Comparative splanchnic blood flow effects of various vasodilator compounds.

We examined the visceral blood flow distribution during infusion of three vasodilators at doses that produced similar depression of systemic arterial pressure. The studies were performed in pentobarbital-anesthetized dogs using the radioactive microspheres technique. Minoxidil did not alter renal, total visceral, or visceral organ flow distribution with the exception of a modest increase in relative stomach blood flow. Nitroprusside increased the percentage of total visceral flow to the spleen and the hepatic artery. Dopamine increased blood flow to the stomach, intestine, and kidney. After phenoxybenzamine, the augmentation of stomach blood flow by dopamine was greatly increased, while blood flow to the splenic, pancreatic, and hepatic arteriolar vascular beds decreased. The decreases in blood flows may be due to decreased perfusion pressure in the absence of active vasodilation or to myogenic or metabolic autoregulation. Thus, at equivalent hypotensive responses, the vasodilator compounds that we studied produced markedly different patterns of visceral blood flow.