The antigonadotrophic effect of melatonin in Syrian hamsters is modulated by prostaglandin.

PGE2 was shown to play an essential role in the gonado-inhibiting effect of melatonin in Syrian hamsters by transforming the neuroendocrine signal to gonadal reactivity. Prostaglandin is a vital link in the transduction of photoperiodic information into gonadal function and the difference in its levels brought about by melatonin given at different times of the day could explain the phenomenon why gonadal involution occurs only upon administration of melatonin towards the end of the day. It appears also that the melatonin signal is decoded in the pituitary, probably involving the short loop negative feedback of LH on LH-RH hormones.