Microsomal membrane dysfunction in ischemic rat liver cells

Toxicological significance of liver hypertrophy produced by inducers of drug-metabolizing enzymes

Changes in enzyme activity due to induction by chemicals is an important property that can determine the type of response seen in tissues exposed to environmental chemicals. Two major types of response, acute irreversible liver cell injury or death (necrosis) and long-term cancer induction, are discussed in terms of their modulation by enzyme induction. Most commonly, enzyme induction leads to a more severe toxic response by the liver, and to more cell death. However, inducers may have a protective effect, especially in carcinogenesis, when they most frequently protect against cancer induction if used early in the process. There is a discrepancy between this observation and the increase in mutagenic activity of liver preparations observed after induction. However, when enzyme induction occurs at a later stage, after initiation, it often accelerates or promotes cancer induction. Also, new cell populations constantly observed during liver carcinogenesis are composed of very hypertrophic hepatocytes containing a large amount of smooth endoplasmic reticulum. This is associated with a radical change in enzyme activities in the reticulum, which may account in part for the characteristic resistance exhibited by initiated cells to hepatotoxins and carcinogens. The resistance is considered to be an important property that may play a key role in the development of cancer under some circumstances.

Behavior of cholinesterase and liver mitochondrial function in dogs submitted to normothermic ischemia and reperfusion

PURPOSE: The plasmatic activity of the cholinesterase (CHE) and the liver mitochondrial function, expressed by the ratio of respiratory control (RCR), were studied during normothermic ischemia. METHODS: Sixteen adult mongrels, eight females and eight males were submitted to ischemia by clamping of the hepatic artery, portal vein and infrahepatic inferior vena cava, infra-hepatic, for two h, follwed by reperfusion for 1 h. The CHE and the mitochondrial function were evaluated at 60 and 120 min. of ischemia and at 15 and 60 minutes of reperfusion. RESULTS: The CHE decreased, significantly, during ischemia and in reperfusion. The RCR was decreased at 120 min. of ischemia, returning to the initial values on reperfusion. CONCLUSION: In this study, the CHE was a sensitive indicator of ischemic injury , suggesting irreversibility of ischemia injury. The RCR, by other side, showed a greater sensibility than the CHE in detection sense, during the studied period, the reversibility of the hepatic ischemic injury.

Pathophysiological effects of nicotine on the pancreas: an update

Epidemiological evidence strongly suggests an association between cigarette smoking and pancreatic diseases. It is well recognized that nicotine, a major component in cigarette smoke, is an addictive agent and, therefore, reinforces smoking behavior. The current review update focuses on the genetics of nicotine dependence and its role on the development of pancreatic diseases. The role of smoking and nicotine in pancreatitis and pancreatic cancer development is also discussed. Exposure of laboratory animals to nicotine clearly supports the notion that nicotine can induce pancreatic injury. The mechanism by which nicotine induces such effects is perhaps mediated via signal transduction pathways in the pancreatic acinar cell, leading to enhanced levels of intracellular calcium release, resulting in cytotoxicity and eventual cell death. The induction of pancreatic injury by nicotine may also involve activation and expression of protooncogene, H-ras, which can increase cytosolic calcium via second messenger pathways. Development of pancreatic carcinoma in cigarette smokers as observed in human populations may be the result of activation and mutation of the H-ras gene. A possible pathogenetic mechanism of nicotine in the pancreas activating multiple signal transduction pathways is schematically summarized in Figure 1.

CLORORPROMAZINA E FUNÇÃO MITOCONDRIAL NA ISQUEMIA-REPERFUSÃO RENAL

Introdução e objetivo - em transplante renal com doador cadáver, a função do enxerto depende da manutenção da integridade celular e subcelular, principalmente mitocondrial. Neste estudo o objetivo foi analisar a função mitocondrial do rins submetidos a período prolongado de isquemia fria, seguido de reperfusão por uma hora, empregando-se, ou não, a clorpromazina previamente à isquemia. Métodos - utilizando autotransplante renal em cães, subdivididos em dois grupos, foram extraidas mitocôndrias de rins submetidos à isquemia fria de 48 horas, seguida de 1 hora de reperfusão pós-transplante. Um grupo recebeu clorpromazina antes da nefrectomia. A análise da fosforilação oxidativa e do intumescimento osmótico ("swelling") mitocôndrial foi comparada com dados obtidos de rins normais, sem isquemia. Resultados - Os dados obtidos para o estado III e IV da respiração não mostraram diferença significativa entre os grupos experimentais. A primeira fase do "swelling" ocorreu em tempo semelhante em todos os grupos experimentais. Durante a reversão, os grupos I e II se comportaram de maneira estatisticamente semelhante, com frações de reversão de 57%, e 68%, respectivamente, valores significativamente menores que os obtidos para o grupo normal (99%) (grupo I: p = 0,0374 e grupo II: p = 0,0221). Discussão - é conhecida a ação protetora da clorpromazina na isquemia renal normotérmica. Entretanto, os dados aqui obtidos mostram que após 48 horas de isquemia fria, o grupo II (clorpromazina) comportou-se de maneira semelhante ao grupo I (hipotermia isolada) tanto no estudo da fosforilação oxidativa, quanto no "swelling", embora os valores apresentem tendência a serem maiores no grupo II. Isto pode ser devido a alguns fatores, como: 1) a clorpromazina possui efeito protetor mínimo quando o tempo de isquemia é prolongado; 2) seu efeito pode ser afetado ou sua ação protetora sobreposta àquela imposta pela hipotermia; 3) tempo de reperfusão curto para manifestação de seus efeitos.

Deleterious effects of xanthine oxidase on rat liver endothelial cells after ischemia/reperfusion

Previous studies have demonstrated that reactive oxygen species are involved in ischemic injury. The present work was undertaken to determine in vivo the role of xanthine oxidase in the oxygen free radical production during rat liver ischemia and to examine the activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) during the same period. Our results indicate a 4-fold increase in xanthine oxidase activity between 2 and 3 hours of normothermic ischemia, in parallel with a decrease in cell viability. Moderate hypothermia delays both events. Under the same conditions, the activity of oxygen radical scavenging enzymes remains unchanged. Moreover, we have compared in vitro the susceptibility of isolated liver cells to an oxidative stress induced by O2.-, H2O2 and .OH. Our results reveal that endothelial cells are much more susceptible to reactive oxygen species than hepatocytes, probably because they lack H2O2-detoxifying enzymes. These findings suggest that xanthine oxidase might play a major role in the ischemic injury mainly at the level of the sinusoidal space where most endothelial cells are located.

The effects of allopurinol and SOD on lipid peroxidation and energy metabolism in the liver after ischemia in an aerobic/anaerobic persufflation

This study was aimed at examining the vulnerability of the liver to oxygen-free radicals upon reoxygenation after prolonged ischemia. Livers from male Wistar rats were first flushed with Ringer's and Euro-Collins solutions. After ischemic storage in Krebs-Henseleit solution at 37 degrees C for 60 min and in Euro-Collins solution at 4 degrees C for another 60 min, they were then persufflated with either gaseous O2 or N2 for 30 min at 37 degrees C, and rinsed again with Ringer's solution. Enzyme concentrations and calcium ion activities were measured in the effluent rinsing solution after passage through the liver. Treatment with superoxide dismutase (SOD) or allopurinol resulted in a significant reduction of tissue injury, determined by the enzyme loss, calcium uptake, and lipid peroxidation upon persufflation with O2. Allopurinol also improved the tissue levels of ATP and the sum of adenine nucleotides after aerobic persufflation, whereas SOD did not. Notwithstanding, neither treatment had any effect on anoxic persufflation with N2. Thus, we conclude that the postischemic liver is susceptible to oxygen-induced free radical injury and that allopurinol and SOD promote specific antioxidative protection of the liver, with the exclusion of side effects related to substrates or perfusion modalities.

Involvement of oxygen in harvesting injury of the liver. An experimental study including substrate free organ persufflation to evaluate a specific therapeutic approach

The present study was undertaken to assess the role of oxygen free radicals relating to cell damage upon reoxygenation of the ischemically altered isolated rat liver. Livers were excised and flushed via the portal vein with Ringer's solution and Euro-Collins solution, to which superoxide dismutase (SOD) was added in the experimental group. After warm ischemia at 37 degrees C and cold storage at 4 degrees C, the livers were reperfused via the portal vein with carbogen-saturated Krebs-Henseleit solution. Other livers were subjected to a retrograde persufflation via the infrahepatic caval vein with either oxygen or nitrogen and then rinsed with Ringer's solution. During reperfusion, SOD-treated livers showed markedly reduced vascular resistance, lower enzyme release and enhanced VO2 accordingly, energy charge at the end of reperfusion was significantly higher in the treated group. With reference to the tissue content of malondialdehyde, SOD-treated livers showed significantly less damage than the corroboration for these data. Enzyme activities in the eluate were significantly reduced under anoxic conditions as well as in the presence of SOD. We conclude from these data that oxygen free radicals do exert a detrimental impact on the reoxygenated liver, which could be specifically suppressed by application of exogenous SOD.

Histopathological and ultrastructural changes in simulated large colonic torsion and reperfusion in ponies

This investigation examines the histological and ultrastructural lesions of the colonic mucosa during terminal experimental infarction and subsequent reperfusion. Four ponies were anaesthetised and subjected to surgical torsion of the colon. Biopsies were collected at hourly intervals for 3 h, at which point the torsions were corrected. Circulation was re-established for 2 h and the bowel was re-biopsied at hourly intervals. The ponies were killed while under anaesthesia. During the 3 h experimental infarction, the bowel became macroscopically thickened and dark purple. Histologically, the mucosa degenerated from Grade 0 to Grade 3. Ultrastructurally, there was progressive micro-vascular distension with erythrodiapedesis and damage to the interstitial cells. Spaces developed between the bases and sides of the columnar epithelial cells and sloughing followed subsequently. During the 2 h reperfusion interval, the mucosa continued to degenerate rapidly to a Grade 5, and was characterised by extensive interstitial damage, oedema, cellular swelling, necrosis and mitochondrial damage. The results showed that the experimentally infarcted colonic mucosa degenerated sequentially. Following circulatory reestablishment, continued rapid mucosal degeneration characteristic of reperfusion injury occurred. Reperfusion injury is probably responsible, at least in part, for the often poor outcome of infarcted bowel in horses following surgical correction.

Lipid peroxidation is a nonparenchymal cell event with reperfusion after prolonged liver ischemia

A proposed mechanism for irreversible ischemic liver damage has been peroxidation of membrane phospholipids by free radicals. However, the hepatocyte is laden with enzymes which are antioxidants and, therefore, ought to be relatively resistant to oxidative injury. To test the hypothesis that free radical damage from ischemia and reperfusion of the liver is a nonparenchymal cell process, we studied an in vivo model of ischemia. A point of transition from reversible to irreversible ischemia was defined at greater than or equal to 60 min of total ischemia by serial measurements of ATP at control, end of ischemia, and end of reperfusion periods (n = 6 each). Nonparenchymal cells were separated out of 10 livers in each ischemic group using a Percoll gradient. Second derivative spectroscopy did not detect conjugated dienes in any hepatocellular fraction, total cellular, mitochondrial, or microsomal, but did in the nonparenchymal cell fractions of livers from the 60- and 90-min ischemia groups. This in vivo study shows that irreversible ischemia in the rat liver is associated with free radical lipid peroxidation, but that the nonparenchymal cells rather than hepatocytes are the focus of this injury.

Culture and comparison of human bronchial and nasal epithelial cells in vitro

Human nasal and bronchial epithelial cells were cultured in vitro and compared morphologically and functionally. Morphologic assessment by both light and electron microscope and indirect immunoperoxidase staining techniques confirmed the identity of the two cell types as being epithelial. Light microscopy of confluent cultures revealed tightly packed cell monolayers, whilst electron microscopy showed that cells were linked by tight junctions. Estimation of cell size by planimetry found these cells to have a mean width of 10.6 +/- 1.1 microns for nasal cells and a mean width of 10.2 +/- 1.0 microns for bronchial cells. A high proportion of both the nasal and the bronchial cells exhibited features of the mature ciliated cell types, and constituted between 50 and 76% of the total cells at the earlier stages of culture although this decreased to between 16 and 23% of the total by 4 weeks in culture. The ciliary beat frequencies of the nasal and bronchial cells were found to be similar at 10.8 +/- 0.7 Hz and 11.8 +/- 2.3 Hz, respectively. The cilial beat on adjacent cells was synchronous, suggesting the presence of intercellular communication between the neighbouring cells. These studies demonstrated that there was little difference between the cultured nasal and bronchial epithelial cells with respect to either their morphology or ciliary activity.

The mechanism of acute cytotoxicity of triethylphosphine gold(I) complexes. II. Triethylphosphine gold chloride-induced alterations in mitochondrial function

Triethylphosphine gold complexes have therapeutic activity in the treatment of rheumatoid arthritis. Many of these compounds are also highly cytotoxic in vitro to a variety of tumor and non-tumor cell lines. Triethylphosphine gold chloride (TEPAu) is highly cytotoxic to isolated rat hepatocytes at concentrations greater than 25 microM. The earliest changes that could be detected in hepatocytes included bleb formation in the plasma membrane, alterations in the morphology of mitochondria, and rapid decreases in cellular ATP and oxygen consumption. The degradation of ATP could be followed sequentially through ADP and AMP and was ultimately accounted for entirely as xanthine. The sum of adenine and xanthine-derived nucleotides remained constant throughout the experiments. TEPAu (50 microM) caused a significant decrease in the hepatocyte ATP/ADP ratio and energy charge within 5 min. The antioxidant, N,N'-diphenyl-p-phenylenediamine (DPPD), which blocked TEPAu-induced malondialdehyde formation but not cell death, also had no effect on the decreases in oxygen consumption, ATP, ATP/ADP ratio, or energy charge. In isolated rat liver mitochondria, TEPAu (1 microM) caused significant reductions in carbonyl cyanide-4-trifluoromethoxyphenylhydrazone (FCCP) (uncoupled)-stimulated respiration. TEPAu (5 microM) inhibited state 3 respiration and the respiratory control ratio without affecting state 4 respiration and caused a rapid dissipation of the mitochondrial-membrane hydrogen-ion gradient (membrane potential). Concentrations greater than 5 microM also inhibited state 4 respiration. TEPAu caused a concentration-dependent inhibition of FCCP-stimulated respiration with pyruvate/malate and succinate as substrates but had not effect on ascorbate/tetramethyl-p-phenylenediamine-supported respiration. The inhibition of state 4 respiration and FCCP-stimulated respiration by TEPAu (10 microM) could be reversed by the addition of 2 mM dithiothreitol. Dithiothreitol also partially protected cells from TEPAu-induced injury and reversed the TEPAu-induced depletion in cellular ATP. These data indicate that TEPAu may be acting functionally as a respiratory site II inhibitor, similar to antimycin. The reversal of TEPAu-induced inhibition of mitochondrial respiration and cell lethality by dithiothreitol suggests that mitochondrial thiols may be involved.

Abnormal calcium transport into microsomes of grey platelet syndrome

Calcium uptake into isolated membrane vesicles from two patients with a grey platelet syndrome has been investigated. An increase in calcium transport appears in both patients when compared to controls. Determination of the kinetic parameters of the calcium transport system gave similar apparent affinity for calcium and an increase in the calcium uptake velocity. This increase in calcium transport is correlated with the increase of the associated Ca2+ activated ATPase activity. The results would suggest a new relationship between the ultrastructural and functional abnormalities of the grey platelet syndrome.

Evaluation of the role of calcium in cytotoxic injury in isolated rat pancreatic acini

The role of extracellular Ca2+ in pancreatic acinar membrane damage (cellular injury) by nicotine, membrane-active agents (mellitin, snake venom and Ca2+ ionophore A23187) and secretagogues (CCK-8 and secretin) was investigated. Freshly isolated dispersed pancreatic acini from 18 h fasted adult rats were incubated with one of the aforementioned agents, in the absence and presence of Ca2+. Cellular injury was assessed by measuring the release of pulse-labeled 51Cr and LDH. In addition, release of amylase, trypsinogen and chymotrypsinogen was also determined. In the absence of Ca2+ nicotine (6 mM) caused a profound release of 51Cr and LDH as well as amylase, trypsinogen and chymotrypsinogen from the isolated pancreatic acini. Release of these enzymes and 51Cr decreased sharply with addition of increasing concentrations (0.25-5 mM) of Ca2+. Release of 51Cr and amylase by snake venom (50 micrograms/ml) was found to be 100 and 25% higher, respectively, in the absence of Ca2+ than in its presence. On the other hand, the Ca2+ ionophore A23187 (7 micrograms/ml) was found to be effective in releasing 51Cr and amylase only in the presence of Ca2+. CCK-8, (0.25nM), secretin (1 microM) and mellitin (0.5 microgram/ml) although significantly stimulated amylase secretion (225-350%) in the presence of Ca2+, none of the agents induced 51Cr release from acini, either in the absence or in the presence of extracellular Ca2+. It is concluded that the extracellular Ca2+ plays no specific role in cytotoxic injury in isolated pancreatic acini.

Formation of unesterified choline by rat brain

Two preparations of rat brain (ischemic intact brain and homogenized whole brain) formed large amounts of unesterified (free) choline when incubated at 37 degrees C. The accumulation of choline was inhibited by microwave irradiation of brain, or by heating of brain to 50 degrees C, and was maximal at 37 degrees C at pH 7.4-8.5. Choline formation was only observed in subcellular fractions of brain that contained membranes. In homogenates of brain, choline accumulated at a rate exceeding 10 nmol/mg protein per h. There was a significant decrease in brain phosphatidylcholine concentration (of 50 nmol/mg protein) during incubation for 1 h at 37 degrees C. Concentrations of phosphocholine rose (by 2.3 nmol/mg protein), and concentrations of glycerophosphocholine and sphingomyelin did not change during this period. We used radiolabeled phospholipids to trace the fate of phosphatidylcholine and sphingomyelin during incubations of homogenates of brain. Phosphatidylcholine was degraded to form phosphocholine, glycerophosphocholine and free choline. No lysophosphatidylcholine accumulated. Sphingomyelin was degraded to form phosphocholine and a small amount of free choline. Magnesium ions stimulated choline production, while zinc ions were a potent inhibitor. Other divalent cations (calcium, manganese) had little effect on choline accumulation. ATP concentrations in brain homogenates were less than 5 nmol/mg protein (rapidly microwaved brain contained 27 nmol/mg protein). Addition of ATP or ADP to brain homogenates increased ATP concentrations and significantly inhibited choline accumulation. ATP diminished the formation of choline from added phosphatidylcholine, lysophosphatidylcholine, phosphocholine and glycerophosphocholine. The effects of ATP, zinc ion, or magnesium ion upon choline accumulation were not mediated by changes in the rates of utilization of choline for formation of phosphocholine or phosphatidylcholine. In summary, we showed that there was enhanced formation of choline when ATP concentrations within brain were low. This choline was derived, in part, from the degradation of phosphatidylcholine, and we suggest that phospholipase A activity was the primary initiator of choline release from this phospholipid.

Structural alterations of the inner mitochondrial membrane in ischemic liver cell injury

Mitoplasts were prepared from 3-h ischemic livers in an attempt to define the structural alterations in the inner membrane that may account for the functional deficiencies of ischemic mitochondria. Mitoplasts from both control and ischemic livers had similar specific activities of cytochrome oxidase and succinate-cytochrome c reductase. With both preparations, the specific activity of rotenone-insensitive NADH-cytochrome c reductase was 10-fold lower than in the mitochondria from which they were prepared. Ischemic mitoplasts had no respiratory control with ADP, and had a slightly reduced phospholipid to protein ratio and an increased cholesterol to protein ratio. As a result, the cholesterol to phospholipid molar ratio was increased from the control of 0.04 to 0.08. There were also differences in the content of individual phospholipid species. Phosphatidylcholine increased by 15%, while cardiolipin decreased by 60%. There were increases in sphingomyelin and in the lysophospholipids of phosphatidylcholine, ethanolamine, and cardiolipin. Pretreatment with chlorpromazine did not prevent these changes. Linoleic acid was decreased by 35% in ischemic phospholipids, and the content of free fatty acids was increased 4-fold. Electron spin resonance spectroscopy of mitoplasts spin labeled with either 5- or 12-doxyl stearic acid revealed an increased molecular order (decreased fluidity) of ischemic inner mitochondrial membranes consistent with the increased cholesterol to phospholipid ratio. The data indicate activation of a phospholipase A in ischemic mitochondria with the resulting accumulation of products of lipid hydrolysis. This conclusion further emphasizes the close similarity between the structural and functional consequences of ischemia in the intact animal and the effect on isolated mitochondria of the activation of the endogenous phospholipase A. In both cases the major functional alterations are attributable to changes in the permeability of the inner mitochondrial membrane induced by the accumulation of lysophospholipids.

Ultrastructural changes in rat liver sinusoids during prolonged normothermic and hypothermic ischemia in vitro

By means of electron microscopic analysis of liver fragments incubated in an air-tight wrapping (in vitro ischemia), the following facts have been established with regard to the development of signs of irreversible damage in cells from the sinusoidal wall compared with hepatocytes. With normothermic (37 degrees C) in vitro ischemia, signs of irreversible damage appeared in cells of the sinusoidal wall at a a much earlier stage than in hepatocytes (60-90 min and 90 min-2 h respectively). With in vitro ischemia in the cold (4 degrees C), these differences were even more marked; irreversible cell damage was apparent after between 24 and 36 h incubation in endothelial cells, whereas in hepatocytes flocculent densities followed by other signs of irreversible damage were found only after 79 h incubation. These findings are discussed in relation to the 'no reflow' phenomenon after ischemia in general. The rule that changes in the vascular system following ischemia may well obscure the actual sensitivity of parenchymal cells is particularly applicable to the liver. Attempts to lengthen the period of ischemia which 'liver tissue' can stand for example, with a view to transplantation, attention should be focussed primarily on the events in the sinusoidal wall.

Plasma ornithine carbamyl transferase level as an indicator of ischaemic injury of rat liver

The activity of ornithine carbamyl transferase (OCT) and glutamate pyruvate transaminase (GPT) in serum has been correlated with the extent of necrosis 24 h after different periods of ischaemia in rat liver. The extent of necrosis has been quantified as the volume density of necrosis in the total ischaemic liver lobes using tetranitro BT. The GPT-activity in serum is maximal between 1 and 5 h after different periods of ischaemia, whereas OCT reaches its maximum between 5 and 12 h after ischaemia. The total amount of leaked enzyme-activity as well as the peak value give a linear correlation with the extent of necrosis for OCT and GPT. There is a difference between the character of these two enzymes in that a small leakage of GPT does not indicate liver cell necrosis later on. However, the appearance of OCT in the blood, an enzyme localized in the mitochondrial matrix, has a predictive value for the extent of necrosis, likely to occur later on. GPT, an enzyme from the cytoplasm, can also occur in the blood during the reversible stage of liver cell damage.

Cerebral phospholipid content and Na+,K+-ATPase activity during ischemia and postischemic reperfusion in the mongolian gerbil

Using bilateral carotid artery occlusion in adult gerbils we examined the effects of ischemia and ischemia/reperfusion on cerebral phospholipid content and Na+,K+-ATPase (EC 3.6.1.3) activity. In contrast to the large changes in phospholipid content and membrane-bound enzyme activity that have been observed in liver and heart tissues, we observed relatively small changes in the cerebral content of total phospholipid, phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylethanolamine (PE) following ischemic intervals of up to 240 min. Following 15 min of ischemia the cerebral content of sphingomyelin (SM) was decreased to less than 50% of control values but returned to near-normal levels with longer ischemic periods. Significant decreases in the cerebral content of phosphatidylinositol (PI) and phosphatidic acid (PA) were observed following shorter intervals of ischemia (15-45 min). Na+,K+-ATPase activity of cerebral homogenates prepared from the brains of gerbils subjected to 30-240 min of ischemia was decreased but significantly different from control activity only after 30 min of ischemia (-29%, p less than or equal to 0.05). With the exception of PS, reperfusion for 60 min following 60 min of ischemia resulted in marked increases in cerebral phospholipid content with PC, SM, PI, and PA levels exceeding and PE levels equal to preischemic values. Longer periods of reperfusion (180 min) resulted in decreases in cerebral phospholipid content toward (PC, SM, PI, and PA) or below (PE) preischemic levels. In contrast, the cerebral content of PS significantly decreased during reperfusion (-51% at 60 min, p less than or equal to 0.05) and remained below preischemic values even after 180 min of reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of fungal toxins on renal slice calcium balance

Citrinin and ochratoxin A disrupt renal function in many animal species. The mechanism(s) underlying these actions is (are) unclear. Although citrinin has been shown to bind covalently to renal tissue, there also is evidence that it is active in the unmetabolized form. Altered calcium homeostasis has been suggested as an event which might mediate cell injury and/or death; a possible role for calcium in citrinin- or ochratoxin A-induced nephrotoxicity is reported here. Renal cortical slice calcium balance was monitored by the uptake of 45Ca. Either ochratoxin A or citrinin added to fresh renal cortex slices enhanced 45Ca accumulation. These effects were evident as early as 5 min after addition of the toxins. Greater 45Ca uptake occurred with bathing solution calcium concentration of 1.1 mM than in the absence of added carrier calcium. Finally, the effect of citrinin to reduce p-aminohippurate accumulation by renal cortical slices was greater in the presence of calcium than in its absence.

Mitochondrial calcium accumulation and respiration in ischemic acute renal failure in the rat

Changes in mitochondrial (Mito) calcium (Ca++) and Mito respiration have been demonstrated 24 hr after a renal ischemic insult. The Ca++ accumulation has been suggested to contribute to impaired Mito function; alternatively, the Mito Ca++ accumulation could be a late event resulting from cell death. The present aim was, therefore, to determine the sequence of changes in Mito function in ischemic acute renal failure (ARF) induced by 45 min of bilateral renal pedicle clamping in the rat. Animals were studied at the end of clamping, 1, 4, and 24 hr after reflow. By 24 hr, the serum creatinine level had risen progressively to almost ten times control values and fractional excretion of sodium and water were increased. Mito respiration (state 3, adenosine diphosphate-stimulated; acceptor control ratio, state 3/state 4; and uncoupled, FCCP) was severely depressed immediately after 45 min of clamping but improved significantly at 1 and 4 hr after reflow although remaining below sham-operated controls. At 24 hr, when ischemic ARF was established, Mito respiration was again severely depressed. Mito Ca++ was increased slightly but significantly at the end of clamping and increased progressively at 1, 4, and 24 hr after reflow. The Mito Ca++ accumulation was not only demonstrated to occur very early after the ischemic insult, but was relatively selective since it was not associated with Mito Mg++ accumulation. Moreover, the increased Mito Ca++ during reperfusion (1, 4, and 24 hr) demonstrated a significant correlation with the decreased state 3 respiration and the rising serum creatinine level (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Accumulation of unesterified arachidonic acid in ischemic canine myocardium. Relationship to a phosphatidylcholine deacylation-reacylation cycle and the depletion of membrane phospholipids

Studies in ischemic canine left ventricle have shown that the depletion of membrane phospholipids is a critical event in the development of a sarcolemmal calcium permeability defect and associated irreversible myocyte injury. The mechanism of phospholipid loss is unclear, but may be due to the activation of endogenous phospholipases. Since arachidonic acid is a fatty acid found almost entirely in phospholipid, increases in arachidonate provide evidence for increased phospholipase activity. The present study was designed to examine the temporal relationship of the accumulation of free arachidonate with the onset of phospholipid depletion during fixed ligation of the left anterior descending coronary artery in canine myocardium. The following results were demonstrated in ischemic canine myocardium: (1) the accumulation of unesterified arachidonate is minimal during 10-30 minutes of ischemia, but is significantly increased after prolonging the duration of ischemia to 1-3 hours; (2) significant increases in arachidonate precede the development of a significant decrease in total phospholipid content; (3) the decrease in the arachidonate content of phosphatidylcholine is accompanied by similar decreases in all of the fatty acyl moieties; (4) the arachidonate content of lysophosphatidylcholine and diacylglycerol are unchanged during myocardial ischemia; (5) there is evidence of a deacylation-reacylation cycle in phosphatidylcholine prior to the accumulation of free arachidonate; (6) the fatty acyl specificity of the lysophosphatidylcholine acyltransferase corresponds to the pattern of fatty acyl remodeling of phosphatidylcholine during early myocardial ischemia. These data suggest that the accumulation of arachidonate may be a more sensitive measure of phospholipid degradation than the decrease in total phospholipid content in ischemic canine myocardium. It is postulated that the defective reacylation of arachidonate into phosphatidylcholine may contribute to the net loss of membrane phospholipid during myocardial ischemia.

Effects of liver ischemia on degradation of different classes of hepatic proteins

The effects of liver ischemia on hepatic protein degradation were studied in rats. In one series of experiments degradation was measured in incubated liver slices as release of trichloroacetic acid soluble radioactivity from proteins prelabelled with L-(14C)-leucine during 4 h (short-lived proteins) or during 24 h (long-lived proteins). In another series of experiments protein degradation was determined in vivo by measuring decay of radioactivity in hepatic proteins prelabelled with (14C)-sodium bicarbonate administered intraperitoneally 4 h or 24 h before induction of liver ischemia. Degradation of short-lived proteins was reduced by 50% both in vitro and in vivo during liver ischemia while breakdown of long-lived proteins was unchanged. Thus, short-lived and long-lived proteins were differently affected by liver ischemia. These results are consistent with the concept of distinct proteolytic pathways for different classes of proteins.

Biochemical and ultrastructural changes in rat liver plasma membranes after temporary ischemia

In this study we have attempted to correlate reversible and irreversible cell damage induced by in vivo or in vitro ischemia with characteristics of the plasma membranes of liver parenchymal cells, as detected biochemically and ultrastructurally. The effects of in vivo or in vitro ischemia appeared to be similar. It was virtually impossible to isolate a substantial membrane fraction from ischemic livers, probably because of changes in the physical properties of the membranes by ischemia. The isolated membranes of ischemic liver cells show ultrastructural changes including the occurrence of many vesicular profiles and alterations in junctional complexes expressed by extended and smudged electron densities along the lateral surfaces. The microvilli of the bile canaliculi disappeared after only 15 min ischemia and cytoplasmic densities associated with junctional complexes also appeared extended and smudged. These changes correspond with the alterations observed in ischemic isolated membranes. After 30 min in vivo ischemia the activity of 5'-mononucleotidase used as a marker enzyme for plasma membranes, decreased by 75%, whereas the activity of thymidine 5'-phosphodiesterase was reduced only slightly. The changes in these enzyme activities were more prominent after in vitro ischemia than after in vivo. The morphological and biochemical changes observed in rat hepatocyte plasma membrane during the early stage of injury have no value in predicting the occurrence of necrosis in a later phase of the process since profound changes occur in plasma membrane properties after even short periods of ischemia (i.e. during the reversible stage).

Role of lipid peroxidation in tissue injury after hepatic ischemia

Ischemia and anoxia are associated with decreased concentrations of cellular antioxidants. The hypothesis that recirculation of oxygenated blood to previously ischemic tissue may result in enhanced free-radical reactions leading to lipid peroxidation and tissue damage was investigated. Elevated hepatic conjugated diene concentrations were detected 60 min after treatment of rats with carbon tetrachloride, a positive control, but were not found after 90 min ischemia or at 5 or 60 min after reperfusion of ischemic tissue. These findings suggest that lipid peroxidation may not be an early event in ischemia-induced necrosis but do not rule out a role of other free-radical reactions in the pathogenesis of ischemic necrosis.

Improved blood flow and protein synthesis in the postischemic liver following infusion of dopamine

To study the effects of dopamine on hepatic blood flow and protein synthesis in a condition with reduced liver blood flow, dopamine (5 micrograms X kg-1 X min-1) or saline was infused intravenously following a period of liver ischemia in rats. Hepatic blood flow was measured by xenon washout technique and protein synthesis by leucine incorporation into proteins in incubated liver slices. Blood flow and protein synthesis in the postischemic liver were restituted faster and more completely in dopamine-treated rats suggesting that dopamine infusion can be of beneficial effect on liver metabolism in situations with reduced hepatic blood flow.

The value of enzyme leakage for the prediction of necrosis in liver ischemia

Following the clamping of the afferent vessels of the left lateral and median lobes in rat liver, a considerable part of these lobes show signs of necrosis 24 h after 90 min of ischemia, whereas no necrotic areas can be detected after 30 min interruption of the blood flow. The purpose of this study was to examine the value of an analysis of the leakage of enzymes from the liver parenchyma in the early phase after restoration of the blood flow after ischemia for a prediction of the occurrence of necrosis. Leakage of the enzymes GPT, GOT and LDH can be detected in the blood plasma with a maximum activity between 1 and 5 h both following 30 and 90 min of ischemia; a considerable difference in clearance is observed, however, in the period afterwards, the normal situation being reached after 24 h with the 30-min ischemic period, but not following the 90-min period. With use of an enzyme histochemical reaction, in situ a depletion of LDH-activity in the hepatocytes could be detected within a short period of time after 30 min temporary ischemia and a restoration during the following period of 24 h; the decrease in LDH-activity persisted during 24 h with a 90-min period of ischemia. Electronmicroscopically cytoplasmic blebs arisen from hepatocytes are observed in the lumen of sinusoids immediately after 30 min of ischemia, whereas after 90 min of ischemia actual leakage of cytoplasmic material takes place through the damaged surface of the hepatocytes. Enzyme leakage probably takes place via these both types of shedding of cytoplasm. It is concluded that the enzyme leakage as such cannot be used as a discriminating test between reversible and irreversible damage of the liver parenchyma.

Role of mitochondria in ischemic acute renal failure

Ischemic ARF is characterized by progressive mitochondrial accumulation of Ca++ which is inversely correlated with the level of oxidative phosphorylation. At least two possibilities exist which would be compatible with these data 1) depressed respiration leads to Ca++ accumulation or 2) increased mitochondrial Ca++ leads to reduced mitochondrial respiration. We favor the latter hypothesis for the reasons outlined above; furthermore, this conclusion is supported by the observations of Lehninger, made some 20 years ago: first, that either oxidative phosphorylation or mitochondrial Ca++ accumulation can be accomplished by intact mitochondria but that these events cannot occur simultaneously and second, that Ca++ accumulation takes precedence over oxidative phosphorylation. Our observation made during post-ischemic reflow that mitochondrial Ca++ accumulation occurs to a significant degree, strongly suggest a potential role for mitochondrial Ca++ overload in the pathogenesis of ARF. Nevertheless, this is not an irreversible pathogenetic process. Clearly, impermeant solutes, vasodilators and Ca++ membrane blockers will alter the natural history of this injury and prevent the severity of the functional defect. A common mechanism of action may involve direct or indirect modification of cellular Ca++ overload in renal vascular and epithelial tissue. The vascular smooth muscle may then revert to a less constricted state with a subsequent more rapid recovery of renal blood flow and that the renal epithelial cell death may be minimized thereby reducing tubular obstruction.

Effect of a transitory ischaemia on the structure-linked latency of rat liver acid phosphatase and beta-galactosidase

The structure-linked latency of acid phosphatase and beta-galactosidase was studied in rat liver lobes made ischaemic for 1 or 2 h and then recirculated with blood for increasing periods. Free activity of acid phosphatase and unsedimentable activity of beta-galactosidase are increased in homogenates of ischaemic livers. When ischaemia had been maintained for 1 h, the recovery of normal latency for both enzymes was observed 1 h after re-establishment of the blood flow. After a 2 h period of ischaemia, unmasked activity markedly decreases during the first 1 h after restoration of blood flow; after that, a large and irreversible secondary rise takes place. Chlorpromazine, injected 30 min before or just after induction of ischaemia, extensively prevents the latency decrease occurring during restoration of blood flow. Modifications of the hydrolase distribution pattern obtained after differential centrifugation are in agreement with the latency changes. These results suggest that a 2 h ischaemia causes an alteration of the liver lysosomes that is largely reversible and that restoration of blood flow induces an irreversible alteration of these organelles. Chlorpromazine treatment prevents the irreversible lesion from taking place.