Evaluation of a reservoir in the main excretory duct of rat submaxillary gland.

Cannulation of salivary gland main excretory duct at its oral opening is routinely used for collecting fluid, in situ, from the luminally perfused duct, or saliva from the stimulated gland. For perfusion of the main excretory duct, in situ, or for saliva collection, rat submaxillary gland is often the organ of choice, since electrolyte transport occurs at high rates both in the whole gland and in the main excretory duct. Recently, it has been reported that there is a pouchlike dilatation of the main excretory duct at its oral end, and that this dilatation may serve as a fluid reservoir. Because of possible effects of such a reservoir on measurements of electrolyte transport by the whole gland or the main duct segment, the size and form of the reservoir have now been examined. For this, techniques of histology, radiography, and microcatherization were employed. It was found that, while the functional volume of the reservoir exceeds that of the main duct proper, the time needed for displacement of reservoir fluid by perfusate or saliva would probably be only on the order of 1-3 min at higher rates of saliva or perfusate flow. Therefore, if adequate allowance is made for equilibration time, collection of saliva or luminal perfusate by oral cannula seems justified.