Abstract
It has been reported that thiamine and its derivatives in large dosis weaken the heart action. However, whether these vitamins in any concentration decrease the contractile power or not is remained to be further investisated. In order to elucidate this problem, the following investigations were performed. (1) Thiamine hydrochloride, thiamine disulfide, oxythiamine, thiamine propyldisulfide, and thiamine tetrahydrofurfuryldisulfide in large dosis increased the contractility of a recycling toad heart. Particularly, the latter two derivatives revealed such marked inotropic action that kymographically recorded contractile deflection, aortic pressure and cardiac output were twicely increased in a final concentration of 1.4×10^<-3>M. Thiamine diphosphate revealed no inotropic action. On the contrary, thiaminic acid depressed the contractile power. (2) Thiamine propyldisulfide (1.4×10^<-3>M) prolonged the latent period and repolarization phase of the transmembrane action potential of toad heart ventricle. (3) Using a specially devised Warburg chamber which enclosed a recycling toad heart, the effects of thiamine propyldisulfide on the oxygen consumption, aortic pressure and cardiac output were studied. The addition of this drug (4.2×10^<-4>M) was followed by the increase of oxygen consumption and external work of the heart. However, cardiac efficiency was never decreased.
