Effects of day of the estrous cycle or pregnancy on protein secretion by caprine endometrial tissues

Our objectives were to evaluate temporal changes in protein secretion by endometrial explant cultures obtained from cycling or pregnant caprine does during the period of maternal recognition of pregnancy. Equal amounts of radiolabeled proteins from explant cultures were separated by one- and two-dimensional PAGE and visualized by fluorography. No consistent difference in proteins with molecular masses greater than 30 kDa was apparent when electrophoretic patterns were compared. However, on Days 18 and 21 of pregnancy there was an increase in the number and intensity of proteins having molecular masses between 18 and 22 kDa (pI = 6.2-7.2) when compared with endometrial secretory proteins obtained from goats on Day 18 of the estrous cycle. Three proteins were also detected in culture supernatants from endometrial explants obtained on Days 18 and 21 of pregnancy but not on Day 18 of the estrous cycle. A basic (pI > 7.5) 14-kDa protein could sometimes be resolved into two (or more) isoelectric variants. A second 14-kDa protein (pI = 6.9) and a less prominent 15-kDa protein (pI = 6.0) were also produced in response to the conceptus. These proteins then decreased in intensity, returning to levels characteristic of those earlier in pregnancy, by Day 30 of gestation. These caprine uterine secretory proteins may be involved in the process of maternal recognition of pregnancy.