RESUMEN
It has been stated that curare has no direct effect upon the heart because the cardiac muscle is deprived of nicotine receptors. While performing an experimental work, we noticed that when high doses of curare were administered to frogs, a change in cardiac activity occurred. In order to elucidate whether the cardiac effects of curare wee the results of a direct action or a reflex response, we studie the effects of increasing doses of d-tubocurarine on the rate and contractility of 8 isolated and perfused frogs'hearts. After testing the d-tubocurarine effects on the heart rate and contractility, we added either acetylcholine, atropine, atenonol or verapamil in orden to find out whether any change ocurred in the cardiac effects produced byd-tubocurarine. Thirty seven measurements were carriet out and it wasfound that 1) high doses (between 1 and 15 micrograms) of d-tubocurarine produced a highly significant decrease in heart rate an contractility; 2) d-tubocurarine did not avoid the acetycholine effect; 3) atropine, atenonol and verapamil did not interfere with d-tubocurarine effects. We conclude that high doses of d-tubocurarine produce "dosis-dependent" heart rate and contratility reductions. These effects are not mediated by muscarinic receptors beta-1 receptors or the show calcium channels