Effects of infantile thymectomy on ovarian functions and gonadotrophin-induced ovulation in prepubertal mice: role of thymulin

The effects of thymectomy performed on 10-day-old (Tx-10) mice on spontaneo us puberty and the ovulatory response induced by gonadotrophin treatment we re analysed, together with the effects of thymulin replacement from 10 days of age. Infantile thymectomy induced a delay of puberty, a decrease ill se rum 17 beta-oestradiol concentration and a reduced total number of follicle s. Injection of thymulin (12, ng/g body weight) to Tx-10 mice resulted in a n earlier onset of puberty, a decrease in the weights of ovaries and uterus , and an increase ill serum 17 beta-oestradiol concentrations. In control a nd Tx-10 mice, treatment with pregnant mere serum gonadotrophin (PMSG) (5 I U) at 25 days of age resulted ill ovulation and the numbers of ova. shed by ovulating animals were similar, When the animals were injected with 1 IU P MSG ovulation did not occur, In Tx-10 mice, both 1 and 5 IU PMSG increased the number of follicles to values similar to those observed ill the control s, In Tx-10 mice the sequential injection of PMSG (1 IU) and human chorioni c gonadotrophin (hCG) (3 IU) resulted in ovulation, but the number of ova s hed was lower than in controls. When these animals were injected daily with thymulin, an increase in the number of ova shed and serum 17 beta-oestradi ol concentrations was observed. The uterine weight of Tx-10 mice was always significantly reduced ill response to gonadotrophin treatment. Thymulin in jection in PMSG-hCG-treated Tx-10 mice provoked a significant increase in u terine weight. The results suggest that the presence of the thymus after th e neonatal period is necessary to normal ovarian development and function. The increase in gonadotrophin-induced ovarian response produced by thymulin replacement indicates that this peptide has a role in this process as one of the connecting signals between thymus and ovaries.