Serotonin as a possible physiological regulator of ovine luteal function

Serotonin (5-hydroxytryptamine, 5-HT) has been found to significantly (P < 0.05) stimulate basal progesterone production by dispersed ovine luteal cells harvested on Days 3 and 10 of the oestrous cycle; these effects were inhibited by mianserin. There was no stimulation of cells from corpora lutea of Day 14 pregnant sheep. High performance liquid chromatography (HPLC) analysis demonstrated the presence of 5-HT in corpora lutea (CL), with the highest concentration in early (Day 3) dispersed luteal cells. However, 5-hydroxyindoleacetic acid, a major metabolite of 5-HT, was not detected in either midcycle (Day 10) or early pregnant (Day 14) CL. Furthermore, 5-HT could not be observed immunohistochemically in any of the CL. These results suggest that serotonin may only have a minor role, if any, in the regulation of ovine steroidogenesis.