Growth hormone reduces glucose transport but not GLUT-1 or GLUT-4 in adult and old rats.
The primary purpose of this study was to investigate the influence of administration of recombinant-derived human growth hormone (rhGH) to adult male rats of several ages (9, 20, and 31 mo) on skeletal muscle glucose transport. Rats were injected with rhGH (0.7 mg/kg) or vehicle twice daily for 10 days. The rhGH treatment led to a doubling of circulating insulin-like growth factor I levels at each age. Skeletal muscle glucose transport activity was evaluated in isolated epitrochlearis muscle with use of 3-O-methylglucose at three insulin concentrations (0, 100, and 20,000 microU/ml). The results indicate that, after 10 days of rhGH administration, 1) an approximately 20-30% reduction in basal glucose transport activity was evident in muscles from every age group, 2) the ability of a submaximally effective insulin concentration (100 microU/ml) to increase glucose transport activity above basal values was not significantly reduced in any age group, 3) maximal insulin-stimulated glucose transport activity (with 20,000 microU/ml) was significantly reduced (approximately 40%) by rhGH treatment only in the oldest rats, and 4) the alterations in glucose transport activity occurred despite no change in skeletal muscle GLUT-1 or GLUT-4 protein levels.
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Biodynamics Laboratory, University of Wisconsin, Madison 53706, USA.
Bohn
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D019325:3-O-Methylglucose; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001786:Blood Glucose / Q000032:analysis; D001835:Body Weight / Q000187:drug effects; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D013006:Growth Hormone / Q000494:pharmacology*; D006824:Hybridization, Genetic; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D008757:Methylglucosides / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344
D001786:Blood Glucose; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D008757:Methylglucosides; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495679:Slc2a1 protein, rat; C495694:Slc2a4 protein, rat; D019325:3-O-Methylglucose; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D005947:Glucose