Relaxin Levels in the Maternal Plasma of Pigs Before, During, and After Parturition and Before, During, and After Suckling1

Open Access
Publisher Website
Google Scholar
Abstract
Relaxin concentrations in peripheral plasma have been measured at frequent intervals before, during, and after parturition and before, during, and after suckling in maternal pigs. Relaxin concentrations rose steadily from 2.7 ng/ml at 0400 h on Day 110 to 15.8 ng/ml at 2400 h on Day 112 of pregnancy. During the 2 days which preceded parturition, there was a marked increase in relaxin levels. In nearly all pigs this prepartum elevation in relaxin levels consisted of two or three sustained surges which lasted for 10 to 20 h. Maximal relaxin concentrations, which ranged from 42 to 257 ng/ml, were obtained approximately 15 h before parturition. This maximum was followed by a sustained decrease in plasma relaxin levels to a mean of 0.4 ng/ml by 37 h after parturition. During parturition relaxin levels were relatively constant and did not exceed those observed immediately before parturition. Relaxin was not detected before, during, or after suckling in the plasma of any of the seven maternal pigs examined on Days 7, 14, 21, and 28 of lactation. Only in four of these pigs was relaxin detected on Day 3 of lactation, and in these cases relaxin levels were only 0.1 to 0.4 ng/ml and were not influenced by suckling.