Serum relaxin levels in young athletic men are comparable with those in women.

Relaxin is a peptide hormone that was first described as a reproductive hormone produced in pregnancy, which acts to loosen pelvic ligaments and soften the cervix in preparation for parturition.1 Relaxin is also produced in nonpregnant women2 and has been shown to have multiple physiologic effects in humans, including improvement of cardiac and renal blood flow through vasodilation3 and prevention of lung fibrosis.4 In the musculoskeletal system, relaxin’s role in ligamentous laxity has been investigated in the anterior cruciate ligament (ACL) and anterior oblique ligament of the basilar thumb joint.5,6 Relaxin secretion has also been demonstrated in men’s reproductive tracts.7 Relaxin has a key influence on prostate growth and development.8 Relaxin receptors have also been shown in the ACLs of men, although less consistently than in women.9 In a study of 9 men and 5 women (mean age, 58 years) with congestive heart failure, serum relaxin levels averaged 20 pg/mL, which was approximately 12-fold lower in age-matched controls.10 Although normative levels of relaxin have been investigated in pregnant and nonpregnant women,2,11 limited data exist on normative serum relaxin levels in men. The majority of reported serum relaxin levels in men are derived from studies of patients with renal or cardiac failure and may be reflective of the effect of chronic disease on this multidimensional hormone. No studies to date have evaluated serum relaxin levels in a cohort of young and physically active men. The purpose of this study was to evaluate serum relaxin in a large population of young athletic men and to compare serum relaxin levels and the proportion with detectable levels between the sexes. A secondary objective was to evaluate the relationship between relaxin and generalized joint laxity.