The nasal mucociliary apparatus. Correlation of structure and function in the rat.

Rats are used extensively in inhalation toxicologic studies, but little information is available on the rat nasal mucociliary apparatus. The function of the rat nasal mucociliary apparatus was studied in vitro by video analysis, and its structure was examined by light and electron microscopy. Video analysis permitted determination of mucus flow rate and ciliary beat frequency without disrupting mucociliary function. In different regions of the nose, there was a characteristic mucus flow rate, flow pattern, and ciliary beat frequency, with minimal interanimal variation. Analysis of data pairs revealed no evidence of a correlation between mucus flow rate and ciliary beat frequency, ciliary length, density of the ciliated cell population, or the products of these factors. Mucus was seen to flow over certain nonciliated areas, and it is proposed that the mucus is pulled over these areas. Mucus flow characteristics indicated that the hypophase was less viscous than, and moved in the same direction as, the epiphase. The nasal mucus was present as a continuous layer over the respiratory epithelium, and had an osmiophilic surface film, which was found to be made up of 2 separate membranous components. On the basis of these studies, it was concluded that the rat nasal mucociliary apparatus represents a useful and readily accessible model for in vitro studies of nasal mucociliary function.