Abstract. The activity of 5α-reductase in the ovary of prepubertal rats decreases prior to first ovulation. To determine whether this decrease causes the onset of first ovulation, prepubertal female were treated with a specific inhibitor of 5α-reductase activity and the effect on the time of first ovulation was studied. The steroid (6-methylene-progesterone, MEP) gives irreversible inhibition of ovarian 5α-reductase activity in vitro with testosterone as well as progesterone as substrate. A MEP-containing silicone tube, releasing 245 nmol per 24 h in vitro, was implanted sc in the back of 25-day-old female rats. This resulted a day 30 in a significantly lower 5α-reductase activity in the ovary than in control rats (42.0 ± 3.8 pmol/min per mg ovary in MEP-treated rats vs 98.8 ± 2.4 pmol/min per mg ovary in control rats). Nearly the same extent of inhibiton was found at day 35 27.4 ± 2.1 in MEP-treated rats vs 56.2 ± 5.9 in control rats). However, implantation of a MEP-containing silicone tube under the skin or inserting a pellet containing MEP under the ovarian capsule did not result in advancement of the first ovulation. These data indicate that in the female rat a decrease of 5α-reductase activity alone is not sufficient to induce the first ovulation.
J. Th. J. Uilenbroek and P. J. A. Woutersen
J. Th. J. Uilenbroek and R. van der Linden
Changes in LH and FSH binding to rat ovaries during sexual maturation were measured by in vitro binding assay and autoradiography. Ovaries were obtained from rats at various ages ranging from 5 till 35 days of age. Animals older than 35 days of age were classified in three groups: anoestrus (uterine weight below 60 mg), early pro-oestrus (uterine weight 60–120 mg) and pro-oestrus (uterus distended with fluid). Measurements were made of specific binding of radioiodinated hCG and rFSH to ovarian homogenates (day 5–35) and to granulosa cells isolated from the largest follicles (day 35–pro-oestrus).
The earliest age at which specific hCG and FSH binding could be demonstrated was day 11. Thereafter hCG binding to ovarian homogenates, expressed in cpm/μg DNA, increased with age. Specific binding of hCG to granulosa cells increased from 1000 cpm/μg DNA at day 35 to 4000 cpm/μg DNA at pro-oestrus. FSH binding to ovarian homogenates increased till day 21 and remained fairly constant thereafter.
Autoradiography revealed the presence of hCG binding to interstitial tissue and thecal cells. hCG binding to granulosa cells was only found in large pre-ovulatory follicles present at early pro-oestrus and pro-oestrus. FSH binding was observed to granulosa cells of all types of follicles, but not to interstitial and thecal cells.
The results demonstrate that during sexual maturation FSH binding to granulosa cells remains constant, whereas LH binding to interstitium and theca and ultimately to granulosa cells increases with age suggesting an increased responsiveness of the ovaries to LH.