The action of intravenous anaesthetic and central depressant drugs on the contractures elicited by tetraethylammonium in the chick biventer cervicis muscle.

A group of intravenous anaesthetic drugs was compared with methohexitone sodium for their ability to potentiate tetraethylammonium induced contractures of the chick biventer cervicis muscle (TEA test). The equipotent concentrations in the TEA test were: methohexitone 8.8 X 10(-5) M, propanidid 1.78 X 10(-4) M, althesin 3.58 X 10(-5) M (in terms of alphaxalone), etomidate 1.6 X 10(-4) M, thiopentone 2.13 X 10(-5) M and valium 4.95 X 10(-5) M. There was no relation between activity in the TEA test and excitatory muscular activity reported clinically. The central depressant drugs ethyl alcohol and urethane also potentiated TEA but they were only active in high concentrations (10(-1) - 10(-2) M). alpha-Chloralose was inactive but paraldehyde (3.8 X 10(-3) M) actually reduced TEA induced contractures. Lipophilicity is only one factor in determining activity in the TEA test, the ability to block Ca2+ reuptake may also be important.