Search

In vivo microdialysis coupled with liquid chromatography was developed for the continuous monitoring of brain neurochemicals during cerebral ischemia in awake, free moving gerbils. The dead volume of the microdialysis system was estimated to be less than 30 microl. The detection limits of the present assay were 0.2 to 2.0 microM for analytes at a signal to noise ratio of five. To validate this assay, a focal cerebral ischemia was produced by occlusion of one common carotid artery for 60 min and then reperfusion for additional 3 h in awake gerbils. A microdialysis probe was inserted into the striatum of the gerbil. Dialysates were autoinjected and analyzed extracellular pyruvate, lactate, and ascorbic acid by liquid chromatography with a UV detector during cerebral ischemia. Significant changes of pyruvate and the lactate/pyruvate ratio were observed. Biphasic and dynamic changes in ascorbic acid and lactate were proposed to correlate a secondary damage. This assay can be used as a tool to study dynamic changes of brain neurochemicals in awake animals.

An improved high performance liquid chromatographic assay for plasma-unbound atenolol is described. The assay has a wide range (10–5000 ng ml−1) of linearity and a detection limit of 5 ng ml−1 (or 0.1 ng per injection) with acceptable intra- and inter-assay reproducibilities using small volumes of plasma (100 μl). Following administration of a single dose of atenolol to the rat, nine blood samples were collected over a period of 8 h. These samples were analyzed for atenolol concentrations by a sensitive and specific microbore high performance liquid chromatograph with a photodiode-array detector. This multi-channel detector was used to acquire spectral information on atenolol and demonstrated a superior performance in comparison to all other techniques in that both qualitative and quantitative information were acquired with the system. Because of its sensitivity and applicability to plasma analysis, the assay can be used for pharmacokinetic studies and is valuable in therapeutic drug monitoring.

The effect of magnesium supplementation on exercise performance remains controversial. In the present study, the effects of magnesium sulfate on exercise performance and blood glucose metabolism were examined. In order to provide a non-invasive measure of continuous exercise, we developed an auto-blood sampling system was coupled to a microdialysis analyzer to detect the dynamic changes in glucose metabolism in conscious and freely moving gerbils subjected to forced swimming. Gerbils were pretreated with saline or magnesium sulfate (90 mg kg−1, ip) 30 min before exercise. The duration times were significantly increased by 71% in the magnesium sulfate-treated groups (p < 0.01) when compared with those in the control. Another group of gerbils were subjected to blood sampling assay. A catheter was implanted in the jugular vein of each gerbil for collecting blood samples by the computer-aided blood sampler. The basal levels of plasma glucose, lactate, and magnesium were 6,245 ± 662, 1,067 ± 309, and 590 ± 50 μM, respectively, with no significant difference between groups. Plasma glucose, lactate, and magnesium levels increased to 134 and 204%, 369 and 220%, and 155 and 422% of basal levels during swimming in both the control and magnesium sulfate-treated groups, respectively (p < 0.05). Pretreatment with magnesium sulfate elevated glucose and magnesium levels to 175 and 302% of the basal levels (p < 0.05), respectively, whereas pretreatment with magnesium sulfate reduced the lactate levels 150% of the basal level (p < 0.05) during swimming. Furthermore, the magnesium levels increased to about 152–422% of basal levels during forced swimming and the recovery period (p < 0.05). The present study demonstrates that magnesium sulfate improved the duration time of forced swimming exercise. In addition, magnesium raised glucose levels and attenuated lactate levels during forced swimming. These results indicate that positive effects of magnesium supplementation may contribute to the enhancement of exercise performance in athletes.

Rapid on-line microdialysis coupled with liquid chromatography was developed for the continuous monitoring of brain neurochemicals during cerebral ischemia. Isocratic separation of these analytes was achieved within 3 min, hence, over 80 analyses could be performed in a 4-h experiment. The dead volume of the microdialysis system was estimated to be less than 10 microl. The detection limits of the present assay, at a signal-to-noise ratio of five, were 2.0, 0.2 and 0.5 microM, for lactic acid, pyruvate and ascorbic acid, respectively. To validate this assay, a transient ischemia was produced by occlusion of two common carotid arteries for 10 min in an anesthetized gerbil. A microdialysis probe was inserted into the striatum of the gerbil to simultaneously monitor pyruvate, lactic acid and ascorbic acid during cerebral ischemia. Significant and dynamic changes in these analytes could be resolved in 3-min intervals. This rapid assay can be used as a tool to study dynamic changes in neurochemicals of the brain, such as during cerebral ischemia.