ALPHA-ADRENERGIC INTERACTION WITH STIMULATORS OF CYCLIC-AMP CONCENTRATIONS IN CANINE THYROID SLICES

Thyroid stimulating hormone (TSH) increased cyclic AMP levels approximately 10-20 fold in canine thyroid slices after 30 min incubation. Thereafter the cyclic AMP level declined reaching about 50% of the maximal by 90 min even in the presence of 10 mM theophylline. When phentolamine, an α-adrenergic blocker, was added with TSH to the incubation medium, the decline of cyclic AMP levels that followed the peak was markedly diminished. The maximal effect of phentolamine was observed at a concentration of 10-6M. A similar decline of the cyclic AMP levels after the peak was observed when the tissues was stimulated by prostaglandin E1 or cholera toxin and the decline was again prevented by phentolamine. Phentolamine alone had no significant effect on the basal cyclic AMP levels. Phenylephrine, an α-adrenergic agonist, diminished the rise of cyclic AMP levels induced by TSH. Norephinephrine, a physiologic adrenergic stimulator, caused a marked inhibition of the elevation of cyclic AMP levels induced by prostaglandin E1 or cholera toxin as was the case by TSH (Life Sciences 21, 607, 1977). The norepinephrine effect was abolished by phentolamine, but not by propranolol, a β-adrenergic blocker. These results indicate that α-adrenergic actions may be involved in the counter-regulation of cyclic AMP levels in canine thyroid glands. © 1979.