The in vitro and in ovo effects of environmental illumination and temperature on the melatonin secretion from the embryonic chicken pineal gland.

Pineal glands of chicken embryos were placed into a perifusion system for 4 days. The pineal glands were illuminated or exposed to elevated temperature for 8 or 12 h during the in vitro experiment and/or in ovo. Both daily illumination and repeated elevations of environmental temperature transitionally inhibited melatonin release before, and controlled the phase of melatonin rhythm after, the 17th day of embryonic life (E17). In addition, the in ovo rhythmic illumination applied before E13 advances the development of the circadian hormone synthesis.