Ovarian steroid concentrations in rats approaching first ovulation

Steroid concentrations were studied in ovarian tissue obtained by means of unilateral ovariectomy during a 10-day period preceding first ovulation. Furthermore, the levels of progesterone were measured in this period in the serum of simultaneous intact control rats. Ovarian concentrations of testosterone and oestradiol were at about 70 and 15 fmol/mg ovary respectively from 10 to 4 days before first ovulation; they clearly increased to a maximum of 170 and 120 fmol/mg ovary during the last 1-3 days before first ovulation. Ovarian concentrations of 5 alpha-reduced androgens (i.e. androsterone and 5 alpha-androstane-3 alpha,17 beta-diol) were high (up to 2500 fmol/mg ovary) from 7 to 4 days before first ovulation, whereas low levels (500-750 fmol/mg ovary) were present during the last 3 days before ovulation. Both ovarian and serum concentrations of progesterone were constantly low (at 500-1000 fmol/mg ovary and at 17-32 nmol/l respectively) from 10 days to 1 day before first ovulation. An inverse correlation was observed between the ovarian content of 5 alpha-reduced androgens and that of oestradiol, which is in agreement with the existence of a prepubertal shift in pathways of steroid production; this shift seems to take place between 4 and 3 days before first ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)