Protein synthesis in isolated rabbit forelimb muscles. The possible role of metabolites of arachidonic acid in the response to intermittent stretching.

Protein synthesis was measured in isolated intact rabbit muscles by the incorporation of [3H]phenylalanine added at a high concentration (2.5 mM) to the incubation medium. Intermittent mechanical stretching substantially increased the rate of protein synthesis relative to that in control muscles incubated under a constant tension. Indomethacin and meclofenamic acid, inhibitors of the enzyme cyclo-oxygenase, which converts free arachidonic acid into the prostaglandins, prostacyclins and thromboxanes, decreased the rate of protein synthesis in intermittently stretched muscles, but had no effect on synthesis rates in the unstimulated controls. Arachidonic acid at concentrations of 0.2 and 1.0 microM gave a highly significant increase in the rate of protein synthesis in muscles incubated under a constant tension. The ability of arachidonic acid to increase protein-synthesis rates was abolished by the addition of indomethacin. Activation of protein synthesis by intermittent stretching persisted for 10-20 min after the stretch stimulation had ceased. Indomethacin, added either during the initial incubation with intermittent stretching or during the subsequent period when protein synthesis was measured after stimulation had ceased, decreased protein-synthesis rates. This decrease was similar whether indomethacin was present during the initial, final or entire incubation period. In experiments analogous with those in (4) above, when Ca2+ was withheld and EGTA added for the entire incubation, rates of protein synthesis were again decreased. The rates of protein synthesis observed when Ca2+ was present during either an initial stimulation phase or a final, unstimulated, measurement phase were similar, and were intermediate between control rates and those in muscles incubated without Ca2+ for the whole experiment. Two prostaglandins, F2 alpha (2.8 microM) and A1 (28 microM), increased rates of protein synthesis in unstimulated muscles, but prostaglandins E2 and D2 and the leukotrienes C4 and D4 failed to do so. It is concluded that the stretch-stimulated increase in protein synthesis may be caused by activation of membrane phospholipases, release of arachidonic acid and a consequent increase in prostaglandin synthesis.