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Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 199 records · Page 11Linked to original sources
PubMed1990

Oxygen dependence of energy state and cardiac work in the perfused rat heart.

The relationship between oxygen concentrations in arteries, cytosol, and mitochondria and high energy phosphate metabolism was studied in perfused rat hearts subjected to low and high workloads during gradual hypoxia. PCr, ATP, and Pi were measured by 31P-NMR. Myoglobin oxygenation and cytochrome aa3 oxidation were measured by the optical method. When influent oxygen tension was decreased gradually, PCr, ATP, %MbO2, %Cytaa3, cardiac work and MvO2 decreased while Pi and Pi/PCr increased in Langendorff and working hearts. These changes occurred, however, at higher PaO2 values in working hearts. The decrease of %MbO2 and %Cytaa3 in Langendorff hearts was parallel where the ratio of %MbO2 / %Cytaa3 was 1:1. However, this ratio was more than 1:1 in working hearts. It had been demonstrated that oxygen gradients change with changing oxygen consumption. Metabolic and heart work changes occurred simultaneously and significant changes occurred at low levels of %MbO2 and %Cytaa3. Some differences were observed between Langendorff and working hearts. Oxidative phosphorylation is a good indicator of ATP synthesis during hypoxia and is regulated by the intracellular oxygen concentration as well as oxygen gradients.

Animals↗
PubMed1990

Experimental brain ischaemia: assessment of injury by magnetic resonance spectroscopy and histology.

Phosphorus magnetic resonance spectroscopy (31P-MRS) was made to measure changes in brain high energy phosphate compounds, adenosine triphosphate (ATP) and phosphocreatine (PCr), inorganic phosphorus (Pi) and intracellular pH (pHi) during a prolonged period of incomplete brain ischaemia produced, in anaesthetized dogs, by bilateral carotid occlusion together with haemorrhagic hypotension for intervals of up to 300 min. Mean arterial blood pressure (MABP) was lowered in a stepwise fashion, until signs of metabolic decompensation (as estimated by MRS) occurred. At that point MABP was varied against further evidence of metabolic decompensation in an attempt to maintain a more constant degree of insult. At the end of the ischaemic period MABP was restored and the animals observed during a 3 h recovery period. At the end of the recovery period the brains were perfusion-fixed for histological examination. A semi-quantitative method of histological evaluation was used to determine the degree of histological damage. This permitted assignment of an 'ischaemic score' to the tissue sampled from each animal. Comparisons were then made between the magnitude of this 'ischaemic score' and the changes in metabolic and physiological variables (ATP, PCr, pHi and MABP) as well as an estimator of phosphorylation potential (PCr/Pi), which were all measured during the ischaemic insult. Histological examination showed a wide variety of neuronal alterations, including dark and pale type injury, which correlated directly with the metabolic derangements brought about by ischaemia. The degree of damage determined from this histological assessment correlated best with the duration and degree of change in PCr/Pi, supporting the use of this ratio as a critical index of cellular energy state. In particular there was a strong linear relationship between the degree of leucocyte recruitment and changes in PCr/Pi. To summarize, metabolic changes, determined by MRS, correlate with the degree of histological damage, and in turn, the classical descriptions of acute ischaemic neuronal injury appear to be validated by MRS determinations of metabolic changes during ischaemia.

Adenosine Triphosphate↗
PubMed1990

Reperfusion hyperoxia in brain after circulatory arrest in humans.

Changes in the electroencephalogram (EEG), mean arterial blood pressure (MABP), and hemoglobin saturation in brain vasculature of lightly anesthetized normothermic humans undergoing induced circulatory arrest for implantation of an automatic internal cardioverting defibrillator were studied. EEG was measured using a four-channel bipolar montage and hemoglobin saturation was measured transcranially using reflectance spectroscopy at 760 nm with an isosbestic reference at 800 nm. Hemoglobin saturation of blood in the quadriceps muscle was also measured. Thirty-two episodes of hypotension due to ventricular fibrillation were studied along with 31 episodes of hypotension related to ventricular tachycardia and rapid ventricular pacing. In a typical fibrillatory event there was a decrease in MABP followed almost immediately by changes in hemoglobin saturation of blood in the brain vasculature. The first changes in EEG were detected an average of 6.5 s (P less than 0.001, paired t test) after the beginning of change of brain vascular hemoglobin. In some cases changes in hemoglobin saturation could be detected without changes in EEG. Desaturation curves from muscle and brain were significantly different, suggesting that the brain probe was measuring hemoglobin change in a rapidly metabolizing volume of tissue that was dissimilar to the skin, muscle, and bone monitored by the probe over the quadriceps muscle. Examination of the 32 episodes of circulatory arrest revealed a marked response that began immediately with recirculation characterized by an increase of the hemoglobin saturation signal from brain vasculature to above baseline as the duration of circulatory arrest exceeded 37 s, this response is termed reperfusion hyperoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Oxidative phosphorylation system during steady-state hypoxia in the dog brain.

The relationship between biochemical and physiological responses and tissue O2 during hypoxia was investigated in vivo in the dog brain by 31P nuclear magnetic resonance (NMR) spectroscopy. Our findings demonstrate how ATP synthesis in the brain can be maintained during hypoxia because of compensatory changes in NADH, ADP, and Pi. Eleven beagle dogs were anesthetized and mechanically ventilated, and a steady-state graded hypoxia was induced by decreasing the fraction of inspired O2 (FIO2) stepwise at 20-min intervals. Biochemical metabolites were measured using 31P-NMR and fluorescence spectroscopy. When sagittal sinus O2 partial pressure (PVO2) had decreased to 15 Torr, NADH increased by 30%, Pi increased by 50%, and phosphocreatine (PCr) decreased by 20%. In contrast, ATP remained constant. There was a 10% increase in ADP in dogs that maintained a steady temperature, but ADP decreased by as much as 30% in dogs in which body temperature decreased with the falling PVO2. PCr/Pi was logarithmically related to the phosphorylation potential during steady-state hypoxia. Compensation for the O2 lack is attributed to increases in ADP, Pi, and NADH as a result of the reciprocal relationship of the Michaelis-Menten equation. If the Michaelis-Menten constants (Km) of ADP, Pi, and O2 are the same as determined in vitro in mitochondria, the minimum brain cytosolic O2 capable of maintaining a steady-state ATP is near its Km (0.1 Torr) at a PVO2 of 7.5 Torr. At this critical O2 level, PCr/Pi is 0.9, intracellular pH is 6.75, phosphorylation potential is 38.5 mM-1, and the calculated maximum velocity of ATP formation by oxidative phosphorylation is 55% of normal.

Adenosine Diphosphate↗
PubMed1990

Metabolic effects of training in humans: a 31P-MRS study.

The purpose of this study was to determine the feasibility of measuring with 31P nuclear magnetic resonance the effects of an endurance training program on the high-energy phosphate metabolism of exercising human skeletal muscle. The system used included a 1.9-T 30-cm-bore Oxford Systems superconducting magnet, a PhosphoEnergetics spectrometer, and a modified Cybex isokinetic ergometer. Seven healthy human volunteers exercised their wrist flexor muscles 20 min/day 5 days/wk for 8 wk. Testing before and after the training period consisted of a performance test to measure muscle functional capacity and a ramp test to measure the work-energy cost relationship of the exercising muscles. The results indicate that the subjects had a significant increase in their work output on the 10-min performance test after training. They also exhibited an increase in the work-energy cost relationship on the ramp test as indicated by a decrease in peak Pi-to-phosphocreatine ratio and an increase in pH at the same relative power output after training. These results indicate that 1) the training program was sufficient to elicit a training effect and 2) this effect was observed with 31P nuclear magnetic resonance as an increased potential for oxidative metabolism, particularly at the high exercise levels.

Adult↗
PubMed1990

Cerebral energy metabolism and oxygen state during hypoxia in neonate and adult dogs.

The relationship between a noninvasive determination of relative oxygen saturation of Hb circulating in brain tissue (StO2) and energy metabolism was investigated with respect to age [dogs in three age groups (0 to 6-d-old, 7- to 21-d-old, and adults)] and to severity of brain hypoxia using double beam spectroscopy of Hb deoxygenation and nuclear magnetic resonance spectroscopy of energy metabolism. The in vivo oxy-Hb dissociation was determined from the relationship between StO2 curve in the adult dog brain and sagittal sinus oxygen partial pressure during graded hypoxemia and found to be sigmoidal with an oxygen dissociation constant of 26.6 mm Hg. This agreed with an in vitro determination for oxygen dissociation constant of 28.2 mm Hg in adult dog red cells. The arterial oxygen pressure at which brain StO2 was reduced by 50% was shifted toward the right with increasing age (22.2, 33.8, and 40.8 mm Hg, respectively). This correlated with an in vitro oxygen dissociation constant of red cell Hb of 17.0, 22.3, and 28.2 mm Hg in the three age groups, respectively. The phosphocreatine-inorganic phosphate ratio (PCr/Pi) was used to relate changes in cellular energy metabolism during hypoxia with changes in StO2. There was no change in PCr/Pi when StO2 had decreased to 50% of the control value. However, when the brain StO2 had decreased to between 7 and 15%, a reduction of PCr/Pi to 50% of the normoxic value occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1990

Continuous in vivo measurement of hepatic lipoperoxidation using chemiluminescence: halothane and chloroform compared.

Hepatic necrosis, rarely occurring after administration of modern halogenated general anesthetics, has been ascribed to free radical-induced lipoperoxidation. As evaluation of hepatic chemiluminescence has been shown to provide a noninvasive assay for oxidative radical reactions, we have made continuous in vivo measurements of hepatic light output in the phenobarbital-induced halothane anesthetized rat and compared them with observations made during chloroform anesthesia. Chloroform produced a far more rapid and more profound increase in chemiluminescence, a phenomenon probably related to depletion of hepatic glutathione. These findings are consistent with significant differences in hepatic pathology associated with the two agents.

Animals↗
PubMed1989

Time-resolved magnetic resonance spectroscopic study of freeze-trapped yeast.

Rapidly changing metabolic events in actively respiring yeast under strictly physiological conditions were approached by freeze-trapping analysis with 31P magnetic resonance spectroscopy. A 50% wet weight/volume suspension of Saccharomyces cerevisiae was freeze-trapped with 20% ethylene glycol and 5% methanol as an antifreezing agent, and with 3 mM creatine phosphate as an external standard. A phosphorus spectrum of the freeze-trapped yeast was measured for 20 min at -18 degrees C at 202.46 MHz, since energy-related phosphate compounds in yeast were stable at least for 20 min at the temperature. The time scale, defined as (time required for NMR measurement)/(time for trapping), was expanded by the freeze-trapping analysis by 67-times, since the time for trapping was 0.3 min. The use of creatine phosphate as an external standard enabled exact quantification of phosphorus resonances. 31P-NMR study of freeze-trapped yeast affords a well time-resolved and highly sensitive method to study phosphate metabolism.

Adenosine Triphosphate↗
PubMed1989

EXAFS studies of the isolated bovine heart Rieske [2Fe-2S]1+(1+,2+) cluster.

Recently the involvement of one or, more likely, two nitrogen-ligands in the Rieske-type [2Fe-2S] cluster has been reported based on the chemical assay and various spectroscopic analyses, such as EPR, Mössbauer, ENDOR, and resonance Raman, of isolated Thermus thermophilus HB-8 protein by Fee and his collaborators. Similarly, the presence of at least one nitrogen ligand was shown in the mitochondrial Rieske [2Fe-2S] cluster. We have conducted EXAFS studies of the Rieske [2Fe-2S] protein isolated from the cytochrome bc1 complex of bovine heart mitochondria. Standard analysis could not distinguish one or two nitrogen ligands per cluster. However, one nitrogen and three cysteine ligands per cluster was found to be, possibly, a better solution in more comprehensive analysis procedures.

Animals↗
PubMed1989

A possible role of inorganic phosphate as a regulator of oxidative phosphorylation in combined urea synthesis and gluconeogenesis in perfused rat liver. A phosphorus magnetic resonance spectroscopy study.

Metabolic control of oxidative metabolism was studied in perfused rat liver by means of phosphorus magnetic resonance spectroscopy. Oxygen consumption, ATP, and Pi were measured with different rates of gluconeogenesis and urea synthesis by varying concentrations of the substrates in the perfusate. Five levels of oxygen consumption (VO2) were obtained: an average control value of 1.94 +/- 0.14 and 2.93 +/- 0.25, 3.29 +/- 0.46, 3.85 +/- 0.26, and 4.18 +/- 0.56 mumol/min/g liver (mean +/- S.D., n = 6). The corresponding ATP concentrations were 2.51 +/- 0.20, 2.39 +/- 0.08, 2.24 +/- 0.09, 2.13 +/- 0.12, and 1.91 +/- 0.13 mM. Pi increased stoichiometrically with the decrease in ATP. Free Pi (Pif) was calculated as NMR-visible Pi in control plus -delta ATP (1.94 mM + (-delta ATP]. The kinetic relationship of oxidative phosphorylation as a function of Pif followed a Michaelis-Menten type of equation: VO2 = 5.55/(1 + 0.24/[( Pif] - 1.81]. The observed Km value for Pi of 0.24 mM approximates the reported Km value in isolated mitochondria of 1 mM. The free Pi concentration of 1.94 mM is in the range of the Km value, while the free ADP concentration of 200 microM exceeds the Km value of 20 microM. Therefore, it is suggested that Pi play a major role in the regulation of mitochondrial oxidative phosphorylation in combined urea synthesis and gluconeogenesis.

Adenosine Triphosphate↗
PubMed1989

Effect of the hinge protein on the heme iron site of cytochrome c1.

X-ray absorption spectroscopic (XAS) studies on cytochrome C1 from beef heart mitochondria were conducted to identify the effect of the hinge protein [Kim, C.H., & King, T.E. (1983) J. Biol. Chem. 258, 13543-13551] on the structure of the heme site in cytochrome c1. A comparison of XAS data of highly purified "one-band" and "two-band" cytochrome c1 [Kim, C.H., & King, T.E. (1987) Biochemistry 26, 1955-1961] demonstrates that the hinge protein exerts a rather pronounced effect on the heme environment of the cytochrome c1: a conformational change occurs within a radius of approximately 5 A from the heme iron in cytochrome c1 when the hinge protein is bound to cytochrome c1. This result may be correlated with the previous observations that the structure and reactivity of cytochrome c1 are affected by the hinge protein [Kim, C.H., & King, T.E. (1987) Biochemistry 26, 1955-1961; Kim, C.H., Balny, C., & King, T.E. (1987) J. Biol. Chem. 262, 8103-8108].

Animals↗
PubMed1989

What are the goals of magnetic resonance research?

Now that both magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) have reached their decadic majority, appropriate questions may be asked as to their accomplishments and prognostications for the future. This article emphasizes the approach of the metabolic biologists/physiologists to magnetic resonance biochemistry as indicated by the currently available multinuclear localized approaches. The viewpoint is emphasized that MRS is a critical care instrument where precipitious changes of oxidative metabolism lead to the well-known stroke, heart failure, liver failure, kidney failure, etc. Generally, the gradation between the classical metabolic steady state of life and the pathway leading to cell death is a narrow one and magnetic resonance in some cases is too finely tuned to delineate the gradations of stability and instability of cell metabolism. To this point, magnetic resonance can be supplemented by other modalities that sense tissue distress. An example of a most useful and predictive measure of hypoxic stress is optical spectrophotometry which uses time resolved ranging methods to measure optical path lengths to quantitate hemoglobin deoxygenation in tissues. With such a complement, the two methods emerge as one of general importance in diagnostic procedures.

Forecasting↗