Initiation of periovulatory events in gonadotrophin-stimulated macaques with varying doses of recombinant human chorionic gonadotrophin

During in-vitro fertilization (IVF) cycles, a large bolus of humanchorionic gonadotrophin (HCG) is used to induce periovulatory events, butthe efficacy of lower doses is undefined. Following follicular stimulationin rhesus monkeys, oocyte nuclear maturation, IVF, granulosa cellluteinization and corpus luteum function were compared after injection of100, 300 or 1000 IU recombinant HCG or 1000 IU urinary HCG. Bioactive HCGrose to peak concentrations within 2 h that were proportional to the doseadministered (100 < 300 < 1000 IU, recombinant HCG = urinary HCG).The duration of surge values (>100 ng/ml) was also dose-dependent (0 h,100 IU; 24 h, 300 IU; >48 h, 1000 IU, recombinant and urinary HCG).While the proportions of oocytes resuming meiosis and undergoing IVF weresimilar among groups, fewer animals yielded fertilizable oocytes following100 and 300 IU (five of nine) compared to 1000 IU recombinant and urinaryHCG (nine of 10). Peak values of serum progesterone in the luteal phasewere similar, but declined 2 days earlier after 100 and 300 IU relative to1000 IU recombinant and urinary HCG. Thus, 3-10 fold lower doses of HCGelicit low amplitude surges of short duration that induce periovulatoryevents such as re-initiation of oocyte meiosis and granulosa cellluteinization. However, oocyte fertilization and luteal function mayoptimally require surges of higher amplitude and longer duration similar tothose produced by standard doses of 1000 IU recombinant or urinary HCG.