pretreated with the combination of L-NAME and the selective angiotensin AT1 receptor antagonist, GR117289 (1 mg kg(-1) i.v.). This suggests that the renal vascular effects of Ang II are mediated through AT1 receptors. Over the same dose range, Ang II also failed to significantly reduce GFR or Uv. 6. In conclusion, the renal haemodynamic effects of Ang II in the rat kidney appear to be modulated by cyclooxygenase-derived prostaglandins and NO. The precise site(s) of such an interaction cannot be determined from the present data, but the data suggest complex interactions at the level of the glomerulus.     

Fc gamma RII on human B cells can mediate enhanced antigen presentation

As several reinjection procedures have shown encouraging results in terms of imaging, we investigated whether the kinetics of thallium-201 would differ between the standard stress-redistribution-reinjection approach and the stress-immediate reinjection approach. In 53 consecutive patients with undiagnosed chest pain, 75 MBq (2 mCi) 201Tl was injected at maximal exercise. In 26 of these patients (group I), 37 MBq (1 mCi) 201Tl was reinjected immediately after completing the exercise images (the immediate reinjection procedure) and in 27 patients (group II), 37 MBq (1 mCi) 201Tl was reinjected after completing 3-h redistribution images (the standard reinjection procedure). Mean peak 201Tl blood activity after exercise was 17.7+/-12.5 kBq/ml (4.8+/-3.4 mCi/ml) for group I versus 16.4+/-9.2 kBq/ml (4.4+/-2.5 mCi/ml) for group II (NS). The relative increase in 201Tl blood activity after reinjection of half the initial dose [37 MBq (1 mCi)] exceeded 50% of the initial peak in both groups. The relative amount of 201Tl delivered to the myocardium was assessed by the area under the curve after both exercise and reinjection, and was 117%+/-72% for group I and 112%+/-73% for group II (NS). Blood clearance of 201Tl was at least biexponential. Mean early decay constants (lambda 1) after exercise and reinjection were 0.30+/-0.18 min-1 and 0.22+/-0.046 min-1 respectively for group I (T 1/2 2.3 min and 3.2 min respectively, NS), and 0.30+/-0.12 min-1 and 0.24+/-0.07 min-1 respectively for group II (T1/2 2.3 min and 2.9 min respectively, NS). For both procedures no significant differences were found between lambda 1 after exercise and lambda 1 after injection. The mean late clearance (lambda 2) from the blood was 0.032+/-0.056 min-1 and 0.012+/-0.012 min-1 respectively for group I (T1/2 21.6 min and 57.7 min respectively, NS), and 0.036+/-0.030 min-1 and 0.014+/-0.014 min-1 respectively for group II (T1/2 19.3 min and 49.5 min respectively, NS). Also, no significant differences were found between lambda 2 after exercise for both groups and between lambda 2 after reinjection for both groups. We conclude that reinjection of 37 MBq (1 mCi) 201Tl (half the initial dose) results in a relative increase in the initial peak and a relative increase in the amount of 201Tl delivered to the myocardium of more than 50% for both the standard and the immediate reinjection procedure. The clearance of 201Tl from the blood was not influenced by exercise or by the time of reinjection. Based on 201Tl kinetics as measured in the peripheral blood, there is no reason to postpone reinjection until 3-4 h following exercise.     

Effect of renal perfusion pressure on excretion of calcium, magnesium, and phosphate in the rat

Abnormalities in renal handling of calcium, magnesium, or phosphate have been implicated in the development and/or maintenance of human hypertension. We have shown recently that renal excretion of these ions is correlated to blood pressure in Dahl salt-sensitive as well as salt-resistant rats. The present study was designed to determine whether renal perfusion pressure per se could affect excretion of these ions. Urinary excretion of calcium, magnesium, and phosphate was studied in anaesthetized Sprague-Dawley rats under basal conditions and during an intravenous infusion of angiotensin II (ANG II), vasopressin (AVP) or phenylephrine (PE). A cuff, placed around the aorta between the two renal arteries, allowed maintenance of normal perfusion pressure in the left kidney, while that in the right kidney was allowed to rise. Infusion of pressor agents raised mean arterial blood pressure to comparable levels (means +/- SE): ANG II (n = 7), before = 102 +/- 4, during = 133 +/- 3 mmHg, AVP (n = 8), before = 110 +/- 7, during = 136 +/- 5 mmHg, PE (n = 6), before = 111 +/- 6, during = 141 +/- 6 mmHg. Although there was no difference in excretion of calcium, magnesium and phosphate between the two kidneys under basal conditions, infusion of ANG II or PE induced hypercalciuria, hypermagnesiuria and hyperphosphaturia in the right kidney which was exposed to the increased arterial pressure. Such effects did not appear in the pressure-controlled left kidney. Infusion of AVP was associated with reduced excretion of calcium and magnesium, and increased excretion of phosphate, in the normotensive kidney. The response to the similarly increased renal perfusion pressure in this group was also reduced for calcium and magnesium, and enhanced for phosphate. The results indicate (1) renal excretion of calcium, magnesium and phosphate is renal perfusion pressure-dependent; the higher the renal perfusion pressure, the greater the excretion of these ions. (2) Independently of perfusion pressure, AVP can inhibit phosphate reabsorption and stimulate divalent cation reabsorption.     

Acute glucosuria after continuous glucocorticoid loading in the rat in vivo

We investigated the effects of the continuous infusion of various steroids in rats on renal tubular reabsorption of glucose in vivo to elucidate the pathogenesis of steroid-induced glucosuria. Urinary glucose excretion increased 60 min after administration of dexamethasone (2.38 mM). By 120 min, urinary excretion of glucose was three times higher in the dexamethasone group than in the control group (24.1 +/- 4.6 versus 72.4 +/- 16.7 micromol); the plasma level of glucose did not increase. Dexamethasone had no effect on the resorption of 1,5-anhydro-D-glucitol, which is a glucose-resembling polyol that is actively absorbed by the renal tubules as glucose. Neither estradiol nor progesterone increased urinary excretion of glucose. These findings suggest that continuous administration of a high-dose glucocorticoid selectively influences the glucose reabsorption system in the kidney.     

The renal handling of parathyroid hormone. Role of peritubular uptake and glomerular filtration

The mechanisms of uptake of parathyroid hormone (PTH) by the kidney was studied in anesthetized dogs before and after ureteral ligation. During constant infusion of bovine PTH (b-PTH 1-84), the renal arteriovenous (A-V) difference for immunoreactive PTH (i-PTH) was 22+/-2%. After ureteral ligation and no change in renal plasma flow, A-V i-PTH fell to 15+/-1% (P < 0.01), indicating continued and significant uptake of i-PTH at peritubular sites and a lesser role of glomerular filtration (GF) in the renal uptake of i-PTH. Since, under normal conditions, minimal i-PTH appears in the final urine, the contribution of GF and subsequent tubular reabsorption was further examined in isolated perfused dog kidneys before and after inhibition of tubular reabsorption by potassium cyanide. Urinary i-PTH per 100 ml GF rose from 8+/-4 ng/min (control) to 170+/-45 ng/min after potassium cyanide. Thus, i-PTH is normally filtered and reabsorbed by the tubular cells. The physiological role of these two mechanisms of renal PTH uptake was examined by giving single injections of b-PTH 1-84 or synthetic b-PTH 1-34 in the presence of established ureteral ligation. After injection of b-PTH 1-84, renal A-V i-PTH was 20% only while biologically active intact PTH was present (15-20 min). No peritubular uptake of carboxyl terminal PTH fragments was demonstrable. In contrast, after injection of synthetic b-PTH 1-34, renal extraction of N-terminal i-PTH after ureteral ligation (which was 13.4+/-0.6% vs. 19.6+/-0.9% in controls) continued for as long as i-PTH persisted in the circulation. These studies indicate that both GF and peritubular uptake are important mechanisms for renal PTH uptake. Renal uptake of carboxyl terminal fragments of PTH is dependent exclusively upon GF and tubular reabsorption, whereas peritubular uptake can only be demonstrated for biologically active b-PTH 1-84 and synthetic b-PTH 1-34.     

Maintenance of baseline angiotensin II potentiates insulin hypertension in rats

Chronic insulin infusion in rats increases mean arterial pressure (MAP) by a mechanism dependent on angiotensin II (Ang II). However, the fact that plasma renin activity (PRA) decreases with insulin infusion suggests that Ang II sensitivity is increased and that the parallel reduction in Ang II may partly counteract any hypertensive action of insulin. This study tested that hypothesis by clamping Ang II at baseline levels during chronic insulin infusion. Sprague-Dawley rats were instrumented with artery and vein catheters, and MAP was measured 24 hours per day. In seven angiotensin clamped rats (AC rats), renin-angiotensin II system activity was clamped at normal levels throughout the study by continuous intravenous infusion of the angiotensin-converting enzyme inhibitor benazepril at 5 mg/kg per day (which decreased MAP by 18+/-2 mm Hg) together with intravenous Ang II at 5 ng/kg per minute. Control MAP in AC rats after clamping averaged 99+/-1 mm Hg, which was not different from the 101+/-2 mm Hg measured before clamping Ang II levels. Control MAP in the 8 vehicle-infused rats averaged 105+/-2 mm Hg. A 7-day infusion of insulin (1.5 mU/kg per minute IV) plus glucose (20 mg/kg per minute IV) increased MAP in both groups of rats; however, the increase in MAP was significantly greater in AC rats (12+/-1 versus 5+/-1 mm Hg). This enhanced hypertensive response to insulin in AC rats was associated with a greater increase in renal vascular resistance (153+/-10% versus 119+/-6% of control) and a significant increase in renal formation of thromboxane (149+/-11% of control). Thus, decreased Ang II during insulin infusion limits the renal vasoconstrictor and hypertensive actions of insulin, and this may be caused, at least in part, by attenuation of renal thromboxane production.     

Insulin and amino acid infusion after cardiac operations: effects on systemic and renal perfusion

OBJECTIVE: The purpose of this study was to answer two questions: (1) Does a mixed amino acid infusion enhance systemic and renal perfusion in the early postoperative period after heart operations? (2) Does the addition of insulin (glucose-insulin-potassium solution) provide additional effects to those of an amino acid infusion? METHODS: Thirty-three male patients undergoing coronary artery bypass grafting (mean age 65.9 +/- 1.2 years) were included in a prospective, controlled, randomized study. Eleven patients (AA group) received infusion of mixed amino acids (11.4 gm), 11 patients (AA + GIK group) received infusion of mixed amino acids (11.4 gm) and insulin solution (225 IU insulin, glucose with glucose clamp technique, and potassium), and 11 patients served as control subjects. RESULTS: Amino acid infusion alone had no effect on systemic vascular resistance or cardiac index but increased renal blood flow 51% +/- 11% (from 114 +/- 13 to 172 +/- 24 ml.min-1.m-2 in one kidney, p < 0.05 vs the control group). Insulin solution in addition to amino acid infusion reduced systemic vascular resistance 24% +/- 3% (from 1280 +/- 85 to 960 +/- 57 dyn.sec.cm-5, p < 0.05 vs the control and AA groups) and increased cardiac index 13% +/- 3% (from 2.3 +/- 0.2 to 2.6 +/- 0.2 L.min-1.m-2, p < 0.05 vs the control and AA groups). Insulin had no significant additive effect on renal blood flow. CONCLUSIONS: Our data imply that (1) infusion of mixed amino acids enhances renal blood flow after cardiac operations but has no effect on systemic perfusion and (2) the addition of insulin solution improves systemic perfusion. The combined treatment may potentially reduce the risk of renal hypoperfusion injury in the postoperative period after coronary artery bypass grafting.     

Reduction of renal uptake of monoclonal antibody fragments by amino acid infusion

The renal uptake of radiolabeled antibody fragments and peptides presents a problem in radioimmunodetection and therapy, compromising lesion sensitivity, especially with intracellularly-retained isotopes. Previously, we showed that cationic amino acids and their derivatives are capable of significantly reducing kidney uptake in animals. We report our initial clinical results of successful renal uptake reduction in five patients who underwent cancer radioimmunodetection with 99mTc-anti-CEA Fab' fragments. METHODS: The patients were infused with two liters of a commercially-available nutritive amino acid solution (containing approximately 2.25 g/liter lysine-glutamate and 2.50 g/liter arginine), whereas 75 control patients received the same volume of saline (quantification of organ and tumor kinetics from conjugate whole-body views by ROI technique). RESULTS: The renal uptake in the amino acid group was significantly lower (p<0.05) than in the control group (11.1 +/- 2.0% injected dose versus 17.7 +/- 7.0% injected dose at 24 hr postinjection), whereas the uptake of all other organs remained unaffected. Gel filtration chromatography of the urine taken from amino-acid-treated patients showed that a significantly higher amount of excreted activity was bound to intact Fab' (53% of excreted activity) in contrast to only less than 10% in the control group. CONCLUSION: The renal uptake of monoclonal antibody fragments in patients can be reduced significantly by amino acid infusion, even at considerably lower doses than those that were safe and effective in animals. As was found in animals, the mechanism seems to rely on an inhibition of the re-absorption of tubularly-filtered proteins by the proximal tubule cells. These results encourage further clinical trials to lower the renal uptake experienced in radioimmunodetection, as well as in therapeutic trials with antibody fragments and peptides.     

Prolonged systemic and regional haemodynamic effects of intracerebroventricular angiotensin II in conscious sheep

1. The haemodynamic mechanisms by which infusion of angiotensin II (AngII), either into the lateral cerebral ventricles (i.c.v.) or intravenously (i.v.), increased arterial pressure were studied in conscious sheep. 2. Sheep were previously fitted with flow probes for measurement of cardiac output and coronary, mesenteric, renal and iliac blood flows. 3. Intracerebroventricular AngII (10 nmol/h for 1 h) increased arterial pressure by 11 +/- 4 mmHg (P < 0.001) due to vasoconstriction, predominantly in the mesentric vasculature. These effects developed over 30 min and took 2 h to return to control. Following the infusion renal conductance increased continuously for 3 h, resulting in a parallel increase in renal blood flow (to 75 +/- 18 mL/min above control, P < 0.001). 4. Intracerebroventricular AngII increased plasma vasopressin from 0.8 +/- 0.3 to 7.2 +/- 1.8 pg/mL (P, 0.01), and reduced plasma renin concentration from 0.9 +/- 0.3 to < 0.4 nmol/L/h. 5. The pressor effect of i.v. AngII (5, 10, 25, 50 nmol/h) also depended on peripheral vasoconstriction, but the pattern of responses was different. The greatest degree of vasoconstriction occurred in the renal, followed by the mesentric and iliac vascular beds; these effects were rapid in onset and offset. 6. In conclusion, the pressor responses to both i.c.v. and i.v. angiotensin depended on peripheral vasoconstriction, but there were contrasting regional haemodynamic changes. ICV AngII caused a prolonged pressor response, mainly due to mesentric vasoconstriction possibly partly due to vasopressin release, and following the infusion there was a pronounced, long-lasting renal vasodilatation. In contrast, i.v. AngII caused vasoconstriction preferentially in the renal vascular bed and its effects were short lasting.     

3D time-resolved contrast-enhanced MR DSA: advantages and tradeoffs

To test whether renal V1-receptors selectively influence blood flow in the renal medulla, we compared the effects of infusion of [Phe2,Ile3,Orn8]vasopressin (3-30 ng/kg/min) by the intravenous, renal arterial, and renal medullary interstitial routes in anesthetized rabbits. Intravenous [Phe2,Ile3,Orn8]vasopressin (30 ng/kg/min) reduced renal medullary perfusion (MBF) by 36 +/- 5% but did not significantly affect cortical perfusion (CBF). MBF was also reduced with the renal arterial (35 +/- 5%) and renal medullary interstitial (40 +/- 7%) routes but, in contrast to the intravenous infusion, CBF was also reduced, by 21 +/- 3% and 15 +/- 3%, respectively. Urine flow and sodium excretion were increased by [Phe2,Ile3,Orn8]vasopressin, and with direct intrarenal administration, this effect was similar for both the infused (left) and noninfused (right) kidneys. After a 20-min renal medullary interstitial infusion of [3H]norepinephrine, radiolabel concentration was approximately fivefold greater in the left medulla than in the left cortex. We conclude that [Phe2,Ile3,Orn8]vasopressin acts on V1-receptors to alter regional kidney blood flow and tubular salt and water handling. The V1-receptors involved are almost certainly within the kidney itself, but given the contrasting effects of the different infusion routes on MBF and CBF, we cannot exclude the possibility that some of the observed effects of [Phe2,Ile3,Orn8]vasopressin are mediated by activation of extra-renal V1-receptors.     

Radioisotopic evaluation of renal function in cyclosporine-treated pediatric and adult renal transplant recipients and their living donors. A study of 152 donor-recipient pairs

Renal function was studied in 2 groups of renal transplant recipients and their donors by technetium-99m diethylenetriamine pentaacetic acid and a gamma camera. The pediatric group (group A) comprised 40 children and their adult kidney donors. The adult group (group B) consisted of 112 consecutive adult renal transplant recipients and their adult donors. All patients received kidneys from living donors and were given the same immunosuppression protocol (PRED plus CSA). Donor glomerular filtration rate (GFR) was determined before nephrectomy and at a mean period of 30 (range 10-50) months after nephrectomy. The graft GFR was measured at 1, 3, 6, and 12 months and at the most recent follow-up visit. Moreover, the functional reserve of the graft was assessed by infusion of dopamine and an amino acid. The postnephrectomy GFR of donors in groups A and B were 74 +/- 18 and 72 +/- 20 ml/min/1.73 m2, respectively. The GFR of pediatric recipients was significantly lower than that of adult recipients at corresponding time points along the course of follow-up. The mean values of graft GFR were 47.6 +/- 20 and 63.8 +/- 29.6 ml/min/1.73 m2 for pediatric and adult recipients, respectively (P < 0.001). Moreover, the graft functional reserve was significantly lower in pediatric recipients. These data demonstrate that adult kidneys transplanted into pediatric recipients have lower GFR than those transplanted into adults, despite corrections for body surface area. Although the reason for this phenomenon is unknown, the observation may have important implications for management of pediatric recipients.     

Normalization of total body and regional sympathetic hyperactivity in heart failure after heart transplantation

BACKGROUND: Sympathetic nerve activity is increased in patients with severe heart failure. Whether this intense sympathoexcitation is normalized after heart transplantation, despite cyclosporine A treatment, is still unsettled. In the present study, regional sympathetic function in 12 patients with severe heart failure, awaiting heart transplantation, was compared with that in 15 heart transplant recipients and 12 healthy subjects. METHODS: Total and regional sympathetic activity in the heart and kidney were evaluated with isotope dilution, using steady-state infusion of [3H] norepinephrine. Sympathetic nerve traffic to skeletal muscle vascular bed was recorded intraneurally with microneurography. RESULTS: Total body, cardiac, and renal norepinephrine spillovers were high in the heart failure group (6792 +/- 455, 385 +/- 74, and 1554 +/- 114 pmol/min, respectively) as was muscle sympathetic nerve activity (82 +/- 5 bursts/min). Transplant recipients showed a marked reduction of total body (3200 +/- 307 pmol/min) and renal (747 +/- 169 pmol/min) norepinephrine spillovers and sympathetic nerve firing to skeletal muscle (22 +/- 6 bursts/min), none of which differed from healthy subjects. CONCLUSIONS: The augmentation of total body and regional sympathetic outflow to the kidney and skeletal muscle vascular beds, associated with a failing heart, was normalized after transplantation. Thus, sympathoexcitation in heart failure is reversible. Furthermore, because all heart transplant recipients received cyclosporine A, the findings do not support the concept that cyclosporine-induced hypertension is mediated by increased sympathetic nerve activity.     

Reversal of advanced digitoxin toxicity and modification of pharmacokinetics by specific antibodies and Fab fragments

The effects of Fab fragments of high-affinity specific antibodies have been studied in a canine experimental model of lethal digitoxin toxicity. Selected antiserum from sheep immunized and boosted with a digoxin-serum albumin conjugate contained antibodies that cross-reacted with digitoxin with an average intrinsic association constant of 1.4 x 10(10) M(-1) as determined by equilibrium dialysis. Rapid second-order association kinetics (k(f) = 3.7 x 10(6) M(-1) per s) and slow dissociation kinetics (k(r) = 1.9 x 10(-4) per s) were documented for the antibody-digitoxin complex. Eight dogs given 0.5 mg/kg digitoxin intravenously developed ventricular tachycardia after 23+/-4 (SEM) min. Control nonspecific Fab fragments were then given. All animals died an average of 101+/-36 min after digitoxin administration. Another eight dogs given the same digitoxin dose similarly developed ventricular tachycardia after 28+/-3 min. This group then received a molar equivalent dose of specific Fab fragments intravenously over 3 min, followed by a 30-min infusion of one-third of the initial dose. All dogs survived. Conducted sinus beats reappeared 18+/-4 min after initial Fab infusion, and stable normal sinus rhythm was present at 54+/-16 min. Plasma total digitoxin concentrations increased threefold during the hour after initial Fab infusion, while plasma free digitoxin concentration decreased to less than 0.1 ng/ml. Effects on digitoxin pharmacokinetics of these Fab fragments and the antibody population from which they were derived were further investigated in a primate species. Unlike common laboratory animals previously studied, the rhesus monkey was found to have a prolonged elimination half-life, estimated at 135 and 118 h by radioimmunoassay and [(3)H]digitoxin measurements, respectively, similar to man and thus providing a clinically relevant experimental model. Intravenous administration of 2 mol of specific Fab fragments per mole of digitoxin 6 h after 0.2 mg of digitoxin produced a rapid 4.3-fold increase in plasma total digitoxin concentration followed by a rapid fall (t((1/2)) 4 h) accompanied by a 14-fold enhancement of urinary digitoxin excretion over control values during the 6-h period after Fab was given. Analytical studies were consistent with increased excretion of native digitoxin rather than metabolites, and the glycoside was found in equilibrium dialysis studies to be excreted in the urine in Fab-bound form. Administration of 2 mol of specific antibody binding sites per mole of digitoxin as intact IgG caused a greater and more prolonged increase in plasma total digitoxin concentration, peaking 13-fold above control levels. In contrast to the effects of Fab, however, specific IgG reduced the rate of urinary digitoxin excretion substantially below control values. We conclude that Fab fragments of antibodies with high affinity for digitoxin are capable of rapid reversal of advanced, otherwise lethal digitoxin toxicity, and are capable of reducing the plasma half-life and accelerating urinary excretion of digitoxin.     

Improved kidney function with intravenous prostaglandin E1 in patients with terminal heart failure

In end stage congestive heart failure activation of a series of compensatory mechanisms increase renal vascular resistance and impair renal function. Prostaglandin E1 is increasingly used in the treatment of severe heart failure for its vasodilating actions. In various experimental settings prostaglandin E analogues are known to improve renal function by modulating renal filtration pressure and redistribution of renal blood flow. However, prostaglandin E1 decreases systemic blood pressure and thus, also renal perfusion pressure, a fact by which renal function might be further compromized in heart failure patients. The aim of the study was to evaluate the effects of prostaglandin E1 on excretory renal function in patients with end stage heart failure and to prove the hypothesis, that the well known local actions of prostaglandins on renal microcirculation might outweigh the negative impact of an expected decrease in perfusion pressure. 25 patients with terminal congestive heart failure were investigated. 13 patients received prostaglandin E1 at a dose of 13.5 +/- 1.9 ng/kg/min in combination with constant rates of dopamine and dobutamine (group A), 12 patients received prostaglandin E1 at a dose of 10.3 +/- 1.7 ng/kg/min without catecholamines (group B). There was no significant difference in prostaglandin dosages between groups. Kidney function was assessed by measuring plasma creatinine and urea nitrogen, urinary output, creatinine clearance, osmotic and free water clearance at baseline and after 72 h of infusion therapy. Hemodynamic parameters were measured by using a balloon tipped pulmonary arterial catheter. Hemodynamic measurements during infusion showed a significant improvement in all patients. At the same time as expected mean arterial pressure decreased in both groups (p < 0.001). Nevertheless, in both groups a significant increase of creatinine clearance during infusion was observed (in group A from 45 ml/min to 78 ml/min., p < 0.05, in group B from 59 ml/min to 105 ml/min., p < 0.001). Creatinine clearance in group B (without catecholamines) reached higher levels than group A (p < 0.05). Urinary volumes did not change during infusion therapy, whereas free water clearance significantly decreased, as an indication of an improvement of renal concentrations ability. We conclude, that in patients with end stage heart failure continuous infusion of prostaglandin E1 improves excretory kidney function. These findings suggest that the local effects of prostaglandin E1 on renal microcirculation can counterregulate the negative impact of prostaglandins on renal perfusion pressure.     

Intrarenal vascular effects of angiotensin I and angiotensin II

The effects of angiotensin I (250 pmol) and angiotensin II (7.5 pmol) on total renal blood flow and its cortical distribution were examined in 25 dogs anesthetized with pentobarbital. These peptides were administered as bolus injections directly into the left renal artery. Right and left renal blood flows were measured with noncannulating electromagnetic flow probes. The distribution of renal cortical blood flow was measured with 15-micrometers radioactive microspheres. Because angiotensin I is converted to angiotensin II extrarenally as well as intrarenally, the distribution of renal blood flow in response to the bolus injection of angiotensin agonists was measured before these peptides could have recirculated through the kidney. This maneuver precluded the possibility that blood flow changes were due to the extrarenal formation of vasoactive metabolites of angiotensin I or angiotensin II. Control total renal blood flow averaged 3.0 +/- 0.1 ml.min-1.g kidney wt-1 and was decreased 25% by both angiotensin I and angiotensin II. Outer renal cortical flow (zone I) was 5.1 +/- 0.3 ml.min-1.g-1 and was decreased to 3.9 +/- 0.3 ml.min-1.g-1 by both angiotensin I and angiotensin II. On the average, angiotensin I decreased inner cortical renal blood flow from a control of 1.8 +/- 0.2 to 1.2 +/- 0.2 ml.min-1.g-1; angiotensin II decreased inner cortical renal blood flow from a control of 1.9 +/- 0.2 to 1.4 +/- 0.2 ml.min-1.g-1. Analysis on a per-experiment basis revealed that angiotensin I, compared with angiotensin II, produced a proportionally greater decrease in inner cortical renal blood flow relative to its effects on outer cortical blood flow.     

Nitric oxide release as an essential mitigating step in tubuloglomerular feedback: observations during intrarenal nitric oxide clamp

Nitric oxide synthase inhibition in the kidney enhances tubuloglomerular feedback (TGF) responsiveness. This may reflect either the effect of reduced basal nitric oxide (NO) availability or the effect of impaired NO release that is physiologically induced by TGF activation. However, it is unknown whether the latter actually takes place. In this study, it was hypothesized that NO is released (from macula densa cells or endothelium) as part of the normal TGF loop, and mitigates the TGF response. In Sprague Dawley rats, TGF responsiveness was assessed (fall in tubular stop flow pressure, deltaSFP, upon switching loop of Henle perfusion rates from 0 to 40 nl/min) during an intrarenal NO clamp (systemic infusion of nitro-L-arginine, 10 microg/kg per min, followed by intrarenal nitroprusside infusion adjusted to restore renal blood flow [RBF]). This maneuver was presumed to fix intrarenal NO impact at a physiologic level. To validate the approach, TGF responsiveness during an intrarenal angiotensin II (AngII) clamp (systemic infusion of enalaprilat 0.2 mg/kg per min, followed by intrarenal AngII infusion) was also studied. AngII is presumed to modulate but not mediate, TGF, thus not to increase as part of the TGF loop. In untreated animals, RBF was 7.4 +/- 0.4 ml/min, and deltaSFP was 5.7 +/- 1.6 mmHg. Nitro-L-arginine infusion alone reduced RBF to 5.3 +/- 0.5 ml/min (P < 0.05); with nitroprusside infusion, RBF was restored to 8.3 +/- 0.7 ml/min. In this condition (NO clamp), deltaSFP was markedly increased to 19.6 +/- 3.2 mmHg (P < 0.05). By contrast, deltaSFP, which was virtually abolished during enalaprilat alone (0.2 +/- 0.3 mmHg), was not significantly different from controls during AngII clamp (8.2 +/- 1.0 mmHg). These data suggest that NO may well be released upon TGF activation. By contrast, AngII is not dynamically involved in TGF activation, but may modulate the TGF response. Thus, dynamic release of NO during TGF activation mitigates the TGF response, so that it will offset the action of a primary, as yet undefined, vasoconstrictor mediator. The source of this NO, macula densa or endothelium, remains to be elucidated.     

Ouabain-containing Euro-Collins solution prevents ATN following renal cold storage

In view of the hypothesis that suppression of energy demand may prevent ischemic cell damage, it seemed possible that suppression of ATP utilization during ischemia might ameliorate the severity of renal failure following kidney preservation. To test this possibility, a short-term in situ kidney preservation model was prepared in dogs. Euro-Collins solution containing 10(-5) M ouabain (O-EC) was used as the preservation solution. The kidney was preserved with cold O-EC for two hours and reperfused with auto blood. As the control, the kidney was treated with Euro-Collins solution (EC) alone. Three hours after reperfusion, recovery of creatinine clearance was 47.4 +/- 8.0% in the control and 71.6 +/- 14.0% in the O-EC group (p < 0.02). The increase in urinary excretion of N-acetyl-beta-D-glucosaminidase was significantly lower in the O-EC group. It was 21.3 +/- 4.5 nU/gr renal weight for three hours after reperfusion in the control group and 7.2 +/- 1.5 nU/gr renal weight in the O-EC group (p < 0.05). Fractional excretion of sodium three hours after reperfusion was 1.42 +/- 0.44% and 5.51 +/- 0.63% in the control and O-EC groups (p < 0.002), respectively. There were no significant differences in renal blood flow, urine volume and urine osmolality between the two groups. These results suggest that ouabain-containing EC was effective in protecting the kidney, especially renal proximal tubular cell, against ischemic damage.     

Renin vs. angiotensin-converting enzyme inhibition in the rat: consequences for plasma and renal tissue angiotensin

To compare the effects of a potent rat renin inhibitor peptide (RIP) and angiotensin-converting enzyme (ACE) inhibitor on the intrarenal and plasma renin-angiotensin systems, anesthetized Sprague-Dawley rats were treated with an infusion of vehicle, ramipril or graded doses of the rat RIP (acetyl-His-Pro-Phe-Val-statine-Leu-he-NH2) for 30 min. Kidney and plasma samples were processed rapidly, and angiotensin peptides were separated by high-pressure liquid chromatography before measurement by a double-antibody radioimmunoassay. Blood pressure fell identically, by approximately 15 mm Hg, after either the RIP or ACE inhibitor. Plasma Ang II was 83 +/- 20 fmol/ml in vehicle-treated rats and fell to 28 +/- 3 fmol/ml with ramipril (10 mg/kg), the dose-response zenith. Plasma Ang II was significantly lower, 9 +/- 2 fmol/ml, with the highest RIP dose used. Control renal tissue Ang II was 183 +/- 18 fmol/g, fell with ramipril to 56 +/- 6 and then fell to a similar level (47 +/- 10 fmol/g) after RIP. Ang I/Ang II ratios indicated the expected sharp drop in Ang I conversion after ramipril in plasma and tissue. RIP did not influence conversion rate in plasma but was associated with an unanticipated fall in Ang I conversion in renal tissue, perhaps reflecting local aspartyl protease inhibition, which contributes to normal Ang II formation. Also unanticipated was a rise in tissue Ang I concentration during RIP administration. Renin inhibition is more effective than ACE inhibition in blocking systemic Ang II formation, supporting studies suggesting that quantitatively important non-ACE-dependent pathways participate in Ang II formation.     

Breakdown of blood pressure and body fluid homeostasis in heart transplant recipients

OBJECTIVES: This study was designed to investigate disturbances in arterial blood pressure and body fluid homeostasis in stable heart transplant recipients. BACKGROUND: Hypertension and fluid retention frequently complicate heart transplantation. METHODS: Blood pressure, renal and endocrine responses to acute volume expansion were compared in 10 heart transplant recipients (57 +/- 9 years old [mean +/- SD]) 20 +/- 5 months after transplantation, 6 liver transplant recipients receiving similar doses of cyclosporine (cyclosporine control group) and 7 normal volunteers (normal control subjects). After 3 days of a constant diet containing 87 mEq/24 h of sodium, 0.154 mol/liter saline was infused at 8 ml/kg per h for 4 h. Blood pressure and plasma vasopressin, angiotensin II, aldosterone, atrial natiuretic peptide and renin activity levels were determined before and at 30, 60, 120 and 240 min during the infusion. Urine was collected at 2 and 4 h. Blood pressure, fluid balance hormones and renal function were monitored for 48 h after the infusion. RESULTS: Blood pressure did not change in the two control groups but increased in the heart transplant recipients (+15 +/- 8/8 +/- 5 mm Hg) and remained elevated for 48 h (p < or = 0.05). Urine flow and urinary sodium excretion increased abruptly in the control groups sufficient to account for elimination of 86 +/- 9% of the sodium load by 48 h; the increases were blunted (p < or = 0.05) and delayed in the heart transplant recipients, resulting in elimination of only 51 +/- 13% of the sodium load. Saline infusion suppressed vasopressin, renin activity, angiotensin II and aldosterone in the two control groups (p < or = 0.05) but not in the heart transplant recipients. Heart transplant recipients had elevated atrial natriuretic peptide levels at baseline (p < or = 0.05), but relative increases during the infusion were similar to those in both control groups. CONCLUSIONS: Blood pressure in heart transplant recipients is salt sensitive. These patients have a blunted diuretic and natriuretic response to volume expansion that may be mediated by a failure to reflexly suppress fluid regulatory hormones. These defects in blood pressure and fluid homeostasis were not seen in liver transplant recipients receiving cyclosporine and therefore cannot be attributed to cyclosporine alone. Abnormal cardiorenal neuroendocrine reflexes, secondary to cardiac denervation, may contribute to salt-sensitive hypertension and fluid retention in heart transplant recipients.