In vivo monitoring of myocardial interstitial norepinephrine by dialysis technique

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Abstract
To estimate local sympathetic nerve activity of the heart in vivo, we applied a dialysis technique to the heart and attempted to monitor norepinephrine levels in local myocardial interstitial fluid. The dialysis probe consisted of an 18 x 0.31 mm dialysis fiber with a 50,000-mol wt cutoff. When the probe was perfused at 5 microliters/min in vitro, the average relative recovery rate of norepinephrine was 31.3 +/- 0.6%. Dialysis probes were implanted in the left ventricular lateral wall of the beating heart in anesthetized cats and perfused with Ringer solution at 5 microliters/min. Dialysate norepinephrine concentration was measured using high-performance liquid chromatography with electrochemical detection. 1) After probe implantation, dialysate norepinephrine concentration decreased over the first 120 min and then reached an almost steady level (41.1 +/- 4.7 pg/ml). 2) Electrical stimulation of the left stellate ganglion increased dialysate norepinephrine concentration significantly, from control level of 39.0 +/- 5.8 to 82.0 +/- 7.7 pg/ml (P less than 0.01). After stimulation, dialysate norepinephrine concentration returned to the prestimulation level. The dialysis technique using high-performance liquid chromatography permits monitoring of norepinephrine levels in local myocardial interstitial fluid and detection of changes in local cardiac sympathetic nerve activity in vivo.

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