Uterine Space Affects Placental Protein Secretion

The effect of altering uterine space available to developing conceptuses on placental and endometrial protein secretion and endometrial 3 H-thymidine incorporation on Days 25 and 35 of gestation was tested. Gilts bred at estrus (Day 0) were laparotomized on Day 4, and the uterine horn ipsilateral to the ovary with the most ovulations was ligated midway between the uterine tip and uterine bifurcation to create a crowded and a roomy uterine environment. On Day 25 (n = 7) or 35 (n = 6), gilts were killed and the reproductive tract was dissected from each. Each placenta and fetus was weighed, and a sample of endometrium adjacent to each placenta was collected. Within each uterine environment, tissues (500 mg) from the heaviest and lightest (by weight) placentae and adjacent endometrial tissue were cultured for 24 h at 37'C in 15 ml Minimal Essential Medium having 0.1 times the normal amount of leucine plus 50 liCi H-leucine. Aliquots (2 ml) of dialyzed medium were subjected to twodimensional PAGE and fluorography to examine proteins with molecular weight ranges of approximately Mr 20 000-130 000, and a further aliquot was subjected to SDS-PAGE to examine low molecular weight proteins (Mr 2000-20 000). In addition, endometrium (200 mg in duplicate) adjacent to the heaviest and lightest placentae within each uterine environment was incubated for 4 h in 5 ml MEM plus 1 LCi H-thymidine to measure DNA synthesis. After culture, 3 H-thymidine incorporation and total DNA were determined. Fetal survival in the crowded uterine environment decreased (p < 0.05) on Day 35 compared to Day 25. On both days, the heaviest and lightest placentae from the crowded uterine environment weighed less (p < 0.01) than the heaviest and lightest placentae from the roomy uterine environment. The fetuses associated with the heaviest and lightest placentae from the crowded uterine environment also weighed less (p < 0.05) than fetuses associated with the heaviest and lightest placentae from the roomy uterine environment. Nondialyzable radioactivity in medium per gram of tissue cultured from placental cultures decreased (p < 0.05) and from endometrial culture increased (p < 0.05) between Days 25 and 35. Placental secretion of a protein with Mr 46 000, p 5, decreased between Days 25 and 35. Endometrial secretion of three proteins (Mr 35 000, p 6.2; Mr 25 000, p 4.9; and Mr 14 000, p unknown) increased, and secretion of three other proteins (Mr 24 000, pI 6.5 doublet; Mr 22 000, p 7.5, and Mr 7000, p unknown) decreased from Day 25 to Day 35 of pregnancy. Endometrial Hthymidine incorporation per microgram of total DNA decreased (p < 0.1) between Days 25 and 35 and was also less (p < 0.1) for endometrium adjacent to the lightest placentae within each uterine environment than for endometrium adjacent to the heaviest placentae. The amount of uterine space available to conceptuses had no detectable effect on endometrial H-thymidine incorporation or endometrial protein secretion. Placental secretion of two proteins (Mr 36 000, pi 4, and M, 46000, p 4) was increased (p < 0.05), and secretion of another protein (Mr 46000, p 5) was decreased when the amount of uterine space available decreased. These results indicate that the amount of uterine space available to conceptuses affects placental protein secretion on Days 25 and 35 of pregnancy.