Secretion of progesterone, estradiol-17β, PGE, PGF(2α), and pregnancy- specific protein B by 90-day intact and ovariectomized pregnant ewes

Ninety-day pregnant ewes were either laparotomized, ovaries left in situ or bilaterally ovariectomized, and a jugular venous catheter and an inferior vena cava catheter via the saphenous vein were installed. Seven days later, placenta slices were collected and incubated in vitro for 4 h. Secretions of progesterone, PGE, estradiol-17β and pregnancy-specific protein B (PSPB) in vitro by placenta from ovariectomized ewes were increased (P ≤ 0.05) by 2.7- , 3.6-, 2.2-, and 2.4-fold, respectively, when compared to placenta slices from intact 90-day pregnant ewes. Secretion of PGF(2α) in vitro was unchanged (P ≥ 0.05). Ovariectomy decreased (P ≤ 0.05) jugular venous progesterone for 78 h followed by a quadratic increase (P ≤ 0.05), whereas progesterone remained unchanged (P ≥ 0.05) in intact ewes over the 162-h sampling period. Ovariectomy increased (P ≤ 0.05) PGE in inferior vena cava plasma over the last half of the 162-h sampling period, whereas concentration of PGF(2α) did not change (P ≥ 0.05). Increases in PGE occurred before the increase in progesterone. Concentrations of PSPB in inferior vena cava plasma of ovariectomized pregnant ewes increased (P ≤ 0.05) during the last half of the 162-h sampling period, but not in intact ewes (P ≥ 0.05). PSPB increased before PGE and progesterone. Concentrations of estradiol-17β in jugular venous plasma of ovariectomized pregnant ewes increased (P ≤ 0.05) during the last half of the sampling period, but not in intact ewes (P ≥ 0.05). Increases in estradiol-17β occurred before increases in PSPB. It is concluded that these data support the hypothesis that estradiol-17β may control placental secretion of PSPB; PSPB may regulate placental secretion of PGE; and PGE may regulate placental secretion of progesterone.