Relationship between light, calcium influx and cAMP in the acute regulation of melatonin production by cultured chick pineal cells.

Chick pineal cells in primary culture 'spontaneously' synthesize and release melatonin at 'night'. Exposing the cells to 'unexpected' white light, or to agents which retard calcium influx (nitrendipine, low external calcium), or which reduce cAMP levels (norepinephrine), acutely decreases nocturnal melatonin production. Conversely, agents which promote calcium influx (Bay K 8644) or mimic cAMP (8BrcAMP) increase nocturnal melatonin output. When these agents were used in combination, neither nitrendipine nor low external calcium reduced melatonin output in the presence of 8BrcAMP. Norepinephrine, however, did lower melatonin release in the presence of Bay K 8644. Addition of 8BrcAMP blocked the acute inhibitory effect of 'unexpected' light, but Bay K 8644 did not. Taken together with previous data, these results favor the hypothesis that both light and calcium influx acutely regulate melatonin production in the chick pineal through cAMP.