Movement of horseradish peroxidase in submandibular glands of dogs after ductal injection.

Small volumes of solutions of a tracer enzyme, horseradish peroxidase (HRP), have been injected retrogradely via the main duct of submandibular glands in dogs, and the distribution of the peroxidase reaction product within the glands has been studied light microscopically and electron microscopically at different times after the injection. Tissue taken immediately after injections of 0.25 ml, given over 10 sec, showed that HRP had penetrated into the interstitial spaces of the gland. It was usually irregularly distributed and appeared to have reached the interstices of the gland by passing through the intercellular junctions of adjacent acinar cells. In time the tracer gradually disappeared from the interstices of the gland. Most of this removal was probably via lymphatic and blood vessels, into both of which peroxidase rapidly passed after ductal injection. At 5 hours after the HRP injection only very weak interstitial staining was present and at later times none was detected. An inflammatory reaction occurred in the gland, starting within minutes after the injection of this foreign protein and reaching a peak after about 12 hours. The events in dogs and those occurring in rabbits under similar experimental conditions have been compared. This study has given some indication how foreign substances may be distributed after retrograde injection into salivary glands.