Effect of recombinant human luteinizing hormone versus human chorionic gonadotrophin: effects on ovulation, embryo quality and transport, steroid balance and implantation in rabbits.

A total of 40 New Zealand female rabbits which had been given follicular stimulation and artificial insemination received 50 IU of either recombinant human luteinizing hormone (rhLH; n = 20) or human chorionic gonadotrophin (HCG; n = 20) to induce ovulation. In each hormone group, 10 animals were killed 72 h later to study the ovulatory process and the number, location, morphological quality and variation in the degree of development of recovered embryos. Pre-ovulatory and post-ovulatory oestradiol and progesterone concentrations were determined in these 10 animals; the remaining 10 animals of each group were killed at 14 days to study implantation up to day 14. At 72 h the number of luteinized follicles and the total number of embryos in the rhLH group were lower than in the HCG group, and the number of pre-ovulatory follicles was higher. The percentage of good quality embryos was higher with rhLH, whereas the percentage of degenerated embryos was lower. Oviductal transit of the embryos was slower and variation in the degree of embryo development greater after HCG. Progesterone concentrations were comparable with pre-ovulatory concentrations at 24 h in the rhLH group, but not in the HCG group where they increased. In the study performed at 14 days, the implantation rate was significantly higher with rhLH versus HCG. These observations suggest that rhLH induces a lower number of follicles to ovulate than does HCG, probably due to its shorter half-life; however, the better embryo quality produced by rhLH may ultimately lead to a better implantation rate; rhLH may mimic the physiological endogenous LH surge more closely than HCG.