Permeability of submandibular salivary glands in dogs to blood-borne horseradish peroxidase (HRP)

Abstract

Horseradish peroxidase (HRP) was administered to the submandibular glands of dogs by close-arterial bolus-type injections, and its localisation was examined histochemically by light and electron microscopy. The HRP became widespread in the interstices of the glands and reached many central acinar lumina via scattered localised parts of their "tight" junctional complexes. Reaction product was less often found in the lumina of demilunes, which suggested that the intercellular junctions there were less "leaky". HRP was often found in sizeable spaces between myoepithelial cells and the underlying parenchymal cells; such large spaces have not been observed in this situation in other species. The possibility that permeability pathways may arise intermittently at different sites in the adhering mechanisms between the acinar cells is discussed. It is concluded that potential paracellular permeability pathways for macromolecules exist in these glands and, if the concentration gradient is sufficiently high, molecules even as large as those of HRP can to some extent permeate passively from the interstices to the saliva. In "resting" glands the principal permeability site is between the central acinar cells.

Permeability of Canine Submandibular Glands to Blood‐borne Horseradish Peroxidase During Parasympathetic Secretion

“…3). As in the previous study (Garrett et al 1981) intercellular staining was not always strong around the most positive lumina and conversely not all sites with moderately strong staining between cells showed very much activity in the lumina.…”

“…Similar studies are now being made with dogs and, using bolus-type close-arterial injections of HRP, we have shown that some of it can pass by the paracellular route to enter acinar lumina in 'resting' submandibular glands (Garrett, Klinger & Parsons, 1981).…”

“…Accumulations of the protein were observed in spaces lying between myoepithelial cells and the underlying acinar cells, and this suggests the possibility that compression of such spaces by myoepithelial contraction may have exerted a filtration force on any leaky sites at underlying luminal tight junctions. Although such spaces are rare in resting salivary glands from other species studied so far, they were frequently present in 'resting' submandibular glands of dogs (Garrett et al 1981), as well as in the present secreting glands. Thus it appears that these sub-myoepithelial spaces, into which ready diffusion from the interstices can occur, are a regular feature in normal submandibular glands of dogs.…”

“…A time factor plays an important role. (Garrett et al 1981). Thus it seems that during gentle parasympathetic secretion no additional sites of leakiness had been created.…”

“…Moderate staining for HRP was evident in the glands but it was never as strong as with bolus-type injections (Garrett et al 1981). This presumably relates to the lower concentrations of HRP delivered (although the total amounts were similar), plus the dilution from both the vasodilatation and the secretion caused by stimulation of the parasympathetic nerves.…”