PERIPHERAL-BLOOD FLOWS DURING COLORECTAL DISTENSION IN ANESTHETIZED DOGS

Distension of the descending colon elicits reflex cardiovascular respo nses, including increases in heart rate and arterial blood pressure. T o study the relative contribution of vasoconstriction in individual va scular beds to this reflex response, experiments were performed on sev en dogs anaesthetised with chloralose and instrumented with electromag netic flowmeters around the superior mesenteric, the left renal and th e left external iliac arteries. The colorectal portion of the intestin e was distended at constant pressure (36.6 mm Hg, 4.9 kPa mean; range 25-50 mm Hg, 3.3-6.7 kPa) with warm Ringer solution for periods of 2 m in. After a set of control distensions, the experiments were performed whilst the reflex rise in arterial pressure was prevented by removal of blood from the arterial tree. In control distensions arterial press ure increased by 11.3 +/- 1.5 mm Hg, 1.51 +/- 0.12 kPa (mean +/- SEM). In distensions at constant arterial pressure, peripheral blood flows were altered to different extents in the three territories studied: va scular resistance increased by 30.8 +/- 5.6% (P < 0.01) in the mesente ric, by 4.1 +/- 1.5% (P < 0.03) in the renal, and by 15.2 +/- 6.8% (NS ) in the external iliac bed. We conclude that colorectal distension ma y reflect activation of a function-specific pathway of the sympathetic nervous system, which leads to much greater vasoconstriction in the s planchnic circulation than in renal or musculocutaneous circulations.