Effect of furosemide on the response of laryngeal receptors to low-chloride solutions.

Laryngeal irritant receptors are stimulated by water and solutions lacking chloride ions, such as isotonic dextrose. It has been reported that furosemide (frusemide) reduces cough evoked by inhalation of low-chloride solutions. We studied the effect of furosemide on the response of laryngeal receptors to isotonic dextrose. Experiments were performed on nine dogs anaesthetized, spontaneously breathing through a tracheostomy, and with the upper airway functionally isolated. We recorded the activity of 13 laryngeal irritant receptors. Isotonic dextrose (4 ml) was instilled into the laryngeal lumen, before and after administration of a furosemide solution (3.75 mg.ml-1) into the upper airway. Before furosemide, dextrose increased the activity of the 13 receptors from 1.0 +/- 0.5 to 25.0 +/- 3.5 impulses (imp).s-1 (average discharge in the first 10 s of activation) and, 1-2 min after furosemide, from 0.3 +/- 0.2 to 13.4 +/- 3.2 imp.s-1; the difference between the stimulation by dextrose before and after furosemide was statistically significant. In contrast, the response to distilled water of four respiratory-modulated mechano-receptors (known to be activated by low-osmolality solutions) was not modified by furosemide. These results suggest that the furosemide-mediated inhibition of cough induced by inhalation of low-chloride solutions is, at least in part, due to the inhibitory effect of this substance on irritant receptor stimulation.