[Using specific radioimmunoassay for guinea pig VIP (GP VIP), immunoreactive GP VIP levels in respiratory tract tissue of normal and airway-allergic guinea pigs].

Vasoactive intestinal polypeptide (VIP) has recently received widespread attention with respect to its control of airway constriction, and is now regarded as the most promising candidate as a neurotransmitter for nonadrenergic noncholinergic inhibitory nerves in the airway. A specific system of radioimmunoassay (RIA) was devised to measure guinea pig VIP (gp VIP) concentration in airway tissue. An antiserum, R 550, was obtained by immunizing rabbits with newly synthesized gp VIP. The detectable VIP concentration was assessed to be 10 fmol/tube with the RIA system. The concentration of gp VIP in the respiratory tract tissue of normal guinea pigs was 0.04-0.22 pmol/g wet weight of tissue. The VIP level was highest in the trachea, in contrast to lower levels in both the major bronchus and lower lung. After being passively sensitized with ovalbumin, the experimental guinea pigs were exposed to the same antigen. After three minutes, as the expiration time was prolonged and the respiratory resistance increased, the immunoreactivity in the trachea and the major bronchus was significantly higher than the pre-exposure levels. After six hours, however, they returned to the original levels except in the lower lung where the level was constant throughout the respiratory change. As described above, the possibility of controlling airway constriction by VIPergic nerve in immediate-type allergic reactions is suggested by our findings.