Follicular development and ovulation in hypothyroid rdw rats.

In this paper, we summarized our recent studies on follicular development and ovulation in the presence or absence of thyroxine (T4) and equine chorionic gonadotrophin (eCG) treatment in infertile immature spontaneously hypothyroid rdw rats. T4 therapy once daily from postnatal day 21 to day 29 resulted in increases in ovarian weight on day 30 (P 0.01). Similar populations of both healthy and atretic antral follicles ranging in diameter from 101-400 microm were observed in control rdw and normal rats. T4 treatment markedly increased the numbers of healthy antral follicles of 101-400 microm or larger than 550 microm in diameter in the absence or presence of eCG, respectively, in rdw rats. On the other hand, T4 treatment did not affect the population of atretic antral follicles, but decreased the number of atretic large antral follicles (>400 microm) in the presence of eCG. Although a few (5+/-2) eggs were obtained from immature rdw rats treated with gonadotrophins alone, significantly more eggs (85+/-5) were ovulated from females treated with gonadotrophins and T4. As a control, normal littermates ovulated 45 eggs when treated with gonadotrophins only and 68 eggs when to them were also given T4. In conclusion, the results of the present study indicated that T4 treatment improved follicular development in the presence of eCG and significantly increased the number of ovulated eggs following hCG treatment in rdw rats.