CARDIAC-OUTPUT MEDIATES THE ANTIHYPERTENSIVE EFFECT OF VASOPRESSIN INSPONTANEOUS HYPERTENSION

The contribution of cardiac output and total peripheral resistance to the fall in arterial pressure that follows cessation of a 3-h intraven ous infusion of arginine vasopressin (AVP; 20 ng . kg(-1). min(-1)) wa s studied in conscious spontaneously hypertensive rats (SHR) and Wista r-Kyoto (WIN) rats instrumented with radiotelemetric probes for record ing of blood pressure and ultrasonic transit-time flow probes for meas uring cardiac output. Cessation of a 3-h. infusion of AVP resulted in a significant decrease in arterial pressure in SHR (14-17 mmHg below p reinfusion control levels) but not in WKY or in vehicle-treated contro ls. The fall in pressure persisted for several days, The fall in press ure was associated with a large decrease in cardiac output of 22 +/- 2 ml/min below control levels in SHR, and the time course of the cardia c output response over several days approximated the time course of th e pressure response. By contrast, total peripheral resistance remained elevated for some time on withdrawal of the AVP infusion. We conclude that the withdrawal-induced antihypertensive phenomenon in SHR is med iated by a fall in cardiac output and not by a decline in total periph eral resistance.