Decompression sickness risk in rats by microbial removal of dissolved gas.

We present a method for reducing the risk of decompression sickness (DCS) in rats exposed to high pressures of H2. Suspensions of the human colonic microbe Methanobrevibacter smithii were introduced via a colonic cannula into the large intestines of the rats. While the rats breathed H2 in a hyperbaric chamber, the microbe metabolized some of the H2 diffusing into the intestine, converting H2 and CO2 to methane and water. Rate of release of methane from the rats, which was monitored by gas chromatography, varied with chamber H2 pressure. This rate was higher during decompression than during compression, suggesting that during decompression the microbe was metabolizing H2 stored in the rats' tissues. Rats treated with M. smithii had a 25% (5 of 20) incidence of DCS, which was significantly lower (P < 0.01) than the 56% (28 of 50) incidence of untreated controls, brought on by a standardized compression and decompression sequence. Thus using a microbe in the intestine to remove an estimated 5% of the body burden of H2 reduced DCS risk by more than one-half. This method of biochemical decompression may potentially facilitate human diving.

A difference of 5 degrees C between ear and rectal temperatures in a febrile patient.

A 4-year-old boy with a history of seizures triggered by fever presented at an emergency department (ED) with tachycardia, skin vasoconstriction, and a rectal temperature of 42.2 degrees C. However, his ear temperature (as repeatedly measured in two ears, by two experienced nurses, and with two infrared thermometers) was between 36.4 degrees C and 37.6 degrees C. Antipyretic therapy resulted in skin vasodilation, a rapid decrease of rectal temperature, restoration of heart rate, and disappearance of the difference between the two temperatures. Seizures did not occur. This case shows that infrared ear thermometry cannot be recommended in EDs as the procedure of choice for detecting fever in small children, especially when they are vasoconstricted.

Chicken embryo fibroblasts exposed to weak, time-varying magnetic fields share cell proliferation, adenosine deaminase activity, and membrane characteristics of transformed cells.

Chicken embryo fibroblasts (CEF) exposed to a sinusoidally varying magnetic field (SVMF) (100 Hz, 700 microT, for 24 h) showed a remarkable rise of segmental rotational relaxation rate of adenosine deaminase (ADA, EC 3.5.4.4) as determined by multifrequency phase fluorometry. Pyrene-labeled, small subunit ADA was applied to cultured (normal) CEF, which have available and abundant ADA complexing protein (ADCP) on their plasma membranes. Sine-wave-modulated fluorometry of the pyrene yielded a profile of phase angle vs. modulation frequency. In SVMF-treated cells and in Rous-sarcoma-virus (RSV) transformed cells the differential phase values at low modulation frequencies of the excitation are remarkably reduced. This effect is magnetic rather than thermal, because the temperature was carefully controlled and monitored; nevertheless to further check this matter we studied CEF, infected by the RSV-Ts68 temperature-sensitive mutant (36 degrees C transformed, 41 degrees C "revertant"). When grown at 36 degrees C in the SVMF, cells did not show the slightest trend towards reversion, as would be expected had there been local heating. Concomitant with the increased segmental rotational relaxation rate of ADA, there was a decrease in fluorescence lifetime and a slight, yet significant, increase in membrane lipid "microfluidity." These biophysical observations prompted us to examine the effect of SVMF on cell proliferation and ADA activity (a malignancy marker): higher rates of cell proliferation and reduced specific activity of ADA were observed.

Measurement of Erythrocyte 2,3-diphosphoglycerate with a centrifugal analyzer.

Intra-erythrocytic concentration of 2,3-diphosphoglycerate is a major determinant of the oxygen affinity of hemoglobin. We report here the adaptation of its assay to a centrifugal analyzer, with use of a commercially available reagent. Results are calculated by using the reagent-blank-corrected absorbance change at 340 nm between 120 and 300 s for the samples and a 2.5 mmol/L standard. Under these conditions the standard curve is linear to 5 mmol/L. The compound in a 101-fold aqueous hemolysate is stable for several weeks at either -4 or -70 degrees C. Assay sensitivity and precision are excellent and results agree well with those by the corresponding manual method.

Pressure, anesthetics, and membrane structure: a spin-probe study.

Fatty acid spin-probe analyses at various depths in the membrane bilayer of intact erythrocytes indicate that compressional effects of pressure and fluidizing effects of lipid-soluble anesthetics are detectable only in hydrated regions of the membrane bilayer. Since current theories of anesthetic action cannot explain these observations, a proposal to do so is outlined.

[14C]palmitate uptake in isolated rat liver mitochondria: effects of fasting, diabetes mellitus, and inhibitors of carnitine acyltransferase.

The rapid association of Na-[16-(14)C]palmitate with isolated rat liver mitochondria was measured by an oil separation method. This association was time and temperature-dependent and was absolutely dependent on the presence of exogenous ATP and CoASH and partially dependent on exogenous carnitine. Carnitine dependence was enhanced at lower concentrations of [(14)C]palmitate. At 6.5 micro M [(14)C]palmitate (molar ratio of palmitate to albumin equal to 0.54), the rate of association was linear for 20 sec and was increased more than 100% in the presence of carnitine. Carnitine-dependent association was inhibited by 2-bromopalmitate, an inhibitor of carnitine acyltransferase I, but not by (+)-octanoylcarnitine, a presumed inhibitor of carnitine acyltransferase II. The association of [(14)C]palmitate with mitochondria was enhanced from 190 to 330% in mitochondria isolated from fasted animals and from 160 to 230% in mitochondria isolated from diabetic, ketotic animals as compared to control animals. The enhanced association with mitochondria from fasted animals was inhibited by 2-bromopalmitate. These studies demonstrate a method of evaluating fatty acid association with mitochondria which, because of its dependence on carnitine and carnitine acyltransferase I activity, most likely represents true uptake into mitochondria. Furthermore, these studies indicate that the carnitine-dependent uptake of fatty acids into mitochondria is enhanced in the two ketotic states evaluated and that the carnitine acyltransferase system may be a regulatory site in ketone body production.

Consumptive coagulopathy as biochemical mechanism in oxygen toxicity and its enhancement by lead(II) ions.

Consumptive coagulopathy and disseminated intravascular coagulation can be observed in rats exposed to 4 ata of oxygen. These events clearly precede the death of the animal and appear to be initiated by an activation of coagulation factor XII (Hageman). The onset and the extent of consumptive coagulapathy are greatly enhanced by a single and low intravenous dose of lead acetate. Mechanisms of activation of the intrinsic coagulation system and its role in oxygen toxicity are being discussed.

Inhibition of carbon dioxide fixation by lead acetate in rat liver mitochondria.

These studies were undertaken to determine the mechanism by which intravenously administered lead salts inhibit hepatic gluconeogenesis. Within 1 h after the intravenous administration of lead acetate (10 mg), there is 97% inhibition of CO2 fixation in isolated rat liver mitochondria. This effect is concentration-dependent. The induction of phosphoenolpyruvate carboxykinase activity observed with starvation was also inhibited by intravenously administered lead acetate, but the activities of pyruvate kinase, glucose 6-phosphate dehydrogenase and pyruvate carboxylase were unaffected, as was the oxidation of palmitate and palmitoyl-CoA by mitochondria from Pb2+-treated animals. The addition of reduced glutathione to mitochondria from Pb2+-treated animals had no effect on the inhibited CO2 fixation. ATP concentrations in mitochondria from Pb2+-treated animals are decreased and the dose-response relationships for the effect of Pb2+ on CO2 fixation and ATP concentrations correspond. We conclude that the decrease in mitochondrial ATP in Pb2+-treated animals is probably responsible for the marked inhibition ov CO2 fixation, and hence the impairment of gluconeogenesis from alanine, lactate and pyruvate observed by others.

Phosphoribulokinase from Nitrobacter winogradskyi: activation by reduced nicotinamide adenine dinucleotide and inhibition by pyridoxal phosphate.

CO2 fixation by particle-free extracts from Nitrobacter winogradskyi increased by addition of reduced nicotinamide adenine dinucleotide (NADH). Ribulose-1,5-diphosphate, however, increased CO2 fixation, even in the absence of NADH. Phosphoribulokinase (EC 2.7.1.19) was the enzyme of Nitrobacter extracts that was activated specifically by NADH. Pyridoxal-5-phosphate inhibited both CO2 fixation and NADH-activated phosphoribulokinase from Nitrobacter. However, it did not affect phosphoribulokinase from spinach leaves. Since the spinach enzyme had also no requirement for reduced pyridine nucleotides, it appears that pyridoxal phosphate interferes only with the binding of NADH and not with the binding of ribulose-5-phosphate and adenosine-5'-triphosphate. The regulation of phosphoribulokinase activity by NADH provided Nitrobacter with an energy-dependent control mechanism of CO2 assimilation.

pH-dependent Soret difference spectra of the deoxy and carbonmonoxy forms of human hemoglobin and its derivatives.

The transition from deoxy to oxystructure of hemoglobin A (Hb) is accompanied by the breaking of the salt bridges formed by C-terminal residues in deoxy-Hb. This, in turn, changes the state of the heme. The switch between these different allosteric forms can be followed by changes in the optical absorbance spectra (Perutz, M. F., Ladner, J. E., Simon, S. R., and Ho, C. (1974), Biochemistry 13, 2163). Using difference spectroscopy in the soret region, pH-dependent spectral changes of Hb and its derivatives (carbamylated at both the alpha-NH2 groups, alpha2cbeta2c; N-ethylsuccinimide hemoglobin, NES-Hb) in their deoxy and carbonmonoxy forms were measured. From these measurements, the pK values of histidine-146beta and valine-1alpha in deoxy-Hb were determined to be 8.6 +/- 0.2 and 7.7 +/- 0.1, respectively. In carbonmonoxy-Hb a pK value of 6.3 +/- 0.1 was found.

Oxygen-induced consumptive coagulopathy and its enhancement by lead acetate.

The exposure of rats to 100% oxygen at 1 atmosphere leads to a prolongation of prothrombin times and activated partial thromboplastin times. This development is associated with a consumption of factor XII, VIII, and VII activities and with the appearance of fibrin monomers and fibrinogen degradation products. Lead acetate enhances all oxygen-induced changes of the coagulation systems drastically. The O2 survival time of chicks which are naturally deficient in factor XII is greatly increased over that of rats and is not affected by lead acetate. Oxygen survival times of rats suffering from chronic respiratory disease (CRD) are also significantly increased when compared with normal rats. It appears that consumptive coagulopathy and disseminated intravascular coagulation are early events in oxygen exposure, and that their development is accelerated by lead ions.

Potentiation of endotoxin-induced consumptive coagulopathy by lead acetate administration.

Since chickens are naturally deficient in several clotting factors normally present in mammalian sera, the ability of lead acetate (PbAc(2)) to sensitize 11-day-old chicks to endotoxin was compared with its ability to sensitize rats. It was found that, although the chicks could tolerate only relatively low doses of PbAc(2), even those doses would produce a greater than 200-fold sensitization to the endotoxin in rats, as compared with little sensitization in the chicks. By using larger doses of PbAc(2), known to maximally sensitize rats to endotoxin, the effect of PbAc(2) sensitization on whole-blood clotting times, platelet counts, plasma factor V and VIII activities, and the appearance of fibrin degradation products was evaluated. It was found that animals treated with lethal doses of endotoxin but no PbAc(2) showed varying degrees of consumptive coagulopathy. On the other hand, the injection of minute quantities of endotoxin into PbAc(2)-sensitized rats invariably resulted in disseminated intravascular coagulation, apparently via a complete activation of the intrinsic pathway. It is concluded that the site of PbAc(2) sensitization to endotoxin is in the blood, and most probably at the level of Hageman factor activation.

Disaggregation of endotoxin by isolated rat liver plasma membranes and lack of product binding.

The interaction of bacterial endotoxin with isolated rat liver cell membranes was studied to determine the extent and nature of any binding. Serratia marcescens endotoxin was incubated with isolated rat liver plasma membranes for varying periods of time at 37 C, and this mixture was then centrifuged through a discontinous sucrose density gradient. The membranes banded primarily at the 35 to 45% sucrose interface, whether or not they had been incubated with endotoxin. The endotoxin distributed itself throughout the gradient except when incubated with membranes, in which case it failed to sediment. This membrane-induced alteration in sedimentation could be prevented by heat inactivation of the membranes, and was found to be pH, time, temperature, and concentration dependent. There was neither associated degradation of the endotoxin, as measured by molecular sieve chromatography, nor loss in toxicity, as determined in lead-sensitized rats. These observations are consistent with an enzymatic disaggregation of the endotoxin by membranes and could represent a step in the uptake of the endotoxin by the reticuloendothelial system. No significant binding of this disaggregated endotoxin to the membranes could be detected, either after gradient separation or after repeated washing. This finding strongly suggests that, at least in cells that are active in the uptake of endotoxin, membrane-endotoxin interactions may be relatively transitory in nature, and that firm adherence to such membranes may not be a central feature of endotoxin toxicity.