Thyrotrophin-releasing hormone-related polypeptides in rabbit prostate and semen are different from those in rabbit hypothalamus.

TRH-related peptides were extracted from the hypothalamus and prostate gland of the rabbit. The peptides were fractionated by gel exclusion chromatography and located by trypsin digestion and radioimmunoassay with antibodies to TRH amide and TRH-Gly Lys. In the hypothalamus TRH-related peptides containing approximately 16 and 30 residues were observed: in these peptides the extensions to the TRH sequence were exclusively in the C-terminal direction. In addition, the three-residue form of TRH was also present. In the prostate complex, the predominant TRH-related peptide contained approximately 50 residues and the extension to the TRH tripeptide was on the N-terminal side; a three-residue form of immunoreactive TRH was also demonstrated. The same pattern of TRH-related peptides was shown to be present in rabbit semen. The results reveal the existence of a novel TRH-related polypeptide in the prostate and semen which does not occur in the hypothalamus. This peptide appears to undergo secretion.