Postnatal expression of high rates of 5 alpha-reductase in the female rat urogenital tract.

5 alpha-reductase activity was measured in the developing rat urogenital tract using [3H] testosterone as substrate. At fetal day 22, the activity in the vagina (67 pmol/h per mg protein) was as high as in the differentiated prostate (41 pmol/h per mg protein). Both tissues are derived from the urogenital sinus. Although the activity of 5 alpha-reductase remained high in the prostate, the enzyme activity in the vagina declined steadily such that by postnatal day 20, the levels were not different from those expressed in urinary bladder which had low, baseline levels (approximately 10 pmol/h per mg protein) throughout the period examined. The uterus, which is derived from the embryonic mullerian duct, also expressed high levels (50-70 pmol/h per mg protein) of 5 alpha-reductase activity initially (before postnatal day 10). In contrast, the "Wolffian-derived" epididymis had levels of activity that were indistinguishable from the relatively low levels seen in the urinary bladder. In the ovary, neither 5 alpha-reductase nor aromatase activities were appreciable at fetal day 22 and at postnatal day 2. By postnatal day 5 both activities increased dramatically in ovaries. After postnatal day 10, aromatase activity declined in ovaries but 5 alpha-reductase remained elevated. These observations suggest (1) that major remodeling of the tissues derived from the urogenital sinus takes place even after differentiation and (2) that 5 alpha-reductase may regulate ovarian estrogen levels at the time of primary folliculogenesis.