Characterization of Porcine Endometrial, Myometrial, and Mammary Oxytocin Binding Sites during Gestation and Labor1

Sep 1, 1996Biology of reproduction

Oxytocin binding sites in pig uterus and mammary glands during pregnancy and labor

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Abstract

The concentration of oxytocin binding sites in porcine tissues increased toward term and remained elevated postpartum.

Binding sites for oxytocin in endometrial and mammary tissues showed the most significant increases during pregnancy.
Myometrial tissues exhibited a gradual rise in oxytocin binding sites over the studied time periods.
Binding of oxytocin was found to be concentration- and time-dependent.
High affinity for oxytocin was confirmed through linear Scatchard plots.
Concentrations of estradiol-17 beta, prostaglandin F2 alpha, and oxytocin were positively correlated with oxytocin binding site concentrations.
Progestone levels were negatively correlated with oxytocin binding site concentrations.

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Changes in oxytocin (OT) receptor expression have been found to be an important determinant of the physiological effect of OT in several species. To date there are no published studies of OT binding sites during pregnancy in the pig. The purpose of the present study is to improve understanding of the role of OT in porcine parturition. The concentration and affinity of OT binding sites were determined for myometrium and endometrium from pregnant and postpartum gilts. Tissues were obtained after slaughter from 7 animals in each of four groups: 1) 90 days gestation, 2) 112 days gestation, 3) term after milk letdown (before delivery), and 4) within 1-3 h after farrowing. Mammary tissues were obtained for some animals in each group (n = 3-5/group). Before slaughter, blood was collected from each animal and assayed for estradiol-17 beta, progesterone, 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM), and OT. Binding of 3H-OT in the three tissues was concentration- and time-dependent. Sites of 3H-OT binding (fmol/mg protein +/- SEM) increased toward term for each tissue and remained elevated in the postpartum group. Endometrial and mammary tissues displayed the most acute increases in OT binding site concentrations while myometrial tissues displayed a more gradual increase in OT binding sites over the times studied. The binding sites displayed high affinity for 3H-OT and were characterized by linear Scatchard plots. Concentrations of estradiol-17 beta, PGFM, and OT (pg/ml +/- SEM) were positively correlated with 3H-OT binding site concentrations, whereas progestrone concentrations (ng/ml +/- SEM) were negatively correlated with binding site concentration, as determined by Pearson's Correlation Analysis. The data represent the first account of changes in the expression of OT binding sites on porcine tissues during gestation and labor.

Characterization of Porcine Endometrial, Myometrial, and Mammary Oxytocin Binding Sites during Gestation and Labor1

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