Developmental changes in glucocorticoid receptor and 11 beta-hydroxysteroid dehydrogenase oxidative and reductive activities in rat Leydig cells

Glucocorticoids directly regulate testosterone production in Leydig cells through a glucocorticoid receptor (GR)-mediated repression of the genes that encode testosterone biosynthetic enzymes. The extent of this action is determined by the numbers of GR within the Leydig cell, the intracellular concentration of glucocorticoid, and 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) activities that interconvert corticosterone (in the rat) and its biologically inert derivative, 11-dehydrocorticosterone . As glucocorticoid levels remain stable during pubertal development, GR numbers and 11 beta HSD activities are the primary determinants of glucocorticoid action. Therefore, in the present study, levels of GR and 11 beta HSD messenger RNA (mRNA) and protein were measured in rat Leydig cells at three stages of pubertal differentiation: mesenchymal-like progenitors (PLC) on day 21, immature Leydig cells (ILC) that secrete 5 alpha-reduced androgens on day 35, and adult Leydig cells (ALC) that are fully capable of testosterone biosynthesis on day 90. Numbers of GR, measured by [H-3]dexamethasone binding, in purified cells were 6.34 +/- 0.27 (x10(3) sites/cell; mean +/- SE) for PLC, 30.45 +/- 0.74 for ILC, and 32.54 +/- 0.84 for ALC. Although GR binding was lower in PLC, steady state levels for GR mRNA were equivalent at all three stages (P > 0.05). Oxidative and reductive activities of 11 beta HSD were measured by assaying the conversion of radiolabeled substrates in incubations of intact Leydig cells. Both oxidative and reductive activities were barely detectable in PLC, intermediate in ILC, and highest in ALC. The ratio of the two activities favored reduction in PLC and ILC and oxidation in ALC (oxidation/reduction, 0.33 +/- 0.33 for PLC, 0.43 +/- 0.05 for ILC, and 2.12 +/- 0.9 for ALC, with a ratio of 1 indicating equivalent rates for both activities). The mRNA and protein levels of type I 11 beta HSD in Leydig cells changed in parallel with 11 beta HSD reductive activity, which increased gradually during the transition from PLC to ALC, compared with the sharp rise that was seen in oxidative activity. We conclude that Leydig cells at all developmental stages have GR and that their ability to respond to glucocorticoid diminishes as net 11 beta HSD activity switches from reduction to oxidation. This provides a mechanism for the Leydig cell to regulate its intracellular concentration of corticosterone, thereby varying its response to this steroid during pubertal development.