Pineal function in the sheep: evidence for a possible mechanism mediating seasonal reproductive activity

Summary The 24-h profiles of plasma melatonin in the intact ewe in natural light indicate that a bimodal pattern of secretion is frequently present in oestrus, whereas a single dark-phase peak is characteristic of anoestrus. Based on these findings, a mechanism for the possible pineal-mediated control of seasonal breeding is proposed.This work was supported by the Medical Research Council and the Agricultural Research Council of Great Britain. Preliminary results from this study were reported in the proceedings of the 1st meeting of the European Pineal Study Group; J. Arendt, Prog. Brain Res.52, 249 (1979).We are grateful for the excellent technical assistance of A. Marston and J. Bradtke.