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N Bitterman

Publications and source records attributed to N Bitterman.

30 records · Page 2Linked to original sources
PubMed1990

Comparison of 18O exchange and pH stop-flow assays for carbonic anhydrase.

The hydration velocity of CO2 (0.002 M) catalyzed by bovine carbonic anhydrase (BCA) was measured at 25 degrees C and pH 7.4 by three different techniques: two initial-rate (steady-state) stop-flow methods, one using a glass pH electrode (in Hannover, method 1) and one using spectrophotometric measurements of a pH indicator (in Philadelphia, method 2), and an exchange method in which the disappearance of C18O16O from a bicarbonate solution was determined at equilibrium (in Philadelphia, method 3). The Michaelis-Menten constant (Km) and the inhibition constants for chloride (Ki,Cl) and ethoxzolamide (Ki,ez) were the same for methods 1, 2, and 3. The turnover numbers were 270,000, 400,000, and 555,000 s-1 by methods 1, 2, and 3, respectively. Values for CO2 hydration velocity measured by methods 2 and 3 on the same solution of BCA at the same time were the same. Km, maximal reaction velocity (Vmax), Ki,ez, and Ki,Cl obtained from normal human hemolysate at 37 degrees C and pH 7.2 by methods 2 and 3 were the same. Km and Vmax of the carbonic anhydrase isozyme CA III of homogenate from rabbit soleus were also identical by methods 1 and 3. According to Michaelis-Menten theory, the values of Km and Vmax obtained by method 3 should have been significantly smaller than those obtained by methods 1 and 2. We conclude that the catalytic step itself is apparently not rate limiting under physiological conditions and that method 3 can be used to obtain Michaelis-Menten characteristics of carbonic anhydrase.

Animals↗
PubMed1990

Statistical approach to the analysis of sensitivity to CNS oxygen toxicity in rats.

Animal models are widely used for the study of CNS oxygen toxicity, but confusion still exists regarding the proper statistical approach to the analysis of the data. This paper is based on data collected from unanesthetized, free-moving rats with chronically implanted cortical electrodes for continuous EEG monitoring, exposed to 5 or 6 ATA oxygen. The index measured for CNS oxygen toxicity is the duration of the latent period preceding the appearance of well-defined electrical discharges in the EEG. At both oxygen pressures studied, the duration of the latent period is not distributed normally, and variability within the groups is not homogeneous. Transformations of the latent period data were found to enhance normality, and the speed of appearance of the discharges in the EEG, which is the reciprocal of the time, seems to be a simple, useful index for CNS oxygen toxicity in rats. Two experimental designs were compared: repeated measurements vs. single exposure. No advantage was demonstrated for the use of each rat as its own control as against the comparison between data from groups of rats. Rats can be used more than once in such research, but not more than once in a single study where individual observations are assumed to be independent, since there is some positive correlation between the first and second exposures to hyperbaric oxygen in individual rats; however, the level of sensitivity of the groups is not significantly different.

Animals↗
PubMed1989

Effects of hyperbaric oxygen in circulatory shock induced by splanchnic artery occlusion and reperfusion in rats.

We studied the effects of hyperbaric oxygen in a severe model of circulatory shock induced by occlusion and reperfusion of major splanchnic arteries (splanchnic artery occlusion (SAO) shock). Pentobarbital-anesthetized rats subjected to total occlusion of the superior mesenteric and the celiac arteries for 40 min developed a severe shock state, resulting in a uniformly fatal outcome after release of the occlusion. Exposure to hyperbaric oxygen at 2 ATA (atmosphere absolute) (1 ATA = 0.1 MPa) was initiated immediately after reperfusion. SAO shock rats exposed to hyperbaric oxygen maintained mean arterial blood pressure at significantly higher values throughout the postreperfusion period compared with untreated SAO shock rats (p less than 0.01), with final mean arterial blood pressures of 88 +/- 9 and 51 +/- 4 mmHg, respectively. Treatment with hyperbaric oxygen attenuated the increase in plasma activities of the lysosomal hydrolase cathepsin D (p less than 0.05), and diminished the increase of hematocrit (p less than 0.01 from untreated shock rats). Splanchnic occlusion shock rats treated with hyperbaric oxygen also exhibited a significantly higher survival rate than the untreated shock group (77 vs. 0%, respectively; p less than 0.01). Our results suggest that the beneficial effects of exposure to hyperbaric oxygen immediately after reperfusion of the splanchnic region outweigh its possible deleterious effect.

Animals↗
PubMed1989

Rate of CO uptake by canine erythrocytes as a function of PO2.

We used a continuous-flow rapid-mixing apparatus with spectroscopic analysis to measure the rate of CO uptake by canine erythrocytes at 37 degrees C at five different PO2 values from 0 to 553 Torr. Fresh blood from five different dogs was used for the experiments. PCO approximated 80 Torr. Corrections for the lower capillary PCO during a measurement of the diffusing capacity of lung CO, as made by Roughton and Forster in 1957 (J. Appl. Physiol. 11: 290-302, 1957), were not used. The regression equation for 1/theta, where theta is milliliters of CO combining for each milliliter of whole blood (capacity 0.2 ml/ml) per minute for a PCO of 1 Torr was 1/theta = 1.45 +/- 0.0042 PO2. This equation is very similar to that for human erythrocytes under the same conditions.

Animals↗
PubMed1988

A micromethod for measuring carbonic anhydrase activity using 18O exchange between CO2 and H2O.

We have developed a method of measuring the activity and characteristics of carbonic anhydrase (CA) using the disappearance of 18O from CO2 in 1 ml of gas contained in a glass chamber as it exchanges with H2O in 0.01 ml 0.25 M NaHCO3 solution in a thin (25 micron) porous membrane. Serial gas samples (approximately 0.02 ml) are analyzed in a mass spectrometer to obtain the rate of disappearance of the label. The enzyme activity can be measured inside intact cell or particle membranes. As little as 10(-15) mol of high-activity type CA can be detected at 25 degrees C, and the activity of 200 times this amount can be measured. The uncatalyzed hydration reaction velocity constant was 0.056 +/- 0.004 s-1, in agreement with published data.

Bicarbonates↗
PubMed1987

Increased axonal excitability during exposure to hyperbaric oxygen.

The effect of high oxygen pressure on neural function was studied in the isolated nervous system of the cockroach. Intracellular and extracellular action potentials were recorded from single giant axons during exposure to 7 ATA (atmosphere absolute) (1 ATA = 0.1 MPa) of oxygen. Axonal excitability was measured as changes in stimulus strength-duration relationship. Initially, a transient increase in the rheobase current was observed followed by a significant decline to 75% of air control values. This decrease was accompanied by a parallel increase in the membrane time constant. The results demonstrate that hyperbaric oxygen increases axonal excitability. Such changes are consistent with the epileptogenic properties of high oxygen pressure.

Animals↗
PubMed1987

The effect of sodium phenytoin on central nervous system oxygen toxicity.

The effect of sodium phenytoin on hyperbaric oxygen (HBO) induced central nervous system (CNS) toxicity was studied in rats. The latency of the epileptic electroencephalographic discharges was measured in 20 phenytoin-treated rats exposed to 6 ATA of 100% oxygen, and compared with that of 20 saline-injected rats exposed to the same pressure of pure oxygen. No statistically significant difference was found in the latency between the two groups. In addition, phenytoin failed to suppress or to modify the clinical seizures. Sodium phenytoin failed to suppress or to modify the clinical seizures. Sodium phenytoin blood levels were determined in the rats, and were found to be within the therapeutic range. We conclude that sodium phenytoin is ineffective in suppressing HBO induced CNS oxygen toxicity.

Animals↗
PubMed1987

CNS oxygen toxicity in oxygen-inert gas mixtures.

Central nervous system oxygen toxicity in hyperbaric oxygen-inert gas mixtures was studied by exposing male rats to various gas mixtures having the same oxygen partial pressure and varying pressures of inert gases. The duration of the latent period until the appearance of electrical discharges in the electroencephalogram was used as the criterion for the sensitivity to CNS oxygen toxicity. Two hundred and twenty rats with chronically implanted cortical electrodes were subjected to a single exposure to 1 of 11 different gas mixtures at ambient pressures ranging from 5 to 10 ATA. All gas mixtures had a constant oxygen partial pressure of 5 ATA and varying pressures of inert gas (helium or nitrogen). The duration of the latent period was found to be significantly different in the 11 experimental groups (P less than 0.001). While increasing the inert gas pressure, the latency gradually shortened, reaching the lowest values in mixtures of 5 ATA oxygen and 3 ATA of either inert gas. On further increase in the inert gas pressure up to a total ambient pressure of 10 ATA, the latency returned to control (pure 5 ATA oxygen) values. No difference was found between nitrogen and helium of equal partial pressures. These findings suggest that the risk of CNS oxygen toxicity in gas mixtures is not determined solely by the PO2, and even a relatively low pressure of inert gas can contribute to the imminence of hyperbaric-oxygen-induced seizures.

Animals↗
PubMed1986

The effect of hyperbaric oxygen on acute experimental sulfide poisoning in the rat.

In order to evaluate the efficiency of hyperbaric oxygen in experimental acute sulfide poisoning, we studied the effect of 1 ATA (atmosphere absolute) oxygen and sodium nitrite therapy. We then studied the effect of oxygen at 3 ATA alone and in combination with intraperitoneal sodium nitrite injection on rats poisoned by intraperitoneal injection of LD75 sulfide. Electroencephalogram and heart rate were continuously monitored. We also studied the effect of sodium nitrite and hyperbaric oxygen administered before the poisoning (protective effect). In our experimental set, death of untreated poisoned animals occurred within 5 min. There is a parallel between modification of the EEG pattern and apnea. Respiratory arrest always preceded cardiac arrest. Pure oxygen (1 ATA O2) is effective in preventing death in experimental sulfide poisoning. 3 ATA oxygen was significantly more effective in preventing death than 1 ATA oxygen, or sodium nitrite alone. The best therapeutic regimen was a combination of 3 ATA oxygen and sodium nitrite administration.

Animals↗
PubMed1986

Horseradish peroxidase as a cytochemical marker of blood-brain barrier integrity in oxygen toxicity in the central nervous system.

The ultrastructural integrity of endothelial tight junctions in cerebral microvessels of the rat exposed to hyperbaric oxygen was examined to find whether or not there are alterations of the blood-brain barrier in the initial phase of central nervous system oxygen toxicity. Rats were pre-implanted with cortical electrodes for continuous EEG and provided with two polyethylene cannulae inserted into the common carotid artery. HRP was administered to unanesthetized rats through a cannula directed into the brain, before the onset of O2 pressurization. As soon as the early electrical discharges of oxygen toxicity were recorded (20 to 30 min), the animal was killed by injection with saturated KCl into the heart. Examination of small blood vessels in both LM and EM did not support the possibility that the blood-brain barrier is altered prior to the first electrical discharge appearing in central nervous system oxygen toxicity.

Animals↗
PubMed1986

CNS oxygen toxicity in the rat: role of ambient illumination.

The effect of ambient illumination on sensitivity to CNS oxygen toxicity was studied in awake male rats. Continuous recording of the EEG was obtained with chronically implanted cortical electrodes. The appearance of the electrical discharges in the EEG was used as an end point for CNS oxygen toxicity. It was found that sensitivity to CNS oxygen toxicity was inversely related to the level of ambient light illumination. The latent period for appearance of the electrical discharges was significantly shorter in darkness than in light over most of the oxygen pressures. Rats with severely depressed retinal function were as sensitive to oxygen at high pressure as normal rats in darkness, demonstrating the importance of visual input in the modulation of sensitivity to CNS oxygen toxicity.

Animals↗