Melatonin inhibits beta-adrenoceptor-stimulated cyclic AMP accumulation in rat astroglial cell cultures

We investigated whether astroglial cells are a site of action for the effect of melatonin on brain cyclic AMP content. Rat astroglial cell subcultures, identified according to morphological and immunochemical criteria, were used. Addition of melatonin to the cultures did not result in changes of cyclic AMP content. However, melatonin at 0.1-1 microM concentrations was able to impair the cyclic AMP increase elicited by 1 microM norepinephrine or isoproterenol in astroglial cultures. This melatonin effect was also shared by its biologically active analogues 5-methoxytryptophol and 6-chloromelatonin. Serotonin was only effective at a 100-fold greater concentration, while the biologically inactive melatonin metabolite 6-hydroxymelatonin was devoid of activity at any concentration used. These results suggest that methoxyindoles modulate negatively beta-adrenoceptor-induced cyclic AMP accumulation in cultured rat astroglial cells.