Multifactorial mediation of post norepinephrine induced intestinal hyperemia

We evaluated several potential endogenous mediators of post norepinephrine induced hyperemia in the mesenteric circulation. Hyperemia was elicited in the anesthetized rat anterior mesenteric artery after cessation of intravenous norepinephrine infusion at 0.125 to 1.0 x 10(-8) M/min x 4 min. Arterial blood pressure was measured with a transducer, and the velocity of arterial blood flow was determined with pulsed Doppler velocimetry. Conductance at the height of mesenteric hyperemia, the post norepinephrine hyperemia volume, and the autoregulatory escape volume were calculated from recorded measurements. The higher doses of norepinephrine increased both the hyperemia volume and peak conductance in both control and capsaicin pretreated rats. Hyperemic parameters were significantly diminished by pretreatment with either yohimbine, propranolol, adenosine deaminase, or methylene blue. Combining adenosine deaminase with propranolol further reduced peak conductance and the hyperemia volume compared with enzyme pretreatment alone. The magnitude of hyperemia was related to the escape volume but not to the extent of norepinephrine induced vasoconstriction. We conclude that post norepinephrine induced hyperemia in the rat mesenteric circulation is modulated by alpha 2 and beta 2 adrenergic receptor activation, adenosine release, and endothelial factors.