MODULATION OF PROSTAGLANDIN-E2 SYNTHESIS IN RAT SKELETAL-MUSCLE

The effect of muscle denervation, inhibitors of protein synthesis, G proteins, and sphingolipids on prostaglandin E2 (PGE2) release by rat soleus muscle in vitro was investigated. To assess the effect of muscle denervation, the sciatic nerve in one hindlimb of rats was interrupted, and soleus muscles from the denervated hindlimb and the contralateral sham (control) hindlimb were excised 1-5 days after surgery. Compared with corresponding sham muscles, PGE2 release by denervated muscles was increased 56, 230, and 435% at 1, 3, and 5 days after denervation, respectively. Protein synthesis inhibitors cycloheximide (10-mu-M) and puromycin (10-mu-M) lowered PGE2 release by sham and denervated muscles 62-80%. The release of PGE2 by sham and denervated muscles was not altered by pertussis toxin (1-mu-g/ml) but was inhibited 30-51% by AlF4-. Addition of 100-mu-M guanosine 5'-O-(3-thiotriphosphate) to saponin-permeabilized sham and denervated muscles had only a moderate, if any, stimulatory effect on PGE2 release. This effect was not counteracted by 1 mM guanosine 5'-O-(2-thiodiphosphate). Increasing muscle ceramide concentration by incubation with sphingomyelinase (100 mU/ml) increased PGE2 release by sham and denervated muscles 43 and 157%, respectively. Because degradation of ceramides yields sphingosine, the effect of sphingosine was also tested. Sphingosine (25-mu-M) increased PGE2 release by sham and denervated muscles 139 and 187%, respectively, without affecting muscle viability, as assessed by the release of lactate dehydrogenase. The data indicate that muscle denervation, treatment with sphingomyelinase, and sphingosine stimulate, whereas inhibitors of protein synthesis inhibit PGE2 synthesis by muscle.