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 5α-reduced androgens (i.e. androsterone and 5α-androstane-3α, 17β-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 5α-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.
Changes in ovarian steroids on the day of the first pro-oestrus were fully comparable to those at pro-oestrus in adults: relatively high levels of ovarian testosterone and oestradiol, reaching values of 339 and 711 fmol/mg ovary respectively during the morning, an increase in progesterone (from 986 to > 40 000 fmol/mg ovary) first observed at 14.00 h and a decline, observed at 17.00 h, in ovarian testosterone and oestradiol concentration, resulting in values of 9 and 3 fmol/mg ovary respectively at 21.00 h.
J. Endocr. (1984) 100, 281–286
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