Chau Fong Chen

Changes in the Oxidant-Antioxidant Balance in the Kidney of Rats With Nephrolithiasis Induced by Ethylene Glycol

PURPOSE We investigated the possible mechanism of increased free radicals, the role of antioxidant enzymes and their correlation with renal tubular damage in the kidney after feeding 0.75% ethylene glycol to male Wistar rats. MATERIALS AND METHODS Rats were divided into 7 experimental groups according to the duration of ethylene glycol feeding (1, 3, 5, 7, 9, 21 or 42 days) and into age matched control groups. Chemiluminescence levels were examined in blood samples (renal artery and vein) and in the kidney. The activities of oxidase and antioxidant enzymes were measured in kidney homogenates. The nitroblue tetrazolium perfusion method and immunohistochemical stains with ED1 and CD45 were performed. Urinary levels of alpha and mu-glutathione S-transferase (GST) were also measured and expressed in gm. urinary creatinine. RESULTS Chemiluminescence levels of renal venous blood samples were elevated on days 1, 3 and 7 (p <0.05), and those of the kidney were elevated only on days 3 and 42 (p <0.05) compared with controls. The infiltration of CD45 positive cells in the kidney increased on day 7 and a further increase in these positive cells was noted on day 21. Fused ED1 positive cells surrounding the calcium oxalate crystals and adjacent to the nitroblue tetrazolium positive area were found on day 42. Xanthine oxidase activity showed no significant change, whereas nicotinamide adenine dinucleotide dependent oxidase activity was higher on day 5 and nicotinamide adenine dinucleotide phosphate dependent activity was elevated in all experimental groups (p <0.05). The activities of catalase and manganese superoxide dismutase were elevated in the early stage. On day 42 almost all antioxidant enzyme activities were attenuated (p <0.05) except that of catalase. The urinary levels of alpha-GST were elevated from day 7 until day 42, whereas levels of mu-GST were elevated from day 3 until day 42 except day 5. CONCLUSIONS The possible mechanism that causes free radical elevation in the kidney may be different in the course of nephrolithiasis after ethylene glycol treatment. Initially the systemic circulation may bring the toxic substance into the kidney and cause it to produce free radicals. In the late stage gradually infiltrating leukocytes and decreased antioxidant enzyme activities may cause the kidney to remain under excessive oxidative stress.

Lipid peroxidation and its correlations with urinary levels of oxalate, citric acid, and osteopontin in patients with renal calcium oxalate stones.

OBJECTIVES To determine whether lipid peroxidation plays a role in patients with calcium oxalate kidney stones and to determine the correlation of lipid peroxidation with tubular damage and the major urinary risk factors. We also used the isoenzymes of glutathione S-transferase (GST) to examine which parts of the renal tubules were injured in patients with renal stones. METHODS This clinical study included two study groups. Group 1 included 32 normal volunteers, and group 2 included 32 patients with calcium oxalate kidney stones. A 24-hour urine sample was collected from each subject, and the levels of Ca, P, Mg, oxalate, citrate, N-acetyl-beta-glucosaminidase (NAG), beta-galactosidase (GAL), alphaGST, piGST, osteopontin (OPN), thiobarbituric acid-reactive substances (TBARS), and malondialdehyde (MDA) were examined. RESULTS Hyperoxaluria, hypocitraturia, and low urinary OPN were the major abnormalities found in the patients with stones. Elevated urinary alphaGST, NAG, and GAL were also noted in the patients with stones; however, urinary piGST showed no statistically significant difference compared with the controls. Urinary TBARS and MDA had statistically significant correlations with alphaGST, GAL, NAG, Ca, and oxalate, but had no correlation with piGST, citrate, OPN, Mg, and P. Urinary citrate had a negative, linear, and statistically significant correlation with alphaGST, GAL, and NAG. CONCLUSIONS Lipid peroxidation correlated with hyperoxaluria and renal tubular damage, indicating that hyperoxaluria can induce tubular cell injury and that this injury may be due to the production of free radicals in patients with calcium oxalate stones. Renal tubular damage in patients with stones may be limited to the proximal tubules.

Small-dose Propofol sedation attenuates the formation of reactive oxygen species in tourniquet-induced ischemia-reperfusion injury under spinal anesthesia

The release of a tourniquet produces reactive oxygen species (ROS), which can cause ischemia-reperfusion injury. We investigated the effects on ROS production in 22 adult ASA physical status I–II patients sedated with small-dose propofol infusion and IV midazolam undergoing elective total knee replacement under intrathecal anesthesia, allocated randomly to one of two groups. In the Propofol group, sedation was performed with propofol 0.2 mg/kg followed by infusion at a rate of 2 mg · kg−1 · h−1. In the Control group, IV midazolam 5 mg was given. ROS production was measured by lucigenin chemiluminescence analysis. Blood samples were obtained from the radial artery after spinal anesthesia, 1 min before release of the tourniquet and 5 and 20 min after reperfusion. The ischemic time was approximately 70 min. ROS production decreased nonsignificantly before reperfusion in both groups but increased significantly 5 and 20 min after reperfusion in the Midazolam group. In the Propofol group, no significant increase of ROS production was found. We conclude that small-dose propofol infusion attenuates ROS production in tourniquet-induced ischemia-reperfusion injury.

Low and high frequency electroacupuncture at Hoku elicits a distinct mechanism to activate sympathetic nervous system in anesthetized rats

To address the effect of electroacupuncture (Ea) on autonomic nerve activity, the responses of rhythmic micturition contraction (RMC), urine excretion (UE), blood pressure (BP), renal sympathetic nerve activity (RNA) and pelvic parasympathetic nerve activity (PNA) to Ea were investigated in urethane-anesthetized rats. The acupoint Hoku (Li-4) was tested with two different stimulation frequencies (2 Hz and 20 Hz). Elongation of the RMC cycle and an increase in UE associated with the elevation of BP and RNA was elicited during Ea at Hoku. However, the pressor response induced by low frequency Ea (LFEa) was different from that by high frequency Ea (HFEa), i.e. a tonic effect was elicited by LFEa, while a phasic one was induced by HFEa. These results imply that: (1) Ea at Hoku may selectively activate the sympathetic, but not the parasympathetic nervous system, (2) Ea at Hoku with a different stimulation frequency may elicit a distinct mechanism to activate the sympathetic nervous system and (3) Ea at Hoku may ameliorate the hyperactive bladder in clinical therapy.

Impaired renal sensory responses after renal ischemia in the rat

Renal sensory responses and reflex function were examined in rats 24 h after 45 min of ischemic injury caused by unilateral renal arterial occlusion (RAO). The integrity of renal pelvic mechanoreceptor (MRu)-mediated renorenal reflex was examined. An increase in ipsilateral afferent renal nerve activity (ARNA) and a reflex decrease in efferent renal nerve activity (ERNA) and contralateral diuresis and natriuresis produced by increasing the intrapelvic pressure were seen in sham-operated (Sham) rats, but it was largely attenuated in RAO rats. Using single-fiber recordings of the renal MRu discharge, graded increases in intrapelvic pressure or renal pelvic administration of substance P (SP) resulted in pressure- or concentration-dependent increases in ARNA in the control kidney of Sham rats, whereas attenuated responses were seen in the postischemic kidney of RAO rats. The unresponsiveness of renal MRus in RAO rats was accompanied by an insufficient release of SP. However, the baseline SP release is higher in RAO kidneys due to a reduced neutral endopeptidase (NEP) activity in the renal pelvis of the postischemic kidney. No changes in NK-1 receptor mRNA levels were demonstrated; however, the expression of NK-1 receptors in the plasma membrane of RAO pelvis were decreased, possibly resulting from the internalization of the receptors associated with beta-arrestin trafficking. Renal excretory responses after saline loading were significantly lower in the postischemic kidney of RAO rats than in Sham rats. Responses of ARNA and ERNA were also lower. It is concluded that the defective activation of renal sensory mechanoreceptors in the postischemic kidney results from an inadequate release of SP after mechanostimulation and the reduced functional NK-1 receptors.

Reduction in renal haemodynamics by exaggerated vesicovascular reflex in rats with acute urinary retention

1 We examined the possibility that a vesicovascular reflex is exaggerated by acute urinary retention, and that the increase in renal vascular resistance caused by this reflex may lead to renal dysfunction. We evaluated the vesicovascular responses to normal micturition (NM, transcystometric condition) and acute urinary retention (isovolumetric condition mimicking complete bladder‐outlet obstruction (CBOO) and partial urethral ligation mimicking partial bladder‐outlet obstruction (PBOO)) in anaesthetized female Wistar rats. 2 Acute urinary retention due to CBOO or PBOO provoked a prolonged or increased intravesical pressure, an enhancement in both bladder pelvic afferent and bladder pelvic efferent nervous activity, and an elevation in mean arterial blood pressure. 3 Single‐unit analysis showed that these vesicovascular reflexes were triggered by activation of low‐threshold and high‐threshold bladder mechanoreceptors, but not by renal uretropelvic mechanoreceptors. 4 Bladder contraction in CBOO and PBOO conditions and graded increases in bladder volume significantly reduced renal blood flow and cortical microvascular blood flow. The acute urinary retention‐induced renal vasoconstriction was mediated by the renal nerve. Renal denervation, but not bilateral ureteral resection, abolished the renal vasoconstriction associated with the vesicovascular reflexes. 5 These findings indicate that exaggerated activation of bladder afferents exerts a positive feedback effect to increase sympathetic outflow to the kidney further, thereby contributing to significant renal vasoconstriction via a renal nerve‐dependent mechanism.

Increase of plasma neuropeptide Y-like immunoreactivity following chronic hypoxia in the rat

In an attempt to understand the changes of circulating neuropeptide Y (NPY) during hypoxia, the plasma level of NPY was investigated by radioimmunoassay. Exposure of rats to hypobaric hypoxia at an altitude of 18,000 ft for 4 weeks causes an increase of pulmonary pressure and an elevation of plasma NPY-like immunoreactivity (NPY-LI). However, the systemic blood pressure was not elevated by this chronic hypoxia. Also, plasma noradrenaline (NA) estimated by chromatographic analysis (HPLC-ECD) was not markedly raised. Failure of bretylium and guanethidine, sympathetic neuron blockers, in reducing the plasma NPY-LI level of these rats ruled out the participation of adrenergic nervous terminals. Adrenal medulla seems responsible for this elevation of plasma NPY-LI because this magnitude disappeared in adrenalectomized rats. These data suggest that chronic hypoxia induced an elevation of circulating NPY from the adrenal gland of rats.

An experimental model to evaluate the in vivo response of rat seminal vesicle to electrical stimulation

This investigation demonstrated a good model to record the pressure change of rat seminal vesicle (SV) in response to electrical stimulation (ES) of lesser splanchnic nerve (LSN) in vivo. LSN was easily identified and isolated grossly. Antegrade catheterization via the SV tail to the main lumen was performed similar to the technique of i.v. catheterization, and the pressure recording was quite satisfactory. The vesicle response to ES was frequency-dependent and reproducible. Under the conditions of 10 V and 1 ms, the maximal vesicle pressure was 81.7 +/- 2.8 mmHg with 80 Hz of ES. The inhibitory response of SV to ES by clomipramine was concentration-dependent. Clomipramine (3 mg/kg) could inhibit 53% of control responses (n = 7). This experimental model is relevant to neurophysiologic and neuropharmacologic studies of SV.

Attenuated response of renal mechanoreceptors to volume expansion in chronically hypoxic rats

Multifiber renal afferent nerve activity responds to volume expansion in sea level rats but not in chronically hypoxic (high altitude) rats. We performed single-unit recordings of renal afferent nerve activity to characterize renal sensory receptors and their responses to volume expansion in these animals. Hypoxia was induced by placing Wistar rats in an altitude chamber (380 Torr, 5,500 m) for 4 wk. Spontaneously firing renal R2 chemoreceptor and arterial, ureteropelvic, and venous mechanoreceptors were identified. The basal activity of each receptor was similar among these rats. In response to specific stimulus, the increasing impulse of R2 chemoreceptor was similar between two groups of rats, but the increasing activity of each mechanoreceptor was less in hypoxic rats. When challenged with saline load, R2 chemoreceptor activity decreased, but all mechanoreceptors activated in all rats. Despite similar increases of arterial, renal ureteropelvic, and venous pressure during saline load, the increasing activity of each mechanoreceptor was significantly less in hypoxic rats. These results indicated chronic hypoxia attenuates the sensitivity of renal mechanoreceptors in response to the stimulation of saline load.

Enhanced expression of nitric oxide synthase in the early stage after increased pulmonary blood flow in rats

OBJECTIVE Evidence that vasodilator nitric oxide mediates normal pulmonary vascular tone has led to the hypothesis that endothelial injury induced by congenital heart disease with increased pulmonary blood flow disrupts these regulatory mechanisms and its associated altered vascular reactivity. Therefore, we hypothesized that increased pulmonary blood flow results in altered expression of endothelial nitric oxide synthase (eNOS). METHODS We created an arteriovenous shunt in female Wistar (5-week-old) and measured the change of pulmonary blood flow and pressure immediately after and 1 month after the shunt operation. The protein levels of eNOS in the lung tissues of rats were assessed. RESULTS The shunt immediately resulted in a significant increase in pulmonary blood flow (16.5 +/- 11.8% , pulmonary artery pressure (2.3 +/- 0.7 mm Hg), and blood O(2) saturation (16.1 +/- 11.8%) in the pulmonary artery. After 4 weeks, there was a significant increase in pulmonary blood flow (30.7 +/- 1.6%), pulmonary artery pressures (4.3 +/- 1.1 mm Hg), and blood O(2) content (43.3 +/- 17.5%). Western blot analysis demonstrated that eNOS protein was increased in the shunt lung 72 h after surgery and recovered to the control level 1 week later. CONCLUSION This simple shunt model can induce early upregulation of eNOS expression with increased pulmonary blood flow and pulmonary artery pressure in rats.