pH of mucus in rat trachea.

The pH of the mucous coat of the trachea was measured in vivo through a tracheal window in anesthetized rats. Readings ranged from 7.42 to 7.57 and averaged 7.52 +/- 0.05 (SD) pH units. Injections of pilocarpine (cholinomimetic) were followed by a statistically significant decrease in pH to 7.46 +/- 0.05 (SD) and a subsequent return to initial values. These readings are in the region of what is accepted as the gel point of mucus. This closeness to the inflection point between sol and gel was not reported before and may explain some of the in situ flow properties of mucus.