Salivary excretion of urea in dogs

The salivary excretion of urea was investigated by collecting parotid saliva (Pr) and mandibular-sublingual saliva (MS) separately in beagle dogs. (1) After intravenous administration of urea (1.5 g/kg), urea concentrations in both Pr and MS were well correlated to but were lower than those in plasma. Urea concentrations in MS were significantly lower than those in Pr (p less than 0.05), indicating that there was glandular difference in salivary excretion of urea. (2) This glandular difference was not explained by Matin's equation, even if all variation factors in this equation were considered. (3) At relatively low salivary flow rates, the increase in saliva/plasma urea concentration ratio (S/P ratio) for both Pr and MS was found in the experiments for endogenous urea. (4) At relatively low salivary flow rates, glandular difference was observed in the S/P ratios of sodium ion. (5) Salivary clearance of urea was highly dependent on salivary flow rate under stimulated condition for salivation, and mean value of the salivary clearance of urea was about 20% of its total body clearance.