Effect of pyridostigmine pretreatment on cardiorespiratory function in tabun poisoning

Abstract

1 The effect of pyridostigmine on cardiorespiratory func tion after oxime+atropine injection was investigated in tabun poisoned guinea-pigs and without tabun poisoning.

2 The trachea, a carotid artery and jugular vein were can nulated in female urethane-anaesthetised Pirbright white guinea-pigs. After baseline measurements the ani mals received pyridostigmine (0.05 μmol kg^-1) and 30 min later atropine (29.5 μmol kg^-1) plus obidoxime, HI 6 or HL6 7 (30 or 100 μmol kg^-1) or tabun (1.85 μmol kg^-1 = 5 x LD₅₀) followed by oxime+atropine treatment (all i.v.). Erythrocyte, brain and diaphragm acetyl cholinesterase (AChE) activity were determined. Similar groups without pretreatment were included for compar ison.

3 Pyridostigmine aggravated the oxime+atropine induced hypotension and prevented the increase in heart rate but not the respiratory stimulation. The pyridostigmine inhibited AChE recovered only in the 100 μmol kg^-1 kg oxime groups at the end of the experiment.

4 In tabun poisoning, pyridostigmine reduced the oxime+atropine induced circulatory recovery and decreased the survival time and rate. It did not affect the therapeutic oxime+atropine effect on respiratory function.

5 These results suggest that pyridostigmine enhances oxime+atropine related circulatory depression which may be the reason for the reduced efficacy of oxime+atropine treatment in tabun poisoning. The pos sible mechanisms are discussed.