High concentrations of thyrotrophin-releasing hormone (TRH) are known to be present in the olfactory lobe, and the processing of the TRH prohormone in this region of the brain has been examined in this study. TRH-extended peptides have been detected in the rat olfactory lobe: these peptides accounted for approximately 11% of the total TRH immunoreactivity present in the tissue and contained the sequence pGlu-His-Pro-Gly-Arg exclusively at their N-termini. Extended peptides containing pGlu-His-Pro-Gly-Lys at their N-termini were not detected suggesting that incomplete cleavage occurs only at Arg-Arg residues in the TRH-prohonnone. In view of the highly specific processing of the prohormone, it is likely that the TRH-extended peptides play important physiological roles.
