Melatonin binding sites in the sheep pars tuberalis.

The localization of [125I]melatonin binding sites has been studied by autoradiography on frozen unfixed sections of the pituitary stalk, the suprachiasmatic area, the pineal and the pituitary glands in sheep. Dense specific labelling has been found exclusively in the pars tuberalis of the pituitary stalk but not in the part of the median eminence surrounded by the pars tuberalis. The labelling was completely excluded by a 200-fold excess of cold melatonin. No comparable labelling was found in the suprachiasmatic nucleus, the pineal and the pituitary glands. These results constitute the first report of melatonin-specific labelling in the ovine species.