EFFECT OF HEATING ON VASCULAR REACTIVITY IN RAT MESENTERIC-ARTERIES

Vasoconstriction in the viscera is one of the primary cardiovascular a djustments to heating. Local temperature can influence vascular respon siveness to catecholamines and sympathetic nerve activity. Therefore, we hypothesized that heating would alter vascular reactivity in rat me senteric arteries. Concentration-response curves to norepinephrine, ph enylephrine, potassium chloride (KCl), calcium, acetylcholine, and sod ium nitroprusside were obtained in vascular ring segments from rat mes enteric arteries at 37 and 41 degrees C. In some rings, basal tension increased slightly during heating. Heating to 41 degrees C did not alt er the contractile responses to norepinephrine in endothelium-intact o r -denuded rings but augmented the responses to KCl and calcium in end othelium-intact rings. The potentiating effect of heating on the respo nses to KCl and calcium was eliminated after endothelium removal. In c ontrast, the relaxant responses to acetylcholine and sodium nitropruss ide were significantly attenuated at 41 degrees C. Collectively, these results demonstrate that heating alters vascular reactivity in rat me senteric arteries. Furthermore, these data imply that heating reduces the ability of vascular smooth muscle to relax, possibly due to a decr ease in sensitivity to nitric oxide.