Inhibition of bradykinin vasodilation and potentiation of norepinephrine and angiotensin vasoconstriction by inhibitors of prostaglandin synthesis in skeletal muscle of the rat.

Recent reports have indicated that vascular responsiveness can be altered by exogenously administered or endogenously released prostaglandins. Furthermore, in certain tissues inhibitors of prostaglandin synthesis have been shown to limit the increase in blood flow in response to bradykinin and to enhance the reduction in blood flow in response to angiotensin and norepinephrine. These findings suggest an important local circulatory role for prostaglandins. We attempted to implicate further prostaglandins in local blood flow regulation by examining the effects of indomethacin (IND) and 5,8,11,14-eicosatetraynoic acid (ETA), inhibitors of prostaglandin synthesis, on microvascular arteriolar responses to bradykinin, prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), histamine, norepinephrine, and angiotensin. Male Wistar rats were anesthetized with sodium pentobarbital, and their cremaster muscle was exteriorized and prepared for in vivo microscopic observation of microvessels. Changes in arteriolar luminal diameters in response to topical administration of vasoactive agents were quantified with an image-shearing measuring eyepiece in conjunction with a television microscope and recorder. Local administration of IND or ETA significantly reduced the arteriolar dilation elicited by bradykinin, whereas the responses to PGE1 and PGE2 remained unaltered. Responses to histamine, although somewhat reduced, were not significantly different from control. Vasoconstrictor responses of arterioles elicited by norepinephrine and angiotensin were potentiated by IND or ETA administration. These results indicate that prostaglandins synthetized in skeletal muscle microcirculation in situ (1) mediate, in part, vasodilator responses to bradykinin and (2) modulate vasoconstrictor responses to angiotensin and norepinephrine. Thus, these findings support the hypothesis that prostaglandins are local regulators of microvascular responsiveness.