Abstract
Although an acute opioid withdrawal markedly modifies LH secretion in the different phases of the menstrual cycle, whether a sustained opioid blockade imbalances spontaneous LH modifications associated with the progression of the follicular or luteal menstrual phases is presently unknown. Accordingly, normal cycling women during either the follicular (n = 14) or luteal (n = 14) menstrual phase, randomly and in double blind fashion, received either placebo (n = 7 for each phase) or 50 mg/day of the oral opioid antagonist naltrexone (n = 7 for each phase). In each subject, LH pulsatility (10-min blood drawing for 8 h) and the pituitary LH response to a 10-micrograms GnRH stimulus were investigated at baseline and on the fifth day of placebo/naltrexone administration. In the follicular phase, after placebo treatment, the number and amplitude of LH pulses did not significantly vary, whereas mean LH levels (P < 0.01) and the LH response to GnRH (P < 0.05) were significantly increased. The same occurred after naltrexone treatment, when significant increases in both mean LH levels (P < 0.02) and LH response to GnRH (P < 0.025) were observed. In the luteal phase, after placebo administration, the frequency of LH pulses and mean LH levels were not modified, but both the amplitude of LH pulses (P < 0.025) and the LH response to GnRH were reduced (P < 0.02). The same occurred after naltrexone treatment, when significant decreases in both the amplitude of LH pulses (P < 0.05) and the LH response to GnRH (P < 0.05) were observed. During both phases of the menstrual cycle, the modifications observed during naltrexone treatment were similar and not significantly different from those observed during placebo. The present data do not support important modulatory functions for endogenous opioid peptides on spontaneous LH modifications occurring with the progression of the follicular or the luteal menstrual phases.
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