The prevention by sulphydryl compounds of the toxicity in the cat of 2,6-dimethoxyphenol and its morpholinopropionyl ester.

1 Intravenous (minus)-2,6-dimethoxyphenyl-2-morpholinopropionate hydrochloride (M&B 16,573) produced anaesthesia of short duration in the mouse, rat, rabbit, cat, dog and monkey. In the cat but not in other species, a severe and usually fatal toxic reaction was seen 1-2 h after administration. 2 This toxic reaction but not the anaesthetic properties of M&B 16,573 was prevented by the intravenous administration of cysteine or N-acetylcysteine. Cysteamine or dimercaprol were ineffective. 3 Intravenous administration of 2,6-dimethoxyphenol or 2,6-dimethoxyquinol in the cat produced a response similar to the delayed toxic effects of M&B 16,573 but not preceded by anaesthesia. The toxic effects of these compounds were prevented by cysteine. 4 Intravenous 4-allyl-2,6-dimethoxyphenyl-2-morpholinopropionate hydrochloride produced anaesthesia in the cat without the delayed toxic effects seen after M&B 16,573. 5 The acute toxicity of 2,6-dimethoxyquinol in mice was reduced by the administration of cysteine or N-acetylcysteine. 6 It is postulated that the delayed effects produced by M&B 16,573 in the cat are due to the formation of 2,6-dimethoxyquinol and 2,6-dimethoxybenzoquinone in this species, the toxicity of the latter being reduced by sulphydryl compounds.