Transforming growth factor beta and related peptides: a role in testicular intercellular communication.

The research reported proposes that transforming growth factor-beta (TGF-beta) and its related peptides represent a family of polypeptides involved in local intercellular communication within the testis. Populations of purified cell types Leydig peritubular myoid and Sertoli cells from the 3-week old hog testis were incubated in defined media. TGF has the characteristics of a local regulator: it is known to be a potent regulator of cell proliferation of epithelial adipose osteocyte steroidogenetic and fibrous matrix-producing cells. It occurs in a family of hetero-dimers as well as latent forms and binds to cell surfaces with high affinity. TGF is related to inhibins activins and Mullerian inhibiting substances. Sertoli cells produce TGF-beta a process inhibited by follicle stimulating hormone (FSH) and enhanced by estradiol glucocorticoids and thyroxine. TGF-beta mRNA was also detected in Leydig and peritubular myoid cells of the testis. TGF-beta causes Leydig cells to elongate during incubation and to lose the ability to bind LH by down-regulating numbers of receptors. TGF-beta stimulated testosterone production at low concentrations up to 0.1 ng/ml and inhibited testosterone release at concentrations over 1 ng/ml a process not affected by cyclic AMP. This effect could be broken down into a biphasic stimulation of 3beta hydroxysteroid dehydrogenase and inhibition of pregnenolone formation in the testosterone pathway. Preliminary experiments showed that TGF-beta is involved in formation of extracellular matrix a Sertoli cell androgenic inhibiting factor and FSH stimulation of lactate production. The authors propose a comprehensive model of intercellular communication in the developing testis involving gonadotropins other steroid and thyroid hormones and other growth factors.