Functional Study of Mucus Secretion of the Eustachian Tube in Guinea Pigs

Objectives: Our aim was to verify neural regulation of submucous gland mucus secretions in the Eustachian tubes of guinea pigs. Study Design: Prospective animal study. Methods: Eustachian tubes harvested from 12 guinea pigs were used for this study. For real-time resolution of pure glandular secretion, we used a modified method of single-gland optical measurement. Secretory monitoring was undertaken after each preparation with phenylephrine, isoproterenol, forskolin, and substance P. To confirm the viability of each tissue, we examined glandular secretion after treatment with carbachol. Secretory effects of each agonist were evaluated by comparing with basal secretion using a Student's t test (p < 0.01). Results: The Ca(2+)-elevating agonists carbachol and substance P showed greater effects on submucous gland secretions of the Eustachian tube than the cyclic adenosine monophosphate (cAMP)-elevating agonists forskolin and isoproterenol. How-ever, phenylephrine, although it belongs to the Ca(2+)-elevating agonist group, did not show any significant secretory effect. Conclusion: The optical measurement method used in this study had the merit of real-time resolution of submucous glandular secretion. Submucous glandular secretion in the Eustachian tube was regulated by both Ca(2+)-and cAMP-elevating agonists, and Ca(2+)-elevating agonists seemed to be more potent than cAMP-elevating agonists except phenylephrine. Our results suggest that not only the autonomic nerve system but also the neuropeptides such as substance P are closely related to glandular secretion in the Eustachian tube, and beta-adrenergic receptors seem to be more related to submucous glandular secretion of the Eustachian tube in guinea pig than alpha-adrenergic receptors.