1. We have collected secretions from a segment of trachea in the neck of cats anaesthetized with chloralose. At the start of experiments sodium [35S]sulphate and [3H]glucose were given into the segment to radiolabel secretions by biosynthesis. Subsequently, changes in output of radiolabelled macromolecules were used to indicate changes in mucin secretion rate.

2. Cigarette smoke, diluted to 10% by volume, was passed through the larynx or through the tracheal segment, or given into the lower airway. Control insufflations of air were given by the same routes.

3. When cigarette smoke was passed through the larynx, it did not change the secretion rate of radio-labelled mucins into the tracheal segment.

4. Cigarette smoke, given directly into the tracheal segment, stimulated the output of 35S-labelled mucins. Cutting the autonomic nerves to the segment failed to alter the response to cigarette smoke, but ganglion blockade with pentolinium abolished it.

5. Cigarette smoke given into the lower airways and lungs stimulated the output of radiolabelled mucins into the segment. Denervation of the segment failed to prevent this, but ganglion blockade abolished the response.

6. Measurements of plasma nicotine concentrations in some experiments showed that nicotine was absorbed from smoke in the lower airway and also suggested some absorption of nicotine from the tracheal segment.

7. We conclude that nicotine, absorbed either directly into the tracheal wall or via the blood, can stimulate the autonomic ganglia which innervate airway submucosal mucous glands. This mechanism outweighed the effect of airway irritant reflexes in these experiments.

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