Role of parotid ducts in secretion of hypotonic saliva

Abstract

A technique is described whereby intraglandular concentration patterns of saliva are developed in the resting dog parotid gland between periods of maximum stimulation. The period of rest was varied from 5 to 70 seconds. The gland was stimulated maximally following this rest period and each drop of saliva (averaging 20 mg) was separately collected and analyzed. This fluid thus represented saliva that was within the gland during the rest period until saliva newly formed in the acinus replaced it. It was found that sodium and chloride concentrations were lowered in a relatively distal segment of the gland and were raised in a more proximal segment. The depth of fall of sodium and chloride was related to the length of time the fluid remained in the gland. No change was noted in the potassium concentration until it rose in a relatively proximal portion. The results suggest that there are at least two sites within the gland which transfer electrolyte; a distal locus which reabsorbs sodium chloride and a proximal locus which elaborates relatively isotonic fluid. The suggestion is made that the former represents the ducts and the latter represents the acinus.