Cardiovascular effects of acute changes in extracellular ionized calcium concentration induced by citrate and CaCl2 infusions in conscious, chronically instrumented dogs and their interactions with ganglionic blockade.

ABSTRACT

To assess the hemodynamic effects of acute changes in extracellular ionized calcium concentration, [Ca2+], seven dogs were chronically instrumented to measure heart rate, aortic, left atrial, and left ventricular (LV) pressures, cardiac output, and coronary and renal blood flows. [Ca2+] was lowered 0.35 mmol.l-1 by citrate infusion and then increased 0.35 mmol.l-1 above control level by CaCl2 infusions. This protocol was performed in the conscious dogs with and without ganglionic blockade (chlorisondamine 2 mg.kg-1). LV dP/dtmax decreased at low [Ca2+] and increased at high [Ca2+] during all conditions. The other hemodynamic variables measured were only slightly changed by changing [Ca2+] without ganglionic blockade and surprisingly even less with ganglionic blockade. Therefore, the lesser hemodynamic effects induced by acute changes in [Ca2+] in the conscious compared with anesthetized dogs cannot be explained by the depressant effects of the anesthetics upon the autonomic nervous system. We have suggested that the binding of Mg2+ to citrate may be of importance for the minor hemodynamic effects in the conscious dogs.