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

Abstract

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.

Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining

“…Our approach allowed for a detailed time course analysis and demonstrated that addition of nuclei appeared to be most intense 6-9 days after the introduction of overload; this fits previous observations that hypertrophic stimuli initiate satellite cell mitosis before this time period (39)(40)(41). An increase in total protein synthesis (but also in degradation) has already been detected within hours after introducing a hypertrophy stimulus (42)(43)(44)(45), including by hypertrophy models similar to ours (46,47). This has led to speculation that enlargement caused by an increase in synthetic capacity per nucleus precedes addition of nuclei and that nuclei might not be obligatory for hypertrophy.…”

Effects of the cyclo‐oxygenase inhibitor, fenbufen, on clenbuterol‐induced hypertrophy of cardiac and skeletal muscle of rats

“…One prostaglandin, PGE2, has been shown to stimulate protein degradation (Rodemann & Goldberg, 1982) and is believed to be involved in some pathological states involving muscle wasting where a large increase in rates of protein degradation has been shown to be inhibited by NSAIDs such as indomethacin and naproxen (Ruff & Secrist, 1984;Tian & Baracos, 1989). PGF2. was shown to stimulate protein synthesis in rat (Rodemann & Goldberg, 1982) and rabbit muscle (Smith et al, 1983) in vitro. The non-steroidal anti-inflammatory drug, indomethacin, which inhibits the action of cyclo-oxygenase and thus reduces the metabolism of arachidonic acid to prostanoids, was shown to inhibit the acute effects of insulin in vivo (Reeds et al, 1985) and in vitro .…”

“…These observations have implicated cyclo-oxygenase metabolites of arachidonic acid, specifically prostaglandin F2", (PGF2a) (Smith et al, 1983) in the control of protein synthesis. Another NSAID, fenbufen ( a pro-drug, which is metabolized in the liver to 4-biphenyl acetic acid) has also been shown to affect rates of protein synthesis in rat muscle .…”

Regulatory interactions between muscle and the immune system during muscle regeneration

“…NSAIDs are strong inhibitors of cycloxygenases (COX), and thereby impair the metabolism of arachidonic acid that is necessary for the synthesis of prostaglandins (8). Prostaglandins are able to affect muscle cell proliferation (142), differentiation (96), and fusion (141), and can also modulate muscle fiber growth and the synthesis and degradation of proteins in muscle (104,121). Thus, perturbation of COX activity in either inflammatory cells or in muscle cells would be expected to have broad effects on muscle growth and regeneration following injury.…”