Effect of age on myofibrillar protease activity and muscle binding of glucocorticoid hormones in the rat.

Age-related and muscle tissue-specific alterations in myofibrillar protease activity were observed in different muscles of the rat. Utilizing exogenous, denatured and 3 H-labelled hemoglobin as substrate, proteolytic activity of the myofibrillar enzyme was found to decrease with age in the gastrocnemius muscle while the same activity in the diaphragm and heart muscles increased with age. The extent of response of the enzymes to administration of the potent glucocorticoid triamcinolone was, however, found to be similar in young and old animals, and each muscle retained its specific mode of response to the exogenous glucocorticoid, for example enhancement of the activity in skeletal and diaphragm muscles and diminution of the activity in the heart. Development was associated with a marked reduction in the number of glucocorticoid-specific binding sites in the cytosol of both gastrocnemius and heart muscles, with only negligible changes in the affinity of hormone binding. It is concluded that while the ability of the enzyme to response to exogenous, pharmacological doses of glucocorticoids is not affected by development, development does modify the myofibrillar protease activity in a tissue-specific manner.