Determination of myocardial norepinephrine in freely moving rats using in vivo microdialysis sampling and liquid chromatography with dual-electrode amperometric detection

Abstract

Myocardial norepinephrine (NE) is considered a meaningful parameter for estimation of cardiac function. Long lasting changes in myocardial NE appear to be not only a consequence of pathologic processes in the myocardium, but may be a factor responsible for some diseases (e.g. increased propensity for arrhythmias or negative effect on left ventricular contractility in congestive heart failure). In this respect monitoring of myocardial NE is of great importance. A microdialysis sampling technique coupled with liquid chromatography with electrochemical detection (LCEC) was developed to measure the in vivo NE concentration in the myocardial interstitium of conscious, freely moving rats. LCEC using a dual-electrode amperometric detection in the series configuration provided detection limits for NE of 10 pg/ml in 20 microl microdialysis samples. Microdialysis probes of the linear design were implanted in the myocardial tissue in the periphery of the left descending coronary artery. The basal steady-state concentration of NE in myocardial dialysate of awake, freely moving rats was found to be 0.17+/-0.026 ng/ml. Delivery through the microdialysis probe of the NE reuptake inhibitor desipramine (DMI) at a concentration of 0.1 mM increased NE release to 153+/-13% of control. If the concentration of DMI in the perfusate was increased to 1.0 mM, NE release increased to only 166+/-21% of control.

Fig. 1

Schematic representation of a microdialysis probe implanted into the rat myocardium.

Fig. 2

Typical chromatograms of norepinephrine standard (A) and myocardial dialysate (B) using series configuration dual-electrode detection. Detection potentials: upstream electrode, +0.50 V; downstream electrode, +0.02 V.

Fig. 3

Influence of DMI delivery on interstitial myocardial norepinephrine. The basal concentration of NE was determined during perfusion with ACSF, perfusion with a 0.1 mM DMI solution was begun at time = 0 and continued for 70 min (*indicates statistically different from basal concentration with P < 0.0002).