zaprinast and Hypertension

To evaluate the association between hypertension, male erectile function, Rho-kinase, and cyclic GMP pathways, we monitored neurogenic erectile response in spontaneously hypertensive (SHR) vs normotensive rats. We also evaluated SHR erectile function before and after intracavernosal injection of either the specific Rho-kinase inhibitor Y-27632 or a combination of Y-27632 and the PDE5 inhibitor zaprinast to prevent cGMP degradation. SHR had lower resting baseline corpus cavernosum pressure and a higher threshold for development of tumescence than normotensive rats. In SHR, Y-27632 administration reversed hypertension-related changes in male erectile function; Rho-kinase antagonism and PDE5 inhibition in combination had a synergistic effect in improving the neurogenic erectile response. Our data indicate that hypertension is associated with impairment in the SHR neurogenic erectile response that may involve a derangement in hemodynamic mechanisms in penile erectile tissue. Rho-kinase inhibition alone or combined with PDE5 inhibition may be of value in treating hypertension-related ED.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Amides; Animals; Antihypertensive Agents; Blood Pressure; Blotting, Western; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 5; Drug Synergism; Electric Stimulation; Hypertension; Intracellular Signaling Peptides and Proteins; Male; Penile Erection; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Protein Serine-Threonine Kinases; Purinones; Pyridines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; rho-Associated Kinases; rhoA GTP-Binding Protein; Up-Regulation

1. The effect of systemic administration of the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) on the antihypertensive effects of the angiotensin AT1 receptor antagonist, GR138950, the angiotensin-converting enzyme (ACE) inhibitor, enalapril, or hydralazine has been evaluated in unrestrained, conscious renal artery ligated hypertensive (RALH) rats. The effect of the phosphodiesterase type V inhibitor, zaprinast on the antihypertensive effect of GR138950 in RALH rats was also examined. The effect of GR138950 on blood pressure, and plasma and urine cyclic GMP levels was compared to that of zaprinast in conscious RALH rats. 2. GR138950, enalapril or hydralazine caused marked reductions in blood pressure associated with immediate tachycardia in conscious RALH rats. L-NAME pretreatment attenuated the antihypertensive effects of GR138950 or enalapril but not that of hydralazine in conscious RALH rats. The initial tachycardia caused by GR138950 or enalapril but not hydralazine was attenuated by L-NAME pretreatment. L-NAME alone caused a transient (20 min) pressor response and a prolonged (6 h) bradycardia in conscious RALH rats. 3. Pretreatment with indomethacin did not affect the cardiovascular effect of GR138950 in conscious RALH rats. Indomethacin alone did not significantly change basal blood pressure or heart rate in RALH rats. 4. Zaprinast pretreatment did not affect the antihypertensive effect of GR138950 in conscious RALH rats but potentiated the depressor response to sodium nitroprusside. Zaprinast alone caused a small reduction in basal blood pressure but did not change basal heart rate in RALH rats. 5. The antihypertensive effect of GR138950 was not associated with an increase in plasma or urine cyclic GMP levels in conscious RALH rats, whereas zaprinast caused a small fall in blood pressure associated with increases in plasma and urine cyclic GMP. 6. The ability of L-NAME to inhibit the antihypertensive action of GR138950 or enalapril suggests that these agents release nitric oxide (NO) and/or enhance the cardiovascular effects of NO as part of their mechanism of action. However, the inability of zaprinast to potentiate the antihypertensive effects of GR138950 and the finding that GR138950 did not increase urine and plasma cyclic GMP levels are not consistent with this view. Attenuation of the response to GR138950 or enalapril, but not hydralazine, suggests a selective interaction between L-NAME and inhibitors of the ren

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Antihypertensive Agents; Benzofurans; Blood Pressure; Cyclic GMP; Drug Interactions; Enalapril; Enzyme Inhibitors; Hydralazine; Hypertension; Indomethacin; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Phosphodiesterase Inhibitors; Purinones; Rats; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Receptors, Angiotensin

The purpose of this study was to determine if significant relationships exist between plasma and aortic cyclic GMP (cGMP) levels and pharmacodynamic effect after the i.v. administration of the cGMP-selective phosphodiesterase inhibitor zaprinast to conscious, spontaneously hypertensive rats. Zaprinast dose-dependently increased plasma and aortic cGMP levels at 10, 18 and 30 mg/kg and decreased mean arterial blood pressure (MAP) at 18 and 30 mg/kg. The concentrations of cGMP in the plasma and in the aorta were significantly correlated (r = 0.765, P < 0.0001). The changes in MAP were significantly correlated to aortic (r = -0.750, P < 0.0001) and plasma (r = -0.762, P < 0.0001) cGMP levels. We conclude that plasma cGMP may be an index of cGMP-selective phosphodiesterase inhibition in vivo.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Analysis of Variance; Animals; Aorta, Abdominal; Blood Pressure; Cyclic GMP; Dose-Response Relationship, Drug; Hypertension; Injections, Intravenous; Male; Purinones; Radioimmunoassay; Rats; Rats, Inbred SHR

The purpose of this study was to determine whether cross-tolerance develops between nitroglycerin and endothelium-derived relaxing factor (EDRF)-mediated vasoactive agents in vivo. Spontaneously hypertensive rats (SHR) were made tolerant by pretreatment with high doses of nitroglycerin (100 mg/kg s.c., 3 times/day, for 3 consecutive days). The hypotensive effect of challenge doses of nitroglycerin (1, 10, 300, 100 micrograms/kg i.v.) was completely abolished in nitroglycerin-pretreated SHR. To evaluate cross-tolerance, the effects of the following EDRF-dependent vasoactive agents on blood pressure were determined in groups of nitroglycerin-pretreated and vehicle-pretreated SHR: acetylcholine, bradykinin and L-arginine. In addition, the hypotensive effects of zaprinast (M & B 22,928), a cyclic guanosine monophosphate (cGMP) phosphodiesterase inhibitor, and the hypertensive effects of the nitric oxide-synthase inhibitor N omega-nitro-L-arginine were also evaluated. In all cases, there was no difference in the effects of these agents on blood pressure when compared in nitroglycerin-pretreated (tolerant) and vehicle-pretreated (non-tolerant) SHR. The use of a variety of agents which modulate EDRF release or its effects by several different mechanisms suggests that cross-tolerance does not occur between nitroglycerin and EDRF in vivo.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Acetylcholine; Animals; Arginine; Blood Pressure; Bradykinin; Drug Tolerance; Hypertension; Male; Nitric Oxide; Nitroarginine; Nitroglycerin; Purinones; Rats; Rats, Inbred SHR; Vasodilator Agents