| Abstract: | It has been suggested that part of the increased beta-catecholamine responsiveness in hyperthyroid animals is due to a decrease in alpha-catecholamine action. The present results indicate that neither hyperthyroidism nor hypothyroidism altered the alpha 2-adrenergic inhibition of adenylate cyclase or the alpha 1-adrenergic stimulation of phosphatidylinositol turnover in adipocytes from the white adipose tissue of hamsters. No effect of hyperthyroidism was found on the Kd for binding of [3H]dihydroergocryptine or the number of binding sites in membranes prepared from hamster adipocyte tissue. The stimulation of cyclic AMP due to beta-catecholamines was enhanced in adipocytes from hyperthyroid hamsters, as was lipolysis. However, in adipocytes from hyperthyroid hamsters the maximal stimulation of cyclic AMP due to isoproterenol, ACTH or epinephrine plus yohimbine, as seen in the presence of adenosine deaminase and theophylline, was less than in adipocytes from euthyroid hamsters. The activation of adenylate cyclase by isoproterenol was the same in membranes from hyperthyroid as compared to those from euthyroid hamsters in the absence or presence of guanine nucleotides. These data suggest that thyroid status has little effect on alpha-catecholamine action by enhances the activation of lipolysis by beta-catecholamine agonists. |
