Regulation by gonadotropins of the messenger ribonucleic acid for P450 side-chain cleavage, P450(17) alpha-hydroxylase/C17,20-lyase, and 3 beta-hydroxysteroid dehydrogenase in cultured pig Leydig cells.

Abstract

The Leydig cell from the immature pig provides a good model for studying testicular steroidogenesis. Regulation of the enzymes involved, which has been well studied in rodents, has not been characterized in the pig. The objectives of this study were to examine the regulation of three steroidogenic enzymes in pig Leydig cells by LH/hCG and testosterone. The mRNA for P450 side-chain cleavage and P450(17) alpha-hydroxylase/C17-20-lyase, although constitutively expressed, decreased over time in culture, while that for 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) remained relatively constant. The mRNA for all three enzymes was increased in a dose- and time-dependent manner by treatment with hCG. Run-on experiments demonstrated that the main effect of the hormone was at the level of transcription. Treatment with hydroxyflutamide, either alone or in combination with hCG, had no effect on the mRNA for these enzymes. Treatment with hCG plus aminoglutethimide, an inhibitor of steroidogenesis, had no effect on the mRNA for the two P450 enzymes, but resulted in an increase in mRNA for 3 beta HSD when compared to treatment with hCG alone. However, exogenous testosterone could not block the effect of aminoglutethimide. Therefore, the steroidal regulation of 3 beta HSD in pig Leydig cells may act through a mechanism separate from the androgen receptor. While aspects of the regulation of these enzymes are similar to those seen in rodents, some significant differences exist. Our results support the concept that regulation of steroidogenic enzymes in Leydig cells is species-specific.