THE ANTIGONADOTROPHIC EFFECT OF MELATONIN IN SYRIAN-HAMSTERS IS MODULATED BY PROSTAGLANDIN

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