Characterization of neuropeptides by reversed-phase, ion-pair liquid chromatography with post-column detection by radioimmunoassay : Application to thyrotropin-releasing hormone, substance P, and vasopressin

Neuropeptide contents of rat brain samples were determined by radioimmunoassay (RIA) after fractionation of tissue extracts by high-performance liquid chromatography (HPLC). Solvent systems were composed of acetic acid, acetonitrile and short-chain (5–8 carbons) alkylsulfonic acids. Separate solvent systems were developed for thyrotropin-releasing hormone, substance P, arginine vasopressin and biologic analogs, and the enkephalins. All separation systems tested gave 80–90% recovery of picogram quantities of peptides. When lyophilized, the HPLC solvents did not interfere significantly with the RIAs, allowing quantitation of tissue concentrations of isolated neuropeptides using the lyophilized eluent from the HPLC. The combination of liquid chromatography with RIA should allow for very accurate identification and quantification of peptides in biologic samples containing large numbers of potentially cross-reacting species of molecules.