The effects of ajmaline, cocaine, diphenylhydantoin, lidocaine, procainamide, propranolol, quinidine and trimetazidine on the contractility, functional refractory period and responsibility to electrical stimuli of rat isolated papillary muscle were studied and the following results were obtained:
1) Ajmaline, procainamide and trimetazidine decreased scarcely the contractile tension of the muscle in the concentration of 10
-6,10
-3 or 10
-4 (g/ml) respectively, quinidine, propranolol, cocaine and diphenylhydantoin decreased remarkably it in the concentration of 10
-6,10
-8,10
-6 or 5 ×10
-6 (g/ml) respectively. However, lidocaine decreased the muscle tension in a concentration of 5 x10
-5(g/ml), but did scarcely it in the lower concentration.
2) The func t ional refractory period of the muscle was increased by lidocaine, ajmaline, quinidine or procainamide in the concentration of 5 ×10
-6,5 ×10
-7,5 ×10
-6 or 5 ×10
-4(g/ml) respectively, The period was slightly increased by propranolol or diphenylhydaintoin in each concentration of 10
-5(g/ml) and that was scarcely influenced by trimetazidine or cocaine in the concentration of 10
-5 or 10
-4(g/ml) respectively.
3) The response pattern of the muscle to electrical stimuli of 60 to 660 cycles per minute was studied and found to be influenced in the presence of lidocaine, ajmaline, quinidine or procainamide: these drugs, in the concentration of 10
-6,10
-7,10
-6 or 4 × 10
-4(g/ml) respectively, suppressed the muscle responses to electrical stimuli of low frequencies and this effect was seen remarkably in lidocaine and ajmaline. This kind of effect of propranolol was seen when the stimulation frequencies were low and it was characteristic in lower concentrations than 10
-8(g/ml). Cocaine, trimetazidine and diphenylhydantoin, in any concentration, showed scarcely this effect when the stimulation frequencies were high or low.
From these results it was assumed that ajmaline, lidocaine, procainamide and propranolol may act to depress the ectopic contractions of rat papillary muscle and that quinidine is the depressant of the papillary muscle of rat ventricle.
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