Testosterone is the dominant reproductive hormone, and the only important one that is present in the blood stream. It is secreted by the Leydig cells of the testes
(stimulated by LH), and is moderated in the testes by the Sertoli cells, which secrete
estradiol and androgens locally (stimulated by FSH) and can inhibit LH and therefore testosterone.
This ebb and flow between the Leydig and Sertoli cells constitutes the male equivalent of the estrogen- progesterone ambivalence in women, and the balance of yin and yang in the testes maintains fertility, prostate health, and prevents testosterone over dominance in the body.