TIME-COURSE EFFECTS OF HUMAN RECOMBINANT LUTEINIZING-HORMONE ON PORCINE LEYDIG-CELL SPECIFIC DIFFERENTIATED FUNCTIONS

Since recombinant hormones are considered as safer and more reliable i n their bioactivity than extractive hormones, the recently available h uman recombinant luteinizing hormone (r-hLH), will probably replace hC G in the near future, for clinical purposes. This prompted us to inves tigate whether or not, and by which mechanisms, r-hLH can induce a des ensitization of signal transduction and/or an up-regulation of steroid ogenic capacity in Leydig cells. The effects of a 30 min to 24 h expos ure to r-hLH (10(-9) M) on the differentiated functions of cultured im mature porcine Leydig cells were studied by measuring the following pa rameters: LH/hCG receptor number and mRNA, hCG-, cholera toxin- and fo rskolin-induced cAMP production, G protein alpha(s) subunit content of the membrane, hCG-, cholera toxin-, forskolin-, 8Br-cAMP-, 22R-OH-cho lesterol-, progesterone-, 17OH-progesterone-, DHEA-, Delta 4-androsten edione-induced testosterone secretion and StAR, 3 beta-HSD, cytochrome P-450scc and p450c17 mRNAs. hCG binding sites and LH/hCG receptor mRN A were slowly down regulated by r-hLH, reaching 47 +/- 1 and 18 +/- 7% of control at 24 h, respectively. Down-regulation of both hCG- and ch olera toxin-induced cAMP production occurred earlier and was more mark ed, and at 24 h represented only 2.7 +/- 0.5 and 12.5 +/- 3.6% of cont rol. Due to the synergistic effect of r-hLH and forskolin on cAMP prod uction, the forskolin-induced cAMP was higher in r-hLH treated than in control cells, but this response also declines with time and was, at 24 h, only 32% of that observed at 30 min. This decreased cAMP product ion was associated with a less marked decline in the amount of membran e content of G alpha(s) protein. The testosterone production in respon se to hCG, cholera toxin, forskolin and 8Br-cAMP declined to reach a n adir at 6 h but increased thereafter and at 24 h was significantly hig her than in control cells. In contrast, the conversion of several prec ursors into testosterone remained stable or increased slightly during the first hours of r-hLH treatment and significantly increased at 24 h and this was associated with an increase of StAR, 3 beta-HSD, P-450sc c and P-450c17 mRNAs. Taken together, the present results indicate tha t, despite the marked down-regulation of transmembrane signaling, r-hL H increased the steroidogenic capacity of Leydig cells by increasing t he expression of several genes encoding the proteins involved in testo sterone synthesis. (C) 1998 Elsevier Science Ireland Ltd. All rights r eserved.