Recombinant human complement C5a receptor antagonist reduces infarct size after surgical revascularization.

OBJECTIVES: This study tested the hypothesis that a recombinant human C5a antagonist, CGS 32359, attenuates neutrophil activation and reduces infarct size in a porcine model of surgical revascularization. METHODS: CGS 32359 (0.16-16 micromol/L) dose-dependently inhibited superoxide production by human C5a-activated porcine neutrophils (18 +/- 3.7 vs 1.6 +/- 0.5 nmol/5 min/5 x 10(6) neutrophils; P <.05) and reduced neutrophil adherence to coronary endothelium from 194 +/- 9 to 43 +/- 6 neutrophils/mm(2) (P <.05). The left anterior descending coronary artery was occluded for 50 minutes, after which saline solution (n = 8), mannitol-buffer vehicle (n = 9, 102 mg/kg bolus, 102 mg. kg(-1). h(-1)), or CGS 32359 (CGS, n = 7, 60 mg/kg bolus, 60 mg. kg(-1). h(-1)) was infused. After ischemia, 1-hour arrest was achieved by means of multidose hypothermic (4 degrees C) blood cardioplegia, followed by 2.5 hours of off-bypass reperfusion. The ligature on the left anterior descending artery was released before the second infusion of cardioplegic solution. RESULTS: Area at risk was similar in all groups (saline solution, 27% +/- 2%; mannitol-buffer vehicle, 26% +/- 2%; CGS, 26% +/- 2% left ventricular mass). Infarct size (area necrosis/area at risk) was significantly reduced by CGS (18% +/- 6%, P <.05) versus saline solution (52% +/- 3%) and mannitol-buffer vehicle (60% +/- 4%). Postischemic systolic shortening (sonomicrometry) in the area at risk was significantly improved with CGS (0.8% +/- 0.9%) compared with saline solution (-3.7% +/- 1.1%) and mannitol-buffer vehicle (-6.4% +/- 1.0%). Myeloperoxidase activity from accumulated neutrophils was less in the ischemic zone of CGS (0.014 +/- 0.002 U/100 mg tissue; P <.05) than mannitol-buffer vehicle (0.133 +/- 0.012 U/100 mg tissue). CONCLUSIONS: We conclude that the recombinant human C5a receptor antagonist CGS 32359 inhibits surgical ischemia-reperfusion injury after coronary occlusion.

Antihypertensive and natriuretic effects of CGS 30440, a dual inhibitor of angiotensin-converting enzyme and neutral endopeptidase 24.11.

Dual angiotensin-converting enzyme (ACE)/neutral endopeptidase (NEP) inhibitors, by decreasing angiotensin-II production and by preventing the degradation of atrial natriuretic peptide (ANP), may be useful for the treatment of hypertension and congestive heart failure. The thiol dipeptide CGS 30440 (prodrug of CGS 30008, IC50: ACE/NEP = 19/2 nM) administered to rats (10 mg/kg p.o.) inhibited lung tissue ACE activity by 98% and 61% at 1 and 24 hr (P < .001) and inhibited the angiotensin-I pressor response by 75 to 90% for more than 6 hr. Renal tissue NEP activity was reduced by 80% at 1 hr and 73% at 24 hr (P < .001). In rats supplemented with exogenous ANP, CGS 30440 (1 mg/kg p.o.) elevated the concentration of circulating ANP (133%, P < .025) for 4 hr and increased the excretion of urine (300%, P < .001), sodium (194%, P < .025) and cyclic GMP (238%, P < .005). CGS 30440 (10 mg/kg p.o.) administered to hypertensive rats with aortic ligation between the renal arteries (mean arterial blood pressure, 209 +/- 4 mm Hg) produced a 48 mm Hg blood pressure reduction (P < .001) within 4 hr. CGS 30440 given to cynomolgus monkeys at 2 mg/kg inhibited plasma ACE activity by 96% within 1 hr (P < .001), and this inhibition was maintained for 7 and 21 days in monkeys receiving the compound orally at 2.5 mg/kg b.i.d. These studies demonstrate that CGS 30440 is an orally active agent which produces tissue ACE and NEP inhibition in rats and plasma ACE inhibition in primates and suggest that the compound may be useful in the treatment of hypertension and congestive heart failure.

Prevention and reversal of cerebral vasospasm by an endothelin-converting enzyme inhibitor, CGS 26303, in an experimental model of subarachnoid hemorrhage.

Delayed cerebral ischemia due to cerebral vasospasm is a major cause of morbidity and mortality in patients with aneurysmal subarachnoid hemorrhage (SAH). Increasing evidence implicates the potent vasoconstrictor peptide endothelin (ET) in the pathophysiology of cerebral vasospasm. In the present study the authors examined the therapeutic value of blocking the production of ET-1 by inhibiting the conversion of its relatively inactive precursor, Big ET-1, to a physiologically active form. An inhibitor of ET-converting enzyme (ECE), CGS 26303, was injected intravenously after inducing SAH in New Zealand white rabbits. Injections of CGS 26303 were initiated either 1 hour after SAH (prevention protocol) or 24 hours after SAH (reversal protocol). One of three concentrations (3, 10, or 30 mg/kg) of CGS 26303 was injected twice daily, and all animals were killed by perfusion fixation 48 hours after SAH occurred. Basilar arteries were removed and sectioned, and their cross-sectional areas were measured in a blind manner by using computer-assisted videomicroscopy. Treatment with CGS 26303 attenuated arterial narrowing after SAH in both the prevention and reversal protocols. The protective effect of CGS 26303 achieved statistical significance at all dosages in the prevention protocol and at 30 mg/kg in the reversal protocol. These findings demonstrate that inhibiting the conversion of Big ET-1 to ET-1 via intravenous administration of an ECE inhibitor can be an effective strategy for limiting angiographic vasospasm after SAH. Moreover, the results demonstrate that treatment with the ECE inhibitor is capable of reducing vasospasm even when initiated after the process of arterial narrowing has begun. Finally, the results provide further support for the role of ET in the establishment of cerebral vasospasm. The ECE inhibitor CGS 26303 thus represents a promising therapeutic agent for the treatment of cerebral vasospasm following aneurysmal SAH.

Systemic administration of an inhibitor of endothelin-converting enzyme for attenuation of cerebral vasospasm following experimental subarachnoid hemorrhage.

The potent vasoconstrictor peptide, endothelin-1 (ET-1), has been implicated in the pathophysiology of cerebral vasospasm that occurs after subarachnoid hemorrhage (SAH). This peptide is synthesized as a large prepropeptide that requires a series of modifying steps for its activation. The last of these steps involves the proteolytic conversion of a relatively inactive propeptide, Big ET-1, to its active, 21-amino acid peptide form. The enzyme responsible for converting Big ET-1 to ET-1 is a metalloprotease called endothelin-converting enzyme (ECE). In the present study the authors examined the effects of a newly developed inhibitor of ECE on responses to ET peptides in the normal basilar artery and on pathophysiological constriction in the spastic basilar artery after SAH. In the first series of experiments the authors examined normal basilar arteries in the rabbit, which were exposed transclivally and measured on-line using videomicroscopy. Intravenous administration or topical application of an active inhibitor of ECE, CGS 26303, blocked vasoconstrictor responses to topically applied Big ET-1 but not to ET-1. In contrast, topical application of a structurally related compound that does not inhibit ECE, CGS 24592, was ineffective in blocking vasoconstriction that was elicited by a topical application of Big ET-1. These findings indicate that CGS 26303 when administered systemically is capable of blocking the conversion of Big ET-1 to ET-1 in the basilar artery without affecting the ability of the vessel to respond to ET-1. In the second series of experiments the authors examined the effects of the ECE inhibitor on cerebral vasospasm after experimental SAH. Intraperitoneal administration of CGS 26303 via osmotic minipumps significantly attenuated the delayed spastic response of the basilar artery to an intracisternal injection of autologous blood. This study provides the first evidence that systemic administration of an inhibitor of ECE is capable of preventing cerebral vasospasm after SAH. The results reinforce a growing body of evidence that ETs play a critical role in the development of spastic constriction after SAH. Moreover, the findings indicate that blocking the conversion of Big ET-1 to its active ET-1 form using CGS 26303 may represent a feasible strategy for ameliorating cerebral vasospasm.

In vitro and in vivo evaluation of an endothelin inhibitor reveals novel K+ channel opening activity.

A low molecular weight endothelin (ET-1) inhibitor (Ex. 127, European Patent Application 404 525 A2, Takeda Chemical Ind., 1991), CGS 26061, was synthesized and evaluated to determine its mechanism of action. CGS 26061 (10 microM) failed to inhibit binding of [125I]ET-1 in porcine thoracic aorta and was without effect on ET-1-induced [3H]inositol phosphate accumulation in A7r5 cells. However, CGS 26061 relaxed porcine coronary arterial rings precontracted with ET-1. In addition, contractions to PGF2 alpha and low K+ (20 mM) but not high K+ were attenuated, suggesting that CGS 26061 (1, 10 microM) is a potassium channel opener. Patch-clamp experiments confirmed the K+ channel activity (0.1-10 microM). The originally re ported inhibition of ET-1-induced pressor responses by Ex. 127 (CGS 26061) was not replicated in the anesthetized dog or conscious rat nor was it shown to be antihypertensive in SHR. These data have identified CGS 26061 as a novel K+ channel opener with a unique cardiovascular profile.

Effects of metalloprotease inhibitors on the conversion of proendothelin-1 to endothelin-1.

The IC50 values of phosphoramidon, CGS 25015, CGS 26129, thiorphan and benazeprilat for inhibition of endothelin converting enzyme partially purified from porcine aortic endothelial cells were 3.5, 18, 58, > 100 and > 100 microM, respectively. A similar rank order of potency was observed for inhibition of the proendothelin-1 (proET-1) -induced pressor response in the rat where phosphoramidon, CGS 25015, CGS 26129, thiorphan and benazeprilat at 30 mg/kg i.v. produced 65, 57, 27, 12, and 0% inhibition, respectively. A slightly different rank order of potency was obtained in the proET-induced contraction of porcine coronary arteries where IC50 values of < 10, 10-30, 10-30, 30-100 and 30-100 microM were exhibited by CGS 25015, CGS 26129, phosphoramidon, thiorphan and benazeprilat, respectively. These data indicate that the endothelin converting enzymes in the three systems studied are similar, except that phosphoramidon is a slightly more potent inhibitor in the in vitro assay and the in vivo pressor test than in the smooth muscle contraction assay.

Comparison of hirudin and heparin as adjuncts to streptokinase thrombolysis in a canine model of coronary thrombosis.

Recombinant desulfatohirudin (HI), a potent and specific thrombin inhibitor, was compared with heparin (HE) as an adjunct to streptokinase thrombolysis. In pentobarbital-anesthetized dogs, an occlusive thrombus (whole blood+thrombin) was introduced into the left anterior descending coronary artery (LAD) with superimposed endothelial damage and distal high-grade stenosis. Intravenous infusion of saline (vehicle), HI (0.3 mg/kg followed by 0.3 mg/kg per hour, 1 mg/kg followed by 1 mg/kg per hour, or 2 mg/kg followed by 2 mg/kg per hour), or HE (60 units/kg followed by 40 units/kg per hour or 100 units/kg followed by 60 units/kg per hour) was initiated 15 minutes before streptokinase (750,000 units for 60 minutes) administration. Vessel patency was monitored for 180 minutes after streptokinase administration with a volume flow probe on the proximal LAD. In dogs treated with no adjunctive agent (saline control), none of the vessels were recanalized with streptokinase. Both HI and HE promoted reperfusion, inhibited reocclusion, and reduced the residual thrombus mass in a dose-dependent fashion. However, at comparable levels of therapeutic anticoagulation (activated partial thromboplastin time [APTT] = 1.5-2.0 times baseline) HI exhibited a higher incidence of reperfusion (eight of eight dogs [100%] versus one of eight dogs [12%]), a shorter time to reperfusion (33 +/- 6 versus 59 minutes), a longer duration of initial reperfusion (106 +/- 21 versus 10 minutes), and a smaller residual thrombus mass than did HE. Likewise, the slope of the relation between the APTT prolongation and the total reperfusion time ("anticoagulation/antithrombosis profile") was almost five times higher for the combined HI data than for the HE data. Our results indicate that HI is more effective than HE in enhancing and sustaining coronary recanalization with streptokinase at a HI dose that modestly prolongs coagulation time and does not alter bleeding times.

Functionally distinct endothelin B receptors in vascular endothelium and smooth muscle.

IRL 1620 (Suc-[Glu9,Ala11,15]-ET-1 (8-21)) (0.1 nM - 1 microM), a novel ETB-selective endothelin (ET) agonist, produced endothelium-dependent relaxations in precontracted rabbit mesenteric artery (2 nM, EC50) and endothelium-independent contractions in porcine coronary artery (18 nM, EC50). ET-3 (0.1 nM-10 nM) produced qualitatively similar responses in the two tissues. The maximal contractions induced by IRL 1620 or ET-3 were substantially smaller (< 20%) than that produced by ET-1. BQ-123 (1 microM), an ETA receptor antagonist, inhibited responses to ET-1 without affecting IRL 1620- or ET-3-induced responses in either tissue. Thus functionally distinct ETB receptors mediating vasodilator and vasoconstrictor effects are located on the vascular endothelium and smooth muscle, respectively. The overall effect of ETB receptor activation on vascular tone is tissue-specific and presumably reflects differing receptor distribution at the two sites.

Coupling of endothelin receptors to ion channels in rat glomerular mesangial cells.

Endothelin (ET) induces depolarization and contraction of glomerular mesangial cells (MCs), thereby influencing intraglomerular hemodynamics and filtration rate. In an attempt to clarify the ionic mechanism by which ET regulates MC function, we examined, using the whole-cell configuration of the patch-clamp technique, the effects of ET-1 and its related peptides, ET-3, sarafotoxin 6c (S6c), and IRL 1620, on ion currents and membrane potential in the primary culture of rat MCs. The resting potential of MCs was -48.4 +/- 1.9 mV (n = 23). It depolarized in response to ET-1, ET-3, and IRL 1620 by 14 (n = 7), 8 (n = 5), and 13 mV (n = 9), respectively. Whole-cell recording in combination with ion substitution ascertained the coexistence of potassium (IK) and chloride (ICl) currents. ET-1 (0.01-100 nM), ET-3 (1-100 nM), IRL 1620 (0.1-100 nM), and S6c (0.01-10 nM) augmented ICl in a concentration-dependent fashion, with ET-1 and S6c being the most potent. These actions were blocked by IRL 1038, a selective ETB receptor antagonist, but not by 1 microM BQ 123 (a selective ETA receptor antagonist) or 0.1 microM nifedipine (an L-type Ca(2+)-channel blocker). These results suggest a close coupling of the ETB receptor to ICl. ET-1, IRL 1620, and SRTX-6c in a similar concentration range also caused suppression of IK. This action was partially blocked by IRL 1038 and minimally affected by BQ 123, indicating a contributory role for ETB receptors in the regulation of IK.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential responsiveness of conduit and resistance coronary arteries to endothelin A and B receptor stimulation in anesthetized dogs.

The effects of endothelin-1 (ET-1), an ET(A)/ETB-receptor agonist, and IRL 1620, a potent and selective ETB-receptor agonist, were assessed on left circumflex coronary artery diameter (sonomicrometry) and flow (electromagnetic flow probe) in pentobarbital-anesthetized dogs. Intracoronary (i.c.) bolus injections of ET-1 (80 pmol/dose) caused large, sustained coronary diameter decreases (281 +/- 39 microns) and transient flow increases (5.6 +/- 2.6 ml/min), followed by transient (10.0 +/- 1.9 ml/min) and then sustained flow reductions (6.6 +/- 2.5 ml/min) before terminating in ventricular fibrillation after two to five doses (max delta s; n = 4 dogs). IRL 1620 boluses (5-2,000 pmol/dose i.c.; max delta s; n = 3) also dose-dependently and transiently increased (16.8 +/- 1.4 ml/min; 200 pmol), then transiently decreased (12.8 +/- 1.5 ml/min; 1,600 pmol) flow but had minimal effects on diameter (delta = -23 +/- 4 microns; 2,000 pmol). Doses of IRL 1620 beyond 400 pmol were accompanied by a slowly responding, sustained decrease in baseline flow (-9.2 +/- 2.7 ml/min) and baseline diameter (232 +/- 150 microns). In a separate group of dogs (n = 5), IRL 1620 (400 pmol i.c.) was evaluated before and after sequential inhibition of cyclooxygenase (indomethacin; 10 mg/kg i.v.) and then nitric oxide synthase (N omega-nitro-L-arginine methyl ester, L-NAME; 50 mg/kg i.v.). Indomethacin alone did not affect the flow increase to IRL 1620 (11.0 +/- 2.0 versus 11.8 +/- 1.8 ml/min) but blunted the flow decrease by 30 +/- 6% (10.6 +/- 1.4 versus 7.1 +/- 0.7 ml/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic characterization of an endothelinA (ETA) receptor antagonist in conscious rats.

The present experiments describe the endothelin-1 (ET-1) antagonist activity of BQ123 (cyclic D-Asp-L-Pro-D-Val-L-Leu-D-Trp) in conscious Sprague-Dawley (SD) rats, and we also examined the effect blockade of ETA receptors had on blood pressure in four experimental models of hypertension. Rats were anesthetized with methoxyflurane and instrumented with femoral arterial and venous catheters. In SD rats, BQ123 (0.1-10.0 mg/kg i.v.) administered 5 or 60 min prior to ET-1 inhibited both the magnitude and duration of the ET-1 (0.25 nmol/kg i.v.) pressor response. In addition, BQ123 (10.0 mg/kg) inhibited the pressor response evoked by administration of the ET-1 precursor, proendothelin-1 (1.0 nmol/kg). However, BQ123 (10.0 mg/kg) had no effect on the pressor response evoked by ET-3 (0.75 nmol/kg). In Wistar-Kyoto rats, BQ123 (10.0 mg/kg) reversed the hypertension produced by an infusion of ET-1 (0.01 nmol/kg/min). Administration of BQ123 produced a mild antihypertensive effect in normal- to low-renin models of hypertension, but no blood pressure lowering was observed in high-renin models of hypertension. These studies demonstrated the selectivity of the ETA receptor antagonist, BQ123 for ET-1, but not ET-3-induced pressor responses. Furthermore, ET-1 does not appear to be a major contributing factor to the maintenance of elevated levels of blood pressure in four experimental models of hypertension.

In vitro and in vivo interactions of nitrovasodilators and zaprinast, a cGMP-selective phosphodiesterase inhibitor.

We have examined the interaction of zaprinast, a selective inhibitor of cGMP phosphodiesterase, with guanylate cyclase activators on vascular smooth muscle relaxation in vitro and in vivo. Isolated porcine coronary arterial rings precontracted with prostaglandin F2 alpha (PGF2 alpha) were relaxed dose dependently by the guanylate cyclase activators nitroglycerin and nitroprusside, the cGMP phosphodiesterase inhibitor zaprinast and the endothelium-dependent agent bradykinin. A 1 h pretreatment with 0.5 mM nitroglycerin shifted the dose-response curve to nitroglycerin to the right by a factor of 90, reflecting the development of tolerance. The dose-response curve to sodium nitroprusside was also affected, albeit to a much lesser degree (9-fold increase in IC50). Both zaprinast and bradykinin remained unaffected by nitroglycerin pretreatment. A 30 min pretreatment of rings with zaprinast (1 microM) had no effect on nitroglycerin- or nitroprusside-induced relaxation in control rings, but enhanced vasorelaxation to both nitrovasodilators 7- and 2-fold, respectively, in tolerant rings. Similarly, a 30 min pretreatment of rings with 0.1 microM nitroprusside enhanced zaprinast-induced vasorelaxation 4- and 8-fold, respectively, in control and tolerant rings. Similar observations were made in vivo in anesthetized spontaneously hypertensive rats where zaprinast (0.1-3.0 mg/kg i.v.), caused dose-dependent reductions in mean arterial pressure. This effect was enhanced when rats had been pretreated with nitroprusside (1 micrograms/kg per min). In comparison, in zaprinast-pretreated rats the magnitude of depressor responses to nitroprusside (0.5-5.0 micrograms/kg) was not altered, but the duration of hypotensive response to the highest dose of nitroprusside was enhanced by zaprinast. These data demonstrate an enhanced vasodilatory response of nitrocompounds in combination with peak I-selective phosphodiesterase inhibitors.

Selective adenosine-2 agonist produces both direct and reflex tachycardia in normotensive rats.

Hemodynamic responses to intravenous (i.v.) injection of DPMA [N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl] adenosine); PD 125,944], a potent adenosine agonist with a 32-fold selectivity for the adenosine-2 (A2) receptor subtype, were characterized in conscious and anesthetized rats. In conscious rats instrumented with miniaturized pulsed-Doppler flow probes, i.v. injection of increasing doses of DPMA (3-30 micrograms/kg) had little effect on mean arterial pressure (MAP, maximal decrease -8 +/- 4 mm Hg) or renal and mesenteric resistance (maximal change 8 +/- 14 and 0 +/- 15%, respectively). In contrast, DPMA markedly reduced MAP (maximal decrease -61 +/- 8 mm Hg) in a dose-dependent (1-30 micrograms/kg) fashion in pentobarbital-anesthetized rats. The A2 agonist also caused a sustained, dose-dependent increase in heart rate (HR, maximal increase 75 +/- 12 beats/min) in conscious rats. The tachycardia and decrease in arterial pressure were completely reversed by i.v. administration of CGS 15943 (250 micrograms/kg), a selective adenosine receptor antagonist. Pretreatment with propranolol or hexamethonium significantly reduced but did not abolish the tachycardia, suggesting that the increase in HR was mediated only partially through reflex increases in sympathetic tone. These data indicate that (a) anesthesia potentiates the depressor actions of DPMA and (b) stimulation of A2 receptors increases HR through both direct and indirect mechanisms of action.

Demonstration of vasorelaxant activity with an A1-selective adenosine agonist in porcine coronary artery: involvement of potassium channels.

The vasodilator activity of adenosine has been associated with selective stimulation of A2 receptors. In the present study, the vasorelaxant (VR) activity of an A1-selective agonist, CPA (cyclopentyladenosine), was examined in isolated porcine coronary arterial rings precontracted with prostaglandin F2 alpha and compared to the A2-selective agonist DPMA (N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)-ethyl] adenosine). DPMA, approximately 13-fold selective for the rat brain A2 receptor, relaxed isolated coronary arterial rings with an EC50 of 0.59 +/- 0.19 microM (n = 23) whereas CPA, 2200-fold selective for the rat brain A1 receptor, was approximately 5-fold less potent with an EC50 of 3.18 +/- 0.6 microM (n = 11). At low concentrations (10-300 nM) CPA caused vasoconstriction, indicative of the A1-selective nature of this agonist. CGS 15943 (100 nM), a nonselective adenosine antagonist, attenuated the VR activity of DPMA and CPA, causing a 9- and 12-fold rightward shift of the dose-response curves, respectively, whereas 8-cyclopentyl-1,3-dipropylxanthine (20 nM), a highly A1-selective blocker, had no such effect. Both adenosine antagonists abolished the vasoconstrictor response of CPA at low concentrations. The contributions of the cyclic GMP pathway to adenosine-induced VR was assessed using an inhibitor of endothelium-dependent relaxing factor (L-nitroarginine). L-nitroarginine had no effect on the EC50 for CPA-induced VR and, marginally, but not significantly, attenuated DPMA effects. Moreover, no elevation in cyclic GMP levels could be observed in tissues stimulated with CPA or DPMA.(ABSTRACT TRUNCATED AT 250 WORDS)

Infusion of recombinant human prorenin into rhesus monkeys. Effects on hemodynamics, renin-angiotensin-aldosterone axis and plasma testosterone.

Prorenin, the biosynthetic precursor of active renin, is present in high concentrations in the kidney and reproductive organs. We have proposed that prorenin may be the vehicle of local renin systems, separating the functions of circulating and tissue renin. In the present study, we investigated the effect of increasing plasma prorenin 3- to 4-fold by infusing recombinant prorenin, 400 ng/min for 40 min, into male rhesus monkeys. The prorenin was first warmed to 37 degrees C to reduce the endogenous renin activity to a minimum. The study included a 20 min baseline and a 40 min recovery period. Plasma prorenin increased from 72 +/- 14 ng/mL/h to a maximum of 246 +/- 18 ng/mL/h during the infusion (P less than .001) and fell to 169 +/- 23 ng/mL/h 40 min after the infusion was stopped. Active renin did not change significantly. Plasma aldosterone increased slightly during the prorenin infusion (by 13%) and returned to baseline during the recovery period (P less than .05 compared to the infusion period). Plasma testosterone fell significantly from 1.9 +/- 0.1 ng/mL to 1.6 +/- 0.1 ng/mL during the infusion and further to 1.4 +/- 0.1 ng/mL during the post-infusion period (P less than .05). Blood pressure fell slightly but not significantly. Heart rate, glomerular filtration rate and renal blood flow, as well as urine flow and urine sodium and potassium excretion showed no significant change. These results demonstrate that human recombinant prorenin is not converted to active renin in the circulation of rhesus monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of atrial natriuretic factor in conscious rhesus monkeys with acute volume expansion.

The renal and hemodynamic responses to intravenous anaritide, a human atrial natriuretic factor [102-126] at 0.3 to 20 micrograms/kg in conscious rhesus monkeys with and without acute extracellular hypervolemia were analyzed and compared. Acute isotonic saline loading (intravenous bolus at 10 mL/kg plus continuous infusion at 0.25 mL/kg/min 30 min prior to and maintained throughout experiment) significantly augmented urine output (UV) and urinary Na+ excretion rate (UNaV) by 31% and 91%, respectively. Radial mean arterial pressure (MAP) and heart rate (HR) were not affected by volume expansion. Anaritide at doses higher than 0.3 micrograms/kg reduced MAP in a dose-dependent fashion in euvolemic monkeys. In contrast, reduction in MAP was observed only at the highest dose (20 micrograms/kg) of anaritide in hypervolemic monkeys. The hypotensive responses to anaritide at 20 micrograms/kg in euvolemic and hypervolemic animals were similar (-26 +/- 5 v -24 +/- 5 mm Hg, respective maximum changes in MAP). UV and UNaV were increased by anaritide at 3 to 20 micrograms/kg in both euvolemic and hypervolemic monkeys; however, the increases at each effective dose of anaritide were greater or tended to be greater in hypervolemic rhesus monkeys compared with euvolemic rhesus monkeys. Compared to vehicle responses, HR was not affected by anaritide in either group of animals. In conclusion, acute extracellular hypervolemia potentiates the renal but suppresses the hypotensive responses to anaritide in conscious rhesus monkeys.

Hypotensive response to atrial natriuretic factor in conscious chronic pulmonary hypertensive rats.

The hypotensive effects of anaritide (Wy-47,663), a 26 amino acid atrial natriuretic factor, were examined in conscious, monocrotaline-induced chronic pulmonary hypertensive rats. Anaritide (0.25-8 micrograms/kg per min i.v.) decreased systemic arterial pressure at 2-8 micrograms/kg per min by as much as -15.6 +/- 0.4 mm Hg. The pulmonary hypotensive response to anaritide was not different from vehicle treatment. We conclude that anaritide is more effective in decreasing systemic than pulmonary arterial pressures in monocrotaline-induced pulmonary hypertensive rats.

Cardiovascular effects of central calcitonin gene-related peptide in conscious rats.

Calcitonin gene-related peptide (CGRP) is a potent peripheral vasodilator. In the present study, the cardiovascular effects of centrally administered CGRP were examined in conscious, normotensive rats. The rats were chronically instrumented with miniaturized pulsed Doppler flow probes to allow measurement of regional blood flow in the conscious animals. Injection of increasing doses of CGRP (0.3 to 3.0 micrograms/kg) in the lateral cerebroventricles transiently increased arterial pressure (maximal change = 13 +/- 3 mm Hg) and markedly increased heart rate (maximal increase = 88 +/- 10 b/min). The heart rate response was sustained over a period of 20 to 30 minutes. Central CGRP decreased hindquarter vascular resistance but had no effect on renal or mesenteric vascular resistances. In contrast, intravenous injections of CGRP reduced arterial pressure and renal, mesenteric, and hindquarter vascular resistances. The tachycardia response to central CGRP was attenuated by pretreatment with propranolol or hexamethonium, indicating that the heart rate response was mediated, in part, through increases in cardiac sympathetic tone. These data indicate that central CGRP may alter cardiovascular function through alterations in sympathetic outflow.

Bronchoprotective and bronchodilator activity of anaritide (human atrial natriuretic factor [102-126]) infusion in the anesthetized guinea pig.

The present study examined the bronchoprotective and bronchodilator efficacy of infused human atrial natriuretic factor [102-126] (Anaritide) in the guinea pig. Anesthetized and paralyzed male guinea pigs, ventilated via a tracheal cannula, were placed in a plethysmograph for measurement of agonist-induced changes in pulmonary mechanics. Reductions in dynamic compliance of the lung and airway conductance were produced either by 3 to 7 tidal volume breaths of leukotriene D4 (0.125 micrograms/ml) delivered through an ultrasonic nebulizer or by intravenous histamine (2.8 +/- 0.2 micrograms/kg). Infusion of Anaritide (1 microgram/kg/min), before evoking bronchoconstriction with either LTD4 or histamine, produced a significant protection against bronchoconstriction produced by aerosol LTD4, but not against histamine-induced bronchoconstriction of similar magnitude. In other experiments, Anaritide infusion (0.5-2 micrograms/kg/min) also rapidly reversed a stable LTD4-induced decrease in airway conductance, but did not produce a similar reversal of the decrease in dynamic compliance. The data provide evidence that intravenous Anaritide exerts both bronchoprotective and bronchodilator effects against LTD4-induced bronchospasm.