Effects of bromocriptine on the heart and the peripheral circulation of anesthetized cats

Dopaminergic stimulants such as bromocriptine have multiple effects on the circulation. Based on dose-response curves obtained in preliminary experiments, we compared the effects of 30 micrograms/kg bromocriptine and 0.4 mg/kg dihydralazine infused intravenously over a period of 10 min into seven chloralose-urethane-anesthetized cats each. A third group of cats received placebo solution. The effect of both drugs on blood pressure was comparable, but other systemic hemodynamic variables and regional blood flows, measured with tracer microspheres, were altered differently. Bromocriptine lowered heart rate, did not change cardiac output, and increased total peripheral conductance modestly, whereas dihydralazine produced marked increases in cardiac output and total peripheral conductance. Bromocriptine dilated the vascular beds of the brain, kidneys, adrenal glands, and skeletal muscle without increasing flow through most of them. Dihydralazine caused striking vasodilation in the heart, brain, small intestine, and colon and a modest increase in conductance in the kidneys, adrenal glands, and skeletal muscle. Flow through the heart, brain, small intestine, and colon was increased. Vasoconstriction was observed in the pancreas with bromocriptine and in the liver, spleen, and, to a small extent, pancreas with dihydralazine. The distribution of effects was somewhat similar to the effects of dihydropyridine-derived calcium antagonists. With dihydralazine the fall in blood pressure was caused by peripheral vasodilation only, whereas with bromocriptine both peripheral vasodilation and effects on the heart contributed to the fall in blood pressure.