Neuroendocrine control of ovarian function in the primate

Summary. This article reviews the neuroendocrine factors which control the menstrual cycle in the macaque monkey. It describes the pulsatile characteristics of gonado-trophin secretion, the control of LH pulses by an arcuate neural Gn-RH oscillator and the significance of pulsatile Gn-RH secretion. The factors which may modulate the activity of the Gn-RH arcuate neural oscillator are anaesthesia, ovarian hormones and endogenous opiates, as well as the possible significance of changes in Gn-RH pulsatile characteristics. Finally, the oestrogen and progesterone feedback control of the mid\x=req-\ cycle gonadotrophin surge and the site of action (hypothalamic or hypophysial) of these steroids are contrasted in the monkey and rat. This article, which reviews salient features of the neuroendocrine mechanisms controlling the menstrual cycle, is based on experimental results obtained in several primate research centres as well as our laboratory, using the macaque monkey as a model. The length of the menstrual cycle and the pattern of hormonal secretion in this animal indeed replicate closely those of the human. The article will underline the physiological features of gonadotrophin secretion and of its control and modulation by hypothalamic and ovarian hormones. Mean levels of gonadotrophins and ofovarian steroids throughout a menstrual cycle in monkeys are illustrated in Text-fig. 1. Briefly, follicular maturation is characterized by increasing circulatory oestradiol concentrations, which reach a peak at the time of the mid-cycle LH and FSH surges. This gonadotrophin surge in turn induces ovulation (in about 36 h), followed by the transformation of-5 O 5 10 Days from LH surg