A Luteolytic Interaction Between Estradiol and Prostaglandin F2α in Hysterectomized Ewes

The hypothesis that the luteolytic interaction between prostaglandin F2α (PGF2α) and estradiol is independent of the uterus was evaluated in hysterectomized and hysterectomized, ovarian X-irradiated ewes. Hysterectomies and either sham or X-irradiations were performed 7 or 8 days after observation of estrus. After a 72 h recovery period the effects of injections on two consecutive days of: 1) the vehicles for PGF2α and estradiol benzoate (E2B), 2) 3.5 mg PGF2α, 3) 750μg E2B, and 4) 3.5 mg PGF2α + 750 μg E2B were compared in sham and ovarian X-irradiated ewes. Results of plasma progesterone determinations and mean corpus luteum weights showed that treatment with PGF2α alone was not luteolytic. Treatment with E2B alone had marginal effects on corpus luteum function. For example, plasma progesterone concentrations were depressed (P<0.05) when compared to vehicle treated controls at isolated times between 60 and 96 h after the first injection in both sham and X-irradiated ewes, and the mean corpus luteum weight for the X-irradiated group was less than that found for the control groups (P<0.05). However, following treatment with both PGF2α and E2B, complete luteolysis was observed in three of four sham and three of four X-irradiated ewes. These data suggest a luteolytic interaction between estradiol and PGF2α that is independent of the uterus. In a second experiment, hysterectomized sham and X-irradiated ewes were treated with 7.0 mg PGF2α. Plasma progesterone determinations and corpus luteum weights suggested that complete luteolysis was observed in all sham-irradiated ewes and in two of four X-irradiated ewes. This dose of PGF2α also proved to be effective in three of four X-irradiated, uterine intact ewes. These results suggest that ovarian follicles are not an absolute requirement for PGF2α-induced luteolysis.