EFFECT OF DIAZINON PLUS ON RAPIDLY ADAPTING RECEPTORS IN THE RABBIT

The effects of Diazinon PLUS aerosol on the activities of rapidly adap ting receptors (RARs) and slowly adapting receptors (SAR) of the airwa ys 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 fr om the left cervical vagus nerve. Aerosols (particle size 3 mu m) mere generated by a Mini-HEART nebulizer. We observed that an aerosol of D iazinon PLUS (1:10 vol/vol dilution in normal saline decreased the bas eline RAR activity (n = 10) significantly (P < 0.05) from 209 +/- 77 t o 120 +/- 40 impulses/min. in the post-Diazinon PLUS control period, t he RAR activity recovered partially to 185 +/- 75 impulses/min and dec reased significantly to 131 +/- 52 impulses/min (P < 0.05) after a sec ond exposure of Diazinon PLUS (undiluted) aerosol. Aerosols of normal saline in the control state did not produce a significant change in th e RAR activity. A group of SAR (n = 8) were examined under similar con ditions, and it was found that only the exposure to Diazinon PLUS (und iluted) aerosol decreased the activity significantly (P < 0.05) from 1 ,536 +/- 206 to 1,367 +/- 182 impulses/min. The effect of Diazinon PLU S on the response to increasing mean left atrial pressure was examined in seven RARs. In the control state, RAR activity increased significa ntly (P < 0.05) during elevation of mean left atrial pressure. This re sponse was abolished after exposure to Diazinon PLUS. These findings s uggest that diazinon may interfere with airway defense mechanisms by r educing the activity of RARs.