Extracellular ascorbic acid fluctuation during the protective process of ischemic preconditioning in rabbit renal ischemia-reperfusion model measured / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Ascorbic acid has important antioxidant properties, and may play a role in the protective effects of ischemic preconditioning on later ischemia-reperfusion. Herein, we examined the role of endogenous extracellular ascorbic acid in ischemic preconditioning in the kidney.</p><p><b>METHODS</b>We developed a solitary rabbit kidney model where animals received ischemia-reperfusion only (ischemia-reperfusion group, n = 15) or ischemic preconditioning followed by ischemia-reperfusion (ischemic preconditioning group, n = 15). Ischemia-reperfusion was induced by occluding and loosening of the renal pedicle. The process of ischemic preconditioning included 15-minute brief ischemia and 10-minute reperfusion. In vivo microdialysis coupled with online electrochemical detection was used to determine levels of endogenous extracellular ascorbic acid in both groups. The extent of tissue damage was determined in kidney sections stained with hematoxylin and eosin. Serum creatinine and urea nitrogen were also detected to assess renal function.</p><p><b>RESULTS</b>During ischemia-reperfusion, the extracellular ascorbic acid concentration during ischemia increased rapidly to the peak level ((130.01 +/- 9.98)%), and then decreased slowly to near basal levels. Similar changes were observed during reperfusion (peak level, (126.78 +/- 18.24)%). In the ischemic preconditioning group there was a similar pattern of extracellular ascorbic acid concentration during ischemic preconditioning. However, the ascorbic acid level was significantly lower during the ischemia and early reperfusion stage compared to the ischemia-reperfusion group. Additionally, the extent of glomerular ischemic collapse, tubular dilation, tubular denudation, and loss of brush border were markedly attenuated in the ischemic preconditioning group. Levels of serum creatinine and urea nitrogen were also decreased significantly in the ischemic preconditioning group.</p><p><b>CONCLUSIONS</b>Ischemic preconditioning may protect renal tissue against ischemia-reperfusion injury via use of extracellular ascorbic acid. In vivo microdialysis coupled with online electrochemical detection is effective for continuous monitoring extracellular ascorbic acid in the renal cortex.</p>

Change of extracellular ascorbic acid in the brain cortex following ice water vestibular stimulation: an on-line electrochemical detection coupled with in vivo microdialysis sampling / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Ascorbic acid (AA) represents one of the most important enzyme co-factors, antioxidants and neuromodulators and plays an important role in the cerebral system. Increasing evidence has suggested that AA could treat certain kinds of vertigo diseases such as Meniere's disease. To elucidate the neurochemical functions associated with AA in vertigo, the change of extracellular AA in the brain cortex following caloric vestibular stimulation (CVS) was evaluated.</p><p><b>METHODS</b>An on-line electrochemical detection was coupled with in vivo microdialysis to continuously monitor the change of extracellular AA in the primary somatosensory (SI) area of guinea pigs following a caloric vestibular stimulation. Sixteen guinea pigs were divided into three groups, i.e., experimental group with irrigation of the ear canal with ice water (0 degrees C) (n = 8), and two control groups, one with irrigation of the ear canal with warm water (38 degrees C) (n = 4) and the other with irrigation of the auricle with ice water (n = 4).</p><p><b>RESULTS</b>In the experimental group, the ice water irrigation of the left external ear canal induced a horizontal nystagmus towards the right side lasting about 45 seconds. No nystagmus was induced by warm water irrigation of the external ear canal or by ice water irrigation of the auricle. The extracellular AA concentration significantly increased following the ice water vestibular stimulation, reaching a maximum of (130 +/- 20)% (n = 8) of the basal dialysate level (2.61 +/- 0.92) micromol/L (n = 8), lasting at least for an hour. AA level did not change distinctly after the irrigation of the left external ear canal with warm water or the irrigation of the auricle with ice water.</p><p><b>CONCLUSIONS</b>The concentration of extracellular AA in the brain cortex of the SI area increased following the ice water vestibular stimulation. This demonstration may be useful for the investigation of the neurochemical processes associated with AA in the process of vertigo.</p>