The relaxin-like factor is a hormone

Abstract

The relaxin-like factor (RLF) circulates in the bloodstream of humans, interacts with a membrane protein with all the characteristics of ligand- receptor binding, and must therefore be considered a hormone by definition. The polyclonal antibody raised against synthetic human RLF showed no crossreactivity to other structurally related hormones, like insulin and relaxin. The sensitivity of this assay (ED50 at 100 pM) allowed the direct measurement of RLF concentrations in serum. The highest levels were detected in the serum of postpuberty males (190 pM), whereas in females and children, the RLF concentration was one order of magnitude lower.