Rat tail suspension causes a decline in insulin receptors.
Decreased muscular activity results in weakness and muscular atrophy. Coincident with this protein catabolic state is glucose intolerance and hyperinsulinemia. Rats were tail suspended for 7 to 14 days to accomplish unloading of the hindlimbs. Insulin resistance was documented in these animals by a 14 day tail suspension-related 26% increase in serum glucose in spite of a 253% increase in serum insulin concentration. Microsomal membranes were prepared from hindlimb muscles and specific binding of insulin and insulin-like growth factor I (IGF-I) were determined in these membranes. Insulin binding was decreased by 27% at 7 days and by 21% at 14 days. In contrast, IGF-I binding was unchanged at 7 days and was increased by 24% at 14 days. Liver membrane insulin receptors also had declined by 14 days of suspension, suggesting that the change in insulin receptors was a generalized, humorally-mediated phenomenon. These data suggest that tail suspension in rats results in insulin resistance, hyperinsulinemia, a decline in insulin receptors in liver and muscle, and a relative increase in muscle membrane IGF-I receptors. These data are consistent with the hypothesis that resistance to insulin's effects on protein metabolism in skeletal muscle may contribute to the protein catabolism associated with decreased muscular activity.
Stuart
C A
CA
Department of Internal Medicine, University of Texas Medical Branch at Galveston 77555-1060.
Kidder
L S
LS
Pietrzyk
R A
RA
Klein
G L
GL
Simmons
D J
DJ
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D007328:Insulin / Q000097:blood / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008566:Membranes / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism; D009133:Muscular Atrophy / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism*; D012149:Restraint, Physical; D013623:Tail
D001786:Blood Glucose; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin