A REAPPRAISAL OF THE FEEDBACK EFFECTS OF ESTRADIOL UPON LUTEINIZING-HORMONE SURGE

The objective of this study was to assess the temporal relationships o f serum oestradiol and luteinizing hormone (LH) with regard to the fee dback mechanism leading to the LH surge, Daily measurements of oestrad iol, LH and follicle stimulating hormone were made in 65 women with ov arian failure undergoing an evaluation of endometrial response to oral cycle stimulation, Patients received incremental oral oestradiol vale rate for varying durations at the in-vitro fertilization unit of the S heba Medical Center, Tel Hashomer, Israel, The treatment protocol invo lved the administration of daily oestradiol valerate, starting with 1 mg/day, followed by a daily increment of 1 mg for a total of 4, 6 and 8 days, After the last day, a daily maintenance dose of 2 mg was conti nued, Serum oestradiol concentrations correlated with the dose of oral oestradiol valerate, Peak oestradiol concentrations (mean +/- SEM) we re 572 +/- 60, 721 +/- 42 and 797 +/- 53 pg/ml for 4, 6 and 8 days of oestradiol valerate administration respectively, Serum LH, after an in itial suppression, peaked 2 days after maximal oestradiol valerate dos e and 1 day after peak serum oestradiol, The magnitude of the LH peak was proportional to the duration of incremental oestradiol valerate tr eatment, In conclusion, the LH surge is temporally related to the cess ation of serum oestradiol increase, Consequently, the occurrence of th is surge can be explained by a simple negative feedback inhibition of pituitary LH release rather than by a dual negative/positive mechanism .