Differential regulation of rat testicular 5-reductase type 1 and 2 isoforms by testosterone and FSH K Pratis, L O’Donnell, G T Ooi, P G Stanton, R I McLachlan and D M Robertson Prince Henry’s Institute of Medical Research, PO Box 5152, Clayton, Victoria 3168, Australia (Requests for offprints should be addressed to D M Robertson; Email: david.robertson@med.monash.edu.au) Abstract Testosterone is metabolised to the more potent androgen, dihydrotestosterone, by the 5-reductase (5R) 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 5R isoforms, type 1 (5R-1) and type 2 (5R-2), in the rat during hormone manipulation in order to under- stand the factors that regulate the testicular concentration of 5R and testicular 5-reduced androgen biosynthesis. Testicular 5R-1 and 5R-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. 5R-1 mRNA and enzyme activity increased when testosterone was suppressed, yet restoration of testosterone decreased 5R-1 mRNA and enzyme activity, suggesting that testosterone negatively regulates 5R-1. Suppression of FSH decreased 5R-1 mRNA yet FSH administration increased 5R-1 mRNA, but no changes in 5R-1 activity were observed within the 6 day period. In contrast to 5R-1, testosterone did not affect the testicular con- centration of 5R-2 mRNA or activity, but there was evidence for modulation of 5R-2 activity by FSH. Measurement of testicular androgens revealed that 5R-1 was primarily responsible for the production of 5-reduced metabolites. It is concluded that the 5R isoforms in rat testis are differentially regulated by testosterone and FSH: testosterone negatively regulated 5R-1 mRNA and enzyme activity but had no affect on 5R-2, whereas FSH positively regulated 5R-1 mRNA and appeared to regulate 5R-2. Journal of Endocrinology (2003) 176, 393–403 Introduction Testosterone is the predominant androgen involved in the regulation of normal spermatogenesis in the rat due to its high intratesticular concentration (Wright & Frankel 1979). The process of spermatogenesis is critically depen- dent on testosterone and the amount of sperm produced is dose-responsive to the level of testosterone in the testis (Awoniyi et al. 1989, McLachlan et al. 1994). The 5-reduction of testosterone to the more potent androgen, 5-dihydrotestosterone (DHT), is postulated to be important for maintaining spermatogenesis when intra- testicular testosterone concentrations are low (Anderson et al. 1996, O’Donnell et al. 1996, 1999). Testosterone has been the target for suppressing spermatogenesis in numerous contraceptive trials. In both primates (Narula et al. 2002) and men (McLachlan et al. 2002), gonadotrophin suppression by exogenous testoster- one administration caused a marked reduction in testicular testosterone levels yet maintenance of 5-reduced andro- gen levels. It is thought that maintenance of testicular 5-reduced androgen levels may be responsible for con- tinued low levels of sperm production in the 30% of normal men whose sperm counts do not fall to zero (azoospermia) after testosterone contraceptive treatment (Anderson et al. 1996, 1997). In the rat model of sperma- togenic suppression, administration of a 5-reductase (5R) inhibitor to prevent DHT production suppressed spermatogenesis (O’Donnell et al. 1996, 1999). Further- more, administration of the androgen receptor (AR) antagonist flutamide during spermatogenic suppression in the rat increased the production of 5-reduced metabolites in the testis, suggesting that 5R may be hormonally regulated (O’Donnell et al. 1999). Taken together, these studies suggest that testicular 5R may be regulated by gonadotrophins and/or testosterone and that 5R activity is important for determining the amount of bioactive androgen in the testis. 393 Journal of Endocrinology (2003) 176, 393–403 0022–0795/03/0176–393  2003 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology.org Downloaded from Bioscientifica.com at 06/17/2022 06:12:58AM via free access