The composition of tracheal mucus and the nervous control of its secretion in the cat

Abstract

A new method for measuring the output of mucus proteins (specifically the sulphated glycoproteins) from the trachea of anaesthetized cats is described. The method has been used to measure the effects of nervous and pharmacological stimuli on mucus output and the mucus collected has been fractionated and analysed chemically. There is a resting output of mucus which does not depend on autonomic nerves. We have shown that sympathetic nerve stimulation and sympathomimetic amines increase tracheal mucus output. These effects were prevented by $\beta $-adrenergic blocking agents but not by $\alpha $-adrenergic blockade. Sympathetic efferent fibres to tracheal mucus glands run through the stellate ganglia, then some of the fibres pass up into the lower part of the cervical sympathetic nerves before looping back into the chest and passing rostrally again to the trachea. We have confirmed that parasympathetic nerve (vagal) stimulation increases mucus protein output and shown that the strength of this effect is about the same as that of sympathetic nerve stimulation. Atropine blocked this effect. Pilocarpine, a parasympathomimetic agent, greatly increased mucus protein output. Chemical analysis of the secretions showed that they contained two groups of glycoproteins which could be separated by electrophoresis. Only the slower-moving of these was sulphated. Gel filtration on Sephadex G-200 and ion-exchange chromatography on DEAE-cellulose DE-52 showed that the $^{35}$S-sulphated material was heterogeneous in both molecular size and charge density. The principal monosaccharides in tracheal mucus glycoproteins are galactose, N-acetylglucosamine, N-acetylgalactosamine, fucose and sialic acid. Mannose was not detected. Three cell types contributed to the glycoprotein secretion of the cat trachea, mucous and serous cells of the submucosal glands and goblet cells of the overlying epithelium. The histochemical investigations suggest that most mucous and goblet cells produced a sulphated mucin; the results for the serous cells are ambiguous. Autoradiography confirms all three cell types produced sulphated secretions which were labelled when $^{35}$SO$_{4}$ was given intrasegmentally. The tracheal mucosa showed only minor degrees of damage in a small proportion of cases.