Pineal gland in organ culture. II. Role of adenosine 3',5'-monophosphate in the regulation of radiolabeled melatonin production.

Abstract

N5,O2′-dibutyryl adenosine 3′,5′- monophosphate (dibutyryl cyclic AMP) mimics some of the effects of norepinephrine (NE) on indole metabolism of cultured rat pineal glands. This nucleotide increases the concentrations of radiolabeled N-acetylserotonin and melatonin in the media from cultures containing substrate concentrations of 3H-tryptophan and 14C-serotonin. The concentrations of the oxidation products of serotonin are not affected. 3H-melatonin production from 3H-tryptophan is stimulated by theophylline, but not by adenosine 3′,5′-monophosphate (cyclic AMP), guanosine 3′,5′-monophosphate, or inosine 3′,5′-monophosphate. The combined treatments with high doses of theophylline and NE or dibutyryl cyclic AMP and NE do not stimulate 3H-melatonin production more than that which is observed with any one of these compounds. The activity of the final enzyme in melatonin synthesis, hydroxyindole- O-methyltiansferase, is apparently not affected by dibutyryl cyclic AMP treatment. p-Chlorophenylalanine, an inhibitor of serotonin synthesis, enhances the dibutyryl cyclic AMP-stimulated conversion of exogenous 14C-serotonin to 14C-melatonin. This indicates that new serotonin synthesis is not required for the effect of this nucleotide on melatonin synthesis. Cycloheximide and actinomycin D block the stimulation of 3H-melatonin production by dibutyryl cyclic AMP. 3H-cyclic AMP appears to be taken up by pineal glands in organ culture. Most of the 3Hcyclic AMP that enters the pineal cells is broken down. This may explain why cyclic AMP fails to stimulate melatonin production. These studies support the hypothesis that melatonin production by intact pineal glands is controlled through a cyclic AMP mechanism which appears to regulate the rate of conversion of serotonin to Nacetylserotonin. (Endocrinology89: 453, 1971)