Estradiol-17β (E2) decreases the effectiveness of prostaglandin F2α (PGF2α) to induce luteolysis in hysterectomized gilts, and E2 locally increases corpus luteum (CL) weight in pigs, suggesting a direct luteotropic effect. This study examined the effect of intraluteal E2 implants on utero-ovarian vein (UOV) progesterone (P4), E2, PGF2α and CL weight in cyclic gilts. Eight gilts were laparotomized on day 11 (day 0 =first day of estrus), catheters were placed in both UOV, and gilts were then divided into two equal groups (E2-treated and controls). Each CL on one ovary of E2-treated gilts was injected with a quick-curing silastic implant containing E2, and each CL on the contralateral ovary received a vehicle implant. Control gilts received bilateral vehicle implants. Blood was collected at 10-min intervals for 1 h beginning at 06.00 and 18.00 h from days 11 to 18. Gilts were subsequently ovariectomized on day 19. Corpora lutea were weighed, homogenized and assayed for P4. UOV plasma was assayed for P4, E2 and PGF2α by validated RIA. No side differences were observed in CL weight or UOV P4 within groups. CL were maintained in E2-treated, but not control gilts, as evidenced by CL weight (333±20 vs 154±12 mg), CL P4 content (21.8±2.1 vs 0.3±0.1 μg) and CL P4 concentration (65.7±5.5 vs 2.3±0.6 ng/mg), respectively. UOV P4 values were similar between groups up to 18.00 h on day 15, declining from 346±122 ng/ml at 18.00 h on days 11 to 147±20 ng/ml on day 12, then remaining constant to 18.00 h on day 15. Thereafter, UOV P4 in E2-treated gilts returned progressively to day 11 values by 18.00 h on day 18 (364±97 ng/ml) while values of control gilts declined to low levels (5.4±0.6 ng/ml). In E2-treated gilts, UOV plasma E2 was elevated 13-fold ipsilateral, and 4-fold contralateral, to the E2-treated ovary when compared with levels in control gilts. Further, uterine PGF2α release was suppressed in E2-treated when compared with control gilts. Although E2 did not prevent the initial decline in UOV P4 observed between days 11 and 15 in all gilts, reduced uterine PGF2α release may have facilitated the progressive return in CL function observed in E2-treated gilts.
ASJC Scopus subject areas
- Animal Science and Zoology