STIMULATING EFFECT OF BOTH HUMAN RECOMBINANT INHIBIN-A AND ACTIVIN-A ON IMMATURE PORCINE LEYDIG-CELL FUNCTIONS IN-VITRO

In addition to the regulation of FSH secretion, it has been clearly sh own that inhibin and activin have paracrine/autocrine effects in the g onads. We have studied the effect of human recombinant inhibin A and h uman recombinant activin A on immature porcine Leydig cells in vitro. Leydig cells were prepared by collagenase digestion of testes from 3-w eek-old piglets, purified on Percoll gradient, then cultured in a chem ically defined medium. The cells were treated with increasing amounts of inhibin A or activin A (0.5-200 ng/ml). Direct application of eithe r inhibin A or activin A on Leydig cells for 4 or 48 h did not stimula te basal testosterone secretion. Conversely, treatment of the cells fo r 48 h with either factor resulted in a dose-dependent increase in hCG -stimulated testosterone secretion (10(-9) M hCG, 2 h) with a maximal effect of 2.40 +/- 0.37- and 2.43 +/- 0.37-fold increases for inhibin A and activin A, respectively, and these changes were associated with a slight increase in LH/hCG-binding sites (1.37 +/- 0.19- and 1.24 +/- 0.11-fold increases). In addition, both inhibin A and activin A enhan ced messenger RNA (mRNA) levels of LH/hCG receptor (2.75 +/- 0.40- and 2.53 +/- 0.60-fold increases) and cytochrome P450 17 alpha-hydroxylas e (6 +/- 1- and 3.5 +/- 0.6-fold increases), but had no effect on side -chain cleavage cytochrome P450 or cytochrome P450 aromatase mRNAs. 3 beta-Hydroxysteroid dehydrogenase mRNA levels were increased (3.1 +/- 1.3-fold increase) by activin A, but not by inhibin A. However, inhibi n A blocked the stimulatory action of activin A. In keeping with these changes in the steroidogenic enzyme mRNAs, both peptides enhanced the conversion of exogenous 22R-hydroxycholesterol and progesterone, but only activin A increased the conversion of dehydroepiandrosterone into testosterone. In conclusion, our findings demonstrate that both inhib in A and activin A have a stimulatory effect on immature porcine Leydi g cell differentiated function in vitro. As inhibin has a stimulatory and activin has an inhibitory effect on rat Leydig cell function in vi tro, the effects of these factors on Leydig cells seem to be species d ependent.