Dopamine produces vasodilation in specific regions and layers of the rabbit gastrointestinal tract

The effect of intravenous dopamine infusion (25 and 60 micrograms per kg and min consecutively) on blood flow distribution in the splanchnic region of anesthetized rabbits was studied applying the microsphere technique. During infusion of the low dose, blood flow increased most markedly in the stomach, less in the pancreas, jejunum and descending colon, and decreased in the spleen. In the stomach the increase was confined to the mucosa-submucosa. Raising the dose of dopamine resulted in a slight fall of arterial blood pressure, a further increase in blood flow through the mucosa-submucosa of the gastric fundus (+493 % as against control), but not through the other tissues studied. In another series, blood flow through the left gastric artery was measured with an electromagnetic flowmeter. The infusion of dopamine produced a dose-dependent increase in regional blood flow, which was inhibited by the dopamine antagonist bulbocapnine. Furthermore, the control blood flow was transiently decreased, and resistance to flow was increased by bulbocapnine. The results indicate that the dopamine-induced vasodilation in the gastrointestinal tract of the rabbit is largely restricted to the gastric circulation and suggest that specific receptors mediating this vasodilation are located in the mucosa-submucosa. It is hypothesized that endogenous dopamine functions as a vasodilatory tissue hormone in the gastric mucosa of the rabbit.