Abstract
Summary
Atria from fed and starved rats developed essentially the same tension and are equally stable in glucose medium. Contraction is depressed in glucose-free medium and pyruvate or lactate (2.75-S.5 mM) partially restore the tension developed, but higher concentrations of pyruvate (11 mM) produce slower and less sustained recovery. Readmittance of glucose fully restores developed tension but has little effect in the presence of 11 mM pyruvate. In glucose medium, 2.75 mM pyruvate stimulates contractility slightly, 5.5 mM pyruvate has no effect, and 11-22 mM pyruvate depresses. This depression occurs even when the entry of pyruvate into the tricarboxylate cycle is prevented by arse-nite. Lactate (2.75-5.5 mM) produces stimulating effects somewhat more marked than those of pyruvate but at higher concentrations (11-22 mM) is not quite depressant. The uptake or utilization of glucose through the Embden-Meyerhof pathway seems to be important for a fraction of atrial contractility, and thus high concentrations of pyruvate or lactate might depress by altering some phase of the initial metabolism of glucose.
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