Atropine potentiates the pressor response to arginine-vasopressin in conscious dogs

The haemodynamic effects of bolus injections of increasing doses of arginine-vasopressin (AVP) were examined in conscious dogs chronically instrumented for the measurement of arterial pressure and cardiac output (aortic electromagnetic flowmeter), both before and after administration of the antimuscarinic agent atropine, 250 micrograms/kg. Haemodynamic variables were monitored and analysed using computerized techniques. The pressor response to AVP was markedly enhanced by atropine treatment, which decreased the relative fall of cardiac output but did not affect the relative increase in total peripheral resistance. It is therefore concluded that the fall in cardiac output which follows AVP administration is in part vagally mediated, and that preventing the vagal component of the cardiac output decrease contributes to the exaggerated pressor response induced by atropine.