The effect of thiamine on the contractile responses of the isolated heart muscle.

Isolated papillary muscles of cats were exposed to increasing concentrations of thiamine during which the contractile response of myocardium to stimulation were measured. The results indicate that thiamine has no direct negative inotropic effect on the isolated heart muscle over a wide concentration range (0.1-1 mmol/l). Higher concentrations resulted in a concentration-related depression of all variables. The data indicate that thiamine in high doses as sometimes used in anesthesia (greater than 50 mg/kg) does not inhibit the contractile state of the myocardium. Blood pressure falls after massive doses of intravenous vitamin B1 are probably due to the synaptic blockade which is induced by the compound.