Effects of Norepinephrine Infusions on Mesenteric Arterial Blood Flow and Its Tissue Distribution 1

Infusions of norepinephrine into the superior mesenteric artery or stimulation of the mesenteric periarterial nerves of cats or dogs produces a transient reduction in mesenteric blood flow but, as stimulation or infusion continues, flow returns to near control values (1-3). Studies based on India ink injections, changes in capillary filtration coefficient and isotope clearances suggested that a redistribution of intestinal blood flow occurred during the “escape” from the vasoconstrictor influence (4, 5). Vasoconstriction in the mucosa appeared to be well maintained throughout whereas blood flow in the submucosa increased. However, other observations (6, 7) have indicated that escape may be due to relaxation of the same vascular elements which were initially constricted.

The purpose of the present investigation was to determine whether norepinephrine escape occurred in animals other than the dog and cat and to reexamine the possibility that escape is associated with a redistribution of blood flow among the intestinal layers.

Methods. Two Sprague-Dawley rats, two rabbits, two monkeys (Macaca mulatta and Aotus trivirgatus) and 18 cats were used in the study. The rats, rabbits, and cats were anesthetized with intraperitoneal sodium pentobarbital and the monkeys with intravenous sodium pentobarbital 30 mg/kg after premedication with intramuscular Sernylan 5 mg/kg. Catheters were inserted into a common carotid artery and external jugular vein for arterial pressure measurement and intravenous administration of supplemental anesthesia, respectively. The abdomen was opened in the mid-line. Anastomotic connections between the superior and inferior mesenteric arteries were divided. The superior mesenteric artery was dissected free from the enveloping nerves which were cut. A non-cannulating electromagnetic flow probe was placed on the vessel, and flow was determined with a Biotronex BL-610 flowmeter used in conjunction with a Beckman S11 Dynograph recorder.