Effects of norepinephrine, vasopressin, isoproterenol, and histamine on blood flow, oxygen uptake, and capillary filtration coefficient in the colon of the anesthetized dog.

Segments of colon were denervated, vascularly isolated, and autoperfused at normal arterial pressure in the anesthetized dog. Norepinephrine, vasopressin, isoproterenol, and histamine were infused i.a. in graded doses. Norepinephrine and vasopressin reduced colonic blood flow and increased the arteriovenous oxygen difference; oxygen uptake by the colon fell, and the capillary filtration coefficient (Kf,c) was reduced. Isoproterenol and histamine increased colonic blood flow and reduced the arteriovenous oxygen difference; oxygen uptake by the colon did not change significantly. The Kf,c increased with isoproterenol, but changes due to histamine were more variable. Vasoconstrictor drugs tend to reduce, and vasodilators tend to increase oxygen uptake by the colon; the effects of altered blood flow are, however, alleviated by changes in colonic oxygen extraction, such that moderate drug-induced changes in blood flow (-25 to +50%) are not associated with appreciable (less than or approximately 10%) changes in oxygen uptake.