Characterization of peptide histidine isoleucine-like immunoreactivity in the rat, human, guinea-pig and cat gastrointestinal tracts--evidence of species differences.

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.