title: Inhibition of renin secretion by clonidine after alpha-adrenoceptor blockade in anesthetized dogs.
abstract: Dogs anaesthetised with pentobarbital were used to study the effects of the alpha-adrenoceptor antagonists phentolamine and piperoxan on the clonidine-induced suppression of plasma renin activity (PRA). Given alone, clonidine (30 microgram/kg, i.v.) produced an initial rise in mean arterial pressure (MAP) which was followed by a hypotensive response. These changes in blood pressure were accompanied by decreased in PRA and heart rate (HR). Pretreatment with phentolamine, 1 mg/kg i.v. or 3.3 microgram/kg/min infused into the third cerebral ventricle, or piperoxan, 20 microgram/kg stat. + 5 microgram/kg/min infused either i.v. or intraventricularly, did not modify the clonidine-induced falls in PRA, MAP or HR. All pretreatment regimes, with the exception of intraventricular phentolamine, virtually abolished the initial pressor response to clonidine. These results demonstrate that the renin-lowering action of clonidine in the dog is not inhibited by two classical alpha-adrenoceptor antagonists.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology*; D004285:Dogs; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010646:Phentolamine / Q000494:pharmacology; D010883:Piperoxan / Q000494:pharmacology; D012083:Renin / Q000378:metabolism; D000092502:Renin Inhibitors
chemical_list: D000317:Adrenergic alpha-Antagonists; D003000:Clonidine; D010646:Phentolamine; D010883:Piperoxan; D012083:Renin; D000092502:Renin Inhibitors