Effects of vasoactive agents on intestinal oxygen consumption and blood flow in dogs

A comparison study of several vasoconstrictor and vasodilator agents was conducted measuring changes in intestinal blood flow and oxygen consumption during 10 min periods of intra arterial infusion. Blood flow was measured in a branch of the superior mesenteric artery of anesthetized dogs with an electromagnetic blood flow meter, and the arteriovenous oxygen content difference across the gut segment was determined photometrically. Vasopressin (4 x 10^-3 and 7 x 10^-4 U/kg min) diminished blood flow 60 and 28% and reduced oxygen consumption 54 and 22% respectively (all P<0.001). In a dose which did not lower blood flow, vasopressin still caused a decline in oxygen consumption (P<0.01). Epinephrine (5 x 10^-2 μg/kg min) decreased blood flow 19% (P<0.001) but did not reduce oxygen consumption. After β adrenergic blockade, however, the same dose of epinephrine decreased blood flow 41% and oxygen consumption 33% (both P<0.001). Responses to angiotensin II, calcium chloride, and prostaglandin F₂α resembled effects of vasopressin rather than those of epinephrine, namely decreased blood flow and decreased oxygen consumption. The vasodilator agents, prostaglandin E₁, isoproterenol, and histamine, increased (P<0.001) both blood flow (130, 80, and 98%, respectively) and oxygen consumption (98, 64, and 70%, respectively). Vasopressin, angiotensin II, calcium chloride, and prostaglandin F₂α appear to contract arteriolar and precapillary sphincteric smooth muscle indiscriminately to evoke both intestinal ischemia and hypoxia. Epinephrine is the exceptional constrictor in this case, producing diminished blood flow without a reduction in oxygen uptake.