Decrease In Tissue pH Research Articles

A dangerous liaison: Spreading depolarization and tissue acidification in cerebral ischemia.

Brain pH is precisely regulated, and pH transients associated with activity are rapidly restored under physiological conditions. During ischemia, the brain's ability to buffer pH changes is rapidly depleted. Tissue oxygen deprivation causes a shift from aerobic to anaerobic metabolism and the accumulation of lactic acid and protons. Although the degree of tissue acidosis resulting from ischemia depends on the severity of the ischemia, spreading depolarization (SD) events emerge as central elements to determining ischemic tissue acidosis. A marked decrease in tissue pH during cerebral ischemia may exacerbate neuronal injury, which has become known as acidotoxicity, in analogy to excitotoxicity. The cellular pathways underlying acidotoxicity have recently been described in increasing detail. The molecular structure of acid or base carriers and acidosis-activated ion channels, the precise (dys)homeostatic conditions under which they are activated, and their possible role in severe ischemia have been addressed. The expanded understanding of acidotoxic mechanisms now provides an opportunity to reevaluate the contexts that lead to acidotoxic injury. Here, we review the specific cellular pathways of acidotoxicity and demonstrate that SD plays a central role in activating the molecular machinery leading to acid-induced damage. We propose that SD is a key contributor to acidotoxic injury in cerebral ischemia.

A potential post-removal pH neutralization strategy to mitigate nasal button battery injuries

ObjectiveButton batteries (BBs) impacted in the nose of children can cause septal perforation, synechia, atrophy, necrosis and deformities such as saddle nose. Developing mitigation strategies that can reduce tissue damage after BB removal can decrease these complications. Methods3 V lithium BBs were placed on the cadaveric sheep nasal septum model segments. After 3, 6, 12 and 24 h, BB on each segment was removed and intermittent irrigation was performed with 0.25% acetic acid solution. Irrigation with saline was performed as the control. Visual tissue damage that occurred just before and after irrigation was photographed. BB voltage, temperature and pH changes in the tissue were recorded. Each segment was examined after irrigation for the depth of necrosis and presence of cartilage necrosis. ResultsThe voltage of 3 V lithium BB was observed to drop to about half at the end of the 3rd hour. It was observed that full-thickness mucoperichondrial necrosis occurred in the nasal septum segments at all time points. Although 0.25% acetic acid irrigation significantly decreased tissue pH compared to saline without increasing temperature, it did not show a significant superiority compared to saline in reducing neither visually nor histologically damage. While cartilage necrosis was not observed for the first 12 h, it was measured 105 μm in the segment irrigated with 0.25% acetic acid at the end of 24 h, and 518 μm in the segment irrigated with saline. ConclusionsThe pH neutralization strategy with post-removal 0.25% acetic acid irrigation to mitigate nasal BB injury appears to be ineffective in reducing the full-thickness mucoperichondrial necrosis starting within 3 h. Although this strategy seems to decrease the progression of cartilage necrosis starting after 12 h, the development of pre-removal strategies for the first 3 h may be more effective and superior in reducing mucoperichondrial damage.

Electrophysiological evidence for light-activated cation transport in calcifying corals.

Light has been demonstrated to enhance calcification rates in hermatypic coral species. To date, it remains unresolved whether calcifying epithelia change their ion transport activity during illumination, and whether such a process is mediated by the endosymbiotic algae or can be controlled by the coral host itself. Using a modified Ussing chamber in combination with H+ sensitive microelectrode measurements, the present work demonstrates that light triggers the generation of a skeleton positive potential of up to 0.9 mV in the hermatypic coral Stylophora pistillata. This potential is generated by a net flux of cations towards the skeleton and reaches its maximum at blue (450 nm) light. The effects of pharmacological inhibitors targeting photosynthesis 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and anion transport 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) were investigated by pH microelectrode measurements in coral tissues demonstrating a rapid decrease in tissue pH under illumination. However, these inhibitors showed no effect on the electrophysiological light response of the coral host. By contrast, metabolic inhibition by cyanide and deoxyglucose reversibly inhibited the light-induced cation flux towards the skeleton. These results suggest that ion transport across coral epithelia is directly triggered by blue light, independent of photosynthetic activity of algal endosymbionts. Measurements of this very specific and quantifiable physiological response can provide parameters to identify photoreception mechanisms and will help to broaden our understanding of the mechanistic link between light stimulation and epithelial ion transport, potentially relevant for calcification in hermatypic corals.

Abstract 9919: PH-low Insertion Peptide (pHLIP) Targets Ischemic Myocardium

pHLIP molecule (∼3 kD) inserts into a lipid bilayer when ambient pH is low. Originally, this property was used for targeted delivery of small molecules, liposomes and nanoparticles conjugated with pHLIP to visualize and treat tumors. Since cardiac ischemia causes a decrease in tissue pH we hypothesized that pHLIP can selectively bind to ischemic myocardium. METHODS. We studied pH-sensitive (Var7) and a pH-insensitive (kVar7) variants of pHLIP conjugated with fluorescent dye Alexa488 in three models. (1) Local myocardial ischemia was induced by repetitively occluding (10 min) and reperfusing (5 s) left coronary artery of anesthetized mice for 2 hr; 100 μL of 80 μM pHLIP were administered IV 3 min prior to the first occlusion. In the end, hearts were excised and retrogradely perfused with Evans Blue to delineate the area at risk. Hearts were frozen and sectioned to measure mean intensity of fluorescence (F). (2) Low flow (5% of normal flow rate) global ischemia was induced in Langendorff-perfused mouse hearts paced at 5 Hz and perfused with 1 μM pHLIP for 15 min. (3) Effects of 10 μM pHLIP on transmembrane potential and developed force were studied in isolated preparations of paced (4 Hz) murine left atrial appendages (AA) at normal and low (6.5) pH. RESULTS. In the model of local ischemia, when pH-sensitive Var7 was used, area of bright fluorescence coincided with the area at risk. F in the area at risk normalized to F in intact myocardium was higher with Var7 (3.89±.43, n=4) than with pH-insensitive kVar7 (1.11±.09, n=5, p.05). In global ischemia, F was higher in the hearts perfused with Var7 vs either kVar7 or Var7 in the absence of ischemia (Var7: 76±8, n=5; kVar7: 25±5, n=4; Var7 + no ischemia: 12±4, n=3, p<.05). In AA exposed to pH 6.5 (but not at pH 7.4), F was higher with Var7 than with kVar7 (76±9 vs 28±3, n=5; p<.05). Neither at the normal or low pH, pHLIP variants affected parameters of transmembrane potential or developed force. CONCLUSIONS. pH-sensitive pHLIP selectively binds to ischemic myocardium without affecting either ectrical or mechanical activity. Based on analogy with applications in oncology, pHLIP can be used for targeted delivery of contrasting agents and drugs to ischemic regions of the heart.

Inhibition of acid‐sensing ion channels by amiloride protects rat articular chondrocytes from acid‐induced apoptosis via a mitochondrial‐mediated pathway

A significant decrease in tissue pH or acidosis is a common feature of numerous diseases, including RA (rheumatoid arthritis). Cartilage homoeostasis is profoundly affected by local acidosis in the joints. The diuretic, amiloride, is neuroprotective in models of cerebral ischaemia, a property attributable to the inhibition of ASICs (acid-sensing ion channels) by the drug. However, little is known about the effect of amiloride on apoptosis induced by extracellular acid in articular chondrocytes. We have found that amiloride could restrain the acid-induced apoptosis of rat articular chondrocytes in vitro. Primary rat articular chondrocytes were isolated, cultured and induced to apoptose by exposure to extracellular solution (pH 6.0), while simultaneously treated with 50-200 μM amiloride. Apoptotic rate, mitochondrial function, levels of apoptosis-related gene Bcl-2 family mRNA and activity of caspase 3/9 in chondrocytes were examined. Amiloride inhibited chondrocyte apoptosis in a dose-dependent manner. Furthermore, amiloride partly restored the levels of mitochondrial membrane potential by regulation of Bcl-2 family gene mRNA expression, and activity of caspase 3/9 in chondrocytes induced by extracellular acid. Our results indicated that amiloride protected against acid-induced apoptosis in rat articular chondrocytes by increasing anti-apoptotic ability and down-regulation of pro-apoptotic factors, thus protecting mitochondrial function.

Acid sensing ion channels - novel therapeutic targets for ischemic brain injury

Ischemic stroke is a leading cause of death and long-term disability in the United States. Unfortunately there is no effective therapeutic intervention other than the use of thrombolytics, which has a limited therapeutic time window of approximately 3 h and the potential side effect of intracranial hemorrhage. The absence of neuroprotective therapy is particularly apparent following the failure of multiple clinical trials using glutamate antagonists as therapeutic agents. Understanding the detailed biochemical changes associated with brain ischemia and the cellular mechanisms involved in ischemic brain injury are critical for establishing new and effective neuroprotective strategy. Dramatically decreased tissue pH, or acidosis, is a common feature of ischemic brain, and has been suggested to play a role in neuronal injury. However, the detailed cellular and molecular mechanisms of such acid induced injury remain elusive. The recent finding that acidosis activates a distinct family of cation channels, the acid-sensing ion channels (ASICs), in both peripheral and central neurons has dramatically changed the landscape of brain ischemia neurochemistry and provided a novel therapeutic target. In CNS neurons, lowering extracellular pH to the level commonly seen in ischemic brain activates inward ASIC currents resulting in membrane depolarization. In the majority of these neurons, ASICs are also permeable to Ca2+. Therefore, activation of these channels induces an increase of [Ca2+]i. Incubation of neurons with acidic solutions reproduces Ca2+-dependent neuronal injury independent of glutamate receptor activation. The acid-induced currents, membrane depolarization, [Ca2+]i increase, and neuronal injury can be inhibited by the blockade of ASIC1a. In focal ischemia, ASIC1a blockade, or ASIC1a gene knockout both protect brain from injury. The blockers of ASIC1a also demonstrate a prolonged therapeutic time window, beyond that of the glutamate antagonists. Thus, Ca2+-permeable ASIC1a may represent a novel therapeutic target for ischemic brain injury.

A microarray study of post-mortem mRNA degradation in mouse brain tissue

Background: Although there is evidence that post-mortem interval (PMI) is not a major contributor to reduced overall RNA integrity, it may differentially affect a subgroup of gene transcripts that are susceptible to PMI-related degradation. This would particularly have ramifications for microarray studies that include a broad spectrum of genes. Method: Brain tissue was removed from adult mice at 0, 6, 12, 18, 24, 36 and 48 h post-mortem. RNA transcript abundance was measured by hybridising RNA from the zero time point with test RNA from each PMI time point, and differential gene expression was assessed using cDNA microarrays. Sequence and ontological analyses were performed on the group of RNA transcripts showing greater than two-fold reduction. Results: Increasing PMI was associated with decreased tissue pH and increased RNA degradation as indexed by 28S/18S ribosomal RNA ratio. Approximately 12% of mRNAs detected on the arrays displayed more than a two-fold decrease in abundance by 48 h post-mortem. An analysis of nucleotide composition provided evidence that transcripts with the AUUUA motif in the 3′ untranslated region (3′UTR) were more susceptible to PMI-related RNA degradation, compared to transcripts not carrying the 3′UTR AUUUA motif. Consistent with this finding, ontological analysis showed transcription factors and elements to be over-represented in the group of transcripts susceptible to degradation. Conclusion: A subgroup of mammalian mRNA transcripts are particularly susceptible to PMI-related degradation, and as a group, they are more likely to carry the 3′UTR AUUUA motif. PMI should be controlled for in human and animal model post-mortem brain studies, particularly those including a broad spectrum of mRNA transcripts.

Changes in tissue pH and temperature after incision indicate acidosis may contribute to postoperative pain.

Incisional pain is a common form of acute pain. Previously, the authors studied persistent pain behaviors caused by incisions, using animal models for postoperative pain. In this study, the authors measured tissue pH and hind paw temperature before and after incision to understand factors that may activate and sensitize nociceptors in the incision. Rats underwent a plantar incision, a gastrocnemius muscle incision, or a cutaneous paraspinal incision. For the hind paw incision, pain behaviors were measured. Tissue pH was measured using a pH-sensitive needle electrode in halothane-anesthetized rats. The pH in the incision was compared to a corresponding control site on the contralateral side of the rat or to the sham-operated group. Plantar tissue pH was 7.16 +/- 0.04 in sham-operated rats. Ten minutes after plantar incision, tissue pH was decreased to 6.91 +/- 0.20 (P < 0.05), and this decrease was sustained through 60 min after incision, when pH was 6.99 +/- 0.06 (P < 0.05). Tissue pH values were 6.95, 6.90, 6.89, and 6.95 (P < 0.05 vs. sham) 4 h and 1, 2, and 4 days after incision, respectively. On postoperative day 7, when plantar pH was same as for the control side (7.13 +/- 0.05), guarding behavior, heat responses, and responses to mechanical stimuli recovered. Outside the incised area in the hind paw, tissue pH was normal. Tissue pH was significantly correlated with all pain behaviors. In the gastrocnemius muscle, tissue pH was 7.14 +/- 0.7 in the sham-operated side. Ten minutes after incision, tissue pH was 6.54 +/- 0.12 (P < 0.05), and muscle pH remained decreased through 60 min after gastrocnemius incision when pH was 6.76 +/- 0.17 (P < 0.05). Tissue pH was also significantly decreased (P < 0.05) on day 1 (6.96 vs. 7.20) and day 4 (7.06 vs. 7.18) after gastrocnemius incision but was not reduced on postoperative day 8 (7.11 vs. 7.15). A paraspinal incision also decreased tissue pH in the hairy skin of the rat compared with the preincision value. Hind paw skin temperature did not change after incision. A decrease in pH occurs immediately after incision and is sustained for at least 4 days. During the period of decreased tissue pH, pain behaviors are evident. When the tissue pH returns to normal, pain behaviors are diminished. The decreased pH is localized at the incision site and not to areas surrounding the incision. Decreased pH likely contributes to nociceptor sensitization and pain related behaviors after incision. The magnitude of the pH change varies among tissues. An increase in hind paw skin temperature does not play a role in these pain-related behaviors.

PH is decreased in transplanted rat pancreatic islets.

Recent studies of transplanted pancreatic islets have indicated incomplete revascularization. We investigated the pH, in relation to oxygen tension (Po(2)), in endogenous islets and islets syngeneically transplanted to the renal subcapsular site of nondiabetic and streptozotocin-diabetic recipients. Tissue pH and Po(2) were measured using microelectrodes. In the endogenous islets, tissue pH was similar to that in arterial blood. In the transplanted islets, tissue pH was 0.11-0.15 pH units lower. No differences in islet graft pH were seen between nondiabetic and diabetic animals, and none if the islet grafts were investigated 1 day or 1 mo posttransplantation. The Po(2) in the endogenous islets was approximately 35 mmHg. Transplanted islets had a markedly lower tissue Po(2) both 1 day and 1 mo after transplantation. A negative correlation between the tissue Po(2) and the hydrogen ion concentration was seen in the 1-mo-old islet transplants in diabetic animals. In conclusion, decreased Po(2) in transplanted islets is associated with a decreased tissue pH, suggesting a shift toward more anaerobic glucose metabolism after transplantation.

Differential depression of myocardial function and metabolism by lactate and H+.

The effects of both high blood H+ concentration ([H+]) and high blood lactate concentration ([lactate]) under ischemia-reperfusion conditions are receiving attention, but little is known about their effects in nonischemic hearts. Isolated rat hearts were Langendorff perfused at constant flow with media at two pH values (7.4 and 7.0) and two [lactate] (0 and 20 mM) in various sequences (n = 6/group). Coronary flow and arterial O2 content were kept constant at levels that allowed hearts to function without O2 supply limitation. We measured contractility, O2 uptake, diastolic pressure, and at the end of the protocol, tissue [lactate] and pH. Perfusion with high [lactate] raised tissue [lactate] from 5.5 +/- 0.1 to 17.5 +/- 2.6 micromol/heart (P < 0.0001), whereas decreasing the pH of the medium decreased tissue pH from 6.94 +/- 0.02 to 6.81 +/- 0.06 (P = 0.002). Heart rate was not affected by high [lactate] but was reversibly depressed by high [H+] (P = 0.004). Developed pressure declined by 20% in response to high [lactate], high [H+], and high [lactate] + high [H+] (P = 0.002). After the high-[lactate] challenge was withdrawn, pressure continued to decline. In contrast, withdrawing the high [H+] challenge allowed partial recovery. The behavior of diastolic pressure mirrored that of developed pressure. Although unaffected by high [lactate], the O2 uptake was reversibly depressed by high [H+]. This suggests higher O2 cost per contraction in the presence of high [lactate]. We conclude that for similar acute contractility depression, high [lactate] induces irreversible damage, likely at some point in the pathway of O2 utilization. In contrast, the effect of high [H+] appears reversible. These differential behaviors may have implications for heart function during heavy exercise and ischemia-reperfusion events.

Focal central chemoreceptor sensitivity in the RTN studied with a CO2 diffusion pipette in vivo.

We describe and use a CO2 diffusion pipette to produce a quickly reversible focal acidosis in the retrotrapezoid nucleus region of the rat brain stem. No tissue injection is made. Instead, artificial cerebrospinal fluid (aCSF) equilibrated with CO2 circulates within the micropipette, providing a source for continued CO2 diffusion into the tissue from the pipette tip. Tissue pH electrodes show the acidosis is limited to 500 micron from the tip. In controls (aCSF equilibrated with air), 1-min pipette perfusions increased tissue pH slightly and decreased phrenic nerve amplitude. In moderate- and high-CO2 groups (aCSF equilibrated with 50 or 100% CO2), 1-min perfusions significantly decreased tissue pH and increased phrenic nerve amplitude in a dose-dependent manner. The responses developed and reversed within minutes. Compared with our prior use of medullary acetazolamide injections to produce a focal acidosis, in this approach the acidosis 1) arises and reverses quickly and 2) its intensity can be varied. This allows study of sensitivity and mechanism. We conclude from this initial experiment that retrotrapezoid nucleus region chemoreceptors operate within the normal physiological range of CO2-induced tissue pH changes.

Seed dormancy in red rice. X. A 13C‐NMR study of the metabolism of dormancy‐breaking chemicals

The metabolism of organic dormancy‐breaking chemicals is poorly defined and may provide clues to their mode of action. Therefore, hydrated, dormant seeds of red rice (Oryza sativa L.) were exposed to dormancy‐breaking treatments of propionate‐2‐13C (22 mW) or propanol‐1‐13C (75 mM) for 24 h at 30°C. Embryo extracts were analyzed by 13C‐nuclear magnetic resonance spectroscopy. Metabolism of propionate and propanol to 3‐hydroxypropionate, an intermediate of the modified β‐oxidation pathway, was detected after 2 and 4 h, respectively. This occurred prior to the onset of dormancy‐breaking which required 12 h of chemical exposure. Accumulation of 3‐hydroxypropionate was rapid and linear in the embryos of propionate‐treated seeds. In the embryos of propanol‐treated seeds, the level of 3‐hydroxypropionate reached a plateau at 4 h. Following 24 h of contact with propionate, labeled citrate was detected in the embryos. The decrease in tissue pH associated with the dormancy‐breaking process was fully accounted for by direct acid uptake and metabolic production of 3‐hydroxypropionate.

Metabolic changes associated with altering blood glucose levels in short duration forebrain ischemia

31P nuclear magnetic resonance spectroscopy was used to follow changes in cerebral pH and high-energy phosphate metabolites during forebrain ischemia in hypo-, normo- and hyperglycemic rats, and during reperfusion in animals in which the blood glucose level was altered post-ischemia. Pre-ischemia, no differences in the levels of inorganic phosphate (P i) and adenosine triphosphate (ATP) relative to phosphocreatine (PCr) or in tissue pH between blood glucose groups were observed. During ischemia, the decrease in tissue pH was found to be dependent on the pre-ischemic blood glucose concentration, being greatest in hyperglycemic and least in hypoglycemic animals. The increase of P i, a consequence of the hydrolysis of high-energy phosphate metabolites, also depended on the blood glucose concentration, being greatest in hypoglycemic and least in hyperglycemic animals. ATP and PCr decreased more rapidly in hypoglycemic rats compared to normo- or hyperglycemic animals, which showed no differences in the rates of depletion. Post-ischemic hyperglycemia resulted in delayed recovery of tissue pH in all groups and of PCr and ATP in animals hyperglycemic throughout the experiment. Insulin administration immediately following ischemia increased the rate of recovery of pH, ATP and PCr in hyperglycemic animals. ATP remained significantly below pre-ischemia level in all subgroups at 1 h post-ischemic, while PCr was lower than it was pre-ischemia only in those subgroups hyperglycemic prior to and/or following ischemia. In animals maintained severely hypoglycemic throughout the experiment, erratic blood pressure and cerebral energy failure during the reperfusion interval were observed.

Modification of human tumour and normal tissue pH during hyperthermic and normothermic antiblastic regional isolation perfusion for malignant melanoma: a pilot study.

Human tumour and normal tissue pH were investigated during hyperthermic and normothermic antiblastic regional isolation perfusion and the effects of vascular occlusion, artificially induced hypoxia, hyperglycaemia, haemoglobin level of the perfusate and hyperthermia on tumour and normal tissue pH were evaluated. A pilot study was performed on 10 patients, with locally inoperable recurrent and primary malignant melanoma of the leg. The treatment consisted of a regional isolation perfusion with hyperthermia (120 min at 42-43 degrees C), at femoral level, followed by a normothermic regional isolation perfusion with Melphalan (60 min at 37-38 degrees C), at iliacal level, 7-10 can be distinguished: (1) first ischaemic anoxia period; (2) extracorporeal circulation, during which the leg is heated to the desired temperature, after which either hyperthermia or Melphalan is applied; (3) second ischaemic anoxia period. During the anoxia periods the large vessels that supply the leg are temporarily clamped and the effects on tissue pH can be investigated. During extracorporeal circulation, high-dose glucose can be administered to the isolated leg, to acutely decrease tumour tissue pH. Such a decrease is expected to sensitize tumours to hyperthermia, when applied immediately prior to or during heating. At the beginning of the treatment the mean tumour pH was significantly lower than normal tissue pH (7.14, with a mean tumour volume of 39.2 cm3, and 7.38, respectively; p < 0.01). During the perfusions with hyperthermia and Melphalan, tissue pH decreased by -0.41 units and -0.20 for tumour, and -0.11 units for normal tissue, respectively (all statistically significant). The two anoxia periods accounted for approximately half of the net decrease. During these periods tumour pH appeared to decrease more selectively, although there was great variation. The other investigated modalities, such as hyperglycaemia and hyperthermia, also decreased tissue pH, but to a lesser extent. However, a combination of more than one modality caused a larger decrease than a single one, but no preference for tumour could be detected. Before the second perfusion mean tumour pH was significantly increased by 0.14 units, and was no longer significantly different from normal tissue pH in the course of the regional isolation perfusion. This could be the reflection of the reduced tumour volume (by 30%, n.s.). Similar pH changes occurred during this Melphalan perfusion, but they were less pronounced since the total treatment time was shorter. Summarizing, tumour pH can be decreased more than normal tissue pH in the course of the regional isolation perfusion. In particular, vascular occlusion appeared to be tumour pH selective.(ABSTRACT TRUNCATED AT 400 WORDS)

Ischemically sensitive visceral afferents: importance of H+ derived from lactic acid and hypercapnia.

Ischemically sensitive abdominal visceral afferents reflexly stimulate the cardiovascular system. To explore the role of H+ contribution by lactic acid and hypercapnia, we recorded single-unit activity of ischemically sensitive abdominal afferents in anesthetized cats. The individual responses to sodium lactate, lactic acid, and hypercapnia then were examined. Abdominal ischemia significantly decreased organ tissue pH from an average of 7.21 +/- 0.03-7.05 +/- 0.03 (P less than 0.05), during which impulse activity of 13 A delta- and 32 C-fibers significantly increased. Although hypercapnia (12% CO2) induced a similar decrease in tissue pH, impulse frequency increased in 0 of 4 A delta- and only 2 of 13 C-fibers. In contrast, lactic acid decreased tissue pH significantly less than ischemia or hypercapnia but increased impulse activity in 7 of 10 A delta- and 11 of 12 C-fibers. Conversely, only 1 of 3 A delta- and 0 of 10 C-fibers responded to sodium lactate. Thus ischemically sensitive visceral afferents respond to the H+ derived from lactic acid rather than hypercapnia. However, these afferents do not respond to sodium lactate. These data suggest that ischemically sensitive abdominal visceral afferents are responsive specifically to lactic acid rather than to the dissociated ions lactate or H+ or to changes in PCO2.

Energetic recovery from hypothermic preservation in the rat liver

Changes in energy metabolism induced by norepinephrine were observed in liver perfused immediately after dissection and in liver stored in Euro-Collins solution at 0°C for 24 hr. Oxygen consumption, glucose output, ATP content, and tissue pH were measured in isolated perfused rat liver at 37°C. In fresh liver, a two-fold increase in glucose output and oxygen consumption was induced by norepinephrine (1 μ M), while changes in ATP content and tissue pH were minimal. In stored liver, the cumulative increments in glucose output and oxygen consumption induced by norepinephrine were 30 and 27% those of fresh liver, respectively. ATP content of the unstimulated liver was 76% that of the fresh liver, then decreased to 50% during stimulation. A transient decrease in tissue pH (0.14 pH unit) was significant compared with that of fresh liver. These results suggest that norepinephrine stimulation is useful for assessing energetic and functional recovery of reperfused liver following hypothermic storage.

Comparative response of muscle and subcutaneous tissue pH during arterial and venous occlusion in musculocutaneous flaps.

Clinical measures often fail to detect early tissue ischemia in inadequately perfused flaps. This study investigates the application of a new pH electrode system to monitor tissue metabolism continuously in porcine and human musculocutaneous flaps. Bilateral rectus abdominis flaps based on the deep inferior epigastric pedicle were elevated in eight mixed-breed pigs. Tissue pH was measured in the subcutaneous and muscular layers with miniature glass-tip electrodes. The deep inferior epigastric artery and vein were serially and then concomitantly occluded for 20-minute periods. The decrease in tissue pH was greater following either arterial or pedicle occlusion (each 0.21 +/- 0.03 units) when compared with venous occlusion (0.10 +/- 0.02 units; p less than 0.02). Changes in muscle and subcutaneous hydrogen ion concentration were similar during arterial and venous occlusions (probability not significant). Measurement of subcutaneous pH appears to be a reliable experimental and clinical physiological tool for detecting early tissue ischemia in reconstructive flaps.

The use of conductive thermoplastic wires as oxygen sensors in microwave fields.

Local microwave induced hyperthermia is considered standard treatment in the management of maligant disease, specifically recommended for locally recurrent tumors and for primary cancer where other treatment modalities have a poor history of success Several mechanisms of action of heat on tumors have been determined including, among others, vascular damage which disturbs the already poor tumor blood supply resulting in increased heat retention and deprivation of oxygen and nutrition in tumors (2-10) leading to a decrease in tissue pH and tumor death. In previous publications we have described the possible prognostic value of clinically determining PO2 levels during hyperthermia treatments to predict the effectiveness of the given therapy (3), however, when measurements are to be made in strong electromagnetic or microwave fields such as occur during hyperthermic treatment of cancerous tumors, the metallic nature of the sensing electrodes cause the formation of electrical eddy currents that induce self heating of the sensors leading to erreous readings and can also induce thermal burns on the treated tissues.

Cerebral energy metabolism following fluid-percussion brain injury in cats.

Clinical and experimental evidence suggests that head injury can cause alterations of cerebral energy metabolism. However, the etiology of this metabolic perturbation is not known. The objective of this study was to determine the effect of fluid-percussion trauma on cerebral energy metabolism. Seven ventilated, chloralose-anesthetized cats were subjected to a 3.2-atm fluid-percussion brain injury. Before and for 8 hours after trauma, continuous phosphorus-3 1 magnetic resonance spectrography was obtained to noninvasively monitor tissue pH, phosphocreatine (PCr), and inorganic phosphate (Pi) levels. Measurement of cerebral blood flow (CBF) by the radioactive microsphere technique and calculation of oxygen and glucose consumption (CMRO2 and CMRG1) were also performed before trauma as well as 30 minutes and 1, 2, 4, and 8 hours after trauma. The data showed a moderate decrease in tissue pH from 7.04 to 6.89 at 30 minutes following trauma with return to control levels by 3 hours posttrauma. During the 8-hour observation period, CBF, CMRO2, and CMRG1 remained at control levels. Tissue PCr and Pi levels were also unchanged. Fluid-percussion trauma at the 3.2-atm level in ventilated cats causes a moderate and transient decrease in tissue pH that returns to control levels after trauma. No other metabolic changes are seen later than 30 minutes posttrauma. This indicates that a mild metabolic disturbance occurs after trauma in the ventilated animal and quickly returns to normal.

Effect of hyperglycemia on brain pH levels in areas of focal incomplete cerebral ischemia in monkeys.

The adverse effect of a minimal cerebral blood flow (CBF) in models of global ischemia has been noted by many investigators. One factor believed important in this situation is the level of blood glucose, since a continued supply of this metabolite results in increased tissue lactate, decreased brain pH, and increased cell damage. The authors have extended these observations to a model of focal incomplete ischemia. Brain pH was measured in fasted squirrel monkeys in regions of focal incomplete ischemia after transorbital occlusion of the middle cerebral artery (MCA). In both control and hyperglycemic animals, CBF was reduced to less than 30% of baseline. At 3 hours after MCA occlusion, brain pH in the control group was 6.66 +/- 0.68 as compared to 6.27 +/- 0.26 in the glucose-treated group. This difference was statistically significant by Student's unpaired t-test (p less than 0.05). Thus, hyperglycemia results in decreased tissue pH in regions of focal incomplete cerebral ischemia in monkeys.