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.     

Bovine serum albumin and lysophosphatidic acid stimulate calcium mobilization and reversal of cAMP-induced stellation in rat spinal cord astrocytes

We conducted studies in conscious chronically catheterized, trained young (3-5 months) and old (18-20 months) rats to assess the impact of aging on baseline renin activity (PRA) and metabolic clearance rate (MCR) of angiotensin II (ANG II). We observed that under unstressed conditions the baseline values of PRA and plasma ANG II were no different in young versus old rats (1.8 +/- 0.2 versus 1.5 +/- 0.2 ng Al/ml/h and 18 +/- 3 versus 15 +/- 2 fmol/ml, respectively). Values of PRA in the present study were similar to those reported by others for old rats, but our young rat values were lower than usually reported. This probably reflects our use of an unstressed preparation. We also observed a blunted increase in PRA in old rats in response to acute converting enzyme inhibition. Overall, our observations suggest that old rats may lose their ability to increase PRA in response to acute stimuli, including perhaps, the stress of blood drawing in emotionally or surgically stressed preparations. We also observed that the MCR of ANG II increased with age, despite similar baseline plasma ANG II concentrations in young and old. This suggests that with aging, an increase occurs in the rate of synthesis of ANG II. These results emphasize the importance of establishing true baseline values for indices of the renin-ANG II system in aging.     

Disparity between blood pressure and PRA inhibition after administration of a renin inhibitor to anesthetized dogs: methodological considerations

A dissociation between changes in blood pressure (BP) and plasma renin activity (PRA) has been noted after administration of renin inhibitors. In the present study, the renin inhibitor PD 132002 was given to salt-deplete, anesthetized dogs. PRA was measured at pH 6.0 by a conventional angiotensin I (ANG I) RIA method (PRA-C) and by an ANG I antibody-trapping RIA method (PRA-AT) performed at pH 7.4. PD 132002 at 0.01, 0.1, 1, and 10 mg/kg IV, reduced BP by 3 +/- 2, 9 +/- 2, 24 +/- 4, and 39 +/- 4 mm Hg, respectively, (baseline of 136 +/- 8 mm Hg, N = 5), when infused IV over 30 minutes with a 30 minute recovery between doses. The BP response at 10 mg/kg equaled that of saralasin (20 micrograms/kg/min IV). PRA-AT (baseline of 20 +/- 6 ng ANG l/ml/hr, N = 4) was inhibited by 0%, 28% +/- 12%, 75% +/- 10%, and 97% +/- 1% at 0.01, 0.1, 1, and 10 mg/kg, respectively. Plasma concentrations of immunoreactive ANG II were also reduced dose-dependently and paralleled changes in BP. In contrast, PRA-C (baseline of 13 +/- 4 ng ANG l/ml/hr, N = 4) was inhibited by 82% +/- 8% at 0.01 mg/kg and by > 98% at higher doses. After a single dose of PD 132002 at 10 mg/kg infused over 30 minutes, BP recovery paralleled changes in immunoreactive ANG II and PRA-AT, yet PRA-C inhibition showed no recovery over the same time course. Our data support the conclusion that BP relates better to PRA-AT than PRA-C. Thus the dissociation sometimes observed in studies with renin inhibitors between changes in BP and PRA may be attributed to the assay used to determine PRA.     

Elevated plasma catecholamines without alteration in cardiovascular responsiveness in young men with borderline hypertension

Plasma catecholamines and cardiovascular responses to upright posture, exogenous noradrenaline (NA), and isoproterenol (IP) were examined in 20 young men with borderline hypertension and in 10 age-matched normotensive volunteers. Resting plasma NA and adrenaline (Ad) levels were higher in the borderline hypertensive patients. Significant correlations were found among plasma NA and mean blood pressure (MBP) or heart rate (HR), and between plasma Ad and HR in all individuals in the supine position. The increases in plasma NA were similar between groups for orthostatic positions. Pressor response to exogenous NA and chronotropic response to exogenous IP were not augmented in borderline hypertensives. A negative correlation was found between plasma NA before infusion and the increases of MBP produced by NA or the increases of HR produced by IP in all the individuals. Our observations suggest that there is hyperactivity of the sympathoadrenal system without enhancement in cardiovascular reactivity to catecholamines in young men with borderline hypertension.     

The urinary bladder angiotensin system: response to infusions of angiotensin I and angiotensin-converting enzyme inhibitors

The circulating and urinary bladder tissue concentrations of angiotensin I (ANG I) and angiotensin II [ANG-(1-8)] were examined in anesthetized Sprague-Dawley male rats given an intravenous bolus infusion of either ANG I, the angiotensin-converting enzyme (ACE) inhibitors enalaprilat or ramiprilat, or saline. The mean concentrations of ANG I and ANG-(1-8) were markedly higher in the urinary bladder tissue than in whole blood. There was a significant increase in the concentration of ANG I and ANG-(1-8), both in the urinary bladder tissue and the circulation, after the ANG I infusion. Both ACE inhibitors were associated with an increase in the concentration of whole blood ANG I; however, tissue ANG I levels were significantly increased only following ACE inhibition with ramiprilat but not with enalaprilat. Both plasma and urinary bladder tissue ANG-(1-8) levels decreased significantly following ACE inhibition, but only with ramiprilat. The elevated urinary bladder tissue levels of ANG I and ANG-(1-8) at baseline, compared with circulating levels, and the maintenance of ANG-(1-8) in bladder tissue in the face of inhibition of the circulatory renin-angiotensin system with enalaprilat support the presence of an autocrine/paracrine renin-angiotensin system in the urinary bladder. Under the current experimental conditions, ramiprilat appears to have enhanced bladder activity compared with enalaprilat.     

Development of a sensitive and specific assay system for cholecystokinin tetrapeptide

Cholecystokinin is a gastrointestinal and neuropeptide which has been implicated in a wide range of physiological and behavioral processes. We have developed a sensitive and specific assay system to measure the various forms of cholecystokinin (CCK) in human plasma. This 3-step system involves i) extraction of CCK fragments from plasma using reverse phase chromatography; ii) separation of peptides by high performance liquid chromatography; and iii) detection and quantification of peptides with a double-antibody radioimmunoassay, using an antibody raised against cholecystokinin tetrapeptide (CCK-4) coupled to thyroglobulin and 125I Bolton-Hunter CCK-4 as tracer. The antibody detects CCK-4, sulfated CCK-8 (CCK-8S) and nonsulfated CCK-8 (CCK-8ns) with equal affinity. The lower limit of detection is 2.7 fmol, with an ED50 of 10.6 +/- 2.2 fmol. Mean CCK-like immunoreactivity (CCK-LI) in the plasma of 12 healthy subjects was determined to be 12.9 +/- 2.1 pM CCK-4 equivalents. Concentrations of each individual peptide in plasma were determined to be 1.0 +/- 0.2 pM, 3.4 +/- 0.8 pM and 1.9 +/- 0.4 pM for CCK-4, CCK-8s and CCK-8ns respectively.     

Germline mutations of the BRCA1 and BRCA2 genes in a breast and ovarian cancer patient

Nitric oxide (NO) has been implicated as a modulator of the vascular effects of angiotensin II (ANG II) in the kidney. We used a NO-sensitive microelectrode to study the effect of ANG II on NO release, and to determine the effect of selective inhibition of the ANG II subtype I receptor (AT1) with losartan (LOS) and candesartan (CAN). NO release from isolated and perfused renal resistance arteries was measured with a porphyrin-electroplated, carbon fiber. The vessels were microdissected from isolated perfused rat kidneys and perfused at constant flow and pressure in vitro. The NO-electrode was placed inside the glass collection cannula to measure vessel effluent NO concentration. ANG II stimulated NO release in a dose-dependent fashion: 0.1 nM, 10 nM and 1000 nM ANG II increased NO-oxidation current by 85+/-18 pA (n = 11), 148+/-22 pA (n = 11), and 193+/-29 pA (n = 11), respectively. These currents correspond to changes in effluent NO concentration of 3.4+/-0.5 nM, 6.1+/-1.1 nM, and 8.2+/-1.3 nM, respectively. Neither LOS (1 muM) nor CAN (1 nM) significantly affected basal NO production, but both AT1-receptor blockers markedly blunted NO release in response to ANG II (10 nM): 77+/-6% inhibition with LOS (n = 8) and 63+/-9% with CAN (n = 8). These results are the first to demonstrate that ANG II stimulates NO release in isolated renal resistance arteries, and that ANG II-induced NO release is blunted by simultaneous AT1-receptor blockade. Our findings suggest that endothelium-dependent modulation of ANG II-induced vasoconstriction in renal resistance arteries is mediated, at least in part, by AT1-receptor-dependent NO release.     

Cerebral circulation dysfunction and hemodynamic abnormalities in syncope during upright tilt test

OBJECTIVE: To assess the hemodynamic features, including monitoring of cerebral circulation, blood pressure and heart rate, in syncope patients during upright tilt test. DESIGN: Nonrandomized sequential patients with history of syncope of uncertain etiology compared with healthy subjects. SETTING: Noninvasive hemodynamic laboratory of a tertiary referral centre. PATIENTS: Twenty patients with history of syncope and 10 controls without syncope. PROCEDURES: Transcranial Doppler measurement or middle cerebral artery flow velocity, noninvasive and invasive blood pressure monitoring, electrocardiography and pulse oximetry monitoring during upright tilt testing. Measurements were taken in patients at the height of symptoms in supine and upright posture. MAIN RESULTS: Ten patients, while still normotensive, had a drop of 53 +/- 10% (mean +/- SD) in cerebral bloodflow velocity (P = 0.0001) and an increase in heart rate by 58 +/- 35%. The remaining 10 patients had a 58 +/- 15% reduction in cerebral bloodflow velocity (P = 0.0001), a drop in blood pressure of 33 +/- 8% (P = 0.0001) and no change in heart rate. The controls showed no significant changes in cerebral bloodflow velocity and a 25 +/- 12% increase in heart rate (P = 0.0002). CONCLUSIONS: Transcranial Doppler monitoring of cerebral bloodflow velocity during upright tilt testing may improve insight into the complex physiology of syncope.     

Losartan and angiotensin II inhibit aldosterone production in anephric rats via different actions on the intraadrenal renin-angiotensin system

Angiotensin II (ANG II) is a major stimulator of aldosterone biosynthesis. When investigating the relative contribution of circulating and locally produced ANG II, we were therefore surprised to find that ANG II, given chronically s.c. (200 ng/kg x min), markedly inhibits a nephrectomy (NX)-induced rise of aldosterone concentrations (from 10 +/- 2 to 465 +/- 90 ng/100 ml in vehicle infused, and from 9 +/- 2 to 177 +/- 35 in ANG II infused rats 55 h after NX and hemodialysis). We further observed, by in situ hybridization, that bilateral NX increases the number of adrenocortical cells expressing renin and that this rise was prevented by ANG II. Moreover, the rise of aldosterone levels was also inhibited by the AT1-receptor antagonist, losartan (10 microg/kg x min, chronically i.p. from 8 +/- 2 to 199 +/- 26 ng/100 ml), despite the absence of circulating renin and a reduction of ANG I to less than 10%. These data demonstrate that aldosterone production, after NX, is regulated by an intraadrenal renin-angiotensin system and that this system is physiologically suppressed by circulating angiotensin. Because the effects of losartan or ANG II on aldosterone production involved a latency period of at least 30 h after NX and were associated with a modulation or recruitment of renin-producing cells, we suggest that the intraadrenal renin-angiotensin system operates via regulation of cell differentiation on a long-term scale, rather than or additionally to its short-term effects on aldosterone synthase activity.     

Proinsulin: recent observations and controversies

INTRODUCTION: Defibrillation thresholds (DFTs) usually are determined with the patient in the supine position. However, patients may be in the upright position when a shock is delivered during follow-up, which may explain some first shock failures observed clinically. This study investigated whether body posture affects defibrillation energy requirements of nonthoracotomy implantable cardioverter defibrillators with biphasic shocks. METHODS AND RESULTS: Using a step up-down protocol, DFTs were compared intraindividually in 52 patients ("active-can" sytems in 41 patients, two-lead systems in 11 patients) for the supine and upright positions as achieved by a tilt table. The mean DFT was 7.3 +/- 4.2 J in the supine versus 9.2 +/- 4.8 J in the upright position (P = 0.002). Repeated comparison in reversed order 3 months after implantation in 22 patients revealed thresholds of 6.2 +/- 2.5 J (supine) versus 8.4 +/- 3.7 J (upright; P < 0.03) 1 week and 4.4 +/- 2.4 J (supine) versus 6.2 +/- 4.1 J (upright; P < 0.04) 3 months after implantation. DFTs decreased significantly for both body positions from 1 week to 3 months after implantation (P < 0.04). CONCLUSION: (1) DFTs for biphasic shocks delivered by nonthoracotomy defibrillators are higher in the upright compared to the supine body position. (2) Differences remain significant 3 months after implantation. For both body positions, DFT decreases significantly from 1 week to 3 months after implantation. These findings have important implications for programming first shock energy to lower than maximal values or for development of devices with lower maximal stored energy.     

Cloning and sequencing of the Sphingomonas (Pseudomonas) paucimobilis gene essential for the O demethylation of vanillate and syringate

A growing body of evidence supports the existence of a tissue-based renin-angiotensin system (RAS) in the vasculature, but the functional capacity of vascular RAS was not investigated in humans. In 28 normotensive healthy control subjects, the metabolism of angiotensins through vascular tissue was investigated in normal, low, and high sodium diets by the measurement of arterial-venous gradient of endogenous angiotensin (Ang) I and Ang II in two different vascular beds (forearm and leg), combined with the study of 125I-Ang I and 125I-Ang II kinetics. In normal sodium diet subjects, forearm vascular tissue extracted 36+/-6% of 125I-Ang I and 30+/-5% of 125I-Ang II and added 14.9+/-5.1 fmol x 100 mL(-1) x min(-1) of de novo formed Ang I and 6.2+/-2.8 fmol x 100 mL(-1) x min(-1) of Ang II to antecubital venous blood. Fractional conversion of 125I-Ang I through forearm vascular tissue was about 12%. Low sodium diet increased (P<.01) plasma renin activity, whereas de novo Ang I and Ang II formation by forearm vascular tissue became undetectable. Angiotensin degradation (33+/-7% for Ang I and 30+/-7% for Ang II) was unchanged, and vascular fractional conversion of 125I-Ang I decreased from 12% to 6% (P<.01). In high sodium diet subjects, plasma renin activity decreased, and de novo Ang I and Ang II formation by forearm vascular tissue increased to 22 and 14 fmol x 100 mL(-1) x min(-1), respectively (P<.01). Angiotensin degradation did not significantly change, whereas fractional conversion of 125I-Ang I increased from 12% to 20% (P<.01). Leg vascular tissue functional activities of RAS paralleled those of forearm vascular tissue both at baseline and during different sodium intake. These results provide consistent evidence for the existence of a functional tissue-based RAS in vascular tissue of humans. The opposite changes of plasma renin activity and vascular angiotensin formation indicate that vascular RAS is independent from but related to circulating RAS.     

The role of angiotensin AT1 receptors in the diuretic, natriuretic, kaliuretic and blood pressure responses induced by angiotensin II activation of the median preoptic nucleus in conscious rats

We determined the effects of two classical angiotensin II (ANG II) antagonists, [Sar1, Ala8]-ANG II and [Sar1, Thr8]-ANG II, and losartan (a nonpeptide and selective antagonist for the AT1 angiotensin receptors) on diuresis, natriuresis, kaliuresis and arterial blood pressure induced by ANG II administration into the median preoptic nucleus (MnPO) of male Holtzman rats weighing 250-300 g. Urine was collected in rats submitted to a water load (5% body weight) 1 h later. The volume of the drug solutions injected was 0.5 microliters over 10-15 s. Pre-treatment with [Sar1, Ala8]-ANG II (12 rats) and [Sar1, Thr8]-ANG II (9 rats), at the dose of 60 ng reduced (13.7 +/- 1.0 vs 11.0 +/0 1.0 and 10.7 +/0 1.2, respectively), whereas losartan (14 rats) at the dose of 160 ng totally blocked (13.7 +/- 1.0 vs 7.6 +/- 1.5) the urine excretion induced by injection o 12 ng of ANG II (14 rats). [Sar1, Ala8]-ANG II impaired Na+ excretion (193 +/- 16 vs 120 +/- 19), whereas [Sar1, Thr8]-ANG II and losartan block Na+ excretion (193 +/- 16 vs 77 +/- 15 and 100 +/- 12, respectively) induced by ANG II. Similar effects induced by ANG II on K+ excretion were observed with [Sar1, Ala8]-ANG II, [Sar1, Thr8]- ANG II, and losartan pretreatment (133 +/- 18 vs 108 +/- 11, 80 +/- 12, and 82 +/- 15, respectively). The same doses as above of [Sar1, Ala8]-ANG II (8 rats), [Sar1, Thr8]-ANG II (8 rats), and losartan (9 rats) blocked the increase in the arterial blood pressure induced by 12 ng of ANG II (12 rats) (32 +/- 4 vs 4 +/- 2, 3.5 +/- 1, and 2 +/- 1, respectively. The results indicate that the AT1 receptor subtype participates in the increases of diuresis, natriuresis, kaliuresis and arterial blood pressure induced by the administration of ANG II into the MnPO.     

Detection of endothelin 1,2 and endothelin-like immunoreactant in wound surface and plasma in mice with thermal injury

Endothelin is a well known vasoconstrictive peptides produced by endothelial cells and has been reported to regulate the systemic circulation. The authors investigated changes in endothelin in plasma and the surface of wounds induced with thermal injury using an experimental ear burn model in mice. At 0, 15, 30, 60, 120 and 180 minutes after thermal injury the plasma endothelin-like immunoreactant levels were 1.50 +/- 0.21, 1.86 +/- 0.36, 2.81 +/- 0.55, 2.62 +/- 0.27, 1.54 +/- 0.14 and 1.25 +/- 0.19 fmol/ml (N = 8), respectively. Endothelin-like immunoreactant levels in the plasma increased gradually until 30 minutes after the thermal injury. Endothelin-like immunoreactant content in the ear before thermal injury and at 60 minutes after injury were 7.04 +/- 0.64 and 8.61 +/- 1.24 fmol/ear (N = 8), respectively. The change in endothelin-like immunoreactant after thermal injury originated from endothelin 1,2; that is, the endothelin-1,2 content of the burned ear increased significantly 15 and 60 minutes after thermal injury to 12.52 +/- 0.68 and 11.58 +/- 1.04 fmol/ear, respectively, compared with 1.78 +/- 0.91 fmol/ear (N = 8) obtained before injury. These results suggested that endothelin 1,2 existed in the region of the wound caused by thermal injury.     

Central interaction between atrial natriuretic peptide and angiotensin II in the control of sodium intake and excretion in female rats

We investigated the effects of estrogen on sodium intake and excretion induced by angiotensin II (ANG II), atrial natriuretic peptide (ANP) or ANG II plus ANP injected into the median nucleus (MnPO). Female Holtzman rats weighing 250-300 g were used. Sodium ingestion and excretion 120 min after the injection of 0.5 microliters of 0.15 M NaCl into the MnPO were 0.3 +/- 0.1 ml (N = 12) and 29 +/- 7 microEq in intact rats, 0.5 +/- 0.2 ml (N = 10) and 27 +/- 6 microEq in ovariectomized rats, and 0.2 +/- 0.08 (N = 11) and 36 +/- 8 microEq in estrogen-treated ovariectomized (50 micrograms/day for 21 days) rats, respectively. ANG II (21 microM) injection in intact, ovariectomized, and estrogen-treated ovariectomized rats increased sodium intake (3.8 +/- 0.4, 1.8 +/- 0.3 and 1.2 +/- 0.2 ml/120 min, respectively) (N = 11) and increased sodium excretion (166 +/- 18, 82 +/- 22 and 86 +/- 12 microEq/120 min, respectively) (N = 11). ANP (65 microM) injection in intact (N = 11), ovariectomized (N = 10) and estrogen-treated ovariectomized (N = 10) rats increased sodium intake (1.4 +/- 0.2, 1.8 +/- 0.3, and 1.7 +/- 0.3 ml/120 min, respectively) and sodium excretion (178 +/- 19, 187 +/- 9, and 232 +/- 29 microEq/120 min, respectively). Concomitant injection of ANG II and ANP into the MnPO of intact (N = 12), ovariectomized (N = 10) and estrogen-treated ovariectomized (N = 10) rats caused smaller effects than those produced by each peptide given alone: 1.3 +/- 0.2, 0.9 +/- 0.2 and 0.3 +/- 0.1 ml/120 min for sodium intake, respectively, and 86 +/- 9, 58 +/- 7, and 22 +/- 4 microEq/120 min for sodium excretion, respectively. Taken together, these results demonstrate that there is an antagonistic interaction of ANP and ANG II on sodium intake and excretion, and that reproductive hormones affect this interaction.     

Short exposure to endotoxin increases the constriction induced by angiotensin II in rat aorta

The contraction elicited by angiotensin II (ANG II) was studied by using standard isometric tension techniques in aortic rings exposed for 1 h to 1 or 10 micrograms/ml Escherichia coli lipopolysaccharide endotoxin (LPS). This contraction was 18 and 71% greater for the two doses of LPS, respectively, than in unexposed control rings. In endothelium-denuded rings, the LPS-induced increase in contraction in response to ANG II was completely abolished. Because the contraction induced by ANG II is modulated by the simultaneous release of prostaglandins, we tested the hypothesis that LPS interferes with this modulation. We found that the LPS-induced increase in contraction to ANG II was inhibited in the presence of the cyclooxygenase inhibitor indomethacin (10(-5) M) or the prostaglandin H2/thromboxane A2-receptor antagonist SQ-29548 (2 x 10(-7) M). Conversely, the LPS-induced increase in contraction in response to ANG II was not inhibited by the presence of dexamethasone (10(-6) M), which inhibits new protein synthesis. In addition, there was no loss of vasodilator response to the endothelium-dependent receptor agonist acetylcholine (10(-8)-10(-4) M) or in the constrictor responses to norepinephrine (10(-9)-10(-5) M) and KCl (20-100 mM). We conclude that short exposure to LPS produces a specific increase in the constrictor response to ANG II via mechanisms mediated by prostaglandin H2/thromboxane A2. This effect could be a LPS-induced shift in favor of constrictor prostanoids in the balance of dilator/constrictor prostanoids, the release of which is associated with stimulation by ANG II.     

Expiratory flow limitation and intrinsic positive end-expiratory pressure in obesity

Breathing at very low lung volumes might be affected by decreased expiratory airflow and air trapping. Our purpose was to detect expiratory flow limitation (EFL) and, as a consequence, intrinsic positive end-expiratory pressure (PEEPi) in grossly obese subjects (OS). Eight OS with a mean body mass index (BMI) of 44 +/- 5 kg/m2 and six age-matched normal-weight control subjects (CS) were studied in different body positions. Negative expiratory pressure (NEP) was used to determine EFL. In contrast to CS, EFL was found in two of eight OS in the upright position and in seven of eight OS in the supine position. Dynamic PEEPi and mean transdiaphragmatic pressure (mean Pdi) were measured in all six CS and in six of eight OS. In OS, PEEPi increased from 0.14 +/- 0.06 (SD) kPa in the upright position to 0.41 +/- 0.11 kPa in the supine position (P < 0.05) and decreased to 0.20 +/- 0.08 kPa in the right lateral position (P < 0.05, compared with supine), whereas, in CS, PEEPi was significantly smaller (<0.05 kPa) in each position. In OS, mean Pdi in each position was significantly larger compared with CS. Mean Pdi increased from 1.02 +/- 0.32 kPa in the upright position to 1.26 +/- 0.17 kPa in the supine position (not significant) and decreased to 1. 06 +/- 0.26 kPa in the right lateral position (P < 0.05, compared with supine), whereas there were no significant changes in CS. We conclude that in OS 1) tidal breathing can be affected by EFL and PEEPi; 2) EFL and PEEPi are promoted by the supine posture; and 3) the increased diaphragmatic load in the supine position is, in part, related to PEEPi.     

Total-body and regional bone mineral content and areal bone mineral density in children aged 8-18 y: the Fels Longitudinal Study

We used a modification of the isolated perfused rat heart, in which coronary effluent and interstitial transudate were separately collected, to investigate the localization and production of angiotensin II (Ang II) in the heart. During combined renin (0.7 to 1.5 pmol Ang I/mL per minute) and angiotensinogen (6 to 12 pmol/mL) perfusion (4 to 8 mL/min) for 60 minutes (n=3), the steady-state levels of Ang II in interstitial transudate in two consecutive 10-minute periods were 4.3+/-1.5 and 3.6+/-1.5 fmol/mL compared with 1.1+/-0.4 and 1.1+/-0.6 fmol/mL in coronary effluent (mean+/-half range). During perfusion with Ang II (n=5), steady-state Ang II in interstitial transudate was 32+/-19% of arterial Ang II compared with 65+/-16% in coronary effluent (mean+/-SD, P<.02). During perfusion with Ang I (n=5), Ang II in interstitial transudate was 5.1+/-0.6% of arterial Ang I compared with 2.2+/-0.3% in coronary effluent (P<.05). The tissue concentration of Ang II in the combined renin/angiotensinogen perfusions (per gram) was as high as the concentration in interstitial transudate (per milliliter). Addition of losartan (10(-6) mol/L) to the renin/angiotensinogen perfusion (n=3) had no significant effect on the tissue level of Ang II, whereas losartan in the perfusions with Ang I (n=5) or Ang II (n=5) decreased tissue Ang II to undetectably low levels. The results indicate that the heart is capable of producing Ang II and that this can lead to higher levels in tissue than in blood plasma. Cardiac Ang II does not appear to be restricted to the extracellular fluid. This is in part due to AT1-receptor-mediated cellular uptake of extracellular Ang II, but our results also raise the possibility of intracellular Ang II production.     

Alveolar oxygen uptake and blood flow dynamics in knee extension ergometry

The relationship was studied between the increase in oxygen uptake (VO2) measured breath-by-breath at the mouth, and the increase in femoral artery blood flow measured continuously with pulsed and echo Doppler methods. Five men exercised at 50 W on a knee extension ergometer in both the supine and the upright posture. The kinetics of the responses were determined by curve fitting to obtain the mean response time (MRT = 63% of the time required to achieve steady state). In the upright position, the increase in blood flow (MRT = 12.4 +/- 9.4 s, mean +/- SD) was faster than the increase in VO2 (29.6 +/- 9.3 s). Likewise in the supine position, blood flow increased more rapidly (25.1 +/- 9.7 s vs. 36.7 +/- 9.6 s). It should be noted that the increase in blood flow appeared to be faster than VO2, yet when blood flow adapted more slowly in the supine posture, it had an impact on the adaptation of VO2. This suggests that blood flow might have important effects on metabolism at the onset of submaximal exercise.     

Adrenomedullin gene expression in the rat heart is stimulated by acute pressure overload: blunted effect in experimental hypertension

The levels of adrenomedullin (ADM), a newly discovered vasodilating and natriuretic peptide, are elevated in plasma and ventricular myocardium in human congestive heart failure suggesting that cardiac synthesis may contribute to the plasma concentrations of ADM. To examine the time course of induction and mechanisms regulating cardiac ADM gene expression, we determined the effect of acute and short-term cardiac overload on ventricular ADM mRNA and immunoreactive ADM (ir-ADM) levels in conscious rats. Acute pressure overload was produced by infusion of arginine8-vasopressin (AVP, 0.05 microg/kg/min, i.v.) for 2 h into 12-week-old hypertensive TGR(mREN-2)27 rats and normotensive Sprague-Dawley (SD) rats. Hypertension and marked left ventricular hypertrophy were associated with 2.2-times higher ir-ADM levels in the left ventricular epicardial layer (178 +/- 36 vs. 81 +/- 23 fmol/g, P<0.05) and 2.6-times higher ir-ADM levels in the left ventricular endocardial layer (213 +/- 23 vs. 83 +/- 22 fmol/g, P<0.01). The infusion of AVP for 2 h in normotensive rats produced rapid increases in the levels of left ventricular ADM mRNA (epicardial layer: 1.6-fold, P<0.05) and ir-ADM (endocardial layer: from 83 +/- 22 to 140 +/- 12 fmol/g, P<0.05), whereas ventricular ADM mRNA and ir-ADM levels did not change significantly in hypertensive rats. Short-term cardiac overload, induced by administration of angiotensin II (33.3 microg/kg/h, s.c., osmotic minipumps) for two weeks in normotensive SD rats resulted in left ventricular hypertrophy (3.05 +/- 0.17 vs. 2.75 +/- 0.3 mg/g, P<0.05) and a 1.5-fold increase (P<0.05) in ventricular ADM mRNA levels. In conclusion, the present results show that pressure overload acutely stimulated ventricular ADM gene expression in conscious normotensive rats suggesting a potential beneficial role for endogenous ADM production in the heart against cardiac overload. Since pressure overload-induced increase in ADM synthesis was attenuated in hypertensive rats, alterations in the ADM system may contribute to the pathogenesis of hypertension in the TGR(mREN-2)27 rat.     

Gravity is an important but secondary determinant of regional pulmonary blood flow in upright primates

Original studies leading to the gravitational model of pulmonary blood flow and contemporary studies showing gravity-independent perfusion differ in the recent use of laboratory animals instead of humans. We explored the distribution of pulmonary blood flow in baboons because their anatomy, serial distribution of vascular resistances, and hemodynamic responses to hypoxia are similar to those of humans. Four baboons were anesthetized with ketamine, intubated, and mechanically ventilated. Different colors of fluorescent microspheres were given intravenously while the animals were in the supine, prone, upright (repeated), and head-down (repeated) postures. The animals were killed, and their lungs were excised, dried, and diced into approximately 2-cm3 pieces with the spatial coordinates recorded for each piece. Regional blood flow was determined for each posture from the fluorescent signals of each piece. Perfusion heterogeneity was greatest in the upright posture and least when prone. Using multiple-stepwise regression, we estimate that 7, 5, and 25% of perfusion heterogeneity is due to gravity in the supine, prone, and upright postures, respectively. Although important, gravity is not the predominant determinant of pulmonary perfusion heterogeneity in upright primates. Because of anatomic similarities, the same may be true for humans.