Hormonal characterization of female SL/Ni mice: a small thymus gland strain exhibiting ovarian dysgenesis.

Female SL/Ni mice have a small thymus gland and show accelerated aging of the reproductive system characterized by an early loss of the follicular apparatus and early onset of ovarian tumors. At 9 months of age, circulating levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were higher in the SL/Ni animals than in controls while prolactin (PRL) was lower in the SL/Ni mice. The trends of these hormones are consistent with the loss of the follicular apparatus which is responsible for estradiol production. The high levels of gonadotropins which precede the onset of the tumors confirm the hypothesis that prolonged stimulation by gonadotropins can be a cause of ovarian tumorigenesis. Further, these data suggest that aging of the reproductive system may be a thymus-dependent phenomenon.