VIPergic transmitter of trachea smooth muscle in guinea pigs

Transmural stimulation of the isolated trachea of guinea pig produced a biphasic response. The inhibitory response was partially reduced (41+/-13%) by propranolol (3 micromol/L), suggesting that the inhibitory response was adrenergic and that non-adrenergic component was also present. Vasoactive intestinal peptide 14-28 decreased the non-adrenergic inhibitory response (NAIR) by 26+/-21% (16+/-14% of all inhibitory responses). This shows that vasoactive intestinal peptide may be a transmitter of NAIR of guinea pig trachea smooth muscle. In sensitized preparations, VIPergic inhibitory response (VIP-IR) was only 7+/-5% of all inhibitory responses. The VIP-IR of trachea smooth muscle of the sensitized guinea pigs was obviously reduced.