TESTOSTERONE DECREASES 3-BETA-HYDROXYSTEROID DEHYDROGENASE-ISOMERASE MESSENGER-RIBONUCLEIC-ACID IN CULTURED MOUSE LEYDIG-CELLS BY A STRAIN-SPECIFIC MECHANISM

We previously reported a strain-related difference in basal 3 beta-hyd roxysteroid dehydrogenase-isomerase (3 beta HSD) activity in response to testosterone in cultured Leydig cells. The data suggested that the response to testosterone was androgen receptor mediated and that testo sterone was acting via a irans-acting factor distal to the androgen re ceptor to regulate Leydig cell basal 3 beta HSD activity. This study w as designed to determine whether the previous reported strain-related difference in basal 3 beta HSD activity in response to testosterone wa s due to a difference at the 3 beta HSD protein and/or at the mRNA lev el, In C57BL/6J Leydig cells, 2.0 mu M testosterone significantly decr eased basal 3 beta HSD immunoreactive mass by day 6 in culture. Treatm ent with 2.0 mu M testosterone and 2.0 mu M hydroxyflutamide, an andro gen receptor antagonist, negated the inhibitory effect of testosterone on C57BL/6J 3 beta HSD immunoreactive mass, Treatment with 2.0 mu M t estosterone also significantly decreased 3 beta HSD mRNA content in C5 7BL/6J Leydig cells, which was detectable on day 3 in culture, In cont rast to Leydig cells from C57BL/6J mice, Leydig cells from C3H/HeJ mic e were not susceptible to the inhibitory effect of testosterone on 3 b eta HSD. Treatment with 2.0 mu M testosterone had no detectable effect on C3H/HeJ 3 beta HSD immunoreactive mass or mRNA content at any time point in culture. These data indicate that the testosterone-induced l oss of basal 3 beta HSD activity in C57BL/6J Leydig cells can he accou nted for by the lass of 3 beta HSD immunoreactive mass, which is prece ded by the loss of 3 beta HSD mRNA, and that the strain-related differ ence in the regulation of 3 beta HSD is present at all three levels. T hus, the putative trans-acting factor involved in the mechanism whereb y testosterone decreases basal 3 beta HSD is likely to regulate the am ount of 3 beta HSD mRNA.