Effects of thymulin on spontaneous puberty and gonadotrophin-induced ovulation in prepubertal normal and hypothymic mice

The effects of thymulin administration beginning on days 19 or 24 of age on spontaneous puberty and gonadotrophin-induced ovulation were analysed in f emale normal and hypothymic mice. In normal and hypothymic mice, the daily administration of thymulin at 24 d ays of age resulted in a delay in the age of vaginal opening, with an incre ase in serum progesterone levels. Normal mice treated with 200 ng thymulin beginning on day 19 of age and injected with pregnant mare serum gonadotrop hin (PMSG) 24 h later had an increase in ovulation. rate, number of ova she d and weight of the ovaries. None of the hypothymic mice treated with thymu lin on day 19 and PMSG on day 20 ovulated. PMSG treatment on day 25 induced ovulation in hypothymic mice. When these animals were injected previously with 200 ng thymulin, the number of ova shed by ovulating animals was lower than in PMSG-treated animals. Administration of thymulin and sequential in jection of PMSG and human chorionic gonadotrophin 54 h later resulted in an increase in ovulatory response in comparison with those receiving only PMS G. The results suggest that thymulin plays a role in the regulation of spontan eous puberty through its effects on adrenal and ovarian endocrine functions . The increase in the ovarian PMSG response-treated animals, previously giv en thymulin, showed that this thymic hormone participates in the regulation of gonadotrophin secretion mechanisms and seems to be dose- and age-depend ent. In hypothymic mice, neuroendocrine mechanisms regulating puberty are d ifferent from those of normal mice.