Pituitary response to LHRH stimulation in women on oral contraceptives: a followup dose response study

Gonadotropic response to bolus intravenous injection of LHRH was measured in 36 women. Thirty of them were taking five different oral contraceptive preparations with six women in each category, and the remaining six served as controls. 150 micrograms LHRH was given during cycle days 20-25. Serum samples were obtained prior to the bolus injection and at 20 minute intervals for two hours. Five different oral contraceptive agents were selected to compare different progestins with same type and dose of estrogen, and different type or dose of estrogen with same type and dose of progestins. Significant suppression of LH response to LHRH stimulation ws observed in the agents containing 50 mcg of ethinyl estradiol or mestranol. No such suppression was noted in the product containing only 20 mcg of ethinyl estradiol. In comparing the different type of estrogenic or progestational components, no statistically significant differences in LH response were demonstrated. This finding suggests that it is not the individual component alone, but the combined action of estrogenic and progestational components which determines the potency of an oral contraceptive agent.