Cardiac output, ventral and dorsal aortic blood pressure, heart rate, and coeliac and mesenteric artery blood flow were recorded simultaneously in the Atlantic cod, Gadus morhua L., at rest, during exercise, during hypoxia and after feeding. In the resting unfed animals, coeliac artery blood flow was 4.1 +/− 0.8 ml min-1 kg-1 and mesenteric artery blood flow was 3.5 +/− 1.1 ml min-1 kg-1 (mean +/− S.E.M., N = 10); together, these flows represent approximately 40% of the cardiac output. Exercise or exposure to hypoxia resulted in increased visceral vascular resistance, leading to reductions in the coeliac and mesenteric artery blood flows. Coeliac and mesenteric blood flows were increased 24 h after feeding and the coeliac and systemic vascular resistances decreased in comparison with the prefeeding values. Phentolamine did not affect the gastrointestinal artery blood flow, but produced a significant decrease in the mesenteric and systemic vascular resistance. Treatment with bretylium and phentolamine revealed differences between the coeliac and the mesenteric vasculature regarding the control mechanisms during hypoxia and during exercise and feeding. During hypoxia, an adrenergic control of the gastrointestinal vasculature with both nervous and humoral components was found, whereas during exercise and after feeding an additional non-adrenergic mechanism controlling gut blood flow was demonstrated.

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