title: Growth hormone restores protein synthesis in skeletal muscle of old male rats.
abstract: The present study was undertaken to determine if the decline in skeletal muscle protein synthesis with age results from diminished secretion of growth hormone (GH). Young rats (3 to 4 months) were injected with vehicle and old rats (19 to 21 months) with bovine GH (2 mg/kg/day), L-dopa (100 mg/kg/day), or vehicle for 8 days, and the rates of phenylalanine incorporated into total diaphragm muscle protein/ug DNA/unit time were compared. After correction for free phenylalanine specific activity, rates of protein synthesis were determined to be reduced by 26% in old as compared with young rats (p less than .05). Treatment of old rats with bovine GH increased the rate of protein synthesis by 55% when compared with vehicle-treated old rats (p less than .05). L-dopa increased protein synthesis by 22% when compared with vehicle-treated old rats, although this was not statistically different from young or old vehicle-treated rats. These data indicate that (a) there is diminished capacity by skeletal muscle of old rats to synthesize protein; (b) this decrease is related to the reduced GH secretion because protein synthesis can be restored by GH administration; and (c) the dose of L-dopa given, although it increased the levels of circulating GH, did not completely restore protein synthetic capacity.
mesh_terms: D000367:Age Factors; D000375:Aging; D000818:Animals; D003964:Diaphragm / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology*; D007980:Levodopa / Q000494:pharmacology; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D010649:Phenylalanine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D009124:Muscle Proteins; D007980:Levodopa; D010649:Phenylalanine; D013006:Growth Hormone