Biomedical subjects

M R Prasad

Publications and source records attributed to M R Prasad.

At least 37 records · Page 2Linked to original sources

PubMed1996

Regional generation of leukotriene C4 after experimental brain injury in anesthetized rats.

Regional concentrations of leukotriene C4 and extravasation of Evans blue were measured after lateral fluid-percussion brain injury in rats. Tissue levels of LTC4 were elevated in the injured cortex at 10 min, 30 min, and 1 h after injury; these levels returned to normal by 2 h after injury. Increases in the levels of LTC4 were also observed in the ipsilateral hippocampus after brain injury, and these elevations persisted for 2 h after injury. No significant increase in levels of LTC4 was observed in the contralateral cortex at any time after injury. A substantial extravasation of Evans blue was observed only in the ipsilateral cortex and hippocampus at 3 h and 6 h after brain injury. Although a temporal association between LTC4 and blood-brain barrier (BBB) breakdown is suggested by these data, no cause-and-effect relationship has been addressed in this study. However, it is possible that, as is true for cerebral ischemia, LTC4 may play a role as a mediator in the BBB breakdown associated with fluid-percussion brain injury in rats.

Animals↗

PubMed1996

Effect of difluoromethylornithine treatment on regional ornithine decarboxylase activity and edema formation after experimental brain injury.

This study examined the effect of difluoromethylornithine (DFMO) on regional activities of ornithine decarboxylase (ODC) and edema formation in bilateral cerebral cortex and hippocampus after a unilateral controlled cortical-impact (CCI) injury in rats. To measure the activity of ODC, the brains of injured and control rats were frozen in situ at 30 min, 3, 6, and 24 h after CCI brain injury of moderate severity. The specific gravity, an indicator of edema formation, was examined in decapitated animals at corresponding time points. Brain injury induced significant increases of ODC in the ipsilateral hippocampus, adjacent and injury-site cortices, and in the contralateral cortex and hippocampus at 3 and 6 h after injury. No significant edema formation was found in any brain region at 30 min after injury. A significant edema formation was first found only in the injury-site cortex at 3 h after injury. At 6 and 24 h after injury, significant edema was found in all regions ipsilateral to the injury-site. At 24 h after injury, significant but less severe edema was also found in the contralateral cortex and hippocampus. DFMO, an irreversible inhibitor of ODC, abolished the increase in ODC in all regions. It also attenuated edema formation in the adjacent cortex and in the contralateral cortex and hippocampus. These findings indicate that polyamines may play a role in posttraumatic brain edema formation, particularly in important brain regions remote from the injury-site.

Animals↗

PubMed1996

Regional activity of ornithine decarboxylase and edema formation after traumatic brain injury.

This study examined ornithine decarboxylase (ODC) activity and edema formation bilaterally in brain cortices and hippocampi after lateral controlled cortical-impact injury in rats. To measure the activity of ODC, the brains of injured and control rats were frozen in situ at 30 minutes and at 6, 24, and 72 hours after controlled cortical-impact injury of moderate severity. The specific gravity of these regions was examined in decapitated animals at corresponding time points as an indicator of edema formation. Thirty minutes after injury, ODC activity did not increase in the injury-site cortex and ipsilateral hippocampus. At 6 hours after injury, ODC activity had increased by nine times that of the control in the injury-site cortex, by five times in the adjacent cortex, and by five and one-half times in the ipsilateral hippocampus. Twenty-four hours after injury, ODC activity had increased by three times that of the control in the injury-site cortex and two times in the ipsilateral hippocampus. Seventy-two hours after injury, activity had returned to control levels. ODC activity increased significantly in the contralateral cortex and hippocampus only at 6 and 24 hours. The injury-site and adjacent cortices and the ipsilateral hippocampus showed significant edema at 6, 24, and 72 hours but not at 30 minutes after injury. These findings indicate that polyamine metabolism is significantly altered in traumatic brain injury. The temporal association between ODC activity and edema formation indicates that polyamines might be a contributing factor in edema formation after traumatic brain injury. The delayed induction of ODC after brain injury suggests a potential therapeutic window for future pharmacological intervention to decrease posttraumatic secondary cerebral injury.

Animals↗

PubMed1996

Protective effect of the 5-lipoxygenase inhibitor AA-861 on cerebral edema after transient ischemia.

This study examined the effect of AA-861, a specific 5-lipoxygenase inhibitor, on brain levels of leukotriene C4 (LTC4) and correlated any changes with changes in edema formation and cerebral blood flow (CBF) after transient ischemia in gerbils. Brain levels of LTC4 were observed to be increased at 1, 2, and 6 hours of reperfusion following 20 minutes of occlusion. At 2 hours of reperfusion, a pretreatment dose of 1000 mg/kg of AA-861 was required to inhibit more than 90% of the reperfusion-induced increases in brain LTC4. At this dose, inhibition of LTC4 production was observed at 2 and 6 hours of reperfusion. The specific gravity of both the cortex and subcortex was decreased at 6 hours of reperfusion after 20 minutes of occlusion. At 2 hours of reperfusion, no significant difference was observed in the specific gravity of the cortex and subcortex regions of gerbils pretreated with AA-861 or with vehicle, but at 6 hours of reperfusion significant positive differences were observed. Cerebral blood flow decreased to approximately 10% of preocclusion values during occlusion and returned to near-preocclusion values after 10 minutes of reperfusion. No significant differences were observed in regional CBF in the AA-861- and vehicle-pretreated gerbils during reperfusion. These findings indicate that LTC4 production after transient cerebral ischemia may be an important contributor to the development of cerebral edema and that CBF does not mediate the LTC4-involved development of edema.

Animals↗

PubMed1995

Activation of phosphatidylinositol bisphosphate signal transduction pathway after experimental brain injury: a lipid study.

Regional levels of phosphatidylinositol 4,5-bisphosphate (PIP2), diacylglycerol (DG) and free fatty acids (FFA), involved in the signal transduction pathway of the excitatory neurotransmitter system, were measured after lateral fluid percussion (FP) brain injury in rats. At 5 min postinjury, tissue PIP2 concentrations were significantly reduced in the cortices and hippocampi of both ipsilateral and contralateral hemispheres. Only levels of stearic and arachidonic acids were substantially decreased in PIP2 in these regions of the brain. At the same time after injury, both DG and FFA were significantly increased in the cortices and hippocampi of both hemispheres. As was true for PIP2, only levels of stearic and arachidonic acids markedly changed in both DG and FFA in these regions of the brain. At 20 min postinjury, a significant decrease in PIP2 concentration and significant increases in levels of DG and FFA were observed only in the injured left cortex. In addition to the increases in stearic and arachidonic acids in FFA, increased amounts of palmitic and oleic acids were also found in the injured left cortex at 20 min after injury. These results suggest that the PIP2 signal transduction pathway is activated in the cortex and hippocampus at the onset of lateral FP brain injury and that the enhanced phospholipase C-catalyzed phosphodiestric breakdown of PIP2 is a major mechanism of liberation of FFA in these sites immediately after such injury.

Analysis of Variance↗

PubMed1995

Direct effects of reactive oxygen species on cochlear outer hair cell shape in vitro.

Reactive oxygen species (ROS) have been implicated in the ototoxicity of various agents. This study examines the effects of superoxide anion (O2), hydroxyl radical (OH.) and hydrogen peroxide (H2O2), on isolated cochlear outer hair cell (OHC) morphology. OHCs were superfused with artificial perilymph (AP) or AP containing a specific ROS scavenger, and then with AP, ROS system or scavenger plus ROS system for 90 min. The generation of ROS as well as the scavenging properties of other agents were confirmed by specific biochemical assays. Control cells decreased 4.8% in mean length, and showed no obvious membrane damage. Generation of O2. or OH. resulted in high rates (85.7 and 42.9%, respectively) of bleb formation at the synaptic pole, and decreased (O2., 15.2%; OH., 17.3%) mean cell length. Length change and bleb formation rate were H2O2 concentration-dependent. 20 mM H2O2 led to 33.3% decreased mean cell length, and only 20% bleb formation; 0.1 mM H2O2 led to 83.3% bleb formation, with no length decrease. Superoxide dismutase, deferoxamine and catalase protected against O2., OH. and H2O2 effects, respectively. Bleb formation and diminished cell length likely represent differential lipid peroxidative outcomes at supra- and infranuclear membranes, and are consistent with effects of certain ototoxicants.

Animals↗

PubMed1995

Ornithine decarboxylase activity and edema formation in cerebral ischemia of conscious gerbils.

General anesthetic agents often affect the biochemical and physiologic changes triggered by cerebral ischemia. This study examined the regional activities of ornithine decarboxylase (ODC) in gerbils subjected to 5 min of bilateral carotid occlusion without anesthesia. At 2, 4, and 6 h of reperfusion, significant ODC activity was observed in both the cortex and the hippocampus. Pretreatment with alpha-difluoromethylornithine (DFMO) significantly blocked the ODC activity at 2, 4, and 6 h. Significant edema formation was found at 2, 4, and 6 h. At 2 h, edema formation was unaffected by administration of DFMO. However, DFMO treatment reduced later edema formation at 4 and 6 h. These results demonstrate that ODC activity and edema formation are delayed in gerbils after the induction of transient ischemia even with the removal of anesthetic agents and their potentially protective effects. These findings suggest that ODC activity and its induction of delayed cerebral edema are specific to cerebral ischemia and not to an anesthetic effect. DFMO treatment reduced both the ODC activity and edema formation, indicating a role for polyamines in postischemic edema formation.

Animals↗

PubMed1994

Enhanced phosphodiestric breakdown of phosphatidylinositol bisphosphate after experimental brain injury.

Regional levels of lactate and inositol 1,4,5-trisphosphate (IP3), a cellular second messenger of the excitatory neurotransmitter system, were measured after lateral fluid percussion (FP) brain injury in rats. At 5 min postinjury, tissue lactate concentrations were significantly elevated in the cortices and hippocampi of both the ipsilateral and contralateral hemispheres. By 20 min postinjury, lactate concentrations were elevated only in the cortices and hippocampus of the ipsilateral hemisphere. Whereas the IP3 concentrations were elevated in the hippocampi of the ipsilateral and contralateral hemisphere and in the cortex of ipsilateral hemisphere at 5 min postinjury, no elevation in these sites was found at 20 min postinjury. Histologic analysis revealed neuronal damage in the cortex and CA3 regions of hippocampus ipsilateral to the injury at 24 h postinjury. The present results suggest activation of the phosphoinositide signal transduction pathway at the onset of injury and of a possible requirement of early persistent metabolic dysfunction (> 20 min) such as the lactate accumulation in the delayed neuronal damage.

Animals↗

PubMed1994

Regional levels of lactate and norepinephrine after experimental brain injury.

The recently developed controlled cortical impact model of brain injury in rats may be an excellent tool by which to attempt to understand the neurochemical mechanisms mediating the pathophysiology of traumatic brain injury. In this study, rats were subjected to lateral controlled cortical impact brain injury of low grade severity; their brains were frozen in situ at various times after injury to measure regional levels of lactate, high energy phosphates, and norepinephrine. Tissue lactate concentration in the injury site left cortex was increased in injured animals by sixfold at 30 min and twofold at 2.5 h and 24 h after injury (p < 0.05). At all postinjury times, lactate concentration was also increased in injured animals by about twofold in the cortex and hippocampus adjacent to the injury site (p < 0.05). No significant changes occurred in the levels of ATP and phosphocreatine in most of the brain regions of injured animals. However, in the primary site of injury (left cortex), phosphocreatine concentration was decreased by 40% in injured animals at 30 min after injury (p < 0.05). The norepinephrine concentration was decreased in the injury site left cortex of injured animals by 38% at 30 min, 29% at 2.5 h, and 30% at 24 h after injury (p < 0.05). The level of norepinephrine was also reduced by approximately 20% in the cortex adjacent to the injury site in injured animals. The present results suggest that controlled cortical impact brain injury produces disorder in the neuronal oxidative and norepinephrine metabolism.

Adenosine Triphosphate↗

PubMed1994

Regional levels of free fatty acids and Evans blue extravasation after experimental brain injury.

The recently developed controlled cortical-impact (CCI) model of brain injury in rats serves as an excellent tool to understand some of the neurochemical mechanisms mediating the pathophysiology of traumatic brain injury. In this study, rats were subjected to lateral CCI brain injury of low-grade severity. Their brains were frozen in situ at various times after injury to measure regional levels of free fatty acids. Tissue total free fatty acids at the injury site within the left cortex were increased at 30 min, 2.5 h, and 24 h postinjury. In injured animals, increases in stearic and arachidonic acids were slightly greater than those in palmitic and oleic acids. The levels of total free fatty acids in the cortex adjacent to the injury site were also increased in injured animals at 2.5 h and 24 h after injury (p < 0.05). Only stearic and arachidonic acids were observed to be significantly increased (p < 0.05) in the adjacent cortex of injured animals at all times after injury. Although no significant increases in total free fatty acids were observed in the left hippocampus adjacent to the injury site, stearate and arachidonate concentrations were increased at 30 min and 2.5 h after injury (p < 0.05). Extravasation of Evans blue was found to be significantly increased in the ipsilateral cortex of injured animals at 30 min and 10 h after brain injury. These results indicate the degradation of membrane phospholipids and blood-brain barrier breakdown in the ipsilateral cortex after lateral CCI brain injury. These results also suggest that arachidonic acid and its metabolites may play a role as a mediator in the blood-brain barrier breakdown associated with cortical impact brain injury in rats.

Animals↗

PubMed1993

Measurement of hippocampal levels of cellular second messengers following in situ freezing.

The in situ freezing technique has been widely used to fix labile metabolites and cellular second messengers in cerebral cortex. In this study, we isolated specific brain regions at 0 degree C from coronal sections of frozen heads following in situ brain freezing and measured regional concentrations of labile metabolites and cellular messengers. These levels in the cortex were compared with those in cortical punches obtained at freezing temperature (less than -40 degrees C) from the same in situ frozen brains and those of cortex dissected from decapitated animals. In both isoflurane- and pentobarbital-anesthetized animals, we observed that the levels of lactate, free fatty acids, inositol 1,4,5-trisphosphate, and diacylglycerol, as well as the proportion of protein kinase C associated with the membrane fraction, were similar in cortical punches taken at freezing temperature and those dissected at 0 degree C. However, with animals decapitated at room temperature, cortical and hippocampal levels of lactate, free fatty acids, and inositol 1,4,5-trisphosphate and the proportion of membrane protein kinase C were significantly higher than those of corresponding brain regions isolated at 0 degree C from in situ frozen brains (p < 0.05). These results indicate that dissection of cortex and hippocampus at 0 degree C following in situ freezing will eliminate decapitation-induced production of artifacts and changes in the levels of cellular second messengers such as inositol 1,4,5-trisphosphate, diacylglycerol, and protein kinase C. The present technique, used in conjunction with in situ freezing, will fix cellular second messengers and labile metabolites in several regions of brain and may facilitate accurate characterization of molecular and cellular mechanisms underlying CNS function.

Animals↗

PubMed1992

Oxygen-derived free radicals and hemolysis during open heart surgery.

Reperfusion injury occurs during open-heart surgery after prolonged cardioplegic arrest. Cardiopulmonary bypass also is known to cause hemolysis. Since reperfusion of ischemic myocardium is associated with the generation of oxygen free radicals, and since free radicals can attack a protein molecule, it seems reasonable to assume that hemolysis might be the consequence of free radical attack on hemoglobin protein. The results of this study demonstrated that reperfusion following ischemic arrest caused an increase in free hemoglobin and free heme concentrations, simultaneously releasing free iron and generating hydroxyl radicals. In vitro studies using pure hemoglobin indicated that superoxide anion generated by the action of xanthine oxidase on xanthine could release iron from the heme ring and cause deoxygenation of oxyhemoglobin into ferrihemoglobin. This study further demonstrated that before the release of iron from the heme nucleus, oxyhemoglobin underwent deoxygenation to ferrihemoglobin. The released iron can catalyze the Fenton reaction, leading to the formation of cytotoxic hydroxyl radical (OH.). In fact, the formation of OH. in conjunction with hemolysis occurs during cardiac surgery, and when viewed in the light of the in vitro results, it seems likely that oxygen-derived free radicals may cause hemolysis during cardiopulmonary bypass and simultaneously release iron from the heme ring, which can catalyze the formation of OH..

Cardiac Surgical Procedures↗

PubMed1992

Reduced free radical generation during reperfusion of hypothermically arrested hearts.

Several studies indicate the presence of hydroxyl radical (OH.) as well as its involvement in the myocardial reperfusion injury. A transition metal-like iron is necessary for the conversion of superoxide anion (O2-) to a highly reactive and cytotoxic hydroxyl radical (OH.). In the present study, we have examined the generation of OH. and free iron in reperfused hearts following either normothermic (37 degrees C) or hypothermic ischemia (5 degrees C). Employing the Langendorff technique, isolated rat hearts were subjected to global ischemia for 30 min at 37 degrees C or 5 degrees C and were then reperfused for 15 min at 37 degrees C. The results of the study suggest that both the OH. generation in myocardium and free iron release into perfusate were significantly lower in hearts made ischemic at 5 degrees C as compared to 37 degrees C. Release of myoglobin and lactic acid dehydrogenase into perfusate also followed a similar pattern. Furthermore, in in vitro studies, chemically generated O2- at 5 degrees C caused a significantly lower rate of oxidation of oxymyoglobin as well as generation of OH. and free iron as compared to 37 degrees C. These results suggest that (1) reperfusion of hypothermic ischemic heart is associated with a reduction in the generation of OH. and cellular damage compared to that of normothermic ischemic heart, and (2) myoglobin, an intracellular protein, is a source of free iron and plays a role in the reperfusion injury mediated by free radicals.

Animals↗

PubMed1992

Decreased alpha 1-adrenergic receptors after experimental brain injury.

The magnitude of neuronal damage in central nervous system (CNS) injury may be related, in part, to alterations in the balance between excitatory and inhibitory neurotransmitters. Previous studies have implicated a role of central inhibitory noradrenergic mechanisms in the pathophysiologic sequelae of traumatic brain injury. In the present study, we examined alpha 1-adrenergic receptor binding after parasaggital lateral fluid percussion (FP) brain injury of moderate severity (2.3 atm) in the rat. At 30 min following injury, the specific binding of [3H]prazosin to membranes isolated from left cortex (injury site) was reduced by 37% in brain-injured animals when compared to sham-operated noninjured animals (p < 0.05). However, there were no significant differences in [3H]prazosin binding to membranes of either contralateral (right) cortex or left and right hippocampi between brain-injured and sham-operated animals. Conversely, at 24 h posttrauma, specific binding to membranes of left cortex, cortex adjacent to injury site, contralateral (right) cortex, and left hippocampus was reduced by 25%, 16%, 27%, and 24%, respectively (all p < 0.05). Scatchard analysis revealed that a reduction of [3H]prazosin binding to membranes of injured animals resulted from a decrease in alpha 1-receptor binding density (B-max) but not from changes in ligand affinity. Histopathologic assessment of neuronal damage at 24 h postinjury revealed neuronal loss within injury site cortex and left hippocampus but no clearly discernible cell loss in contralateral right cortex, suggesting that the decrease in B-max might be a consequence of early pathophysiology of trauma rather than of neuronal cell loss. We suggest that alterations in alpha 1-adrenergic receptors after brain injury may result in decreased inhibitory neurotransmitter action of norepinephrine and may thus contribute to the pathophysiology of traumatic brain injury.

Animals↗

PubMed1992

Enhanced responses to endothelin during perfusion of ischemic myocardium. Myocardial response to endothelin.

Although endothelin perfusion at 50 pM did not reduce the coronary flow, at 200 pM, it reduced the coronary flow to a similar extent in both normal and ischemic hearts. Endothelin at 50 pM concentration enhanced the myocardial levels of inositol-1,4,5-triphosphate (IP3) and diacyl glycerol (DG) in ischemic, but not in normal, hearts. On the other hand, endothelin at 50 pM concentration enhanced the activities of membrane protein kinase C (PKC) and calmodulin dependent (CaM-PK) kinases in normal, but not in ischemic, hearts. The corresponding loss of cytosolic PKC, but not of CaM-PK, suggests a translocation of PKC and an activation of CaM-PK by endothelin. These results suggest that pM concentrations of endothelin activate membrane kinases in normal hearts and enhance PIP2, breakdown in ischemic hearts. The greater CK release and myocardial levels of nonesterified fatty acids by 200 pM concentrations of endothelin in ischemic hearts, as compared to control hearts, suggests that: (1) the myocardial cellular injury and phospholipid breakdown induced by pM concentrations of endothelin are enhanced during reperfusion; and (2) both IP3 and membrane kinase (PKC and CaM-PK) dependent biochemical cascades of reaction, rather than kinases alone, may be involved in the endothelin-induced myocardial cellular injury.

Analysis of Variance↗

PubMed1992

Preconditioning of heart by repeated stunning. Adaptive modification of antioxidative defense system.

Previous studies demonstrated that preconditioning of a heart by repeated stunning can reduce the cellular injury to the heart from subsequent acute ischemic insult. To examine the possible biochemical mechanism for such myocardial preservation afforded by preconditioning, swine heart was subjected to four episodes of 5 min. stunning by occluding the left anterior descending coronary artery (LAD), followed by 10 min. of reperfusion after each stunning. Heart was then made regionally ischemic for 60 min. by LAD occlusion, followed by 6 hrs. reperfusion. Control heart was perfused for 60 min., followed by 60 min. ischemia and 6 hrs. reperfusion. The results of our studies indicated the stimulation of a number of antioxidative enzymes, including Mn-superoxide dismutase (Mn-SOD), catalase, glutathione peroxidase, and glutathione reductase, after repeated stunning and reperfusion. In addition, a number of new proteins were expressed after preconditioning the heart, including some oxidative-stress related proteins and 72 kDa heat-shock protein. These results suggest that preconditioning of a heart by repeated stunning may lead to strengthening of the oxidative defense system of the heart, which is likely to play a role in myocardial preservation during subsequent ischemic and reperfusion injury.

Adaptation, Physiological↗

PubMed1991

Endothelin stimulates degradation of phospholipids in isolated rat hearts.

The abilities of endothelin-1 to cause cellular injury and to enhance the levels of inositol-1,4,5-triphosphate and the breakdown of [14C]arachidonate-labeled phospholipids have been examined in the isolated rat heart model. In 10 minutes, endothelin at 1 and 3 nM concentrations significantly increased the myocardial release of creatine kinase, suggesting endothelin-induced cell injury. The enhanced levels of myocardial inositol-1,4,5-triphosphate and diacyl glycerol by endothelin also suggest the increased breakdown of phosphatidylinositol-4,5-bisphosphate. In addition, endothelin also increased the degradation of other membrane phospholipids as observed by (1) a decrease in [14C]arachidonate radiolabel in phospholipids, (2) an increase in [14C]radiolabel in non-esterified fatty acids and triacyl glycerol, and (3) increased levels of non-esterified fatty acids. The potential role of endothelin-1 in myocardial ischemia-reperfusion injury is discussed.

Animals↗

PubMed1991

Release of endothelin from cultured bovine endothelial cells.

Recently discovered endothelin is a powerful vasoconstrictor of vascular smooth muscle in vitro, which also profoundly affects the mechanical function of the heart. An increased level of plasma endothelin in patients with acute myocardial infarction suggests the enhanced release of endothelin from vascular endothelium under pathophysiological conditions of the heart. The reperfusion of ischemic myocardium is associated with the activation of polymorphonuclear leukocytes (PMN) generating oxygen-derived free radicals (OFR), as well as, enhanced responsiveness of myocardial alpha 1-adrenergic receptor. Both OFR and catecholamines are implicated in the modulation of release of endothelium-derived peptides.

Adrenergic alpha-Agonists↗