Human relaxin will be isolated and an homologous radioimmunoassay used to extend studies in the human. Uterine/placental and testicular relaxin(s) will be isolated from either porcine, ovine or bovine sources and their primary amino-acid sequence(s) compared to the ovarian counterpart. The existence of porcine prorelaxin and preprorelaxin will be confirmed and the amino-acid sequence of the additional amino acids elucidated. The control of relaxin secretion will be studied both in vitro using separated ovarian compartments and whole ovary perfusion as well as in vivo using the quinea-pig as an animal model. The binding of 125I-porcine relaxin to fibroblasts grown in vitro from various tissues will be fully characterized as receptors and used as a model system for the study of relaxin action on collagen formation, structure and degradation. The structure-activity relationships of the relaxin(s) will be studied using chemically modified relaxin(s), insulin/relaxin hybrids and relaxin analogues in radioreceptor assays.