Gholam Abbas Dehghani

Effects of hypercapnia with and without acidosis on hypoxic pulmonary vasoconstriction.

Acute respiratory disorders and permissive hypercapnic strategy may lead to alveolar hypoxia and hypercapnic acidosis. However, the effects of hypercapnia with or without acidosis on hypoxic pulmonary vasoconstriction (HPV) and oxygen diffusion capacity of the lung are controversial. We investigated the effects of hypercapnic acidosis and hypercapnia with normal pH (pH corrected with sodium bicarbonate) on HPV, capillary permeability, gas exchange, and ventilation-perfusion matching in the isolated ventilated-perfused rabbit lung. No alteration in vascular tone was noted during normoxic hypercapnia with or without acidosis compared with normoxic normocapnia. Hypercapnia with normal pH resulted in a transient increase in HPV during the course of consecutive ventilation maneuvers, whereas hypercapnic acidosis increased HPV over time. Hypercapnic acidosis decreased exhaled NO during hypoxia more than hypercapnia with normal pH and normocapnia, whereas intravascular NO release was unchanged. However, inhibition of NO synthesis by nitro-L-arginine (L-NNA) resulted in a loss of the increased HPV caused by hypercapnic acidosis but not that caused by hypercapnia with normal pH. Furthermore, capillary permeability increased during hypoxic hypercapnia with normal pH but not hypoxic hypercapnic acidosis. This effect was NO-dependent because it disappeared during L-NNA administration. Ventilation-perfusion matching and arterial PO2 were improved according to the strength of HPV in hypercapnia compared with normocapnia during Tween nebulization-induced lung injury. In conclusion, the increased HPV during hypercapnic acidosis is beneficial to lung gas exchange by improving ventilation-perfusion matching and preserving the capillary barrier function. These effects seem to be linked to NO-mediated pathways.

Contribution of nitric oxide synthase (NOS) in blood–brain barrier disruption during acute focal cerebral ischemia in normal rat

Endogenous level of nitric oxide (NO) is increased in the brain following the stroke, and deactivation of NO synthase has been shown to attenuate its destructive actions in animal stroke models using middle cerebral artery occlusion (MCAO) procedures. However, little is known about the effects of NO in cerebral vascular integrity and edema during acute cerebral ischemia. Here we investigated whether NO plays any role in the progression of blood-brain barrier (BBB) disruption and edema formation in ischemia/reperfusion injury. Intraperitoneal administration of NO substrate l-arginine (300mg/kg), or NOS inhibitor (l-NAME, 1mg/kg), was done in normal rats at 20min before a 60-min MCAO. Mean arterial blood pressures (MAP) and regional cerebral blood flow (rCBF) were continuously recorded during experiment. Neurological deficit score (NDS) was evaluated 12h after termination of MCAO followed with evaluations of cerebral infarction volume (CIV), edema formation and cerebral vascular permeability (CVP), as determined by the Evans blue dye extravasations (EBE) technique. No significant changes were observed in the values of MAP and rCBF with l-arginine or l-NAME during ischemia or reperfusion periods. There was a 75-85% reduction in rCBF in during MCAO which returned back to its pre-occlusion level during reperfusion. Acute cerebral ischemia with or without l-arginine augmented NDS (4.00±0.44 and 3.00±0.30), in conjunction with increased CIV (518±57mm(3) and 461±65mm(3)), provoked edema (3.09±0.45% and 3.30±0.49%), and elevated EBE (8.28±2.04μg/g and 5.09±1.41μg/g). Inhibition of NO production by l-NAME significantly improved NDS (1.50±0.22), diminished CIV (248±56mm(3)), edema (1.18±0.58%) and EBE (1.37±0.12μg/g). This study reconfirms the cerebroprotective properties of reduced tissue NO during acute ischemic stroke, and it also validates the deleterious actions of increased NOS activity on the disruption of cerebral microvascular integrity and edema formation of ischemia/reperfusion injuries in normal rat, without changing arterial blood pressure or blood flows to ischemic regions.

Candesartan Attenuates Ischemic Brain Edema and Protects the Blood-Brain Barrier Integrity from Ischemia/Reperfusion Injury in Rats

Background: Angiotensin II (Ang II) has an important role on cerebral microcirculation; however, its direct roles in terms of ischemic brain edema need to be clarified. This study evaluated the role of central Ang II by using candesartan, as an AT1 receptor blocker, in the brain edema formation and blood-brain barrier (BBB) disruption caused by ischemia/reperfusion (I/R) injuries in rat. Methods: Rats were exposed to 60-min middle cerebral artery (MCA) occlusion. Vehicle and non-hypotensive doses of candesartan (0.1 mg/kg) were administered one hour before ischemia. Neurological dysfunction scoring was evaluated following 24 h of reperfusion. Animals were then decapitated under deep anesthesia for the assessments of cerebral infarct size, edema formation, and BBB permeability. Results: The outcomes of 24 h reperfusion after 60-min MCA occlusion were severe neurological disability, massive BBB disruption (Evans blue extravasation = 12.5 ± 1.94 µg/g tissue), 4.02% edema, and cerebral infarction (317 ± 21 mm3). Candesartan at a dose of 0.1 mg/kg, without changing arterial blood pressure, improved neurological dysfunction scoring together with significant reductions in BBB disruption (54.9%), edema (59.2%), and cerebral infarction (54.9%). Conclusions: Inactivation of central AT1 receptors, if not accompanied with arterial hypotension, protected cerebral micro-vasculatures from damaging effects of acute stroke.

Effects of hypercapnia and NO synthase inhibition in sustained hypoxic pulmonary vasoconstriction

BackgroundAcute respiratory disorders may lead to sustained alveolar hypoxia with hypercapnia resulting in impaired pulmonary gas exchange. Hypoxic pulmonary vasoconstriction (HPV) optimizes gas exchange during local acute (0-30 min), as well as sustained (> 30 min) hypoxia by matching blood perfusion to alveolar ventilation. Hypercapnia with acidosis improves pulmonary gas exchange in repetitive conditions of acute hypoxia by potentiating HPV and preventing pulmonary endothelial dysfunction. This study investigated, if the beneficial effects of hypercapnia with acidosis are preserved during sustained hypoxia as it occurs, e.g in permissive hypercapnic ventilation in intensive care units. Furthermore, the effects of NO synthase inhibitors under such conditions were examined.MethodWe employed isolated perfused and ventilated rabbit lungs to determine the influence of hypercapnia with or without acidosis (pH corrected with sodium bicarbonate), and inhibitors of endothelial as well as inducible NO synthase on acute or sustained HPV (180 min) and endothelial permeability.ResultsIn hypercapnic acidosis, HPV was intensified in sustained hypoxia, in contrast to hypercapnia without acidosis when HPV was amplified during both phases. L-NG-Nitroarginine (L-NNA), a non-selective NO synthase inhibitor, enhanced acute as well as sustained HPV under all conditions, however, the amplification of sustained HPV induced by hypercapnia with or without acidosis compared to normocapnia disappeared. In contrast 1400 W, a selective inhibitor of inducible NO synthase (iNOS), decreased HPV in normocapnia and hypercapnia without acidosis at late time points of sustained HPV and selectively reversed the amplification of sustained HPV during hypercapnia without acidosis. Hypoxic hypercapnia without acidosis increased capillary filtration coefficient (Kfc). This increase disappeared after administration of 1400 W.ConclusionHypercapnia with and without acidosis increased HPV during conditions of sustained hypoxia. The increase of sustained HPV and endothelial permeability in hypoxic hypercapnia without acidosis was iNOS dependent.

Attenuation of Focal Cerebral Ischemic Injury Following Post- Ischemic Inhibition of Angiotensin Converting Enzyme (ACE) Activity in Normotensive Rat

BACKGROUND Central renin angiotensin system has an important role on the cerebral microcirculation and metabolism. Our previous work showed that inhibition of angiotensin converting enzyme (ACE) activity prior to induction of ischemia protected the brain from severe ischemia/reperfusion (I/R) injuries. This study evaluated the impacts of post-ischemic inhibition of ACE, enalapril, on brain infarction in normotensive rats. METHODS Rats were anesthetized with chloral hydrate (400 mg/kg). Focal cerebral ischemia was induced by 60-min intraluminal occlusion of right middle cerebral artery (MCA). Intraperitoneal injection of enalapril (0.03 or 0.1 mg/kg) was done after MCA reopening (reperfusion). Neurological deficit score (NDS) was evaluated after 24 h and the animals randomly assigned for the assessments of infarction, absolute brain water content (ABWC) and index of brain edema. RESULTS Severe impaired motor functions (NDS = 2.78 ± 0.28), massive infarction (cortex = 214 ± 19 mm3, striatum = 86 ± 5 mm3) and edema (ABWC = 83.1 ± 0.46%) were observed in non-treated ischemic rats. Non-hypotensive dose of enalapril (0.03 mg/kg) significantly reduced NDS (1.5 ± 0.22), infarction (cortex = 102 ± 16 mm3, striatum = 38 ± 5 mm3) and edema (ABWC = 80.9 ± 0.81%). Enalapril at dose of 0.1 mg/kg significantly lowered arterial pressure could not improve NDS (2.0 ± 0.45) and reduce infarction (cortex = 166 ± 26 mm3, striatum = 71 ± 11 mm3). CONCLUSION Post-ischemic ACE inhibition in the normotensive rats without affecting arterial pressure protects the brain from reperfusion injuries; however, this beneficial action is masked by hypotension.

Enalapril attenuates ischaemic brain oedema and protects the blood–brain barrier in rats via an anti‐oxidant action

In the present study, we investigated the effects of postischaemic angiotensin‐converting enzyme (ACE) inhibition with enalapril on vasogenic oedema formation and blood–brain barrier (BBB) integrity following transient focal cerebral ischaemia in rats. Cerebral ischaemia was induced by 60 min occlusion of the right middle cerebral artery, followed by 24 h reperfusion. Vehicle and a non‐hypotensive dose of enalapril (0.03 mg/kg) were administered at the beginning of the reperfusion period. A neurological deficit score (NDS) was determined for all rats at the end of the reperfusion period. Then, brain oedema formation was investigated using the wet–dry weight method and BBB permeability was evaluated on the basis of extravasation of Evans blue (EB) dye. In addition, oxidative stress was assessed by measuring reduced glutathione (GSH) and malondialdehyde (MDA) in brain homogenates. Inhibition of ACE by enalapril significantly reduced NDS and decreased brain oedema formation (P < 0.05 for both). Disruption of the BBB following ischaemia resulted in considerable leakage of EB dye into the brain parenchyma of the ipsilateral hemispheres of vehicle‐treated rats. Enalapril significantly (P < 0.05) decreased EB extravasation into the lesioned hemisphere. Enalapril also augmented anti‐oxidant activity in ischaemic brain tissue by increasing GSH concentrations and significantly (P < 0.05) attenuating the increased MDA levels in response to ischaemia. In conclusion, inhibition of ACE with a non‐hypotensive dose of enalapril may protect BBB function and attenuate oedema formation via anti‐oxidant actions.

Does the Relief of Glucose Toxicity Act As a Mediator in Proliferative Actions of Vanadium on Pancreatic Islet Beta Cells in Streptozocin Diabetic Rats

Background: Data shows vanadium protects pancreatic beta cells (BC) from diabetic animals. Whether this effect is direct or through the relief of glucose toxicity is not clear. This study evaluated the potential effect of oral vanadyl sulfate (vanadium) on glycemic status and pancreatic BC of normal and diabetic rats. Methods: Rats were divided into five groups of normal and diabetic. Diabetes was induced with streptozocin (40 mg/kg, i.v.). Normal rats used water (CN) or vanadium (1 mg/ml VOSO4, VTN). Diabetic rats used water (CD), water plus daily neutral protamine Hagedorn insulin injection (80 U/kg, ITD) or vanadium (VTD). Blood samples were taken for blood glucose (BG, mg/dL) and insulin (ng/dL) measurements. After two months, the pancreata of sacrificed rats were prepared for islet staining. Results: Pre-treated normal BG was 88 ± 2, and diabetic BG was 395 ± 9. The final BG in CD, VTD, and ITD was 509 ± 22, 138 ± 14, and 141 ± 14, respectively. Insulin in VTN (0.75 ± 0.01) and VTD (0.78 ± 0.01) was similar, higher than CD (0.51 ± 0.07) but lower than CN (2.51 ± 0.02). VTN islets compared to CN had larger size and denser central core insulin immunoreactivity with plentiful BC. CD and ITD islets were atrophied and had scattered insulin immunoreactivity spots and low BC mass. VTD islets were almost similar to CN. Conclusion: Besides insulin-like activity, vanadium protected pancreatic islet BC, and the relief of glucose toxicity happening with vanadium had a little role in this action.

Trophic Actions of Oral Vanadium and Improved Glycemia on the Pancreatic Beta-Cell Ultrastructure of Streptozotocin-Induced Diabetic Rats

CONTEXT Oral vanadyl sulfate (vanadium) has potent hypoglycemic effects in diabetes animals, but data about its actions on pancreatic beta-cells (BC) ultrastructure is limited. OBJECTIVE Partial diabetic rats were treated with vanadium and insulin injection and their effects on BC ultrastructure are studied. METHODS Male rats were made diabetic with intravenous streptozotocin injection (STZ, 40 mg/kg). Animals were randomly divided to control (CD), vanadium-treated (1 mg/mL VOSO4 + 5H2O in base solution, VTD) and insulin-treated (80 U/kg/day NPH insulin injection, ITD) diabetic groups. Treatments started 10 days after STZ injection and terminated after 2 months. Intermittent tail blood samples were taken for measurements of blood glucose (BG) and plasma insulin (PI). Finally animals were sacrificed and pancreata prepared for assessments of BC ultrastructure, islets histology and insulin immunoreactivity (IIR). RESULTS Vanadium decreased BG (P<0.0001), elevated the reduced PI (P<0.001), prevented islet atrophy and restored BC ultrastructure. Low BG seen during treatment in VTD and ITD only persisted in VTD after vanadium withdrawal. Hyperglycemia worsened in CD and repaired in ITD shortly after insulin withdrawal. CD islets were atrophied, had scattered IIR spots. BC had pyknotic nuclei, vacuolated cytoplasm and few tiny insulin secretory granules. VTD islets looked normal with compact centered IIR spots. BC had well-developed endoplasmic reticulum, many insulin secretory granules and mitochondria. ITD islet structure was slightly better than CD and BC had some immature insulin secretory granules. CONCLUSION The trophic actions of vanadium in diabetic rats effectively renovated beta cell ultrastructure and prevented pancreatic islets atrophy, whereas the relief of glucotoxicity seen with insulin treatment could repair some beta cells and partially prevented islet atrophy.

Quantitative Assessment of Proliferative Effects of Oral Vanadium on Pancreatic Islet Volumes and Beta Cell Numbers of Diabetic Rats

Background: Oral vanadyl sulfate (vanadium) induces normoglycemia, proliferates beta cells and prevents pancreatic islet atrophy in streptozotocin-induced diabetic rats. Soteriological method is used to quantitate the proliferative effects of vanadium on beta-cell numbers and islet volumes of normal and diabetic rats. Methods: Adult male Sprague-Dawley rats were made diabetic with intravenous streptozotocin injection (40 mg/kg). Normal and diabetic rats were divided into four groups. While control normal and diabetic (CD) groups used water, vanadium-treated normal (VTN) and diabetic (VTD) groups used solutions containing vanadyl sulfate (0.5-1 mg/mL, VOSO4+5H2O). Tail blood samples were used to measure blood glucose (BG) and plasma insulin. Two months after treatment, rats were sacrificed, pancreata prepared, and stereology method was used to quantitatively evaluate total beta cell numbers (TBCN) and total islet volumes (TISVOL). Results: Normoglycemia persisted in VTN with significantly decreased plasma insulin (0.190.08 vs. 0.970.27 ng/dL, P<0.002). The respective high BG (53249 vs. 14446 mg/dL, P<0.0001) and reduced plasma insulin (0.260.15 vs. 0.540.19 ng/dL, P<0.002) seen in CD were reversed in VTD during vanadium treatment or withdrawal. While the induction of diabetes, compared to their control, significantly decreased TISVOL (1.90.2 vs. 3.030.6 mm3, P<0.003) and TBCN (0.990.1 vs. 3.20.2 x 106, P<0.003), vanadium treatment significantly increased TISVOL (2.90.8 and 4.071.0 mm3, P<0.003) and TBCN (1.50.3 and 3.80.6 x 106, P<0.03). Conclusion: Two-month oral vanadium therapy in STZ-diabetic rats ameliorated hyperglycemia by partially restoring plasma insulin. This action was through proliferative actions of vanadium in preventing islet atrophy by increasing beta-cell numbers.