Relationship Between Uterine Progesterone and Fetal Development in Pigs1

Abstract

The potential relationship between uterine arterial and venous concentrations of progesterone, and porcine fetal size and viability was examined. Sixteen Yorkshire gilts were laparotomized at 27-37 days of gestation to count corpora lutea and embryos. Samples of blood were drawn from uterine arteries and veins at each embryonal location of 10 gilts but not from the 6 control gilts. At 60-76 days of gestation, a 2nd laparotomy was performed to determine rates of fetal survival and to draw blood samples from uterine vessels at all fetal locations in each of the 12 gilts remaining from the 1st surgery. The percentages of embryos surviving between 1st and 2nd surgeries were 51.0% for the experimental gilts and 65.6% for the control gilts (P > 0.05). Progesterone concentrations were higher in arteries than in veins at each fetal location at both surgeries (P < 0.01). The disappearance or utilization of progesterone in the uterine tissues surrounding either normal or mummified fetuses was greater late in pregnancy compared with the early embryonic stage (P < 0.05). Uterine arterial and venous progesterone concentrations were unrelated to fetal weight; fetal weight was correlated with arterial-venous differences. Some progesterone entering the uterine arterial system apparently is metabolized or utilized and does not reenter the uterine venous system; this utilization may be related to fetal weight and stage of development.