No effect of aging on skeletal muscle insulin-like growth factor mrnas. Hamilton, Marc T., Daniel R. Marsh, David S. Criswell, Wei Lou, and Frank W. Booth. Department of Physiology and Cell Biology, University of Texas Medical School, Houston Texas, 77030
APStracts 2:0176R, 1995.
This study examined the hypothesis that during aging insulin-like growth factor (IGF) mRNAs are reduced in skeletal muscle. IGF-I, IGF -II, and insulin-like growth factor binding protein five (IGFBP-5) mRNAs were measured with a ribonuclease protection assay in the gastrocnemius of specific pathogen free Fischer 344 rats. We hypothesized that IGF-I, IGF-II, and IGFBP-5 mRNA concentration (normalized to 18S RNA) in the gastrocnemius muscle of growing animals (3 mo) would be down-regulated in a coordinated manner with muscle size during aging-associated atrophy. As indicated by muscle wet weight and total protein content, the gastrocnemius muscle was growing in the 3 mo group (P &LT 0.01 smaller compared to 12 mo), fully developed at 12 mo, and was atrophied at 24 mo of age (P &LT 0.05 compared to 12 mo). IGF-I mRNA concentration in the gastrocnemius of 12 and 24 mo old rats was 39-49% less than in 3 mo old rats (P &LT 0.05). Contrary to our hypothesis, there was not a significant skeletal muscle IGF-I mRNA difference between middle-age (12 mo) and senescence (24 mo). Thus, IGF-I mRNA changed during maturation (3 mo to 12 mo) but not during aging (12 to 24 mo). Skeletal muscle IGF-II mRNA concentration was not different between 3, 12, and 24 mo old animals. Furthermore, animal age did not have an effect on IGFBP-5 mRNA concentration. We conclude that the aging -associated atrophy of skeletal muscle is not caused by altered pretranslational regulation of IGF-I, IGF-II, or IGFBP-5 in skeletal muscle. 

Received 12 April 1995; accepted in final form 13 June 1995.
APS Manuscript Number R237-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.