Effects of the estrous cycle and early pregnancy on bovine uterine, luteal, and follicular responses.

Abstract

Uterine, luteal, and follicular responses associated with the estrous cycle and early pregnancy in cattle were examined. Dairy (n = 19) and beef (n 19) cattle were slaughtered either on Day 4, 8, 12, 14, 16, or 19 postestrus (estrus = Day o). Corpus Iuteum (CL) weight, specific PGF20 binding by the luteal particulate fraction (100,000 X g pellet), in vitro estradiol (E2) production by the two largest follicles, total recoverable uterine luminal protein (TP), total recoverable iinmunoreactive uterine luminal PGF (TPGF), and peripheral plasma steroids were evaluated. In a parallel study, beef cattle (n 22) were slaughtered either on Day 8, 12, 14, 16, or 19 of pregnancy for measurements of TP, TPGF, and plasma steroids. Uterine luminal proteins, from cyclic and pregnant cattle (Day 19), were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) for determination of protein molecular weights and protein profile characterization. In cyclic cattle, CL regression was not completed by Day 19. Follicle E2 secretion varied among animals within day (,i = 4.0-24.0 ng E2 /follicle/3.5 h; P<0.O1), but not among days. Total PGF2a binding (fmole/CL) for Days 4, 8, 12, 14, 16, and 19 was 14.29, 145.79, 177.34, 111.82, 174.51, and 199.17 (P<O.ol). TPGF (ng) varied among cycle Days 4 (14.4), 8 (13.9), 12 (19.7), 14 (47.7), 16 (17.4), and 19 (111.0 ng: P<0.01). In contrast, TPGF (ng) from pregnant cattle was 481.6 and 1187.8 ng on Day 16 (n 5) and 19 (n = 6). TP (mg) in cyclic cattle varied (P<0.05) among Days 4 (7.34), 8 (7.03), 12 (4.14), 14(15.92), 16 (5.88), and 19 (11.35). Mean TP (mg) for pregnant cattle ranged from 2.73 to 12.09. Thirty-two protein categories were identified in cyclic cattle uterine flushings by SDS-PAGE (Mr range X i(T� = 18.7 to 292.0). Proteins appeared with greater frequency later in the cycle than earlier (Days 14, 16, 19: 60% vs Days 4, 8, 12: 45%). Composite SDS-PAGE profiles from Days 8-12 and Days 14-16 differed (P<0.10) suggesting luteal phase stimulation of protein secretion. Protein profiles (SDS-PAGE) from Day 19 of pregnancy differed from Day 19 of the estrous cycle, resembled those of midluteal phase, and revealed four protein constituents possibly unique to early pregnancy. In summary, uterine luminal PGF increased with luteal phase of the estrous cycle at a time when there appeared to be a stable population of specific PGF2a binding sites in the CL. Higher PGF in utero at Days 16 and 19 of pregnancy and changes in TP and SDS-PAGE protein profiles may reflect responsiveness of endometrium to changes in ovarian status (cyclic) and/or conceptus activity (pregnancy comparisons).