Effect of preovulatory estradiol concentrations on luteinizing hormone diurnal secretory patterns: a hypothesis for the timing of the luteinizing hormone surge.

The effect of preovulatory estradiol concentrations on 24-hour patterns of luteinizing hormone secretion was studied in six women with normal menstrual cycles. Blood samples were collected every 15 minutes for 24 hours before and after 7 days of estradiol benzoate administration, which achieved mean (+/- SE) estradiol concentrations of 424 +/- 54 pg/ml. The luteinizing hormone pulse frequency decreased significantly during sleeping hours both before (p less than 0.05) and after (p less than 0.005) estradiol benzoate administration. After estradiol benzoate, there also was diurnal variation in overall mean luteinizing hormone concentrations, which markedly increased secretion in the morning hours. The diurnal changes in luteinizing hormone secretion varied inversely with those of prolactin. These findings are consonant with the observation that the onset of the preovulatory luteinizing hormone surge in women occurs most frequently in the early morning hours.