| Abstract: | Epinephrine treatment of the perfused rat heart led to an increase in glucose uptake, detritiation of 5-3H] glucose, glycogenolysis, and the formation of lactate. The change in the rate of formation of 3H2O from 5-3H]glucose was slower to develop (commencing at approximately 30 s) than changes in cyclic AMP concentration, hexose-6-P concentration, and the phosphorylase a/(a + b) ratio which were maximal at 24 s. Epinephrine plus propranolol (alpha-adrenergic combination) treatment of the perfused heart also led to increases in glucose uptake, detritiation of 5-3H]glucose, and the formation of lactate, but these occurred without significant changes in cyclic AMP concentration, hexose-6-P concentration, or the phosphorylase a/(a + b) ratio. Half-maximal stimulation of glucose uptake occurred at 0.2 microM epinephrine, 1.5 microM methoxamine, and 1 microM isoproterenol. The increase in glucose uptake mediated by 1 microM epinephrine was blocked by 10 microM prazosin but unaffected by 10 microM propranolol. The increase in glucose uptake mediated by 10 microM epinephrine plus 10 microM propranolol was partly blocked by yohimbine and completely blocked by prazosin. A role for Ca2+ in the adrenergic regulation of glucose uptake was indicated by the sensitivity of the epinephrine dose curve to Ca2+ and the dependence of epinephrine on Ca2+. In addition the increases in glucose uptake mediated by 1 microM epinephrine, 1 microM epinephrine plus 10 microM propranolol, 1 microM isoproterenol, and by 10 mM CaCl2 were each blocked by the Ca2+ channel blocker nifedipine (1 microM). It is concluded that Ca2+-dependent alpha- and beta-adrenergic receptor mechanisms are present in rat heart for controlling glucose uptake. At submicromolar levels of epinephrine the predominant receptors utilized appear to be alpha 1. |
