title: Correlation between decreased heart rate and central inhibition of sympathetic discharge after prazosin administration in the spontaneously hypertensive rat.
abstract: Mean arterial blood pressure, heart rate and splanchnic sympathetic discharge were recorded in conscious and anaesthetized spontaneously hypertensive rats (SHR). Administration of prazosin (1 mg/kg i.v.) reduced heart rate in most rats and this effect was closely parallelled by a decrease in sympathetic discharge. In contrast, administration of hydralazine (1 mg/kg i.v.) caused a sustained tachycardia and increased sympathetic nervous activity. The cardiovascular effects of prazosin (0.2-0.3, 1 and 3 mg/kg i.v.) were examined in different rat strains. Sprague-Dawley and Wistar-Kyoto rats responded with tachycardia whereas a significant bradycardia was observed in SHR following the higher doses of prazosin. It is suggested that the bradycardia obtained after prazosin administration is due to a central inhibition of sympathetic outflow, an effect possibly caused by blockade of alpha-adrenoreceptors. The different heart rate responses in different rat strains may be interpreted to reflect differences in sensitivity of central alpha-adrenoreceptors.
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002319:Cardiovascular System / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects*; D006830:Hydralazine / Q000494:pharmacology; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D011224:Prazosin / Q000494:pharmacology*; D011799:Quinazolines / Q000494:pharmacology*; D051381:Rats; D013564:Sympathetic Nervous System / Q000187:drug effects*
chemical_list: D011799:Quinazolines; D006830:Hydralazine; D011224:Prazosin