Characterization of Peptide Histidine Isoleucine-Like Immunoreactivity in the Rat, Human, Guinea-Pig and Cat Gastrointestinal Tracts – Evidence of Species Differences

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Abstract
Peptide histidine isoleucine-like immunoreactivity (PHI-LI) was measured by radioimmunoassay in various mammalian ileal extracts fractionated by gel filtration and high-performance liquid chromatography (HPLC). The PHI-LI in the cat, human, guinea-pig and rat tissues were of similar molecular size, being indistinguishable from the porcine standard by gel filtration on Sephadex G-50 superfine, but significant differences were noted on HPLC. The major PHI-LI peaks of guinea-pig and rat were less retained than cat and human PHI-LI which had a similar retention time to porcine PHI. Human PHI-LI, although being chromatographically similar to porcine PHI, was immunologically different. This variation in molecular properties of PHI-LI suggests that extrapolation of experimental results of different species should be treated with great caution.