VIP augments cholinergic-induced glycoconjugate secretion in tracheal submucosal glands

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Abstract
Using isolated submucosal glands from feline trachea, we examined the effect of vasoactive intestinal peptide (VIP) on mucus glycoprotein secretion and glandular contraction by measuring released radiolabeled glycoconjugates and induced tension, respectively. VIP (10-10 to 10-6 M) produced a dose-dependent increase in [3H]glycoconjugate release of up to 300% of controls, which was inhibited by VIP antiserum and not inhibited by atropine, propranolol, or phentolamine. VIP at a low concentration (10-9M), which did not produce any significant increases over controls, produced a 2.4- to 5-fold augmentation of the glycoconjugate release induced by 10-9 to 10-7 M methacholine (MCh). Atropine or VIP antiserum abolished the augmentation. VIP did not produce any alteration in isoproterenol- or phenylephrine-evoked glycoconjugate secretion. VIP (up to 10-5 M) did not produce any alteration in the tension, even when the gland had contracted with MCh, or any augmetation of contraction induced by MCh (10-9 to 10-7 M). These results indicate that VIP induces mucus glycoprotein release from secretory cells and also that it potentiates the secretion induced by cholinergic stimulation.