Repetitive mechanical stimulation of differentiated skeletal muscle in tissue culture increased the long-term production of prostaglandin F2 alpha, an anabolic stimulator of myofiber growth. Within 4 h of initiating mechanical stimulation, the enzymatic activity of cyclooxygenase (prostaglandin GH synthase [PGHS]), a regulatory enzyme in prostaglandin synthesis, was increased 82% (P < .005), and this increase was maintained for at least 24 h. Kinetic analysis of stretch-activated cyclooxygenase activity indicated a two to threefold decrease in the enzyme's Km, with little change in its Vmax. Immunocytochemical analysis of the cell cultures indicated the presence of high levels of the mitogen-inducible isoform of cyclooxygenase (PGHS-2) in the skeletal myofibers compared to the interstitial fibroblasts. While the stretch-induced increase in cyclooxygenase enzymatic activity was not inhibited by tetrodotoxin and therefore was independent of cellular electrical activity, the G protein inhibitor pertussis toxin prevented stretch-induced cyclooxygenase activation. Pertussis toxin also inhibited stretch-induced increases in PGF2 alpha production, phospholipase D activation, and cell growth. It is concluded that stretch of skeletal muscle increases muscle cell growth through a G protein-dependent process involving the activation of cyclooxygenase, an immediate early gene product.

Repetitive mechanical stimulation of cultured avian skeletal muscle increases the synthesis of prostaglandins (PG) E2 and F2α which regulate protein turnover rates and muscle cell growth. These stretch‐induced PG increases are reduced in low extracellular calcium medium and by specific phospholipase inhibitors. Mechanical stimulation increases the breakdown rate of 3H‐arachidonic acid labelled phospholipids, releasing free 3H‐arachidonic acid, the rate‐limiting precursor of PG synthesis. Mechanical stimulation also increases 3H‐arachidonic acid labelled diacylglycerol formation and intracellular levels of inositol phosphates from myo‐[2‐3H]inositol labelled phospholipids. Phospholipase A2 (PLA2), phosphatidylinositol‐specific phospholipase C (PLC), and phospholipase D (PLD) are all activated by stretch. The stretch‐induced increases in PG production, 3H‐arachidonic acid labelled phospholipid breakdown, and 3H‐arachidonic acid labelled diacylglycerol formation occur independently of cellular electrical activity (tetrodotoxin insensitve) whereas the formation of inositol phosphates from myo‐[2‐3H]inositol labelled phospholipids is dependent on cellular electrical activity. These results indicate that mechanical stimulation increases the lipid‐related second messengers arachidonic acid, diacylglycerol, and PG through activation of specific phospholipases such as PLA2 and PLD, but not by activation of phosphatidylinositol‐specific PLC. © 1993 Wiley‐Liss, Inc.