The role of inhibin related proteins is not confined to the regulation of pituitary FSH. These proteins are now recognised as growth and differentiation factors and in the testis they regulate both epithelial and interstitial cell functions. In species such as rodents and pigs, inhibin and activin are considered to be paracrine regulators of steroidogenesis whereby they modulate the endocrine LH signal. Porcine and rodent Leydig cells have been shown in vitro to respond to exogenously added activin A. We have previously proposed that activins have a significant role in Leydig cell development and in the fetal testis and at puberty, i.e. activin (like TGF β) holds Leydig cell growth in abeyance until differentiation or puberty. The roles of activins, inhibins and binding proteins for these ligands, such as follistatins, in the development of Leydig cells remains to be determined.
- Leydig cells