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This article discusses the relationship between aging, skeletal muscle physiology and physical inactivity. An analysis of lipoprotein lipase, triglyceride metabolism, and blood lipids is presented.

Research was conducted to examine the role of local contractile activity and muscle fiber type on lipoprotein lipase (LPL) regulation during exercise. A sample of female Sprague-Dawley rats which weighed approximately 175 g were allowed access to voluntary running wheels for 14-20 days. Results are in good agreement with the hypothesis that the effects of local contractile activity are important and sufficient to increase LPL expression during exercise.

Researchers have investigated the temporal expression pattern of messenger RNAs for insulin-like growth factor (IGF)-I, IGF-I receptor and IGF-II in the regenerating tibialis anterior muscle following injection of the myotoxic anesthetic bupivacaine in young, adult and old rats. Five days after injection, IGF-II mRNA was boosted 46-fold in young rats, but only fourfold in adult rats. The results indicate that the impairment of muscle regeneration is a maturation effect, rather than an aging effect.

The tissue water volume and extracellular water volume of isolated cat muscles were analyzed to determine the effects of pressure on water distribution during muscle stimulation. Quantitative analysis of water in isolated cat muscles by nonsteady tracers indicated the role of intracellular osmoles on pressure generation in muscle fluid uptake during exercise. Muscle stimulation also increased the levels of intracellular osmolarity and flow of solute-poor water into the cell.

The (RNA) ribonucleic acid-protein interaction in skeletal rat muscle was analyzed to determine the components of its 3'-untranslated region (3'-UTR) in the cytochrome c mRNA that responds to contractile activity. Prolonged stimulation of the skeletal muscle enhanced cytochrome c gene expression and concentration. Interactions between cytoplasmic proteins in the proximal region of 3'-UTR produced specific RNA-complexes.

Aging muscles do not exhibit a decline in the concentration of precursors to insulin-like growth factors so that these factors cannot account for the muscle atrophy that occurs with aging. The concentration of mRNA for insulin-like growth factors did increase between youth and middle age, but subsequent declines in the growth factors were not seen as the rats progressed from 12 to 24 months of age.

Sucrose on NaCl aid the examination of changes of distribution of fluid in isolated perfused cat calf muscle, induced by quick enhancements in plasma osmolality. The total transsarcolemmal flow is equal to the total transcapillary water flow during steady state, and therefore cell volume shrinkage is approximately equal to the increase in plasma volume. Reductions in intracellular water volume and total tissue water are identical, and there is no variation in steady state interstitial fluid transient with hypertonic NaCl and sucrose.