Basic Biological Sciences Regulation of Tight Junctional Permeability in the Rat Parotid Gland by Autonomic Agonists

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Abstract
The permeability of tight junctions in the rat parotid gland to the ultrastructural tracer myoglobin (m.w. 17,800) was investigated after in vivo stimulation by autonomic drugs. At various times after administration of β-adrenergic (isoproterenol), α-adrenergic (methoxamine), or cholinergic (methacholine) agonists, the parotid duct was cannulated, and a solution of myoglobin was allowed to flow by gravity (16 mm Hg) into the gland for one hr. In resting glands, cytochemical reaction product for myoglobin was localized in the luminal space of acini and ducts. The tracer was also localized to the luminal space after stimulation with methacholine and methoxamine. In contrast, one to four hr after isoproterenol stimulation, reaction product was present in the intercellular and interstitial spaces of the gland. At later times after stimulation (from six to 24 hr), the tracer was again restricted to the luminal space of the acini and ducts. These results indicate that isoproterenol stimulation causes a transient increase in tight junctional permeability, whereas stimulation with methoxamine or methacholine does not change junctional permeability to myoglobin.