Haemodynamic effects of bromocriptine in the conscious spontaneously hypertensive rat

The systemic haemodynamic effects of 0.3 mg kg-1 bromocriptine s.c. in conscious, chronically instrumented spontaneously hypertensive rats (SHR) has been investigated. Bromocriptine caused a gradual, long-lasting significant fall in mean arterial pressure with a maximum of 26 +/- 3 mmHg (-17%). The fall was related to a significant decrease in stroke volume index (-9 +/- 2 microliters 100 g-1; -10%) and cardiac index (-3.9 +/- 0.8 ml min-1 100 g-1; -12%). No significant changes in heart rate or total peripheral resistance index were observed. These data do not support previous suggestions that the antihypertensive effect of bromocriptine is caused by inhibition of the release of vasopressor substances. It is suggested that bromocriptine causes a reduction of venous return of the blood to the heart, possibly related to intrarenal effects.