Autoregulation of superior mesenteric flow in fasted and fed dogs.

Pressure-flow relations in the intestinal vasculature were obtained by producing stepwise reductions of intestinal perfusion pressure with an adjustable metal clamp placed upon the descending thoracic aorta. To eliminate intervention of the baroreceptor reflex, systemic arterial pressure was maintained constant by a pressure compensation system connected to the two carotid arteries. In the fed dogs, autoregulatory vasodilatory responses to reduced perfusion pressure maintained flow within 5% of control in the 85-125 mmHg range. In 30% of the fed dogs, superior mesenteric flow actually increased as perfusion pressure was reduced in the pressure range 85-125 mmHg, indicating superregulation of flow in the intestinal vasculature. The degree of flow autoregulation in the fasted dog was less than in the fed dog. Moreover, superregulation of intestinal flow was not observed in any of the fasted animals. These data suggest an intimate link between parenchymal activity and local flow control in the small intestine.