Abstract
To quantify thymidine incorporation into DNA in the ovary of the intact, cyclic hamster, hamsters were injected at different times throughout the fourβday estrous cycle (day 1 = day of ovulation; day 4 = proestrus). Animals were killed one hour after injection. One ovary was prepared for liquid scintillation counting of DNA and the other for autoradiographic analysis.
Ovarian thymidine incorporation was elevated on days 1 and 4. The peak of thymidine incorporation on day 1 resulted from uptake by small follicles (12 or fewer layers of follicle cells), and coincided with a peak in serum FSH. Stromal and luteal uptake on day 1 was negligible. The peak of thymidine incorporation on day 4 occurred in the morning and was the result of incorporation into small follicles (seven layers of follicle cells and smaller) and antral follicles. This peak occurs when gonadotropin levels are reported to be low, but circulating levels of estradiol are high.
The mean number of follicles at stages 1 and 2 (2β5 granulosa cells) was relatively constant throughout the estrous cycle. Larger follicles were present only at specific times. Small follicles (stages 1 and 2) were most active in thymidine uptake during the latter half of the cycle; stageβ3 follicles were most active on day 4. Follicles of stages 4 and 5 were present only on days 1 and 2, respectively; no measurements of thymidine incorporation were made. Stageβ6 follicles, present on days 3 and 4, showed virtually no variation in activity, as measured by thymidine uptake.
A wave of follicular development was evidenced in larger follicles. Stageβ3 follicles (6 to 7 layers of follicle cells), present on day 4, had developed to stage 4 (eight or more layers of follicle cells) by day 1; stageβ4 follicles had developed to stage 5 (early antral) by day 2. Stageβ5 follicles had developed to stage 6 (antral follicles) by day 3.
Antral follicles consistently incorporated thymidine label (except at 1600 hours and 2400 hours on day 4), especially in the cumulus oophorus and in the granulosa cells bordering the antrum. Despite sudden changes in serum gonadotropins on day 4, stageβ6 follicles showed no discernible differences in labeling.
Thymidine uptake by the corpus luteum (CL) was low on day 1, but higher on day 2 (after the CL was fully developed). Sinuosoidal endothelial cells in the CL were heavily labeled on day 2, but the reason for the late proliferation of these cells and their fate is unknown.