Summary. Hamsters hypophysectomized (hypox.) and concurrently injected i.p. with 2·5 μg ovine LH or 25 μg ovine FSH at 13:00 h on the day of pro-oestrus ovulated the normal complement of ova the next morning (Day 1). At 09:00 h on Day 1, serum levels of progesterone were comparable between sham-hypox. and LH-treated hypox. hamsters. In contrast, there were no differences in serum progesterone between FSH-treated or saline-treated hypox. hamsters; a slight but significant increase in serum progesterone occurred at 15:00 h in the FSH-treated animals and this was continued on Day 2, when values were comparable to those in the LH-treated and sham-hypox. hamsters.
The CL induced by LH or FSH produced significant amounts of progesterone in vitro on Day 1 at 09:00 and 15:00 h. On Day 2, there was a significant increase in production of progesterone by the CL of both groups. Production rates of progesterone by CL in vitro were the same in the LH- and FSH-treated animals on Days 1 and 2. Therefore, once ovulation has occurred in the hamster the newly developed CL gain the ability to synthesize, store and secrete progesterone independently of pituitary hormones for 2 days, although at a delayed rate after FSH treatment.
The results of incubations of the non-luteal (residual) ovarian tissues showed that large quantities of progesterone (about 7 ng/mg/h) were produced on Day 1 by tissue from FSH-treated animals while that of LH-treated hamsters lost progesterone at the rate of about 1 ng/mg/h. In saline-treated hypox. hamsters the residual tissue produced large amounts of progesterone and small amounts of oestradiol-17β and testosterone in vitro for at least 2 days after hypox. Little oestradiol-17β was produced by the CL of hamsters treated with LH, FSH or sham-hypox. By Day 2 the CL of all 3 groups produced appreciable amounts of testosterone in vitro, whereas on Day 1 only the CL induced by LH secreted testosterone.