Inactivation of thyrotrophin releasing hormone by human and rat serum

The inactivation of thyrotrophin releasing hormone (pGlu-His-Pro-NH2, TRH) and its deamidated analogue pGlu-His-Pro-OH (TRH-OH) in human and rat serum has been studied using specific radioimmunoassays. No difference was apparent between human and rat serum with regard to proteolytic activity towards TRH and TRH-OH. It was found that the inactivation of both peptides is a saturable process. The disappearance of TRH was clearly inhibited by TRH-OH, luteinizing hormone-releasing hormone and dithiothreitol. The suppressive action of these compounds was observed to be dependent on their concentration. Proline and EDTA showed little inhibiting activity. Proline amide and pyroglutamic acid left the reaction unaffected. In no single instance could any production of TRH-OH from TRH be demonstrated.