Validation of a homologous canine relaxin radioimmunoassay and application with pregnant and non-pregnant Northern fur seals (Callorhinus ursinus)

Authors

Don R. Bergfelt, US Environmental Protection Agency
Bernard G. Steinetz, New York University School of Medicine
J. Lawrence Dunn, Mystic Aquarium and Institute for Exploration
Shannon Atkinson, University of Alaska Fairbanks
J. Ward Testa, National Marine Mammal Laboratory
Gregg P. Adams, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada

Date of this Version

2010

Comments

Published in General and Comparative Endocrinology 165 (2010) 19–24.

Abstract

The primary objectives of this study were to validate a canine relaxin RIA for use in otariids and phocids and consider practical applications. For 6 captive Northern fur seal females, serum samples were grouped and examined according to pregnancy (n = 13), post-partum (n = 8) and non-pregnancy (n = 6), and, for 2 captive Northern fur seal males, serum samples were grouped and examined together regardless of age (2 mo–15 yrs, n = 6). Placental tissue was available for examination from one Northern fur seal, Steller sea lion and harbor seal. The validation process involved several steps using an acid-acetone extraction process to isolate a relaxin-containing fraction in pools of serum from each group of fur seals and placental tissue from each seal species. A relaxin-like substance was detected in extracts of pregnant, non-pregnant and male serum and placental tissue in a dose-responsive manner as increasing volumes of respective extracts or amounts of canine relaxin were introduced into the assay. In raw serum samples, mean immuno-reactive relaxin concentrations were higher (P < 0.05) during pregnancy than post-partum and non-pregnancy, and lower (P < 0.05) in male than female fur seals. During pregnancy, mean serum concentrations of relaxin progressively increased (P < 0.05) over Months 4–10 and, in serial samples collected from the same fur seals before and after parturition, mean concentrations were higher (P < 0.06) pre-partum than post-partum. In conclusion, validation of a homologous canine relaxin RIA for use in otariids and phocids resulted in the discovery of a relaxin-like substance in extracted and raw serum and placental tissue from Northern fur seals, a Steller sea lion and harbor seal. Distinctly higher immuno-reactive concentrations during pregnancy indicated the potential for relaxin to serve as a hormonal marker to differentiate between pregnant and non-pregnant or pseudopregnant pinnipeds.