CONTRIBUTION OF PROSTAGLANDINS TO MUSCLE BLOOD-FLOW IN ANESTHETIZED DOGS AT REST, DURING EXERCISE, AND FOLLOWING INFLOW OCCLUSION

The role of locally formed cyclo-oxygenase products (endoperoxide intermediates, prostaglandins or prostacyclins) in resitance to blood flow was studied in the hindlimbs of anesthetized dogs during rest, during exercise, and following release of inflow occlusion. Meclofenamic acid, indomethacin, or sodium meclofenamate reduced mean resting blood flows of 86, 133, and 118 ml/min to 54, 82, and 67 ml/min, respectively. Inhibitors of prostaglandin synthesis reduced the vasodilator response to arachidonic acid by 81%. In addition, prostaglandin synthesis inhibitors attenuated the hyperemic responses following occlusions in the resting hindlimb. The attenuation was most marked following a 1-second occlusion (74%) and progressively less following a 10-second (44%) and a 300-second (24%) occlusion. However, the portion of the total postocclusive hyperemic response attributable to prostaglandins was constant and independent of occlusion duration. Inhibition of prostaglandin synthesis did not affect the hyperemia of exercise, but reduced significantly the postocclusion hyperemia that followed the release of a 1-second (63%) and a 2-second (43%) period of inflow occlusion in the exercising hindlimb; attenuation was minor following a 10-second occlusion (10%). In three of four exercising hindlimbs, the portion of the postocclusion hyperemia attributable to prostaglandins was inversely related to the duration of the occlusion. These data indicate that locally synthesized cyclo-oxygenase products, possibly prostaglandins, are important in the maintenance of blood flow in resting but not exercising muscle, contribute significantly to postocclusive hyperemia in resting and exercising hindlimbs, and mediate the hyperemia that follows occlusion of 5 seconds or less in resting and 2 seconds or less in exercising hindlimbs.