The steroidogenic enzymes involved in androgen biosynthesis are present and functional in the Leydig cells of rat testes throughout all stages of sexual maturation. However, the type of testicular androgens secreted changes significantly with age. Sexual maturation marks the shift from testicular secretion of 5a-reduced androgens to testosterone, the principal androgen that is secreted in the adult. Although the biosynthetic pathway from progesterone to testosterone has been well established, the maturational change in testosterone accumulation is not fully understood. The activity of steroid 5a-reductase, an enzyme that converts 3-oxo-4-ene steroids to 5a-reduced metabolites, plays a key role in determining the final steroid products secreted by the testis. The steroid products secreted may have widely differing peripheral and testicular biological actions. In the proposed research, a polyclonal antibody to rat liver 5a-reductase will be make and used to localize the protein in the testis by immunofluorescence. The levels of steroid 5a-reductase protein and mRNA in the testis will be determined throughout puberty in the rat. Results of these studies will provide a basis for studying the regulation of this enzyme and the mechanisms involved in qualitative changes in steroid biosynthesis.
