SUMMARY

The neuromuscular block induced in cats by depolarizing drugs was intensified and the effect of tubocurarine was reduced by intravenous infusions of propranolol, although by themselves they did not affect contraction of skeletal muscle. The use of propranolol in the treatment of ar-rhythmias during anaesthesia has recently been discussed by Vickers (1966). After intra-arterial injection of comparatively large doses, proprano-lol, like the structurally related pronethalol (Tiirker and Kiran, 1965), augments the action of neuromuscular blocking agents (Wislicki and Rosenblum, 1967). It has been shown that pro-pranolol not only blocks adrenergic beta-receptors but that it also has a sympathomimetic effect, apparently by inducing a release of catechol-amines from the adrenal medulla (Kayaalp and Kiran, 1966). Since, under different conditions, sympathomimetic amines may antagonize or in-tensify the action of curarizing drugs (Bowman and Raper, 1966) we investigated whether smaller amounts of propranolol can modify the action of neuromuscular blocking substances. METHODS Cats were anaesthetized with chloralose 40 mg/kg and urethane 1 g/kg, given intravenously after ether induction. The tendons of the right tibialis anterior and soleus muscles were cut at their in-sertions and attached to semi-isometric trans-ducers. The ipsilateral sciatic nerve was sectioned near the sciatic notch and mounted on shielded silver electrodes. The leg was secured in a rigid frame and the muscles were placed under a ten-sion of approximately 200 g. The nerve wa