Establishment of Pregnancy in the Pig: III. Endometrial Secretory Response to Estradiol Valerate Administered on Day 11 of the Estrous Cycle1,2,3

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Abstract
The administration of estradiol valerate (E2V, 5 mg/day) to gilts from days 11 through 15 of the estrous cycle results in maintenance of the corpora lutea. The effect of E2V, administered on day 11 only or days 11, 12 and 13, on uterine endometrial secretory function between days 11 and 14 of the estrous cycle was studied. Each uterine horn within a gilt was randomly assigned to be removed and flushed with 0.9% saline at either 1, 4, 12 or 24 h post-injection. A jugular vein plasma sample was obtained to determine concentrations of estrone (E1) and estradiol (E2). Uterine flushings were analyzed for total Ca, E1, E2, E1 sulfate (E1S), E2S, prostaglandin [PG] E and PGF, protein and acid phosphatase activity (AP). Plasma concentrations of E1 were greater (P < 0.01) in E2V (40.7 pg/ml) vs. control (5.3 pg/ml) gilts at 1 h post-injection and remained higher in E2V gilts at 72 h. Differences in Ca, PGE, AP, protein and estrogens in uterine flushings of gilts receiving either a single or daily injection of E2V were not detected; however, PGF was higher (P < 0.05) at 72 h in gilts receiving daily injections of E2V. Total E2 and E1S in uterine flushings were greater (P < 0.05) in E2V gilts. Protein and Ca increased (P < 0.05) in E2V gilts at 12 h and 24 h post-treatment and then declined, but total protein and AP increased to 48 h and 72 h. Total Ca was unchanged in control gilts, but total protein increased (P < 0.01) by 72 h post-treatment and AP increased between 1 h and 72 h in all gilts. Two-dimensional polyacrylamide gel electrophoresis of proteins in uterine flushings detected 3 selected basic uterine proteins (MW 32-60 k) associated with the increase in Ca and protein 12 h and 24 h post-treatment from E2V gilts. These proteins were not detectable until 48 to 72 h in control gilts. Total recoverable PGF was similar for E2V and control gilts between 1 h and 48 h post-treatment, but increased almost 6-fold between 48 h and 72 h in gilts receiving daily E2V. Total PGE was greater (P < 0.01) in E2V gilts and increased between 48 h and 72 h post-treatment. Increases in total recoverable Ca, protein, PGF and PGE in uterine flushings in response to E2V treatment were similar to those which occur between Days 11 and 12 of pregnancy. Estrogens of conceptus origin apparently induce that endometrial secretory response.

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