Role of the Main Mandibular Excretory Duct in Salivary Excretion of Urea in Dogs

Abstract

The effect of passage through the main mandibular excretory duct on salivary excretion of urea was investigated using anesthetized dogs. Two kinds of mandibular saliva (pre-ductal saliva and post-ductal saliva) were collected from individual dogs. Pre-ductal and post-ductal mandibular saliva samples were collected individually via cannula tubing before and after flowing through the main mandibular excretory duct, respectively. Sublingual saliva was also collected to evaluate the effect of saliva passage through the non-striated duct. Salivation was evoked by electric nerve stimulation. The findings were as follows. (1) There was no significant difference between saliva/plasma concentration ratios (S/P ratios) of urea in the two mandibular salivas. (2) Salivary clearance of urea was not altered by the passage of saliva through the main mandibular excretory duct. (3) In this duct, sodium ion was slightly reabsorbed, but the S/P ratio of potassium ion was almost constant. Therefore, apparent water reabsorption may not take place in this duct. (4) From these results, it was concluded that the main mandibular excretory duct of the dog has no influence on salivary excretion of urea. (5) The mean S/P ratio of urea in sublingual saliva (1.25) was much higher than in mandibular saliva (0.330 to 0.345). Therefore, it is considered that urea might be either reabsorbed or diluted in the striated duct.