Permeability of canine submandibular glands to blood-borne horseradish peroxidase during parasympathetic secretion.

Abstract

Potential permeability pathways exist between central acinar cells in submandibular glands of dogs and they are large enough to allow the passage of molecules of horseradish peroxidase (HRP) under certain conditions. During gentle submandibular secretion caused by parasympathetic nerve stimulation detectable amounts of HRP passed into the saliva as long as the concentration of HRP in the blood reaching the gland was high enough. Morphological results indicated that the passage was mainly via leaky junctions between acinar cells. It is likely that this movement was by passive permeation because it required a high concentration gradient, was slow to occur and gradually reached a peak; the actual amounts to reach the saliva under physiological conditions were small and depended on the effective concentration of HRP reaching the gland. A satisfactory reproducible secretory regime has been developed, using short periods of stimulation alternating with rest pauses. Using these conditions gradually increasing amounts of HRP reached the saliva and first samples of saliva during each stimulation period contained more HRP than subsequent samples from the same stimulation period. It is possible that contraction of myoepithelial cells, at the outset of each stimulation period, contributed to this increased movement by acting on HRP-containing fluid in spaces between themselves and the acinar cells, thereby causing an increased filtration pressure to be exerted on underlying tight junctions.