REGULATION OF THE TRH-LIKE PEPTIDE PYROGLUTAMYL-GLUTAMYL-PROLINEAMIDEIN THE RAT ANTERIOR-PITUITARY GLAND

TRH-like peptides share the N- and C-terminal amino acids with TRH (pG lu-His-Pro-NH2) but differ in the middle amino acid residue. One of th em, pGlu-Glu-ProNH2 (<EEP-NH2; EEP) is present in the rat pituitary gl and, but its biological significance is unknown. We investigated the l ocalization and regulation of this tripeptide in the rat pituitary gla nd. To distinguish between TRH and EEP two antisera were used for RIA: specificity of antiserum 4319 for the TRH-like peptides pGlu-PhePro-N H2 and EEP was equal to or greater than that for TRH, whereas antiseru m 8880 is TRH-specific. Our RIA data showed the presence of a TRH-Like peptide in the anterior pituitary gland (AP) and of TRH in the poster ior pituitary gland (PP). The TRH-Like peptide in the AP was identifie d on anion-exchange chromatography and subsequent HPLC as EEP. Pathoph ysiological conditions such as altered thyroid and adrenal status and suckling did not affect pituitary gland levels of EEP. In general, how ever, there is a clear sex difference: levels of EEP are higher in mal e than in female rats. In both sexes gonadectomy leads to a substantia l two- to threefold rise in EEP levels, abolishing the sex difference. Testosterone administration to gonadectomized male rats normalizes le vels of EEP again. Disulfiram, an inhibitor of the enzyme peptidylglyc ine alpha-amidating monooxygenase, reduced levels of EEP in the AP by approximately 50%. In conclusion: 1) the TRH-like peptide EEP is prese nt in the AP, whereas TRH is confined to the PP, 2) levels of EEP in t he AP are regulated by sex steroids, 3) EEP is actively amidated in th e AP and thus seems to be produced from a glycine-extended progenitor sequence.