Effect of repeated treatments with thyroxine (T4) and gonadotropins on ovulation in hypothyroid rdw rats

摘要

We previously reported that thyroxine (T4) treatment significantly improved follicular development and increased the number of eggs ovulated in immature hypothyroid infertile rdw rats in the presence of gonadotrophins. The present study was conducted to determine whether (1) infertile rdw rats would respond to repeated stimulation with gonadotrophins, and whether (2) T4 treatment would increase the total number of ovulated eggs in an individual rat induced to ovulate up to three consecutive times at intervals of about 30 days. eCG was repeatedly given from the immature stage on postnatal day 28 and then at day of metestrus in the mature stage at intervals of about 30 days, followed by hCG 54 h later in rdw and normal rats, both of which were also given T4 (T4-rdw and T4-Normal), and in normal rats without T4 treatment (Normal). The results indicate that there were no significant differences in the weights of ovaries at any age tested among T4-rdw, T4-Normal and Normal. The number of eggs ovulated in the first treatment was significantly higher than in subsequent treatments in the same group (P<0.05). No significant differences were observed in the number of eggs ovulated in each corresponding treatment among the three groups, although more eggs (85.0 +/- 4.6) were collected after the first treatment in T4-rdw than in the other groups, while fewer eggs (4.0 +/- 2.7) were collected in the third treatment in T4-Normal than in the other groups. There were no significant differences in the percentages of degenerative or fertilized eggs in the same treatment among groups or among subsequent treatments in the same groups. However, the total number of eggs collected in the first three treatments in T4-rdw was significantly more than in Normal (P<0.05). T4 treatment also increased the total number of eggs ovulated in first three treatments in normal rats compared to those in Normal although no significant difference was observed between the two groups. In conclusion, the results of the present study indicate that infertile rdw rats responded well to repeated stimulation with gonadotrophins, and that T4 treatment increased the total number of ovulated eggs in an individual rat treated three times with gonadotrophins.