An extension of Satterthwaite''s approximation applied to pharmacokinetics

Central inhibition of nitric oxide synthase (NOS) by intracerebroventricular (i.c.v.) administration of NG-nitro-l-arginine methyl ester (L-NAME; 150 microg/5 microl) to conscious rats produced a biphasic pressor response characterized by an initial transient increase within 5 min, and a delayed response starting between 60-90 min. The effect was stereospecific, as D-NAME (250 microg/5 microl) did not modify the resting arterial blood pressure, nor did L-arginine (323 microg/5 microl, i.c.v.), indicating the substrate for NOS is not rate-limiting. Intracerebroventricular pretreatment with losartan (25 microg/5 microl), a non-peptide antagonist of the angiotensin II AT1 receptor subtype, or indomethacin (100 microg/5 microl), a blocker of cyclooxygenase, however, prevented the initial increase in blood pressure without affecting the delayed pressor response. In contrast, neither intravenous losartan (10 mg/kg b.wt) nor prazosin, an alpha1 adrenergic receptor antagonist, at doses of 5 microg/5 microl (i.c.v.) or 0.3 mg/kg b.wt (i.v.) were effective in altering the pressor responses. These results indicate that centrally produced NO maintains the resting arterial blood pressure at least partially through modulation of the brain angiotensin system and prostaglandins.     

Restoration of blood pressure by choline treatment in rats made hypotensive by haemorrhage

1. Intracerebroventricular (i.c.v.) injection of choline (25-150 micrograms) increased blood pressure in rats made acutely hypotensive by haemorrhage. Intraperitoneal administration of choline (60 mg kg-1) also increased blood pressure, but to a lesser extent. Following i.c.v. injection of 25 micrograms or 50 micrograms of choline, heart rate did not change, while 100 micrograms or 150 micrograms i.c.v. choline produced a slight and short lasting bradycardia. Choline (150 micrograms) failed to alter the circulating residual volume of blood in haemorrhaged rats. 2. The pressor response to i.c.v. choline (50 micrograms) in haemorrhaged rats was abolished by pretreatment with mecamylamine (50 micrograms, i.c.v.) but not atropine (10 micrograms, i.c.v.). The pressor response to choline was blocked by pretreatment with hemicholinium-3 (20 micrograms, i.c.v.). 3. The pressor response to i.c.v. choline (150 micrograms) was associated with a several fold increase in plasma levels of vasopressin and adrenaline but not of noradrenaline and plasma renin. 4. The pressor response to i.c.v. choline (150 micrograms) was not altered by bilateral adrenalectomy, but was attenuated by systemic administration of either phentolamine (10 mg kg-1) or the vasopressin antagonist [beta-mercapto-beta,beta-cyclopenta-methylenepropionyl1, O-Me-Tyr2,Arg8]-vasopressin (10 micrograms kg-1). 5. It is concluded that the precursor of acetylcholine, choline, can increase and restore blood pressure in acutely haemorrhaged rats by increasing central cholinergic neurotransmission. Nicotinic receptor activation and an increase in plasma vasopressin and adrenaline level appear to be involved in this effect of choline.     

Inhibition of sympathetic outflow by the angiotensin II receptor antagonist, eprosartan, but not by losartan, valsartan or irbesartan: relationship to differences in prejunctional angiotensin II receptor blockade

It is well established that angiotensin II can enhance sympathetic nervous system function by activating prejunctional angiotensin II type I (AT1) receptors located on sympathetic nerve terminals. Stimulation of these receptors enhances stimulus-evoked norepinephrine release, leading to increased activation of vascular alpha 1-adrenoceptors and consequently to enhanced vasoconstriction. In the present study, the effects of several chemically distinct nonpeptide angiotensin II receptor antagonists were evaluated on pressor responses evoked by activation of sympathetic outflow through spinal cord stimulation in the pithed rat. Stimulation of thoracolumbar sympathetic outflow in pithed rats produced frequency-dependent pressor responses. Infusion of sub-pressor doses of angiotensin II (40 ng/kg/min) shifted leftward the frequency-response curves for increases in blood pressure, indicating augmented sympathetic outflow. Furthermore, pressor responses resulting in spinal cord stimulation were inhibited by the peptide angiotensin II receptor antagonist, Sar1, Ile8 [angiotensin II] (10 micrograms/kg/min). These results confirm the existence of prejunctional angiotensin II receptors at the vascular neuroeffector junction that facilitate release of norepinephrine. The nonpeptide angiotensin II receptor antagonist, eprosartan (0.3 mg/kg i.v.), inhibited the pressor response induced by spinal cord stimulation in a manner similar to that observed with the peptide antagonist, Sar1, Ile8[angiotensin II]. In contrast, equivalent doses (0.3 mg/kg i.v.) of other nonpeptide angiotensin II receptor antagonists, such as losartan, valsartan, and irbesartan, had no effect on spinal cord stimulation of sympathetic outflow in the pithed rat. Although the mechanism by which eprosartan, but not the other nonpeptide angiotensin II receptor antagonists, inhibits sympathetic outflow in the pithed rat is unknown, one possibility is that eprosartan is a more effective antagonist of prejunctional angiotensin II receptors that augment neurotransmitter release. Because eprosartan is more effective in inhibiting sympathetic nervous system activity compared to other chemically distinct nonpeptide angiotensin II receptor antagonists, eprosartan may be more effective in lowering systolic blood pressure and in treating isolated systolic hypertension.     

Serotonin is involved in the ACTH-induced reversal of hemorrhagic shock in anesthetized rats

In a rat model of volume-controlled hemorrhagic shock (mean arterial pressure = 20-24 mm Hg) causing the death of all saline-treated animals within 30 min, the i.v. bolus injection of ACTH-(1-24) (160 micrograms/kg) produced an almost complete and sustained reversal of the shock condition, with recovery of arterial blood pressure, pulse pressure and respiratory rate, and with 100% survival at the end of the experiment (2 h). The serotonin-depleting agent p-chlorophenylalanine (316 mg/kg i.p., administered 66-70 h before hemorrhage) almost completely prevented the effect of ACTH. The 5-HT1/5-HT2 receptor antagonist, methysergide, prevented the effect of ACTH completely when injected i.v. (5 mg/kg), but only in part when injected into a brain ventricle (i.c.v.) (15 micrograms/rat); the 5-HT2 antagonist, ketanserin, prevented the effect of ACTH completely when injected i.c.v. (1.5 micrograms/rat), but only in part when injected i.v. (0.5 mg/kg); the 5-HT3 antagonist, MDL 72222, largely prevented the effect of ACTH when injected i.c.v. (10 micrograms/rat), but had no influence at all when injected i.v. (3 mg/kg); finally, the 5-HT4 antagonist, GR 125487, had no effect when injected i.v. (5 micrograms/kg) or when injected i.c.v. (30 ng/rat). Overall, these data indicate that both CNS and peripheral serotonin play an important role in the complex mechanism of the ACTH-induced hemorrhagic shock reversal.     

K-ATP-blocking diuretic PNU-37883A reduces plasma renin activity in dogs

We determined the effects of the K-adenosine triphosphate (ATP)-blocking diuretic PNU-37883A on plasma renin activity (PRA) in conscious and anesthetized dogs. In conscious dogs, oral PNU-37883A (6-60 mg/kg) was less potent than hydrochlorothiazide (0.15-1.5 mg/kg) and furosemide (FURO; 0.3-3.0 mg/kg) but exhibited high natriuretic efficacy with little kaliuresis. Unlike the standard diuretics, PNU-37883A reduced PRA by 46-76%, and its high dose minimally affected 24-h urinary aldosterone excretion. PNU-37883A, 1 mg/kg i.v., also blunted the hyperreninemia induced by 1 mg/kg i.v. FURO. In cannulated dogs, 10 mg/kg i.v. PNU-37883A maximally increased fractional Na+ clearance 140% and reduced PRA 76%, but these effects were accompanied by a mean 13 mm Hg pressor effect. In anesthetized dogs, renal artery-infused PNU-37883A (3 mg/kg/h i.r.a.) increased Na+ excretion and reduced renal venous PRA independent of hemodynamics, whereas half this dosage selectively reduced renal venous PRA and renin release, independent of hemodynamics and natriuresis. These data demonstrate that the K-ATP blocker diuretic PNU-37883A reduces PRA in dogs after oral, i.v., and i.r.a. administration and could be a useful pharmacologic agent for exploring the role of K-ATP channels in regulating renin release.     

Basic evaluation of post-anal preoperative pulmonary mechanism in heart surgery patients under extracorporeal circulation

Effects of clonidine on blood pressure, heart rate and rectal temperature in conscious rats were examined. Clonidine (0.1-1 mg/kg s.c.) caused a prevailing pressor response and dose-dependently a fall in heart rate and body temperature. The pressor response to clonidine (0.3 mg/kg s.c.) was completely reduced by phentolamine (10 mg/kg s.c.), chlorpromazine (10 mg/kg s.c.) but not by hexamethonium (30 mg/kg i.p.), guanethidine (30 mg/kg s.c.) or reserpine (5 mg/kg s.c. 18 hr + mg/kg i.p. 4 hr prior to clonidine). Conversely, a remarkable potentiation of the pressor response to clonidine was observed after treatment with reserpine. The bradycardia with clonidine (0.3 mg/kg s.c.) was significanlty reduced by phentolamine, chlorpromazine or atropine (5 mg/kg s.c.) but was potentiated by reserpine. The hypothermia with clonidine (0.3 mg/kg s.c.) was not influenced by phentolamine or atropine but was significanlty potentiated by chlorpromazine. From the above results it is suggested that the prevailing pressor response to clonidine in conscious rats is due to a stimulation of peripheral alpha-adrenoceptors, the bradycardia with clonidine is exerted through the sympathetic pathway and the baroceptor-vagal reflex, and that the hypothermia with clonidine is mainly due to the central mechanism.     

Two types of modified cardiac Na+ channels after cytosolic interventions at the alpha-subunit capable of removing Na+ inactivation

Repeated oesophageal acidification is a definitive feature of gastro-oesophageal reflux disease, which in turn is caused by relaxation of the lower oesophageal sphincter (LOS). This study in anaesthetised ferrets investigates the reflex pathways involved in effects of oesophageal acidification on motor function of the LOS, with particular focus on the role of tachykinins. LOS pressure was monitored with a perfused micromanometric sleeve assembly. Oesophageal acidification reduced LOS pressure by 48 +/- 5% until washout with saline. This reduction became larger with repeated tests, and was unaffected in amplitude by acute bilateral vagotomy, although the response became slower in onset. Intra-oesophageal capsaicin (0.5% solution) caused a 68 +/- 17% decrease in LOS pressure which remained unchanged with repeated tests. The NK-1 receptor antagonist CP96,345 (1-5 mg/kg intravenous (i.v.) blocked the post-vagotomy LOS responses to both intra-luminal acid and capsaicin. Close intra-arterial (i.a.) injections of capsaicin (1-100 micrograms) gut induced LOS relaxation which was neither vagally nor NK-1 receptor-mediated. Substance P or the selective NK-1 receptor agonist [Sar9, Met(O2)11] substance P (25-500 ng close i.a.) caused a biphasic LOS response, consisting of initial brief contraction followed by prolonged, dose-dependent relaxation. Tetrodotoxin (10 micrograms/kg close i.a.) changed the biphasic response to substance P to excitation only. The neurokinin-1 (NK-1) receptor antagonist CP96,345 (0.3-10 mg/kg i.v.) dose-dependently reduced the inhibitory response to substance P. The excitatory phase of the response to substance P was larger and prolonged after guanethidine (5 mg/kg, i.v.), or propranolol (1 mg/kg, i.v.). L-NAME (100 mg/kg i.v.) reduced the inhibitory phase. The selective NK-2 receptor agonist [beta-Ala8] neurokinin A(4-10) caused LOS excitation only. These data indicate that intra-oesophageal acid causes substance P release from extrinsic afferent nerve endings which activates local inhibitory pathways to the LOS via NK-1 receptors.     

Monocyte chemotactic protein 1 regulates oral tolerance induction by inhibition of T helper cell 1-related cytokines

Intracerebroventricular (i.c.v.) choline (50-150 microg) increased blood pressure and decreased heart rate in spinal cord transected, hypotensive rats. Choline administered intraperitoneally (60 mg/kg), also, increased blood pressure, but to a lesser extent. The pressor response to i.c.v. choline was associated with an increase in plasma vasopressin. Mecamylamine pretreatment (50 microg; i.c.v.) blocked the pressor, bradycardic and vasopressin responses to choline (150 microg). Atropine pretreatment (10 microg; i.c.v.) abolished the bradycardia but failed to alter pressor and vasopressin responses. Hemicholinium-3 [HC-3 (20 microg; i.c.v.)] pretreatment attenuated both bradycardia and pressor responses to choline. The vasopressin V1 receptor antagonist, (beta-mercapto-beta,beta-cyclopenta-methylenepropionyl1, O-Me-Tyr2, Arg8)-vasopressin (10 microg/kg) administered intravenously 5 min after choline abolished the pressor response and attenuated the bradycardia-induced by choline. These data show that choline restores hypotension effectively by activating central nicotinic receptors via presynaptic mechanisms, in spinal shock. Choline-induced bradycardia is mediated by central nicotinic and muscarinic receptors. Increase in plasma vasopressin is involved in cardiovascular effects of choline.     

Oligosaccharide release from frozen and paraffin-wax-embedded archival tissues

Rats (Sprague-Dawley), submitted to a mechanical noxious stimulus (paw pressure), were tested to determine 1) the antinociceptive effects of p.o. (200, 400 and 800 mg/kg), i.v. (50, 100, 200 and 300 mg/kg) and intrathecal (i.t.) (100 and 200 micrograms/rat) administrations of paracetamol; 2) the influence of i.t. administered tropisetron, a 5-hydroxytryptamine3 (5-HT3) receptor antagonist (0.5, 1 or 10 micrograms/rat) on paracetamol-induced antinociception; 3) the influence of indomethacin (25 mg/kg s.c.), naloxone (10 micrograms/rat i.t.) and yohimbine (1 mg/kg i.v.) on the effect of paracetamol (200 mg/kg i.v.) to determine the involvement of prostaglandins, opioids and alpha-2 adrenoceptors. The displacement by paracetamol of radioligand binding to various receptors was also investigated. Paracetamol induced a significant antinociceptive effect after p.o., i.v. and i.t. administration. A total inhibition of the effect of paracetamol, administered p.o. or i.t., occurred at the dose of 0.5 microgram/rat of tropisetron, whereas 10 micrograms/rat of this antagonist was needed to totally inhibit the action of i.v. administered paracetamol. Indomethacin, naloxone and yohimbine failed to modify paracetamol antinociceptive action. In vitro studies failed to show any binding of paracetamol to 5-HT3 and several other receptors and to 5-HT uptake sites. It is concluded that paracetamol has a central antinociceptive effect, based on an indirect involvement of spinal 5-HT3 receptors.     

Role of kinins in the acute antihypertensive effect of enalapril in hypertensive rats

1. We used the kinin antagonist HOE 140 to investigate the role of endogenous kinins in the acute antihypertensive effect of the angiotensin converting enzyme inhibitor enalapril in chronic and acute renal hypertensive rats. 2. In normotensive rats, treatment with HOE 140 (33 micrograms/kg, sc) caused a complete blockade of the depressor effect of bradykinin (100 ng, ia) without affecting the depressor effect of sodium nitroprusside (1 microgram, i.v.) or the basal blood pressure. 3. HOE 140 treatment (33 micrograms/kg, sc, plus 330 ng/min, i.v.) did not affect basal blood pressure of chronic (6-7 weeks) one-kidney, one clip and two-kidney, one clip hypertensive rats and in rats with acute hypertension, elicited by unclamping the renal pedicle that had been occluded for 5 h, but HOE 140 completely blocked the hypotensive response to bradykinin (100 ng, ia) during the 60-min period after enalapril administration (2 mg/kg, i.v.). 4. Acutely hypertensive rats treated or not with HOE 140 (33 micrograms/kg, sc, plus 330 ng/min, i.v.) presented a similar fall in blood pressure after enalapril (165 +/- 5 to 137 +/- 6 mmHg and 166 +/- 5 to 136 +/- 6 mmHg, respectively). 5. Untreated two-kidney, one clip hypertensive rats presented a rapid and sustained fall in blood pressure after enalapril (177 +/- 4 to 148 +/- 4 mmHg) that did not differ from the HOE 140-treated (33 micrograms/kg, sc, plus 330 ng/min, i.v.) group (177 +/- 6 to 154 +/- 4 mmHg). 6. One-kidney, one clip hypertensive rats treated with HOE 140 (33 micrograms/kg, sc, plus 330 ng/min, i.v.) showed a significantly smaller fall in blood pressure after enalapril (204 +/- 7 to 179 +/- 9 mmHg) compared to the untreated rats (197 +/- 7 to 149 +/- 2 mmHg). 7. These results indicate that kinin potentiation plays an important role in the antihypertensive effect of acutely administered angiotensin converting enzyme inhibitor in the one-kidney, one clip model of hypertension.     

Contribution of nitric oxide to the acute antihypertensive effect of blockers of AT1 angiotensin receptors in spontaneously hypertensive rats

The acute vasodepressor effect of AT1 angiotensin receptor blockers losartan and CL329167 was compared in spontaneously hypertensive rats (SHR) pretreated and not pretreated with NG-monomethyl-L-arginine (LNMMA; 15 mg/kg i.v. bolus plus infusion at 10 mg/kg/h), an inhibitor of nitric oxide (NO) synthesis. The antihypertensive effect of losartan (30 mg/kg, i.v.) in SHR pretreated with LNMMA (-13 +/- 4 mmHg) was greatly diminished (P < 0.01) relative to the antihypertensive effect of losartan in SHR not pretreated with LNMMA (-44 +/- 8 mmHg). Similarly, the antihypertensive effect of CL329167 (5 mg/kg, i.v.) in SHR pretreated with LNMMA (-12 +/- 3 mmHg) was surpassed (P < 0.01) by the antihypertensive effect in SHR not pretreated with LNMMA. (-41 +/- 4 mmHg). However, pretreatment of SHR with LNMMA did not minimize the vasodepressor effect of prazosin, isoproterenol or sodium nitroprusside. The impairment in vasodepressor responsiveness to losartan in rats pretreated with LNMMA was not demonstrable in rats concurrently receiving sodium nitroprusside to correct for the loss of endogenous NO, or atrial natriuretic peptide which also increases vascular cGMP. These data suggest that a mechanism mediated by NO and/or cGMP is necessary for the full expression of the acute antihypertensive effect of AT1 angiotensin receptor blockers in SHR.     

Renal vascular responses to angiotensin II in conscious spontaneously hypertensive and normotensive rats

It has been postulated that exaggerated renal sensitivity to angiotensin II may be involved in the development and maintenance of hypertension in the spontaneously hypertensive rat (SHR). The purpose of this study was to compare the renal vascular responses to short-term angiotensin II infusions (50 ng/kg/min, i.v.) in conscious SHRs and Wistar-Kyoto (WKY) rats. Renal cortical blood flow was measured in conscious rats by using quantitative renal perfusion imaging by magnetic resonance, and blood pressure was measured by an indwelling carotid catheter attached to a digital blood pressure analyzer. Renal vascular responses to angiotensin II were similar in control SHRs and WKY rats. Pretreatment with captopril to block endogenous production of angiotensin II significantly augmented the renal vascular response to exogenous angiotensin II in the SHRs but not in the WKY rats. The renal vascular responses to angiotensin II were significantly greater in captopril-pretreated SHRs than in WKY rats (cortical blood flow decreased by 1.66 +/- 0.13 ml/min/g cortex in WKY rats compared with 2.15 +/- 0.14 ml/min/g cortex in SHR; cortical vascular resistance increased by 10.5 +/- 1.4 mm Hg/ml/min/g cortex in WKY rats compared with 15.6 +/- 1.7 mm Hg/ml/min/g cortex in SHRs). Responses to angiotensin II were completely blocked in both strains by pretreatment with the angiotensin II AT1-receptor antagonist losartan. Results from this study in conscious rats confirm previous findings in anesthetized rats that (a) the short-term pressor and renal vascular responses to angiotensin II are mediated by the AT1 receptor in both SHRs and WKY rats, and (b) the renal vascular responses to angiotensin II are enhanced in SHRs compared with WKY rats when endogenous production of angiotensin II is inhibited by captopril pretreatment.     

Lack of involvement of bradykinin in the vascular sympathoinhibitory effects of angiotensin converting enzyme inhibitors in spontaneously hypertensive rats

1. The aim of this study was to investigate the contribution of endogenous bradykinin to the vascular sympathoinhibitory effects exerted by angiotensin I converting enzyme inhibitors (ACEIs) in the spontaneously hypertensive rat (SHR). 2. Adult SHRs were treated daily for 8 days with either perindopril (3 mg kg-1), or a selective angiotensin II AT1 receptor antagonist, losartan (10 mg kg-1) both given orally--these two doses being equipotent in inhibiting angiotensin I (AI)-induced vascular responses--or distilled water (controls). After pithing, the animals were instrumented for determination of blood pressure, heart rate, cardiac output, regional (renal, mesenteric, hindlimb) blood flows (pulsed Doppler technique) and corresponding vascular resistances. Afterwards, half of the animals of each group were given the selective bradykinin B2 receptor antagonist, icatibant, used in a dose (10 micrograms kg-1, i.v.) that achieved B2 receptor blockade, the other half received saline (10 microliters kg-1, i.v.). Haemodynamic responses to increasing frequencies of spinal cord stimulation were then measured. 3. Pressor and vasoconstrictor responses to AI were significantly and similarly reduced in both perindopril- and losartan-treated groups. Perindopril and losartan both decreased to a similar extent the pressor and vasoconstrictor responses to electrical stimulation of the spinal cord. 4. In the dose used, icatibant did not affect any of the investigated haemodynamic parameters in any of the experimental groups. Furthermore, icatibant did not affect the stimulation frequency-response curves in the control animals and did not modify the vascular sympathoinhibitory effects exerted by perindopril and by losartan. 5 Taken together, these results demonstrate that endogenous bradykinin does not, through B2 receptor activation, contribute to the vascular sympathoinhibitory effects of ACEIs in SHRs.     

A further contribution to the question of trophic and hormonal influences on the noradrenaline content of the male reproductive tract: effect of combined androgen and estrogen treatment of prepuberally castrated rats

The pressor response to the intracisternal (i.c.) injection of carbachol (1 mug) in anesthetized rats was analyzed. This response was significantly reduced by the intravenous (i.v.) injection of guanethidine (5 mg), hexamethonium (10 mg) or phentolamine (5 mg), and conversely, potentiated by i.v. desmethylimipramine (0.3 mg), while propranolol (0.5 mg) i.v. selectively inhibited the enlargement of pulse pressure and the tachycardia following i.c. carbachol (1 mug). On the other hand, the pressor response to i.c. carbachol (1 mug) was almost completely blocked by i.c. atropine (3 mug) or hexamethonium (500 mug), and significantly reduced by i.c. chlorpromazine (50 mug) but significantly potentiated by i.c. desmethylimipramine (30 mug). The pressor response to i.c. carbachol (1 mug) remained unchanged after sectioning of the bilateral cervical vagal nerves but disappeared after sectioning of the spinal cord (C7-C8). From the above result it is suggested that the pressor response to i.c. carbachol ortral and peripheral adrenergic mechanisms, and that the sympathetic trunk is the main pathway.     

Phenytoin blocks the reversal of a classically conditioned discriminative eyeblink response in rabbits

The aim of the present study was to assess the role of vascular alpha 1D-adrenoceptors in the sympathetic vasopressor response in vivo. Specifically, we evaluated the effect of a selective alpha 1D-adrenoceptor antagonist, BMY 7378 (8-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-8-azaspiro(4,5)dec ane-7,9- dione 2HCl), on the vasopressor response induced by preganglionic (T7-T9) sympathetic stimulation in the pithed rat. The vasopressor response was dose-dependently sensitive to inhibition by intravenous BMY 7378 (0.1, 0.31, 1 and 3.1 mg/kg), doses of 1 and 3.1 mg/kg being equally effective. Like BMY 7378, 5-methylurapidil (0.1, 0.31, 1 and 3.1 mg/kg) antagonized the vasopressor response to spinal stimulation; doses of 1 and 3.1 mg/kg were also equally effective. In combination experiments, BMY 7378 (1 mg/kg, i.v.) and the alpha 1A-adrenoceptor antagonist, 5-methylurapidil (1 mg/kg, i.v.), showed an additive effect. The present results demonstrate that the alpha 1D-adrenoceptor subtype plays an important role in the pressor response to sympathetic nerve stimulation in the pithed rat, and confirm the participation of the alpha 1A-adrenoceptor subtype in the same response.     

7-D-ALA]-angiotensin 1-7 blocks renal actions of angiotensin 1-7 in the anesthetized rat

Exogenous angiotensin (Ang) 1-7 affects renal function, but the receptor(s) involved in this response remain(s) to be determined. In an in vitro preparation of proximal tubules, Ang 1-7 was shown to act on Ang II AT1 receptors (minor component), but also on a non-AT1, non-AT2 Ang receptor (major component) to inhibit reabsorption. In brain, Ang 1-7 also exerts effects mediated by a non-AT1, non-AT2 binding site; these effects are inhibited, however, by the angiotensin analog [7-D-Ala]-Ang 1-7. Therefore we tested the effect of Ang II AT1-receptor antagonist losartan and [7-D-Ala]-Ang 1-7 on the renal response to exogenous Ang 1-7 in standard renal-clearance experiments in the anesthetized rat. We found that Ang 1-7 (100 pmol/kg/min, i.a.) increased glomerular filtration rate (GFR), urinary flow rate (UV), and urinary sodium excretion (UNaV) without affecting mean arterial blood pressure (MAP) or urinary potassium excretion (UKV), confirming previous reports. Losartan (10 mg/kg, i.v.) blocked the pressor effect of exogenous Ang II (100 pmol/kg/min, i.a.), but did not significantly affect the renal response to Ang 1-7. Conversely, pretreatment with [7-D-Ala]-Ang 1-7 (5 nmol/kg/min) did not affect the pressor effect of Ang II, but abolished the renal response to Ang 1-7. Application of [7-D-Ala]-Ang 1-7 in the absence of exogenous Ang 1-7 did not alter MAP or GFR, but increased UNaV (by 52%). Our data indicate that similar to the response in brain, the renal response to exogenous Ang 1-7 may be mediated predominantly by a distinct non-AT1 binding site, which is sensitive to blockade by [7-D-Ala]-Ang 1-7. Furthermore, ambient endogenous Ang 1-7 acting on this distinct binding site may not contribute significantly to control of MAP or GFR, but exerts an antinatriuretic influence in the anesthetized rat.     

Effects of renin inhibition compared to angiotensin converting enzyme inhibition in conscious dogs with pacing-induced heart failure

OBJECTIVE: To compare the effects of angiotensin converting enzyme inhibition (ACEI) (captopril 1 mg/kg i.v.) to direct renin inhibition (CP80794 3 mg/kg i.v.) on left ventricular and systemic hemodynamics and peripheral blood flows in advanced congestive heart failure (CHF). METHODS: Conscious chronically instrumented dogs (n = 14) were treated with captopril, 1 mg/kg, i.v., or CP80794, 3 mg/kg, i.v., before and after development of advanced CHF induced by 4-7 weeks of rapid ventricular pacing. After advanced CHF, comparisons between the inhibitors were made at equihypotensive doses. RESULTS: In advanced CHF, both agents caused comparable reductions in mean arterial pressure (MAP) (-22% from 79 +/- 4 mmHg) and comparable increases (P < 0.01) in cardiac output (CP80794, 1.4 +/- 0.3 to 1.8 +/- 0.1 l/min; captopril, 1.4 +/- 0.1 to 1.9 +/- 0.1 l/min). Neither agent had a significant effect on LV contractility. In contrast, CP80794 caused a greater (P < 0.05) increase in renal blood flow (66 +/- 6% from 64 +/- 5 ml/min) compared to captopril (33 +/- 4% from 66 +/- 7 ml/min). CONCLUSIONS: Renin inhibition with CP80794 and ACEI with captopril caused comparable hemodynamic effects in advanced CHF. However, CP80794 caused significantly greater increases in renal blood flow and suppressed renin activity to a greater degree than captopril.     

Relationship between decidual leukocyte infiltration and spontaneous abortion in a murine model of early fetal resorption

The cardiovascular effects of KRN2391, N-cyano-N'-(2-nitroxyethyl)-3-pyridine carboximidamide monomethanesulfonate, were compared with those of cromakalim and nitroglycerin in anesthetized dogs. KRN2391 (3-30 micrograms/kg, i.v.), cromakalim (3-30 micrograms/kg, i.v.) and nitroglycerin (1-10 micrograms/kg, i.v.) produced a dose-related decrease of the mean blood pressure with concomitant increase in heart rate. The increase in heart rate caused by cromakalim was lower than that caused by KRN2391 and nitroglycerin. Left ventricular end-diastolic pressure was decreased by all doses of KRN2391 and nitroglycerin. Cromakalim at 3 and 10 micrograms/kg decreased this end-diastolic pressure but increased it at 30 micrograms/kg. Left ventricular dP/dt was increased by KRN2391 and nitroglycerin but was decreased by cromakalim. KRN2391 and cromakalim produced a dose-dependent increase in aortic and coronary blood flow. Nitroglycerin showed biphasic changes in aortic and coronary blood flow, i.e., an initial increase followed by a decrease. At equipotent hypotensive doses, the increase in coronary blood flow induced by KRN2391 was greater than that by cromakalim and nitroglycerin, and total peripheral and coronary vascular resistances were decreased by KRN2391 and cromakalim. Nitroglycerin showed biphasic changes in total peripheral and coronary vascular resistances, i.e., these resistance showed an initial decrease followed by an increase. The relative decrease of coronary vascular resistance compared to the total peripheral vascular resistance was greater for KRN2391 than for cromakalim and nitroglycerin. The changes in hemodynamic parameters caused by KRN2391 were inhibited by pretreatment with glibenclamide (5 mg/kg, i.v.). These results suggest that the hemodynamic profile of KRN2391 is closer to that of cromakalim than to that of nitroglycerin, but that the selectivity for the coronary vascular bed is higher for KRN2391 than for cromakalim. In addition, it is considered that, compared with KRN2391 and nitroglycerin, cromakalim has a low selectivity for the vasculature vs the myocardium.     

Endothelial dysfunction in spontaneously hypertensive rats: consequences of chronic treatment with losartan or captopril

BACKGROUND: Hypertension is associated with endothelial dysfunction characterized by decreased endothelium-dependent relaxations and increased endothelium-dependent contractions. Angiotensin converting enzyme inhibitors and thromboxane A2 receptor antagonists decreased the endothelium dysfunction in hypertensive animals. OBJECTIVE: To investigate the effects of prolonged treatment with losartan on endothelium-dependent and -independent relaxations and contractions in aortic rings from spontaneously hypertensive rats (SHR). MATERIAL AND METHODS: Male SHR aged 16 weeks were treated for 12 consecutive weeks either with 10 mg/kg losartan per day or with 60 mg/kg captopril per day administered via their drinking water. The systolic blood pressure was evaluated basally and during week 12. At the end of the treatment period, the vascular reactivity in aortic rings was studies. A group of rats treated with captopril was studies as a reference group. RESULTS: Losartan and captopril reduced the blood pressure significantly and comparably. Both drugs enhanced acetylcholine-induced relaxations and reduced the maximal contractile response to acetylcholine in the presence of NG-nitro-L arginine methyl ester (L-NAME). Contractile responses to phenylephrine, endothelin-l and U46619 were not affected by these treatments. Increased relaxing responses to superoxide dismutase were observed only in captopril-treated rats. Losartan reduced the contractile response to angiotensin II. By contrast this contractile response was elevated in rats treated with captopril. CONCLUSIONS: Prolonged antihypertensive treatments with losartan and captopril decreased the endothelial dysfunction in aortic rings from SHR not only by enhancing NO-dependent relaxations but also by reducing the contractions in response to an endothelium-derived contracting factor. The results further confirm that an endothelium-derived contracting factor plays a role in vascular dysfunction in SHR and the relationships between this factor and angiotensin II.     

Influence of pentoxifylline on fevers induced by bacterial lipopolysaccharide and tumor necrosis factor-alpha in guinea pigs

In guinea pigs intraperitoneal (i.p.) injections of 50 mg/kg pentoxifylline had no influence on abdominal temperature while higher doses of pentoxifylline caused a hypothermic response lasting for 2-3 h. Administration of 50 mg/kg pentoxifylline 1 h before intramuscular (i.m.) injections of 20 micrograms/kg bacterial lipopolysaccharide reduced the lipopolysaccharide-induced production of endogenous tumor necrosis factor-alpha (TNF-alpha) by 68%. The second phase of lipopolysaccharide-induced fever was significantly attenuated by pretreatment with 50 mg/kg pentoxifylline, a dose which had, per se, no influence on core temperature of guinea pigs. The thermal response of guinea pigs to administration of exogenous TNF-alpha was not modulated by pretreatment with pentoxifylline. Intra-arterial infusions with 5 micrograms/kg TNF-alpha, a dose which yielded the same circulating TNF bioactivity as i.m. injections of 20 micrograms/kg lipopolysaccharide, induced a biphasic febrile response. The magnitude and duration of TNF-induced fever were the same whether guinea pigs were pretreated with pentoxifylline or with 0.9% saline. The results indicate that endogenous formation of TNF-alpha may contribute to the development of fever induced by lipopolysaccharide, but is not its only mediator, since the first phase of lipopolysaccharide-induced fever was not altered by the blockade of TNF production.