The role of protein synthesis in regulation of oestradiol-17 beta in the pro-oestrous hamster.

Injection (s.c.) of 2 mg cycloheximide at 14:00 h on the day of pro-oestrus prevented the normal rise in serum progesterone and significantly lowered progesterone levels at 15:00 h. Values then rose but only to approximately half of the control values between 16:00 h and 19:00 h. Oestradiol levels also decreased drastically by 15:00 h but were significantly higher in cycloheximide-treated animals until 19:00 h. FSH and LH concentrations were not affected when cycloheximide was given at 14:00 h but treatment at 10:00 h resulted in generally lower values. Animals treated with cycloheximide at 14:00 h failed to ovulate (N = 9), but simultaneous injection of 50 micrograms progesterone restored ovulation in 50% of the treated animals. In contrast, hamsters injected with cycloheximide at 10:00 h ovulated the next morning, suggesting that protein synthesis essential for ovulation is limited to the first 4-5 h after the release of LH.