Solid-phase radioimmunoassay for relaxin.

A specific radioimmunoassay (RIA) for porcine relaxin is described in the present report, which also discusses its characterization in terms of its specificity and cross-reactivity to human and rat relaxin. The antibodies used in this assay were developed in rabbits immunized against highly-purified porcine relaxin. They were adsorbed on polystyrene tubes via incubation of a 1:40,000 antibody dilution for 24 hours. NIH relaxin was utilized for iodination by the Bolton-Hunter method and for the standard curve. The RIA was sensitive from 31.3 to 8,000 pg/tube of the porcine hormone. Rat relaxin cross-reacts with the anti-body, but the displacement curve produced by purified rat relaxin was shifted to the right by two orders of magnitude when compared to porcine relaxin. Displacement of 125I-porcine relaxin was also observed with the plasma of pregnant rat or woman, but about 100 times more plasma of these two species was required to produce the same displacement. No cross-reactivity was observed with human, bovine and porcine insulins. This RIA for relaxin will permit clinical evaluation of plasma relaxin concentrations during gestation and in different associated diseases. The concentrations of relaxin in human plasma obtained by this method might represent only a fraction of the actual concentration of the hormone due to low cross-reactivity of the anti-porcine relaxin with human hormone. It is also possible that relaxin is present in lower concentration in the plasma of pregnant woman in comparison to pregnant sow plasma.