Decreased nutrient blood flow during dopamine- and epinephrine-induced intestinal vasodilation

Mesenteric blood flow returned to control values promptly upon termination of i.a. infusions of vasodilator doses of acetylcholine (ACh) and isoproterenol (Iso) into the canine superior mesenteric artery (SMA). However, termination of vasodilator infusions of dopamine (DA) and epinephrine (Epi) into the SMA resulted in an additional increase in flow resembling the reactive hyperemic response observed upon termination of norepinephrine infusion into the SMA. In experiments that measured the effect of these agents on intestinal oxygen kinetics, i.a. ACh and Iso increased oxygen uptake but did not affect percent oxygen extraction. Equivasodilator i.a. infusions of DA and Epi decreased percent oxygen extraction. DA decreased oxygen uptake whereas Epi did not alter oxygen uptake. After administration of phenoxybenzamine, the effects of i.a. DA and Epi on oxygen kinetics became identical to those produced by equivasodilator infusions of ACh or Iso. Moreover, the reactive hyperemia-like response on cessation of DA and Epi infusions was abolished. In experiments that utilized ¹²⁵I absorption from the jejunum as a measure of intestinal mucosal blood flow, i.a. ACh and Iso were found to increase mucosal blood flow in proportion in the increase in total SMA flow. In contrast, i.a. doses of DA and Epi that increased SMA flow nevertheless decreased mucosal flow. It was concluded that vasodilator doses of dopamine and Epi decreased oxygen delivery to the intestine at least in part due to a decreases in mucosal blood flow; this probably involves action on alpha adrenoreceptors.