Campbell, Hillary, Krishnan Ravi, Emigdio Bravo, and C. Tissa Kappagoda. Effect of Diazinon PLUS on rapidly adapting receptors in the rabbit. J. Appl. Physiol. 81(6): 2604-2610, 1996.The effects of Diazinon PLUS aerosol on the activities of rapidly adapting receptors (RARs) and slowly adapting receptors (SAR) of the airways were investigated in anesthetized rabbits. The effects on both the baseline activity and the responses to stimulation by increasing mean left atrial pressure were examined. Action potentials were recorded from the left cervical vagus nerve. Aerosols (particle size 3 µm) were generated by a Mini-HEART nebulizer. We observed that an aerosol of Diazinon PLUS (1:10 vol/vol dilution in normal saline) decreased the baseline RAR activity (n = 10) significantly (P < 0.05) from 209 ± 77 to 120 ± 40 impulses/min. In the post-Diazinon PLUS control period, the RAR activity recovered partially to 185 ± 75 impulses/min and decreased significantly to 131 ± 52 impulses/min (P < 0.05) after a second exposure of Diazinon PLUS (undiluted) aerosol. Aerosols of normal saline in the control state did not produce a significant change in the RAR activity. A group of SAR (n = 8) were examined under similar conditions, and it was found that only the exposure to Diazinon PLUS (undiluted) aerosol decreased the activity significantly (P < 0.05) from 1,536 ± 206 to 1,367 ± 182 impulses/min. The effect of Diazinon PLUS on the response to increasing mean left atrial pressure was examined in seven RARs. In the control state, RAR activity increased significantly (P < 0.05) during elevation of mean left atrial pressure. This response was abolished after exposure to Diazinon PLUS. These findings suggest that diazinon may interfere with airway defense mechanisms by reducing the activity of RARs.