Estrogen and thymic hormone interactions in the female mouse.

This study showed that there are relationships between thymic and adrenal/ovarian endocrine actions. A 4 mg/kg dose of thymosin fraction 5 (TSN5) advanced vaginal opening and elevated estrogen levels. Single estradiol benzoate (EB) injections decreased thymus weight and caused a transient reduction in circulating plasma levels of thymosine alpha 1 (TSN alpha 1), a peptide component of TSN5. Circulating estrogen levels were elevated when TSN alpha 1 levels were undetectable. Also, TSN alpha 1 levels decreased with age and after a prolonged athymic state. The thymus was shown to involute after a single TSN5 injection, suggesting the existence of a negative hormonal feedback on the thymus. Additionally thymectomy at 3 days of age was shown to delay vaginal opening while thymectomy at 30 days of age failed to produce any significant effect on reproductive maturation. Although much research is still needed, our results provide additional evidence of a relationship between the endocrine thymus and ovary.