Abstract: Lactate derived from glucose can serve as an energy source in the brain. However, it is not certain how much lactate, directly taken from the blood circulation, may replace glucose as an energy source. This study aimed to estimate the uptake, release, and utilization of lactate entering the brain from the blood circulation. The change in cerebral venous-arterial glucose and lactate differences after lactate infusions in the anesthetized rat were measured. Ultrafiltration probes were placed in the aorta and in the jugular vein, and connected to a flow injection analysis system with biosensors for glucose and lactate. Measurements were taken every minute. Lactate efflux was observed at baseline, whereas an influx of lactate was seen during lactate infusion. Immediately after the infusion there was a net efflux of lactate from the brain. The results suggest that the majority of lactate moving into the brain is not used as an energy substrate, and that lactate does not replace glucose as an energy source. Instead, the authors propose the concept of a lactate pool in the brain that can be filled and emptied in accordance with the blood lactate concentration, but which is not used as an energy supply for cerebral metabolism.

Abstract: Human serum (4 µL) was diluted 50- to 100-fold with PBS of pH 7.4 containing 2 mM EDTA and 0.5 mM ferrocenemonocarboxylic acid (buffer A), then left for >6 min before analysis. Portions (2.5 µL) were injected into buffer A and carried at 150 µL/min to a sandwich-type enzyme reactor kept at 30°C containing either uricase and horseradish peroxidase or horseradish peroxidase and glucose oxidase physically co-immobilized between cellulose nitrate filters. The reduction current was measured using a vitreous C electrode held at 0 mV vs. Ag/AgCl and a PTFE/C counter electrode. The calibration graphs were linear for up to 200 µM-uric acid and 1 mM glucose; the detection limits were 30 and 60 nM, respectively. The recoveries of uric acid and glucose were 98-102% and 98-109%, respectively, the within-run RSD were 2% and 3%, respectively (n = 10), and the between-day RSD were 4% and 3%, respectively (n = 10). The results agreed with those obtained using conventional clinical laboratory methods. Sample throughput was 60/h. An enzyme-based flow injection amperometric analysis system for monitoring of uric acid and glucose is described. The oxidase and peroxidase enzymes are physically coimmobilized in a sandwich-type reactor and ferrocene serves as a mediator. The assays are based on the measurement of a reduction current resulting from the enzymatic reactions, at a glassy carbon electrode held at 0.00 mV (vs. Ag/AgCl). The high selectivity (ascorbic acid did not interfere) is coupled to high sensitivity (a detection limit of 30 and 60 nmol/l for uric acid and glucose, respectively; signal/noise = 3) and good stability (the enzymes remained active for more than 6 weeks at 30°C). The usefulness of the assay in clinical chemistry is illustrated by the measurement of human serum uric acid and glucose concentration. The results obtained were in fairly good agreement with those obtained using conventional hospital laboratory methods.

Abstract: Early detection of myocardial ischemia is of major importance in critical-care medicine. Changes of lactate or glucose levels in the cardial venous efflux may be useful parameters. We succeeded in integrating an ultrafiltration membrane in a cardiac catheter for continuous sampling. The ultrafiltrate was analyzed outside the body, resulting in a lag-time of about 24 min. Biosensors in a flow injection analysis system were used for minute by minute sample analyzes. The coronary sinus of pigs was catheterized to monitor the effects of 5, 15 or 45 min ischemia by coronary artery obstruction or myocardial stress by dobutamine infusion. A total of 27 h was monitored. The intravascular response time was 1.33±0.61 min (10-90%). Linear regression in vivo of blood and ultrafiltrate samples was 0.977 for lactate and 0.994 for glucose. Lactate levels rose 0.38±0.10 mM above baseline within 5 min after ischemia. Reperfusion was clearly marked by a promptly peaking lactate release (maximum 9.27 mM). Myocardial stress by dobutamine increased glucose but not lactate levels. Once, a wall effect was noted at the catheter tip. In vivo semi-continuous myocardial monitoring of absolute lactate and glucose concentrations was thus achieved by an ultrafiltration catheter. Ischemia and reperfusion can be detected very early by a lactate level rise. Further, development of the ultrafiltration catheter will be focused on the diagnostic potential of lactate monitoring for patients. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: An on-line in vitro perfusion technique is described that allows the continuous quantification of cellular glucose metabolism in vitro. Using biosensor technology, we measure glucose and lactate metabolism at a minute-to-minute time resolution for periods up to several days. The application of our perfusion-detection technique for in vitro monitoring is demonstrated in a wide variety of cells, including primary neuronal and astroglia cultures, yeast cells, and human lymphocytes. The method shows that variations in oxygen delivery or exposure to a noncompetitive pseudosubstrate (here 2-deoxyglucose) affects normal glucose metabolism. The innovative advantage of the present system is that, in contrast to other devices including a recently described system, metabolism per cell can be quantified. The potential of in vitro on-line monitoring is discussed for application in studying normal and abnormal metabolism, toxic and nontoxic drug effects, and human tissue biopsies.