5 alpha-reductase activity in developing urogenital tracts of fetal and neonatal male mice

5 alpha-Reductase activity in testes and urogenital tract tissues from male mice at 14.5 days gestation and 0 days of age (birth) was assessed by measurement of metabolites of testosterone released into the medium in a serum-free culture system. In male mice at 14.5 days gestation, the testis and the cranial portion of the urogenital ridge (UGR), which develops into the epididymis, had little 5 alpha-reductase activity. The caudal portion of the UGR, which develops into the seminal vesicle (SV), and the cranial portion of the urogenital sinus (UGS) had 12-fold higher activity than the cranial portion of the UGR. 5 alpha-Reductase activity in the middle portion of UGR was intermediate between that of its cranial and caudal portions. The highest levels of 5 alpha-reductase activity were detected in the caudal portion of UGS, even though this higher value was not significantly different from those in the caudal UGR or the cranial UGS. In 0-day-old male mice, 5 alpha-reductase activity of testis remained low at a level similar to that observed at 14.5 days gestation. The epididymis also exhibited low 5 alpha-reductase activity in 0-day-old mice, even though this activity had increased 2.2-fold relative to that observed in the cranial UGR at 14.5 days gestation. 5 alpha-Reductase activity of the cranial portion of UGS (prostatic rudiment) was relatively high on day 0 and similar to that in the same region at 14.5 days gestation. The SV and bulbourethral gland (BUG) on day 0 had high 5 alpha-reductase activity, which had increased 1.4- and 1.3-fold, respectively, compared to their 14.5 day embryonic anlage, although the increase was not significant. Through examination of 5 alpha-reductase activity regionally in the developing urogenital tract, it is evident that the concept that testosterone is the active androgen during Wolffian development is overly simplified. The present study suggests the importance of spatial/regional factors in Wolffian duct development in regard to the role of dihydrotestosterone. 5 alpha-reductase activity in the caudal Wolffian duct (SV rudiment) equals or exceeds that in the developing prostate, and at birth, dihydrotestosterone production is virtually identical in the SV and prostate. This suggests that 5 alpha-reduced androgens play a prominent role in the development of SV.(ABSTRACT TRUNCATED AT 400 WORDS)