Evidence for relaxin in corpora lutea of late pregnant cows.

Relaxin was isolated from corpora lutea of third trimester pregnant cows. Fractions having relaxin activity eluted in the 6000 and 1400 molecular weight ranges when chromatographed on Bio-Gel P-10. Both fractions were shown to inhibit spontaneous contractions of the mouse uterus, and the 6000 molecular weight fraction promoted formation of the mouse interpubic ligament. Agar diffusion studies with an antiserum to purified porcine relaxin showed a continuous precipitin line with no spurring between the two bovine relaxin fractions and NIHR-P1 porcine relaxin standard. Electrofocusing of the 6000 molecular weight fraction demonstrated three fractions which were capable of inhibiting contractions of the mouse uterus and which cross-reacted with porcine relaxin antiserum. The isoelectric points of these three fractions were 8.8, 10.1, and 11.5. Large luteal cells in corpora lutea from cows in the midtrimester of pregnancy were detected that gave a positive stain for relaxin with the immunoperoxidase method.