Effect of light and darkness on the in vivo release of N-acetylserotonin and melatonin by the retina of guinea pigs.

The effect of light and darkness on the in vitro release of N-acetylserotonin and melatonin by the retina of male pigmented guinea pigs was studied. One group of the retina was incubated in light and the other group in dark for 12 h. Histological examination of the cultured retinal tissues indicated that the retinal cells appeared intact and healthy. N-acetylserotonin and melatonin released into the medium was extracted and then quantified by radioimmunoassay. The release of N-acetylserotonin and melatonin by retinas cultured in dark was significantly higher than those in light, indicating that the in vitro release of N-acetylserotonin and melatonin in increased by darkness or reduced by light. This supports the notion that the retina may be an important extrapineal source of melatonin in the circulation and may at least help to sustain diurnal rhythms of serum N-acetylserotonin and melatonin.