Inactivation of thyrotropin-releasing hormone (TRH) and (3Me-His) TRH by brain peptidases studied by high-performance liquid chromatography

Abstract

High-performance liquid chromatography (HPLC) has been used to separate and identify the metabolites formed from thyrotrophin-releasing-hormone (TRH) and its hyperactive analogue, (3Me-His)TRH, by subcellular fractions from rat cortex, hypothalamus and thalamus. Deamidation by the proline endopeptidase and formation of histidylproline diketopiperazines by the pyroglutamyl aminopeptidase were found to be the major mechanisms of brain inactivation of both peptides; (3Me-His)TRH was slightly more stable than TRH in the presence of the brain peptidases, and with enhanced receptor binding affinity, this could explain its increased biological activity. The HPLC system used may be applicable to determining the mechanisms of brain inactivation of other TRH analogues and could also be used to define the pathways for inactivation of larger neuropeptides as well.