Opioid regulation of pituitary gonadotropins and prolactin in women using oral contraceptives.

To determine the effect of oral contraceptives on endogenous opioid modulation of the hypothalamic-pituitary axis, we gave a bolus dose of 10 mg of naloxone intravenously in women using Lo/Ovral-28 oral contraceptives and in normal (control) women during the follicular (days 8 to 9) and luteal (days 21 to 23) phases. Plasma follicle-stimulating hormone, luteinizing hormone, and prolactin were measured by radioimmunoassay before and after naloxone at regular intervals. In oral contraceptive users (n = 5) basal plasma follicle-stimulating hormone (3.7 +/- 0.4 mIU/ml) and luteinizing hormone (3.2 +/- 0.5 mIU/ml) levels were significantly lower than in control subjects during both follicular (10.7 +/- 0.9 and 16.7 +/- 2.0) and luteal (7.7 +/- 1.4 and 10.0 +/- 0.9, respectively) phases (p less than 0.05 to 0.001). In contrast the basal plasma prolactin level was significantly higher in oral contraceptive users (25.0 +/- 4.1 ng/ml) than in control subjects during the follicular (11.8 +/- 1.2) and luteal (11.0 +/- 0.8) phases (p less than 0.01). In control subjects, follicle-stimulating hormone, luteinizing hormone, and prolactin levels did not change significantly after naloxone in the follicular phase, but naloxone elicited a significant synchronous release of luteinizing hormone and prolactin during the luteal phase. In contrast, oral contraceptive users showed increases in luteinizing hormone and prolactin after naloxone that were not significantly different from the basal plasma levels.