Blood flow redistribution by dopamine in the feline gastrointestinal tract.

The effect of intravenous infusion of dopamine (10 and 25 micrograms X kg-1 X min-1 consecutively) on visceral blood flow distribution was examined in anesthetized cats using the microsphere technique and electromagnetic flowmetry. Arterial blood pressure did not change in response to dopamine infusion, but blood flow through the superior mesenteric artery, and blood flow in the mucosa-submucosa of the gastric antrum and various gut segments increased significantly. During infusion of the high dose the increase was most marked in the mucosa-submucosa of the antrum (+355%) and distal colon (+371%). By contrast, blood flow decreased in the muscularis-serosa of the gut segments investigated, in the spleen, pancreas, and the hepatic arterial bed. The increase in blood flow through the superior mesenteric artery was blocked by the dopamine antagonist bulbocapnine (10 mg/kg i.v.). The results suggest that the receptors mediating the dopamine-induced vasodilation in the gastrointestinal tract are located in the resistance vessels of the mucosa-submucosa.

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.