[Radioimmunoassay of vasoactive intestinal peptide immunoreactivity in guinea pig respiratory tract].

Although vasoactive intestinal peptide (VIP) has been suggested to be the neurotransmitter of non-adrenergic and non-cholinergic (NANC) inhibitory nerves, its physiological functions and movements in the airway are obscure. In this study, VIP immunoreactivity in the respiratory tract from guinea pigs was measured as a preliminary experiment to elucidate its functions. VIP immunoreactivity was measured by radioimmunoassay. The rate of VIP disappearance during extraction was 52.5 +/- 17.4 (mean +/- SD)%. The dose-response curve of tissue extract almost paralleled the standard curve of authentic VIP. VIP immunoreactivity of tracheas was 939.9 +/- 262.1 pg/g wet weight and that of extrapulmonary bronchi was 858.0 +/- 241.1 pg/g wet weight. Although VIP immunoreactivity of lung extracts was not detectable in 14 samples out of 23, the value of 9 samples was 111.7 +/- 61.5 pg/g wet weight. These results suggest that there may be more VIP immunoreactivity present in tracheas and extrapulmonary bronchi than in lungs.