The Effects of Hypophysectomy on Phosphorylase Activity in Adipose Tissue and Muscle

Abstract

Phosphorylase activity was measured in cell-free homogenates of adipose tissue and diaphragm muscle obtained from normal and hypophysectomized rats. Preincubation of segments of adipose tissue with epinephrine produced a dose-related increase in Phosphorylase activity, but almost 50 times as much epinephrine was required as is needed for activation of lipolysis. Hypophysectomy decreased the amount of AMP-dependent Phosphorylase activity of adipose tissue and markedly reduced its sensitivity to activation by epinephrine. Hypophysectomy also reduced the sensitivity of adipose tissue Phosphorylase to activation by the dibutyryl analog of cyclic AMP. Pretreatment with one mg of cortisone/day had no effect on either basal Phosphorylase activity, or the response to epinephrine. Five µg of T3/day did not increase basal Phosphorylase activity, but allowed a pronounced increase in activity in response to epinephrine. Growth hormone increased the basal activity of Phosphorylase, but had no effect on the response to epinephrine. The combination of growth hormone and cortisone produced effects that were indistinguishable from growth hormone alone. In combination, growth hormone and T3 gave a near normal response. In contrast, hypophysectomy failed to modify the effects of epinephrine on the activation of Phosphorylase in diaphragm muscle. The results indicate that potentiation by the pituitary of the metabolic responses to epinephrine may be tissue-specific. They further suggest that by selectively amplifying the effects of epinephrine in certain tissues, changes in pituitary function may modify qualitatively the overall pattern of responses to catecholamines in vivo. 1 Supported by a grant (AM 06935) from the National Institutes of Health. A preliminary report of these results was given at the 54th Annual Meeting of the Federation of American Societies for Experimental Biology 1970. Fed.Proc. 29:580 Abs. 1970.