Review Relaxin: A hormonal aid to diagnose pregnancy status in wild mammalian species Don R. Bergfelt a, * , Augustine T. Peter b , Mohd A. Beg c a Department of Biomedical Sciences, Ross University School of Veterinary Medicine, Basseterre, St Kitts, West Indies b Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, Indiana, USA c King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia article info Article history: Received 25 April 2014 Received in revised form 26 July 2014 Accepted 27 July 2014 Keywords: Conservation Immunoassay Pregnancy diagnosis Relaxin Wild mammal abstract In the beginning of 1960s, seminal studies characterizing circulating concentrations of immunoreactive relaxin in companion dogs and evaluating the differences in concentra- tions among pregnant, nonpregnant, and pseudopregnant bitches indicated the potential for relaxin to be applied clinically as a diagnostic aid to detect pregnancy status in wild animal species. A brief historical overview of the nature of relaxin and early work to develop and validate immunologic methods to analyze relaxin in the blood of rodents and pigs is initially discussed, which is followed by a summary of the development and vali- dation of relaxin immunoassays to diagnose pregnancy in companion dogs and cats. Thereafter, observation of the pregnancy-specific increase in circulating concentrations of relaxin in laboratory, companion, and farm animal species leads to discussion on the application of radioimmunoassays, enzyme immunoassays, and a rapid immunomigration assay to diagnose pregnancy in wild terrestrial (e.g., wolves, lions, elephants, rhinoceros, panda) and marine (e.g., seals, dolphins) mammal species. A reference table is included with a comprehensive list of numerous species and essential reagents that have been used in various in-house and commercial immunoassays to successfully analyze relaxin quan- titatively and qualitatively in blood (serum or plasma) and to some extent in urine. Although the detection of relaxin concentrations has the potential to aid in the diagnosis of pregnancy in many wild animal species, there are challenges in other species. Future ef- forts should focus on validation of nonradiolabeled relaxin immunoassays for broader application among species and improving techniques (e.g., extraction, purification) to analyze relaxin in samples other than blood (e.g., urine, feces, saliva, blow, skin, blubber) that can be collected in a less-invasive or -stressful manner and processed accordingly for basic and applied purposes, especially with application toward conservation of threatened or endangered species. Published by Elsevier Inc. 1. Introduction The hormone relaxin was discovered approximately 90 years ago by Hisaw [1] when he found that adminis- tration of serum from pregnant guinea pigs or rabbits into virgin guinea pigs induced relaxation of the pubic ligament. Subsequently, in a classical endocrine-related experiment, administration of an aqueous extract of porcine CL into ovariectomized guinea pigs relaxed the pubic ligament. Thus, the physiological basis for the hormone “relaxin” was first established [2]. Most of the early research to isolate and purify relaxin was done with excised pig ovaries because they are a rich source of relaxin, especially during pregnancy. In the early 1930s, it was difficult to establish relaxin as an independent hormone because many researchers were skeptical of the * Corresponding author. Tel.: þ1703 731 6775; fax: þ1 703 349 6453. E-mail address: drbergfelt.don@hotmail.com (D.R. Bergfelt). Contents lists available at ScienceDirect Theriogenology journal homepage: www.theriojournal.com 0093-691X/$ – see front matter Published by Elsevier Inc. http://dx.doi.org/10.1016/j.theriogenology.2014.07.030 Theriogenology 82 (2014) 1187–1198