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Title: Adrenergic control of alpha-melanocyte-stimulating hormone release in frog pituitary is mediated by both beta- and a nonconventional alpha 2-subtype of adrenoreceptors. Author: Lamacz M, Garnier M, Héry F, Tonon MC, Vaudry H. Journal: Neuroendocrinology; 1995 Apr; 61(4):430-6. PubMed ID: 7783856. Abstract: Previous studies have shown that melanotrope cells of the pars intermedia of Rana ridibunda are inhibited by dopaminergic D2 agonists and stimulated by beta-adrenergic agonists. In the present study, we have examined the possible involvement of alpha-adrenoreceptors in the regulation of frog melanotrope cells. Reversed-phase HPLC analysis combined with electrochemical detection revealed the presence of both dopamine and noradrenaline in pars intermedia extracts (74.1 and 3.2 ng/mg protein, respectively), while adrenaline was undetectable. Administration of graded doses of noradrenaline and adrenaline (from 0.1 to 10 microM) to perifused frog neurointermediate lobes induced a dose-dependent inhibition of alpha-MSH release. The inhibitory effect of adrenaline was partially blocked by the D2-dopaminergic antagonist sulpiride and totally suppressed by concomitant administration of sulpiride and yohimbine (an alpha 2-adrenergic antagonist). Conversely, in the presence of sulpiride, noradrenaline provoked a strong stimulation of alpha-MSH secretion which was totally blocked by the beta-adrenergic antagonist propranolol. Taken together, our results indicate that endogenous catecholamines may exert a complex regulatory action on frog melanotrope cells through activation of dopaminergic D2, alpha 2- and beta-adrenergic receptors.[Abstract] [Full Text] [Related] [New Search]