Assessment of the presynaptic effect of atracurium. Train-of-four and tetanic stimulation in in vitro preparations.

The present experiments were designed to study the effect of atracurium on the contractile responses produced by repetitive motor nerve stimulation and by depolarizing drugs in frog, chick and rat skeletal muscle-nerve preparations, using electrophysiological and neurochemical techniques. The presynaptic effect of atracurium was assessed using train-of-four (2 Hz) and tetanic stimulation (50 Hz) in isolated chick and rat neuromuscular junctions. A further measure of the presynaptic effect of atracurium was examined by studying its effect on the uptake of labelled choline, 3H-methylcholine, in the control preparations. The effect of atracurium on postjunctional contractile responses of the chick isolated biventer cervicis skeletal muscle was studied using cholinergic drugs such as acetylcholine and tetraethylammonium. The results indicated that in addition to its postjunctional competitive and non-depolarizing blocking effect, atracurium may have a prejunctional inhibitory action at the neuromuscular junction. Atracurium reduced all the contractile responses produced by both electrical and chemical stimulation.