Cardiovascular responses to blockade of angiotensin and alpha-adrenergic receptors.
Both angiotensin and alpha-adrenergic blocking agents reduce arterial blood pressure in hypovolemic states. We have compared the effects of an angiotensin antagonist (saralasin) and an alpha-adrenergic blocking agent (phenoxybenzamine) in supramaximal dosage on cardiac output, total peripheral resistance, and venous tone in rabbits rendered hypovolemic by restriction of sodium intake, supplemented by a furosemide-induced diuresis 48 h prior to study. Saralasin (10 microgram/kg per min) reduced arterial blood pressure significantly (-15 +/- 1.2 mmHg) despite an unchanged cardiac output (P less than 0.025) due to a fall in total peripheral resistance. Phenoxybenzamine (5 mg/kg) induced a much larger fall in arterial blood pressure (-28 +/- 3.6 mmHg), despite an identical reduction in total peripheral resistance, because cardiac output also fell (+/- 9 ml/kg per min). The reduction in cardiac output was associated with a significant increase in hindlimb venous distensibility (P less than 0.001) after alpha-adrenergic blockade. Saralasin, conversely, had no influence on venous tone. Adrenergic mechanisms contribute to cardiovascular homeostasis through an influence on both arteriolar and venous tone, whereas the effect of angiotensin is directed entirely to the arteriolar side of the circulation.
D000818:Animals; D001794:Blood Pressure; D002302:Cardiac Output; D005260:Female; D010643:Phenoxybenzamine / Q000494:pharmacology; D011817:Rabbits; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011945:Receptors, Angiotensin / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology*; D012504:Saralasin / Q000494:pharmacology; D012769:Shock; D014655:Vascular Resistance
D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011945:Receptors, Angiotensin; D011956:Receptors, Cell Surface; D010643:Phenoxybenzamine; D012504:Saralasin