The aim of the study was to characterize the gastric and mesenteric vascular changes induced by diabetes and the implication of endothelial [nitric oxide (NO) and prostaglandins] and humoral (glucagon) factors in such changes. Diabetes was induced in rats by a single streptozotocin injection. Four weeks later, gastric mucosa, left gastric artery, and superior mesenteric artery blood flows were measured using hydrogen gas clearance and perivascular ultrasonic flowmeter techniques, respectively, in anesthetized and fasted diabetic and control rats. Blood pressure, hematocrit, blood volume, and blood viscosity were also measured. Left gastric (41 +/- 6 vs. 25 +/- 4 ml.min-1.100 g-1) and superior mesenteric artery blood flows (83 +/- 8 vs. 65 +/- 4 ml.min-1.100 g-1) were significantly higher in diabetic than in control rats. The increased blood flow in the left gastric artery was distributed to a hypertrophic mucosa in diabetic rats; therefore, the blood flow per 100 g tissue in the gastric mucosa was not significantly different in diabetic compared with control rats. Pretreatment with indomethacin reduced both increase gastric and mesenteric flows of the diabetic rats to the same levels as in control rats. NG-nitro-L-arginine methyl ester decreased gastric blood flow in a dose-dependent manner and to a similar extent in diabetic and control rats. In contrast, an increased sensitivity to the higher doses of the NO inhibitor was observed in the mesenteric vascular bed of diabetic rats. Glucagon reduction achieved by somatostatin infusion did not influence either gastric or mesenteric blood flow in diabetic rats. In summary, the present study revealed an increase in gastric and mesenteric arterial blood flows in streptozotocin-induced diabetic rats. The gastrointestinal hyperemia seems to be due, at least in part, to the increased demand of a hypertrophic mucosa and is mediated primarily by endogenous prostaglandins. Increased vascular sensitivity to NO may also contribute to the mesenteric vasodilation.