Effect of alpha-chymotrypsin on the nonadrenergic noncholinergic inhibitory system in cat airways

Electrical field stimulation of 5-hydroxytryptamine contracted cat trachea and bronchi in the presence of cholinergic and adrenergic blockade caused relaxation by activating intrinsic nonadrenergic noncholinergic (NANC) inhibitory nerves. Pretreatment of the tissues with the proteolytic enzyme, alpha-chymotrypsin, did not affect NANC inhibitory responses. Relaxations induced by vasoactive intestinal peptide (VIP) were abolished by alpha-chymotrypsin. These results suggest that VIP or related peptides may not act as the NANC inhibitory transmitter in cat airways. However, the possibility remains that peptides not susceptible to degradation by alpha-chymotrypsin may mediate these NANC inhibitory responses.