Interrelationships between endocrine changes in peripheral and uterine-venous blood and uterine activity at parturition in the pig

Abstract

Relationships between endocrine changes and uterine activity were studied by analyses of samples taken at short intervals from sows during late gestation and labor. The initial reduction in peripheral progesterone concentrations occurred prior to the first significant increases in prostaglandin metabolite (PGFM) levels in peripheral blood which occurred 8–24 h prior to parturition. A more marked increase in PGFM occurred within 8–12 h of parturition and was closely associated with increased myometrial activity and higher concentrations of prostaglandin F (PGF) in peripheral and uterine-venous plasma. Prostaglandin E (PGE) was present at higher concentrations than PGF until the onset of labor when PGF concentrations were higher than PGE. Relaxin concentrations increased steadily during the last week of gestation. A relaxin peak coinciding with the increased PGFM levels was seen in all sows 24-12 h before delivery when progesterone levels had declined and before PGF concentrations and uterine activity increased. Other relaxin peaks, unassociated with altered prostaglandin concentrations, were seen at earlier times before term. Estrone concentrations were significantly higher in uterine-venous than in arterial plasma whereas the reverse relationship was found for estradiol-17β.