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.
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