Effects of aminoglutethimide phosphate administration on embryonic development and implantation and on steroid hormone levels in superovulated rats

Abstract

The present study was undertaken to determine the relationship between preimplantation development of embryos and hormone levels in superovulated immature rats treated with aminoglutethimide phosphate (AGP), an inhibitor of steroid synthesis. In addition, the effects of AGP on incidence of pregnancy and the number of implantation sites in superovulated rats were studied. Immature or adult rats were pretreated with 20 or 40 IU of pregnant mare's serum gonadotropin (PMSG) at 11.00–13.00 h followed by 20 or 40 IU of human chorionic gonadotropin (hCG) to the respective groups 52 to 54 h later. Ten or 20 mg AGP/day was administered once on day 0, 1 or 2; twice during days 0 to 2; or three times on days 0 to 2 of pregnancy. Animals were killed 24 to 120 h after hCG injection (estimated 12 or 108 h after ovulation) or on day 8 of pregnancy. Pregnancy rates in superovulated immature and adult rats given 10 or 20 mg AGP for the first 3 days were 73.3–80.0 or 93.3%, respectively. Injection of 10 or 20 mg AGP to these animals resulted in 10.9–16.2 or 20.2–21.6 implantation sites per mated rat, respectively. Transport of ova in superovulated rats receiving no AGP treatment was faster than in AGP-treated rats by 72 h after hCG injection, and most embryos were lost from the uterus at 120 h in the former group, but not in the latter. Serum progesterone concentrations at 48 and 72 h and estradiol-17β levels at 48 h in AGP-treated rats were significantly lower than those in controls ( P < 0.05-0.01). These findings suggest that the diminished incidence of implantations is caused by hypersecretion of estrogen, and this was counteracted by AGP treatment.