Stimulation of adult rat Leydig cell aromatase activity by a Sertoli cell factor

The paracrine control of adult rat Leydig cell aromatase activity was investigated in vitro. After a 24-h preculture period of Percoll-purified Leydig cells (2.5-5 X 10(5) cells), 17 beta-estradiol synthesis reached a maximum at 5 h in the presence of exogenous testosterone (200 ng/ml) as substrate, with or without LH (100 ng/ml), and remained stable for a further 24 h. Aromatase activity was stimulated 2.5-fold by LH. The addition of seminiferous tubule culture medium (STM) from normal, neonatally hemicastrated, or prepubertally irradiated rats as well as Sertoli cell culture medium prepared from these animals enhanced both basal and LH-dependent aromatase activities during 5 h; this effect was diminished after 24 h of culture. When seminiferous tubules (200 mm) were cocultured with Leydig cells, a greater stimulation of 17 beta-estradiol production was observed compared to culture with STM. The association of Sertoli and germ cells with purified Leydig cells further enhanced aromatase activity. These results demonstrate that a Sertoli cell factor regulates Leydig cell aromatase activity. This factor is of proteic nature, thermolabile, has a mol wt ranging between 10,000-50,000, and is different from the LHRH-like substance. This compound is tissue and species specific, since it is not present in rat serum, other cell line media, or guinea pig and mouse STM. Its secretion is independent from FSH and testosterone controls. The stimulation of aromatase activity by this factor requires protein synthesis.