Study of the characteristics of the inotropic effect of insulin in rabbit papillary muscle.

The effect of insulin was examined with emphasis on the alteration in the force-frequency relation. The results show that insulin does not change the time to peak tension nor the time of contraction. The inotropic effect was significant and did not depend upon the frequency of stimulation. However, there was a definite dependence of the magnitude of the inotropic effect on temperature. Previous studies have indicated that the inotropic effect is not a result of increased substrate availability or changes in cAMP phosphodiesterase activity. These results and those reported here are consistant with the hypothesis that insulin's inotropic effect is due to increases in intracellular Ca++.