Leukotriene C4-induced decrease of peptide histidine isoleucine(PHI) like immunoreactivity in the respiratory tract from guinea pigs.

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Peptide histidine isoleucine (PHI) as well as vasoactive intestinal peptide (VIP) is considered to be a neurotransmitter of non-adrenergic and non-cholinergic inhibitory nerves in the respiratory tract. We tried to measure PHI like immunoreactivity in the respiratory tracts from guinea pigs to evaluate the movement of PHI. A high titer of PHI antiserum which did not react with VIP was obtained from a rabbit immunized with rat PHI, and PHI like immunoreactivity in the respiratory tract from guinea pigs was measured by radioimmunoassay. Tracheas, extrapulmonary bronchi and lungs were dissected and treated by microwave irradiation. They were homogenized with 0.5 N acetic acid and centrifuged at 35, 000×g. Lyophilized supernates were used as samples for the radioimmunoassay. PHI like immunoreactivity per g wet weight tissue was 6.85±2.75 (mean±SD) ng in the tracheas, 2.26±0.27 ng in the extrapulmonary bronchi and 0.75±0.90 ng in the lungs, indicating that PHI like immunoreactivity is present more in the central airways than in the peripheral ones. Intravenous administration of leukotriene C4 (3μg/kg/hr) reduced significantly PHI like immunoreactivity in the tracheas and the extrapulmonary bronchi in parallel with the significant increase of dynamic respiratory resistance.