Evidence for local arteriovenous reflex in intestine

¹ Department of Physiology, Indiana University School of Medicine, Indianapolis, Indiana

Studies were made on the hemodynamics of the isolated autoperfused dog intestine preparation. An attempt was made to explain the mechanism involved in the observed increase in venous resistance seen as the arterial pressure in the segment was reduced. This rise in venous resistance was reduced or abolished by sympatholytic agents (phentolamine and Dibenzyline) and by local anesthetics (tetracaine). When areas of intestine were surgically denervated and then subjected to hemodynamic studies 10–19 days later the venous resistance response was nearly or completely absent in all cases. The response was not significantly affected by the infusion of hexamethonium or dichloroisoproterenol or by changes in hematocrit ratio. It was concluded that the rise in venous resistance seen as arterial pressure is reduced is mediated by a local sympathetic axon reflex with the receptor on the arterial side of the circulation and the effector located on the venous side. The decrease in arterial resistance seen as arterial pressure is reduced (autoregulation) is also discussed. None of the drugs mentioned above or chronic denervation had any effect upon this phenomenon, strengthening the concept that it is the result of a myogenic response of the arterial vessels.