Influence of the Rate of Secretion on the Urea Concentration of Saliva.

Abstract

Observations of Hench, 1 Schmitz 2 and others have shown that the concentration of urea in human saliva obtained by chewing paraffin averages about 80% of that of the blood. The published figures from which this average has been obtained show wide variations in different individuals. Those of Hench 1 vary from 50 to 130%, those of Schmitz 2 from 58 to 128%, and unpublished observations made in this laboratory in 1921 from 58 to 110%.

Specimens of saliva secreted at slow and at rapid rates were obtained from each of 16 individuals, and their urea concentrations (urea plus ammonia) compared with that of blood taken at the same time. The slow specimens were obtained without stimulation, the rapid ones by chewing paraffin. (Table I.)

All the subjects show a lower urea concentration in the rapidly secreted specimens, the average difference between slow and fast specimens being 46 mg. per 100 cc. The high figures obtained when the secretion rate was low are no doubt partly due to accumulated ammonium salts in the mouth, as noted by Hench. Since we could not be sure that this source of error was completely eliminated by preliminary washings of the mouth, a similar series of observations was made comparing the blood urea with that of saliva obtained from one parotid gland. Such saliva was found to contain only a negligible amount of ammonia. Solutions of tartaric acid (0.05% and 0.5%) were used as stimuli. The results are given in Table II.

The secretion rates in this table can not of course be compared with those in Table I, but all subjects show a diminution in urea concentration when the secretion rate is increased, averaging 7.2 mg. urea per 100 cc.