Relaxin concentrations in pig plasma following the administration of prostaglandin F2alpha during late pregnancy.

Concentrations of relaxin in peripheral plasma were measured following the injection of 10 mg of PGF2alpha to pregnant sows on day 112 of gestation. The mean concentrations of relaxin before injection of PGF2alpha were less than 13 ng/ml. Relaxin concentrations increased sharply to a mean of 104 ng/ml by 45 min following injection of PGF2alpha and then fell rapidly to a mean of 40 ng/ml 4 h later. Following this initial peak of relaxin, there was a gradual rise and fall of relaxin concentrations during the day preceding parturition. The levels of relaxin during this period were also influenced by PGF2alpha administration since the mean levels of relaxin were significantly lower from the 22nd through the 10th h before parturition in pigs given PGF2alpha, than in pigs given saline.