Inhibitory effect of calcium antagonists on the depletion of cardiac norepinephrine during postischemic reperfusion.

We have investigated whether Ca2+ antagonists of the dihydropyridine type (nifedipine, nisoldipine, and nitrendipine) attenuate or abolish the ischemia-reperfusion-induced depletion of the cardiac stores of norepinephrine (NE). The experiments were performed using isolated, Langendorff-perfused rat hearts. Ischemia (global) was induced for 15 or 60 min at 37 degrees C and was followed by normothermic reperfusion. Left ventricular NE content was assayed by high-performance liquid chromatography with electrochemical detection. The continued presence of nifedipine (0.03 microM), nisoldipine (0.03 microM), or nitrendipine (0.03 microM) before and after the ischemic episode abolished the loss of NE caused by 15 min but not 60 min of ischemia and reperfusion. Nifedipine, 0.03 microM, but not diltiazem, 0.24-1.22 microM, or verapamil, 0.22-1.09 microM, attenuated (p less than 0.05) NE depletion when added only on reperfusion.