Superovulation of immature hypothyroid rdw rats by thyroxine therapy and the development of eggs after in vitro fertilization

The aim of this study was to examine the effect of thyroxine on ovulation i n immature rdw rats and the fertilization and development of the eggs. Seru m thyroxine concentrations at 30 days of age were significantly lower in rd w rats than in normal rats (P < 0.001), and greatly increased after thyroxi ne replacement therapy (P < 0.001). Although few eggs (1-5 +/- 1-2) were ob tained from immature rdw rats treated with gonadotrophins alone, females tr eated with gonadotrophins and thyroxine ovulated significantly more eggs (8 5 +/- 5). As a control, normal littermates ovulated 21-45 eggs when treated with gonadotrophins alone, and 68 eggs when administered with gonadotrophi ns and thyroxine. Of the eggs collected from rdw rats treated with gonadotr ophins and thyroxine, and inseminated with spermatozoa from mature F-1 male s, 98% were penetrated and in almost all (99%) of these eggs, male and fema le pronuclei formed. Forty-seven per cent of the pronuclear eggs developed to the blastocyst stage in vitro. After transfer to recipients, 21% (14/66) of one-cell and 22% (8/37) of two-cell embryos developed to offspring, and 62% (8/13) of pups were of rdw/rdw genotype. The average body weight (6.9 versus 7.8 g) of offspring derived from one-cell embryos was lower than tha t for two-cell embryos. The morulae and blastocysts did not develop to term , although 41% implanted in the uterine horns of recipients. In conclusion, in immature rdw rats, superovulation was induced by gonadotrophins combine d with thyroxine therapy and the superovulated oocytes were fertilized and developed in vitro and developed to term after embryo transfer.