The effect of vasoactive intestinal peptide on smooth muscle tone and mucus secretion from the ferret trachea

The effect of vasoactive intestinal peptide (VIP) was examined on the smooth muscle contraction and mucus secretion produced by methacholine and phenylephrine in the ferret whole trachea in vitro. VIP (0.5 to 800 nM) produced a concentration-dependent relaxation of the ferret trachea contracted by methacholine (1 microM) and phenylephrine (10 microM). The concentration-response curves for methacholine- and phenylephrine-induced contractions were both shifted to the right by VIP (0.1 microM). Methacholine-induced secretion was inhibited in a concentration-dependent manner by VIP, whereas that due to phenylephrine was enhanced. The concentration-response curve for methacholine-induced secretion was shifted to the right by VIP, whereas the curve for phenylephrine was shifted to the left. Methacholine produced a concentration-dependent increase in the rate of output of lysozyme from the ferret trachea with no corresponding increase in the concentration of lysozyme in the mucus. Phenylephrine produced a concentration-dependent increase in the rate of output and in the concentration of lysozyme. VIP (0.1 microM) significantly increased the concentration of lysozyme in the mucus produced by methacholine with no increase in the rate of lysozyme output. However, the rate of lysozyme output due to phenylephrine was significantly increased by VIP (0.1 microM) with no increase in concentration. We suggest that VIP inhibits secretion from mucous cells stimulated by methacholine, and enhances the secretion produced by phenylephrine from serous cells.