PREOVULATORY OXYTOCIN ADMINISTRATION PROMOTES THE ONSET OF THE LUTEINIZING-HORMONE SURGE IN HUMAN FEMALES

Luteinizing hormone (LH) secretion during the ovulatory cycle is belie ved to be predominantly regulated by gonadotrophin-releasing hormone, Investigations in animals have strongly suggested that oxytocin also p articipates in LH control and the physiological events controlling LH surge initiation. In the human female, however, there has been no evid ence supporting oxytocin's involvement in the processes leading to ovu lation. In this study the effect of a preovulatory infusion of oxytoci n on the onset of the LH surge was investigated in women aged 20-35 ye ars who had natural ovulatory menstrual cycles of lengths between 25-3 5 days, Vaginal ultrasound scanning monitored follicular growth during the late follicular phase. When a follicle >14 mm in diameter was obs erved each woman was randomized into one of two groups. One group (n = 8) received an oxytocin infusion of 256 mIU/min for 2 h, the other gr oup (n = 8) received normal saline, The women who were administered ox ytocin at this late follicular stage had an earlier onset of the LH su rge than those who had received saline (P < 0.01). The results indicat e that oxytocin promotes the onset of the LH surge in humans.