Beta-Adrenergic Potentiation of the Increased In Vitro Accumulation of Cycloleucine by Rat Thymocytes Induced by Triiodothyronine

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Abstract

We have previously demonstrated that 3,5,3′-triiodothyronine (T3), whether administered in vivo or added to suspending media in vitro, promptly stimulates the in vitro accumulation of the nonmetabolized amino acids, alpha-aminoisobutyric acid, and cycloleucine (CLE) by thymocytes isolated from weanling rats. In these studies, we have examined the in vitro interaction between catecholamines and T3 with respect to this effect. The previously reported enhancement of CLE accumulation in thymocytes by T3 in vitro (1 μM) was confirmed. When added alone in concentrations ranging between 10 nM and 0.1 mM, the adrenergic agonists, epinephrine and norepinephrine, had no effect on CLE accumulation. At a concentration of 1 μM, isoproterenol, terbutaline, and phenylephrine were also without effect. However, the effect of T3 was clearly potentiated by the concomitant addition of epinephrine, norepinephrine, and possibly isoproterenol, whereas terbutaline and phenylephrine were without effect. Neither basal nor T3-enhanced CLE accumulation was affected by the addition alone of the adrenergic blocking agents, propranolol (0.1 mM), phentolamine (10 μM), or practolol (0.1 mM). Nevertheless, the beta1- and beta2-antagonist, propranol, and the beta1-antagonist, practolol, blocked the increment in CLE accumulation produced by epinephrine; the alpha-antagonist, phentolamine, was without effect.

Authors

James Etzkorn, Patricia Hopkins, Janet Gray, Joseph Segal, Sidney H. Ingbar