Differential regulation of rat testicular 5-reductase type 1 and 2 isoforms by testosterone and FSH

Testosterone is metabolised to the more potent androgen, dihydrotestosterone, by the 5-reductase (5R) enzyme. We previously showed that 5-reduced androgens are important for maintaining androgen action on rat sperma-togenesis when testicular testosterone concentrations are reduced. This study investigated expression and activity of the 5R isoforms, type 1 (5R-1) and type 2 (5R-2), in the rat during hormone manipulation in order to under-stand the factors that regulate the testicular concentration of 5R and testicular 5-reduced androgen biosynthesis. Testicular 5R-1 and 5R-2 mRNA and enzyme activity were measured by real-time PCR and specific enzyme assays respectively. Hormone levels were first suppressed using two models of gonadotrophin suppression: testoster-one and oestradiol treatment (LH/testosterone deficiency) or GnRH immunisation (LH/testosterone and FSH deficiency). Hormones were then either restored or sup-pressed for 6 days by a variety of hormonal treatments. 5R-1 mRNA and enzyme activity increased when testosterone was suppressed, yet restoration of testosterone decreased 5R-1 mRNA and enzyme activity, suggesting that testosterone negatively regulates 5R-1. Suppression of FSH decreased 5R-1 mRNA yet FSH administration increased 5R-1 mRNA, but no changes in 5R-1 activity were observed within the 6 day period. In contrast to 5R-1, testosterone did not affect the testicular con-centration of 5R-2 mRNA or activity, but there was evidence for modulation of 5R-2 activity by FSH. Measurement of testicular androgens revealed that 5R-1 was primarily responsible for the production of 5-reduced metabolites. It is concluded that the 5R isoforms in rat testis are differentially regulated by testosterone and FSH: testosterone negatively regulated 5R-1 mRNA and enzyme activity but had no affect on 5R-2, whereas FSH positively regulated 5R-1 mRNA and appeared to regulate 5R-2