Changes in serum concentration and ovarian content of5α-androstane-3α,17β-diol in the female rat approaching firstovulation

Concentrations of 5α-androstane-3α, 17β-diol (3α-diol) in serum were estimated in rats bled once during a 10-day period preceding first ovulation; ovarian contents of 3α-diol were estimated over the same period. Serum values of 3α-diol, measured at 1100 h, showed a significant decrease towards first ovulation; there was good correlation between mean serum and ovarian concentrations. In 33-day-old rats no significant difference was found in serum concentrations measured at either 1100 or 1500 h. However at first proestrus, significantly elevated serum and ovarian concentrations of 3α-diol were found between 1400 and 2100 h as compared to those at 1100 h. A similar pattern was seen on the afternoon of second proestrus. On the days following first ovulation, serum and ovarian concentrations of 3α-diol were comparable to those during the days preceding this ovulation. The prepubertal decrease in 3α-diol production is discussed in relation to concomitant changes in secretion of estradiol and luteinizing hormone. It is concluded that, in view of the preovulatory resynthesis of considerable amounts of 3α-diol, it is inappropriate to view loss of biosynthetic capacity for 3α-diol as a key event in the onset of puberty.