INTERSTITIAL NOREPINEPHRINE LEVEL BY CARDIAC MICRODIALYSIS CORRELATESWITH VENTRICULAR CONTRACTILITY

Although a cardiac microdialysis technique has made it possible to est imate myocardial interstitial norepinephrine (NE) levels, whether such levels reflect the local NE concentration that would regulate ventric ular contractility remains unknown. If such levels indicate locally re gulating NE concentration, then ventricular contractility should be a unique function of the interstitial NE level regardless of how the lat ter is altered. To examine this hypothesis, we altered the interstitia l NE level endogenously by stimulating the cardiac sympathetic nerves at 1 and 2 Hz while monitoring ventricular contractility. We also alte red the interstitial NE level exogenously by means of intravenous NE i nfusions at 10 and 40 mu g . kg(-1) . h(-1). The basal NE levels did n ot differ between the stimulation and the infusion experiments (42.9 /- 11.2 vs. 40.1 +/- 6.2 pg/ml, means +/- SE). The slopes of regressio n lines relating ventricular contractility and interstitial NE level w ere also not different between the two experiments [1.13 +/- 0.20 vs. 1.17 +/- 0.20%/(pg/ml), means +/- SE]. We conclude that the interstiti al NE level estimated by cardiac microdialysis reflects the local NE c oncentration regulating ventricular contractility.