Norepinephrine, acting via adenylate cyclase, inhibits melatonin output but does not phase-shift the pacemaker in cultured chick pineal cells.

We have recently described a system, using dispersed chick pineal cells in static culture, which displays a persistent, photosensitive, circadian rhythm of melatonin release, and the effects of light upon it. Here we describe the effects of norepinephrine (NE) on melatonin output by these cells. NE inhibited nocturnal melatonin release; it was potent and effective. Pertussis toxin, forskolin, or 8-Br-cAMP blocked or circumvented inhibition by NE, suggesting the involvement of adenylate cyclase. Four hour pulses of NE caused acute suppression of melatonin output, but did not affect the phase of subsequent cycles in constant red light. These results indicate that NE affects melatonin production by mechanisms acting distal to the pacemaker which generates the melatonin rhythm. Insofar as adenylate cyclase appears to be involved in the action of NE, it might be involved in the regulation of melatonin output by the pacemaker, but is not implicated in regulation of the pacemaker by light.