Effect of uterine space and fetal sex on conceptus development and in vitro release of progesterone and estrone from regions of the porcine placenta throughout gestation

Intact (n = 17) and unilaterally hysterectomized-ovariectomized (UHOX, n = 19) gilts were used to study conceptus development and the steroidogenic capability of three regions of the porcine placenta under normal and crowded intrauterine conditions. Gilts were hysterectomized on either Days 30, 50, 70, or 90 of gestation. Placentas were combined according to the sex of the fetus associated with the placental unit, except at Day 30, when all were combined. Placentas were cut into three regions: middle, inner, and polar. Placental tissues were incubated for 0, 1.5, and 3 hr, and concentrations of progesterone (P 4) and estrone (E 1) in the incubation medium were determined. Fetal survival rate was greater (P < 0.01, 0.05, and 0.001 at days 50, 70, and 90, respectively) in intact than in UHOX gilts. Placental length and weight, fetal length and weight, and allantoic fluid volume were greater (P < 0.05, 0.001, 0.05, and 0.001, respectively) in intact than in UHOX gilts. P 4 concentration was lower (P < 0.001, 0.002, and 0.001 at Days 50, 70, and 90, respectively) in the incubation medium of polar region placenta compared with the other regions. The release of P 4 was greater (P < 0.005) from the placentas of intact versus UHOX gilts at Day 90 but was not different at Days 30, 50, or 70. The sex of the fetus did not affect placental P 4 release. The region of the placenta affected E 1 release at Day 30 (P < 0.01, greater in polar section) and Day 50 (P < 0.06, less in polar section). There was no effect of uterine status on E 1 release. The sex of the fetus affected (P < 0.001) E 1 release only at Day 50 (greater in males). Collectively, the results from this experiment indicated 1) a differential release of P 4 and E 1 by the different regions of the placenta at certain days of gestation, and 2) no compensatory increase in the steroidogenic activity of the pig placenta when the total placental mass was reduced.