Testis

5-Reductase Isoenzymes 1 and 2 in the Rat Testis During Postnatal Development

Abstract

The pubertal initiation of spermatogenesis is reliant upon androgens, and during this time 5-reduced androgens such as dihydrotestosterone (DHT) are the predominant androgens in the testis. Two 5-reductase (5R) isoenzymes (5R1 and 2) have been identified, which catalyse the conversion of testosterone to the more potent androgen DHT. This study aimed to investigate the developmental pattern of 5R isoenzymes and their relationship to the production of 5-reduced androgens in the postnatal rat testis. 5R1 and 2 isoenzyme mRNA was measured by real time PCR, isoenzyme activity levels were measured by specific assays and testicular androgens were measured by radioimmunoassay after HPLC separation. Both 5R1 and 2 mRNA and activity levels were low in the 10d (pre-pubertal) testis, peaked between days 20-40 during puberty and then declined to low levels at 60-160d. The developmental pattern of both 5R isoenzyme activity levels was mirrored by the testicular production of 5-reduced metabolites. Although 5R1 was greater than 5R2 at all ages, given the substrate preferences of the two isoenzymes, it is likely that both isoenzymes contribute to the pubertal peak of 5-reduced androgen biosynthesis. The peak in 5R isoenzymes and 5-reduced metabolite production coincided with the first wave of spermatogenesis in the rat, suggesting a role for 5-reduced metabolites in the initiation of spermatogenesis. This was explored by acute administration of a 5R inhibitor (L685,273) to immature rats. L682,273 markedly suppressed testicular 5R activity during puberty by 75-86%, however there was a marked increase in testicular testosterone levels (in the absence of changes in LH), and no decrease in the absolute levels of 5-reduced metabolites. Therefore whether the formation of DHT in the presence of low testosterone levels in the pubertal testis is required for the initiation of spermatogenesis cannot be tested using 5R inhibitors. We conclude that both 5R1 and 2 isoenzymes are involved in the peak of 5-reduced androgen biosynthesis in the testis during the pubertal initiation of spermatogenesis.