Effects of exogenous oestradiol and progesterone on serum levels of prostaglandin F and luteinizing hormone in chronically ovariectomized rats.

ewes injected with progesterone every 2 days over a 12-day period, followed 2 days later by a single injection of oestradiol, the prostaglandin F level in peripheral plasma rose significantly about 6 hr after the oestrogen treatment. Levels of prostaglandin F had returned to those seen before the oestrogen injection by 18 to 24 hr after the oestrogen treatment. In some ovariectomized animals, a slow rise of prostaglandin F was observed during the period of progesterone injections but a peak level was seen only after oestrogen stimula¬ tion. In addition, Blatchley, Donovan, Poyser, Horton, Thompson & Los (1971) and Blatchley, Donovan, Horton & Poyser (1972) have reported that daily injection of 10 μg oestradiol benzoate on Days 4 to 6 of the oestrous cycle of the guinea-pig caused elevated levels of prostaglandin F in the uteroovarian venous plasma on Day 7. It has been postulated by Caldwell et al. (1972) that the rising levels of oestrogen on Day 13 of the oestrous cycle of the