The possible relation between mastication and parotid secretion in the rabbit.

Salivary flow has been recorded from conscious rabbits during 1 min periods whilst continuously chewing standard laboratory dry pellets or pieces of carrot and, in some animals, a mash of pellets with water. Flow was measured using contact drop recorders or a continuous flow recorder via Polythene tubes permanently inserted into one or both parotid ducts. Large variations in flow were obtained with unilateral recordings particularly during dry pellet chewing. Bilateral recordings showed that the flow was always greater on one side than on the other and that dominant secretion alternated from side to side in an apparently random manner. Rabbits chew unilaterally. Videotaped recordings of chewing movements showed that the greater secretion was always produced on the chewing side. To test the possibility that drying of the oral mucosa, or the prolonged hardness of the pellets may result in higher flow rates in animals with cannulated ducts than would normally be seen in intact animals, water was injected downstream into the mouth through a third cannula. This was inserted in an anterograde direction in the parotid duct on one side. Significant reductions in flow were recorded during dry pellet eating, but not during carrot eating. When animals were fed a soft pellet mash, salivary flow was significantly lower than with dry pellets. Recordings have been made from strain gauges attached to the ascending ramus of the mandible. Previous findings that dry pellets produce greater strain than carrots have been confirmed. It has also been shown that less strain is produced with soft pellet mash. The strain gauge data suggested that a relation exists between masticatory force and parotid salivary flow. The results are compatible with the hypothesis that intra-oral mechanoreceptors may be involved in a masticatory-salivary reflex.