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Biology of Reproduction, Vol 25, 281-289, Copyright © 1981 by Society for the Study of Reproduction

Relaxin Activity in the Pregnant Mare

DENNIS R. STEWART 1, and GEORGE STABENFELDT 1

1 Department of Reproduction, School of Veterinary Medicine, University of California, Davis, California 95616


Plasma relaxin activity was measured daily in the mare during the estrous cycle and throughout pregnancy. A radioimmunoassay (RIA) for highly purified porcine relaxin was utilized. While competitive binding curves of dilutions of mare plasma and porcine relaxin standards were not found to be parallel, the material measured by the RIA eluted as one band from gel filtration and had a molecular weight similar to porcine relaxin. Relaxin immunoactivity was not detected during the seven estrous cycles studied. Relaxin activity was below detection in all mares for the first part of gestation and began to increase at about Day 80. Relaxin activity then progressively rose (P<0.05) to peak levels (5.9 ng/ml) between 176-200 days of gestation. Levels of relaxin subsequently declined (P<0.05) to sim 4.2 ng/ml over the next 60 days. Relaxin activity increased (P<0.05) steadily from Day 240 to the day of foaling. Relaxin activity rapidly fell following foaling.

The onset of detectable plasma relaxin was not coincident with elevated equine chorionic gonadotropin (eCG). Since relaxin was not detected during the first 80 days of luteal activity and persisted following luteal regression, the corpora lutea are not a likely source of relaxin in the mare. As relaxin activity was coincident with the onset of placental steroid synthesis, the placenta is a possible site of relaxin production in the mare.

Note:
ACKNOWLEDGMENTS We wish to thank John Lovell for collecting the samples used in this study, Peter Wang for progesterone determinations, and Susan Farmer and Harold Papkoff for providing eCG data. Purified porcine relaxin was donated by the National Pituitary Agency of NIAMDD.

Submitted on December 17, 1980
Accepted on April 9, 1981




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R. H. Renegar and C. R. Owens III
Measurement of Plasma and Tissue Relaxin Concentrations in the Pregnant Hamster and Fetus Using a Homologous Radioimmunoassay
Biol Reprod, August 1, 2002; 67(2): 500 - 505.
[Abstract] [Full Text] [PDF]


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Copyright © 1981 by the Society for the Study of Reproduction.