In-vitro investigation of a new neuromuscular relaxant, AH8165.

AH8165 was compared with other neuromuscular relaxants in an in-vitro rat phrenic nerve-diaphragm preparation. Concentrations of 6-10 mug/ml AH8165 produced progressive decreases in strength of concentration. AH8165 was 0.1 times as potent as d-tubocurarine, and its effects were more rapidly reversed by washing. The times to recovery from 90 per cent blockade were the same for succinylcholine and AH8165, but the time to recovery from 50 per cent blockade was shorter for succinylcholine than for AH8165. Neostigmine reversed blockade induced by d-tubocurarine to 80 per cent of control, while it reversed comparable blockade induced by AH8165 to only 40 per cent of control. Doses of 0.5 to 2 mug AH8165 produced contracture and increased the force of contraction of the superfused chick biventer cervicis muscle preparation. Doses of 8 to 32 mug produced decreased contracture followed by diminution of the strength of contraction. The authors conclude that AH8165 in low concentrations has a depolarizing action, which is obscured by nondepolarizing effects in higher concentrations. (Key words: Neuromuscular relaxants: AH8165.)