Atropine Potentiates the Pressor Effect of Arginine-Vasopressin in Conscious Dogs

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Abstract
The hemodynamic effects of arginine-vasopressin (AVP) injections at different doses were measured before and after administration of atropine (250 .mu.g/kg), propranolol (2 mg/kg) or phenoxybenzamine (5 mg/kg) in conscious dogs. Arterial pressure measurements derived from a chronic indwelling catheter and aortic flow derived from an aortic electromagnetic flow probe were digitized and analyzed by computer to assess mean and pulsatile arterial pressure, cardiac output, total peripheral resistance, heart rate and other hemodynamic variables. AVP alone moderately increased arterial pressure and decreased cardiac output and heart rate. For doses between 20 and 40 ng/kg, mean arterial pressure increased by 17.4 .+-. 1.5 mm Hg. After atropine, the same AVP dose increased pressure by 51.6 .+-. 3.2 mm Hg. The bradycardiac response to AVP and the decrease in cardiac output was blunted by atropine. AVP effect on total peripheral resistance was unaffected by atropine. Neither .alpha.- nor .beta.-adrenergic blockade enhanced the pressor AVP effect. The pressor response potentiation to AVP previously reported with total autonomic blockade evidently is largely due to preventing a vagally mediated decrease in cardiac output in conscious dogs.

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