Arteriolar reactive hyperemia: modification by inhibitors of prostaglandin synthesis

Several studies implicate endogenously synthesized prostaglandins in the mediation of reactive hyperemic responses in the coronary, renal, and skeletal muscle circulations. We sought additional evidence to involve locally released prostaglandins in the mediation of reactive hyperemia in skeletal muscle at the level of the microcirculation. The cremaster muscle of pentobarbital-anesthetized Wistar-strain rats was prepared for direct in vivo observation and measurement of postocclusive responses of single arterioles. Responses of individual arterioles were reproducible over a 3-h test period. The postocclusion increase in diameter and the duration of response were dependent upon the duration of the occlusion. Repetitive occlusions did not influence arteriolar responsiveness to vasoactive substances. Indomethacin and 5-8-11-14-eicosatetraynoic acid, inhibitors of prostaglandin synthesis, did not affect resting arteriolar diameters; however, both drugs decreased the maximum increase in diameter and duration of the vasodilator response following release of the arteriolar occlusion. These findings suggest that in this microcirculatory bed, prostaglandins contribute little to resting vascular tone; in contrast, temporary arteriolar occlusion elicits the local release of dilator prostaglandins which contribute to the reactive hyperemic response.