The Effect of Vitamin D3 Deficiency on the Isolated Chick Heart: Hemodynamic, P-31 NMR and Membrane Studies

The purpose of this study was to investigate whether vitamin D3 deficiency affects the cardiac function of chick hearts directly or whether the influence is secondary through the hormoneʹs effect on serum calcium levels. To this end, three experimental groups were studied: (a) the control group of vitamin D3supplemented chicks, Ds, (b) vitamin D3deficient chicks, Dd, and (c) vitamin D3 supplemented hypocalcemic chicks raised on decreased calcium levels, Dh. The three groups were compared by checking hemodynamic, metabolic and membrane parameters. Total and ionized serum calcium concentrations in the Dh and Dd groups were found to be lower than in the Ds group. Perfusion of the isolated hearts with solutions containing various calcium concentrations (1, 1.5 and 2.5 mM) induced enhanced contractility levels, the magnitude of which was dependent on the difference between the in vivo and perfusate calcium levels. Thus, the inotropic effect was similar and more enhanced for the two hypocalcemic groups. The differences in hemodynamic behaviour could not be explained by variations in the levels of the high energy compounds and acidity, since similar ATP, creatine phosphate and intracellular pH levels were detected for both Ds and Dd groups. However, membrane studies revealed an increase in the number of slow calcium channels for the two hypocalcemic groups and this may be the possible mechanism for the differences in the contractile activity. In conclusion, our study strongly suggests that the effects of vitamin D3 on the heart is mediated only indirectly through its effect on serum calcium levels.