Endogenous Opiates Modulate Pulsatile Luteinizing Hormone Release in Humans*

Abstract

To test the postulate that endogenous opioid peptides may be involved in the neuroendocrine mechanisms controlling the frequency and amplitude of LH pulses, saline and an opioid receptor antagonist, naloxone, were infused sequentially, each for 6-h intervals, in six normal cyclingwomen during the luteal phase of the menstrual cycle. During naloxone infusion (1.6 mg/h), there was a significant (P <0.01) increase in both the frequency and amplitude of LH pulses compared tothose in saline controls. FSH pulses were not discernible in individual subjects; however, a significant increment in FSH levels occurred concomitantly with the increase in LH. These data strongly suggest that endogenous opiates, through an inhibition of hy-pothalamic LRF, participate in the endocrine events leading to the low frequency of episodic LH secretioncharacteristic of the luteal phase of the human menstrual cycle.