Effects of dopamine on intestinal vessels in anesthetized dogs

The effects of dopamine administered in graded intravenous bolus injections (0.1 to 51.2 micrograms.kg-1) were studied simultaneously in a number of splanchnic vessels at organ level in anesthetized dogs with and without preceding administration of phenoxybenzamine. Hemodynamic data are presented for each artery as conductance, which were obtained by dividing mean flow by mean arterial pressure. The data were analyzed by two different means: 1) the response to 12.8 micrograms of dopamine during one minute, and 2) by dose-response curves. Early and late effects during the one minute post injection measurement time could be distinguished after the administration of dopamine. In the superior pancreaticoduodenal, the superior mesenteric, the inferior mesenteric, the left gastric, and the hepatic arteries an early reduction in conductance was seen, while in the femoral artery an increase in conductance was observed. Early reduction was often followed by an increase in conductance above the preinjection level. This early reduction in conductance was absent when dopamine was administered after phenoxybenzamine, while a more pronounced increase was observed during the late phase. There was a slight reduction in renal artery flow, probably caused by a slight reduction in arterial pressure. Because there was no increase in the conductance of the hepatic artery--both with and without phenoxybenzamine--it may be concluded that no specific dopamine receptors are present in this vascular bed in dogs.