Kallikrein-like activity in salivary glands using a new tripeptide substrate, including preliminary secretory studies and observations on mast cells.

The tripeptide substrate D-val-leu-arg-4-methoxy-2-naphthylamine gave a precise localization of reaction product in cryostat sections of aldehyde-fixed salivary glands from a number of species, with Fast Blue B as the capture reagent. In submandibular glands, there was strong staining of the granules in granular tubules of rats and hamsters and somewhat less in mice. Submandibular striated ducts showed variable periluminal staining in a finer granular form; it was abundant in guinea-pigs, strong in cats but somewhat less pronounced in dogs. Parotid glands contained less reactivity with none detectable in hamsters and guinea-pigs. In the rabbit, neither gland showed any reaction. Mast cells were densely stained in glands from cats and dogs; they were less reactive in rats and unstained in the other species. The closely related 7-amino-4-trifluoromethylcoumarin derivative of the tripeptide has been found highly satisfactory for assessing activity in submandibular saliva from cats. Preliminary functional studies indicate that an extensive rapid secretion of enzyme occurs into saliva on sympathetic stimulation, with a corresponding depletion of reactive material from the striated ducts in tissue sections. Far less mobilization of enzyme occurs into saliva on parasympathetic stimulation with no obvious change in the histochemical reaction of striated ducts. The possible significance of these findings in cats is discussed. Extensive qualitative and quantitative studies are required to evaluate enzyme and substrate specificities in each species. Nevertheless, derivatives of D-val-leu-arg offer great promise for the functional testing of kallikrein-like reactivity both by histochemical means on cells and biochemically in their secretions.