Pentobarbital anesthesia and the response of tumor and normal tissue in the C3Hf/sed mouse to radiation

Studies of the effect of pentobarbital anesthesia on the radiation response have been performed using early generation isotransplants of three spontaneous tumors of the C3H mouse: a mammary carcinoma (MCaIV), a fibrosarcoma (FSaII), and a squamous cell carcinoma (SCCVII). The enhancement ratio of pentobarbital [ER(PB)] for TCD50 as the end point was greater than or equal to 1 for all conditions tested. The ER(PB) for O2 3 ATA conditions and two equal doses was 1.46, 1.72, and 2.21 for MCaIV, FSaII, and SCCVII, respectively. The ER(PB) using MCaIV was the same for O2 and carbogen at 1 or 3 ATA. Also, tumor size of MCaIV did not significantly affect the ER(PB) for O2 3 ATA conditions. Further, with the two-dose protocol the anesthesia and the hyperbaric oxygen needed to be used at the second dose; condition at the first dose was not critical. For fractionated irradiation of MCaIV (10 and 15 equal doses) the ER(PB) was smaller than for two-dose treatment; also the effect was less for intratumor temperature of 35 degrees C than 26-27 degrees C. There was no effect of the anesthesia on the acute response of normal skin of the leg. Lung damage by hyperbaric oxygen was not an important factor in these results. Additionally, ERs were computed for O2 at 3 ATA. This ER(O2 3 ATA) was larger for anesthesized than conscious mice. The ER(O2 3 ATA) for MCaIV was high (greater than 1.5) even for radiation given in 10 or 15 equal doses.     

Hyperoxic exposure affects the ventilatory response to hypoxia in awake rats

We tested whether hyperbaric O2 (HBO) has an adverse effect on the hypoxic ventilatory drive. Four groups of rats were exposed for 550 min to O2 at 1.67, 1.90, and 2.15 ATA and to air at 1.90 ATA, respectively. Ventilatory parameters (frequency, tidal volume, and minute ventilation) were measured using whole-body plethysmography, before the hyperbaric exposure, immediately after the exposure, and up to 20 days after the exposure. Resting ventilation was not affected after exposure at 1.90 ATA to air or at 1.67 ATA to O2. HBO at 1.90 and 2.15 ATA caused a reduction of frequency and an elevation of tidal volume at different inspired gases: air, 5% CO2 balance O2, 80% O2, and 4.5% O2. However, minute ventilation on the day after the hyperoxic exposure was not different from the control at either air, 5% CO2, or 80% O2 but was markedly attenuated on the first three breaths at 4.5% O2. The hypoxic ventilation decreased to 48 +/- 13 (SD) and 32 + 11% after 1.90 and 2.15 ATA, respectively. The ventilatory parameters recovered in the days after HBO. We conclude that HBO reversibly depresses the hypoxic ventilatory drive, most probably by a direct effect on the carotid O2 chemoreceptors.     

Correlations between 31P-NMR spectroscopy and tissue O2 tension measurements in a murine fibrosarcoma

Size-dependent changes in therapeutically relevant and interrelated metabolic parameters of a murine fibrosarcoma (FSaII) were investigated in vivo using conscious (unanesthetized) animals and tumor sizes less than or equal to 2% of body weight. Tumor pH and bioenergetics were evaluated by 31P nuclear magnetic resonance spectroscopy (31P-MRS), and tumor tissue oxygen tension (pO2) distribution was examined using O2-sensitive needle electrodes. During growth FSaII tumors showed a progressive loss of phosphocreatine (PCr) and nucleoside triphosphate (NTP) with increasing inorganic phosphate (Pi) and phosphomonoester (PME) signals. Ratios for PCr/Pi, PME/Pi, NTP/Pi, and phosphodiester/inorganic phosphate (PDE/Pi) as well as pH determined by 31P-NMR (pHNMR) and the mean tissue pO2 progressively declined as the tumors increased in size. The only relevant ratio increasing with tumor growth was PME/NTP. When the mean tissue pO2 value was plotted against pHNMR, NTP/Pi, PCr/Pi, PME/Pi, and PDE/Pi for tumor groups of similar mean volumes, a highly significant positive correlation was observed. There was a negative correlation between mean tumor tissue pO2 values and PME/NTP. From these results we concluded that 31P-MRS can detect changes in tumor bioenergetics brought about by changes in tumor oxygenation. Furthermore, the close correlation between oxygenation and energy status suggests that the microcirculation in FSaII tumors yields an O2-limited energy metabolism. Finally, a correlation between the proportion of pO2 readings between 0 and 2.5 mmHg and the radiobiologically hypoxic cell fraction in FSaII tumors was observed. The latter finding might be of particular importance for radiation therapy.     

Hyperoxia increases H2O2 production by brain in vivo

Hyperoxia and hyperbaric hyperoxia increased the rate of cerebral hydrogen peroxide (H2O2) production in unanesthetized rats in vivo, as measured by the H2O2-mediated inactivation of endogenous catalase activity following injection of 3-amino-1,2,4-triazole. Brain catalase activity in rats breathing air (0.2 ATA O2) decreased to 75, 61, and 40% of controls due to endogenous H2O2 production at 30, 60, and 120 min, respectively, after intraperitoneal injection of 3-amino-1,2,4-triazole. The rate of catalase inactivation increased linearly in rats exposed to 0.6 ATA O2 (3 ATA air), 1.0 ATA O2 (normobaric 100% O2) and 3.0 ATA O2 (3 ATA 100% O2) compared with 0.2 ATA O2 (room air). Catalase inactivation was prevented by pretreatment of rats with ethanol (4 g/kg), a competitive substrate for the reactive catalase-H2O2 intermediate, compound I. This confirmed that catalase inactivation by 3-amino-1,2,4-triazole was due to formation of the catalase-H2O2 intermediate, compound I. The linear rate of catalase inactivation allows estimates of the average steady-state H2O2 concentration within brain peroxisomes to be calculated from the formula: [H2O2] = 6.6 pM + 5.6 ATA-1 X pM X [O2], where [O2] is the concentration of oxygen in ATA that the rats are breathing. Thus the H2O2 concentration in brains of rats exposed to room air is calculated to be about 7.7 pM, rises 60% when O2 tension is increased to 100% O2, and increases 300% at 3 ATA 100% O2, where symptoms of central nervous system toxicity first become apparent. These studies support the concept that H2O2 is an important mediator of O2-induced injury to the central nervous system.     

Low-dose photons modify liver response to simulated solar particle event protons

The health consequences of exposure to low-dose radiation combined with a solar particle event during space travel remain unresolved. The goal of this study was to determine whether protracted radiation exposure alters gene expression and oxidative burst capacity in the liver, an organ vital in many biological processes. C57BL/6 mice were whole-body irradiated with 2 Gy simulated solar particle event (SPE) protons over 36 h, both with and without pre-exposure to low-dose/low-dose-rate photons ((57)Co, 0.049 Gy total at 0.024 cGy/h). Livers were excised immediately after irradiation (day 0) or on day 21 thereafter for analysis of 84 oxidative stress-related genes using RT-PCR; genes up or down-regulated by more than twofold were noted. On day 0, genes with increased expression were: photons, none; simulated SPE, Id1; photons + simulated SPE, Bax, Id1, Snrp70. Down-regulated genes at this same time were: photons, Igfbp1; simulated SPE, Arnt2, Igfbp1, Il6, Lct, Mybl2, Ptx3. By day 21, a much greater effect was noted than on day 0. Exposure to photons + simulated SPE up-regulated completely different genes than those up-regulated after either photons or the simulated SPE alone (photons, Cstb; simulated SPE, Dctn2, Khsrp, Man2b1, Snrp70; photons + simulated SPE, Casp1, Col1a1, Hspcb, Il6st, Rpl28, Spnb2). There were many down-regulated genes in all irradiated groups on day 21 (photons, 13; simulated SPE, 16; photons + simulated SPE, 16), with very little overlap among groups. Oxygen radical production by liver phagocytes was significantly enhanced by photons on day 21. The results demonstrate that whole-body irradiation with low-dose-rate photons, as well as time after exposure, had a great impact on liver response to a simulated solar particle event.     

Energy metabolism and blood perfusion in a mouse mammary adenocarcinoma during growth and following X irradiation

Biochemical and blood perfusion changes in a mouse tumor system (MDAH MCaIV) were studied relative to normal tissues under conditions of normal blood flow and clamped blood supply. Further studies were performed during tumor growth and after local X irradiation. The biochemical profiles of three untreated human soft tissue sarcomas were also investigated. Animal tumors were irradiated in situ with either a single or fractionated regime to total doses of 20 or 49 Gy. Assays of lactate, pyruvate, AMP, ADP, and ATP were made on freeze-clamped tissue following authentic or sham treatments. Blood perfusion to tumors treated in the same way was measured using iv injection of 201Tl. The human tumors were found to have a lower lactate to pyruvate ratio (L/P) than the MCaIV tumors; their ATP levels were also lower. L/P was much higher in the MCaIV tumors than in normal liver, kidney, and muscle in the mouse. Occlusion of the blood supplies of the normal kidney and the MCaIV tumor caused an increase in the lactate and L/P levels in both cases. However, whereas the ATP level in the kidney fell, the level in the tumor was maintained. There was some evidence that the adenine nucleotides were not in equilibrium via the adenyl kinase catalyzed reaction. In addition, tumors were found to contain the enzyme creatine kinase. These results suggest that energy charge calculations cannot be computed in a meaningful manner because the creatine kinase catalyzed phosphorylation of ADP would maintain a higher than normal ATP level. Lactate and L/P ratio was found to increase during tumor growth and decrease following X irradiation. The total adenine nucleotides (AMP + ADP + ATP) exhibited a trend toward lower values with increasing tumor size. There was no significant change in total adenine nucleotides after a single 20-Gy dose; however, fractionated radiation caused some fall in total nucleotides. It is concluded that, in this tumor system, lactate level is a sensitive index of radiation-induced biochemical changes which are likely to reflect changes in tumor oxygenation.     

Human skeletal muscle function and metabolism during intense exercise at high O2 and N2 pressures

The maximal contractile force (peak torque) of the quadriceps femoris was studied during 60 repeated unilateral dynamic knee extensions in nine subjects under three different conditions, viz., during air breathing at normal (1 ATA) and raised (6 ATA) ambient pressures and during O2 breathing at 1.3 ATA. In six subjects the electromyographic (EMG) activity of the working muscle was recorded. Muscle biopsies were obtained from the vastus lateralis before, immediately after, and 1 min after exercise. Tissue specimens were subsequently assayed for various muscle metabolites. Peak torque, as an average of the 60 knee extensions, was higher (P less than 0.05) at 1.3 ATA than at 6 or 1 ATA. Peak torque of the exercising muscle declined more rapidly at 1 ATA than at 1.3 ATA, differing in the final 24 contractions by 14%. At 6 ATA peak torque of the initial 12 contractions was 6% lower (P less than 0.05) than at 1 ATA but equaled 1-ATA values in the latter third of the exercise bout. Although the EMG activity at 1 ATA increased relative to that at 6 ATA as exercise proceeded, the rate of force decline was greater at 1 ATA. Despite greater total work produced at 1.3 ATA than at 1 ATA, the metabolic response to exercise was not substantially altered at increased O2 pressure. However, the restitution rate of energy-rich phosphagens and the elimination of lactate during recovery were greater (P less than 0.05) at 1.3 ATA. These results suggest that hyperoxia may enhance the rate of energy release, whereas high N2 pressure and/or high hydrostatic pressure seem to interfere with neuromuscular activity.     

Changes in bromodeoxyuridine labeling index during radiation treatment of an experimental tumor

Cell proliferation kinetics in a spontaneous mouse fibrosarcoma (FSaII) growing in C3H mice has been studied by in vivo pulse labeling of cells synthesizing DNA with bromodeoxyuridine (BrdUrd). A monoclonal antibody to BrdUrd and flow cytometry were used to quantify these cells. Labeling indices (LI) were measured before and after radiation. Unirradiated 10-mm tumors had a mean LI of 17.5%. After a single dose of 20 Gy there was depression of LI after 1 day followed by a rapid increase to greater than control values after 5 days. Analysis performed after five fractions showed that LI was dependent on the dose per fraction and interval between fractions. After 5 and 7 Gy/fraction LI remained similar to control values during daily fractionation but was significantly depressed after twice daily fractionation. With doses greater than 10 Gy/fraction there was marked depression of LI using both fractionation schedules. These changes in LI correlated well with changes in tumor volume after radiation. Tumors were also biopsied after 5 fractions of a 20-fraction course to see if LI would predict for tumor control. LIs of greater than or equal to 10% were associated with lack of tumor control at 90 days while all controlled tumors had a significant depression of LI. Changes in LI after radiation were a reasonable indication of the amount of repopulation occurring and might be useful in selecting patients for altered fractionation schedules.     

Effect of 71 ATA He-O2 on organ blood flow in the rat

Cardiac output and organ blood flow to major organs were investigated in awake rats at 1 atmosphere absolute (ATA) air and at 71 ATA He-O2. Radioactively labeled microspheres [15 +/- 1 (SD) micron] were injected into the left ventricle during constant-rate arterial blood sampling at 1 ATA air and subsequently at 71 ATA He-O2. Intra-arterial blood pressure was continuously recorded. The partial pressure of O2 was kept between 0.4 and 0.6 ATA. The results indicate that the mean blood pressure, heart rate, cardiac output, and organ blood flow are essentially unaltered in the rat at 71 ATA except for increased blood flow to the liver (122%, P less than 0.05), whereas the blood flow to the adrenals, the diaphragm, and the leg muscle fell (P less than 0.05).     

Effects of pentobarbital anesthesia on the energy metabolism of murine tumors studied by in vivo 31P nuclear magnetic resonance spectroscopy

The effects of pentobarbital anesthesia on the energy metabolism of FSaII and MCaIV foot tumors in mice were studied by 31P MRS. Using an 8.5 T spectrometer, in vivo spectra were obtained in 15 animals before and after pentobarbital anesthesia (0.05 mg/g ip). The average phosphocreatine/inorganic phosphate ratios (PCr/Pi) with and without pentobarbital were similar for both tumor histologies. Effects on individual tumors, however, were greater than 20% in 9/15 animals and greater than 50% in 6/15 animals. Pentobarbital anesthesia increased the variability of tumor intracellular pH, and the phosphomonoester/nucleotide triphosphate (PME/NTP) and nucleotide triphosphate/inorganic phosphate ratios (NTP/Pi). When examining the average in a cohort, pentobarbital anesthesia had no significant effect on the PCr/Pi, PME/NTP, NTP/Pi ratios or the pH. However, approximately equal to 50% of individual tumors do have significant changes in these parameters. The anesthesia-induced variability of tumor energy metabolism may explain the decrease in TCD50 observed in previous studies using multifraction radiation.     

Measured and simulated nitrous oxide emissions from ryegrass- and ryegrass/white clover-based grasslands in a moist temperate climate

There is uncertainty about the potential reduction of soil nitrous oxide (N(2)O) emission when fertilizer nitrogen (FN) is partially or completely replaced by biological N fixation (BNF) in temperate grassland. The objectives of this study were to 1) investigate the changes in N(2)O emissions when BNF is used to replace FN in permanent grassland, and 2) evaluate the applicability of the process-based model DNDC to simulate N(2)O emissions from Irish grasslands. Three grazing treatments were: (i) ryegrass (Lolium perenne) grasslands receiving 226 kg FN ha(-1) yr(-1) (GG+FN), (ii) ryegrass/white clover (Trifolium repens) grasslands receiving 58 kg FN ha(-1) yr(-1) (GWC+FN) applied in spring, and (iii) ryegrass/white clover grasslands receiving no FN (GWC-FN). Two background treatments, un-grazed swards with ryegrass only (G-B) or ryegrass/white clover (WC-B), did not receive slurry or FN and the herbage was harvested by mowing. There was no significant difference in annual N(2)O emissions between G-B (2.38±0.12 kg N ha(-1) yr(-1) (mean±SE)) and WC-B (2.45±0.85 kg N ha(-1) yr(-1)), indicating that N(2)O emission due to BNF itself and clover residual decomposition from permanent ryegrass/clover grassland was negligible. N(2)O emissions were 7.82±1.67, 6.35±1.14 and 6.54±1.70 kg N ha(-1) yr(-1), respectively, from GG+FN, GWC+FN and GWC-FN. N(2)O fluxes simulated by DNDC agreed well with the measured values with significant correlation between simulated and measured daily fluxes for the three grazing treatments, but the simulation did not agree very well for the background treatments. DNDC overestimated annual emission by 61% for GG+FN, and underestimated by 45% for GWC-FN, but simulated very well for GWC+FN. Both the measured and simulated results supported that there was a clear reduction of N(2)O emissions when FN was replaced by BNF.     

Brain oxygenation and CNS oxygen toxicity after infusion of perfluorocarbon emulsion

Intravenous perfluorocarbon (PFC) emulsions, administered with supplemental inspired O(2), are being evaluated for their ability to eliminate N(2) from blood and tissue prior to submarine escape, but these agents can increase the incidence of central nervous system (CNS) O(2) toxicity, perhaps by enhancing O(2) delivery to the brain. To assess this, we infused a PFC emulsion (Oxycyte, 6 ml/kg iv) into anesthetized rats and measured cerebral Po(2) and regional cerebral blood flow (rCBF) in cortex, hippocampus, hypothalamus, and striatum with 100% O(2) at 1, 3, or 5 atmospheres absolute (ATA). At 1 ATA, brain Po(2) stabilized at >20 mmHg higher in animals infused with PFC emulsion than in control animals infused with saline, and rCBF fell by ~10%. At 3 ATA, PFC emulsion raised brain Po(2) >70 mmHg above control levels, and rCBF decreased by as much as 25%. At 5 ATA, brain Po(2) was ≥159 mmHg above levels in control animals for the first 40 min but then rose sharply; rCBF showed a similar profile, reflecting vasoconstriction followed by hyperemia. Conscious rats were also pretreated with PFC emulsion at 3 or 6 ml/kg iv and exposed to 100% O(2) at 5 ATA. At the lower dose, 80% of the animals experienced seizures by 33 min compared with 50% of the control animals. At the higher dose, seizures occurred in all rats within 25 min. At these doses, administration of PFC emulsion poses a clear risk of CNS O(2) toxicity in conscious rats exposed to hyperbaric O(2) at 5 ATA.     

Rice allergenic proteins, 14-16 kDa albumin and alpha-globulin, remain insoluble in rice grains recovered from rice miso (rice-containing fermented soybean paste)

The rice grains (RG) and rice seed proteins remaining in rice miso were investigated with a view point to the potential allergenicity of rice miso. RG ranging from 36 to 180 mg dry weight per g dry miso were separated from several samples of commercially available rice miso. Scanning electron microscopy of the recovered RG indicated that starch granules disappeared almost completely while protein bodies remained intact in RG. Most of the major seed proteins were extracted from RG by heating with 1% SDS/2% 2-mercaptoethanol and detected by SDS-polyacrylamide gel electrophoresis. Major rice allergenic proteins, 14-16 kDa albumin (Alb14-16) and alpha-globulin (alpha-Glb) were also detected by immunoblotting using the specific antisera, and their contents were estimated to be 1.7 to 9.0 and 1 to 7 mg protein per g dry RG respectively. However, the major rice proteins, including glutelin and prolamin, in RG were insoluble in salt, alcohol, and urea solutions, but soluble in 6 M guanidine hydrochloride (Gu-HCl). By immunoblotting and ELISA, no Alb14-16 and only a slight amount of alpha-Glb were detected even in the 6 M Gu-HCl fraction, indicating that these major allergenic proteins are denatured and are present in an insoluble form in rice miso.     

Continuous intracellular recording from mammalian neurons exposed to hyperbaric helium, oxygen, or air.

We developed a hyperbaric chamber for intracellular recording in rat brain stem slices during continuous compression and decompression of the tissue bath with the inert gas helium. Air, rather than helium, was also used as the compression medium in some cases to increase tissue nitrogen levels. An important feature is the chamber door, which opens or closes rapidly at 1 atmosphere absolute (ATA) for increased accessibility of the microelectrode. The door also closes and seals smoothly without disrupting the intracellular recording. Hyperbaric oxygen was administered during helium compression using a separate pressure cylinder filled with perfusate equilibrated with 2. 3-3.3 ATA oxygen. Measurements of tissue/bath PO(2) and pH confirmed that the effects of compression using helium or air could be differentiated from those due to increased PO(2). One hundred and thirteen neurons were studied during 375 compression cycles ranging from 1 to 20 ATA (mode 3.0 ATA). We conclude that it is technically feasible to record intracellularly from the same mammalian neuron while changing ambient pressure over a physiologically important range. These techniques will be useful for studying how various hyperbaric environments affect neurophysiological mechanisms.     

Independent cerebral vasoconstrictive effects of hyperoxia and accompanying arterial hypocapnia at 1 ATA.

Breathing 100% O2 at 1 atmosphere absolute (ATA) is known to be associated with a decrease in cerebral blood flow (CBF). It is also accompanied by a fall in arterial Pco2 leading to uncertainty as to whether the cerebral vasoconstriction is totally or only in part caused by arterial hypocapnia. We tested the hypothesis that the increase in arterial Po2 while O2 was breathed at 1.0 ATA decreases CBF independently of a concurrent fall in arterial Pco2. CBF was measured in seven healthy men aged 21-62 yr by using noninvasive continuous arterial spin-labeled-perfusion MRI. The tracer in this technique, magnetically labeled protons in blood, has a half-life of seconds, allowing repetitive measurements over short time frames without contamination. CBF and arterial blood gases were measured while breathing air, 100% O2, and 4 and 6% CO2 in air and O2 backgrounds. Arterial Po2 increased from 91.7 +/- 6.8 Torr in air to 576.7 +/- 18.9 Torr in O2. Arterial Pco2 fell from 43.3 +/- 1.8 Torr in air to 40.2 +/- 3.3 Torr in O2. CBF-arterial Pco2 response curves for the air and hyperoxic runs were nearly parallel and separated by a distance representing a 28.7-32.6% decrement in CBF. Regression analysis confirmed the independent cerebral vasoconstrictive effect of increased arterial Po2. The present results also demonstrate that the magnitude of this effect at 1.0 ATA is greater than previously measured.     

Effects of photon flux density and agricultural fertilizers on the development of <Emphasis Type="Italic">Sarcothalia crispata</Emphasis> tetraspores (Rhodophyta,Gigartinales) from the Strait of Magellan,Chile

Tetraspores of Sarcothalia crispata from San Juan Bay, Strait of Magellan, Chile, were cultivated under different combinations of photon flux densities and agricultural fertilizers in the laboratory. In the experiment, the S. crispata specimens were cultured in combinations of different photon flux densities (50, 100, 150 μmol photons m^-2 s^-1) and enriched seawater solutions (sodium nitrate + monocalcium phosphate, urea + monocalcium phosphate, ammonium nitrate + monocalcium phosphate), always adjusting the N and P concentrations to 10 and 3 mg L^-1, and in sea water as control. After 45 days, the tetrasporeling plants were found to be larger at photon flux densities of 50 and 100 μmol photons m^-2 s^-1 in the nutrient enrichment experiments; growth was greatest in the sea water enriched with ammonium nitrate and urea. An analysis of the combined effect of the photon flux density and nutrients revealed that the best combination for sporeling growth was the ammonium nitrate and urea solution at 50–100 μmol photons m^-2 s^-1.     

Critical water temperature during water immersion at various atmospheric pressures

The present work was undertaken to determine the effect of atmospheric pressure [ranging from a high altitude of 4,300 m above sea level or 0.6 atmospheres absolute (ATA) to depths of 10 m deep or 2 ATA] on the critical water temperature (Tcw), defined as the lowest water temperature a subject can tolerate at rest for 2 h without shivering, of the unprotected subject during water immersion. Nine healthy males wearing only shorts were subjected to immersion to the neck in water at 0.6, 1, and 2 ATA while resting for 2 h. Continuous measurements included esophageal (Tes) and skin (Tsk) temperatures, direct heat loss from the skin (Htissue), and insulation of the tissue (Itissue). The Tcw was significantly higher at 0.6 ATA than 1 and 2 ATA: however, Tcw at 1 ATA was identical to that at 2 ATA. The metabolic heat production remained unchanged among the pressures. During the 2-h immersion in Tcw, Tes was identical among all atmospheric pressures: however, Tsk was significantly higher (P less than 0.05) at 0.6 ATA and was identical between 1 and 2 ATA. The overall mean Itissue was near maximal during immersion in Tcw in each pressure, and no difference was detected among the pressures. However, Itissue at the acral extremities (arm, hand, and foot) decreased significantly at 0.6 ATA, and subsequently heat loss from these parts was increased, which elevated an extremity-to-trunk heat loss ratio to 1.4 at 0.6 ATA from 1.1 at 1 and 2 ATA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chain elongation and desaturation of palmitic acid in liver microsomes of rats subjected to hyperbaric exposure.

The enzyme activities associated with chain elongation and desaturation of fatty acid in hepatic microsomes from rats held at 1 ATA of air, 1 ATA of He-O2, and 20 ATA of He-O2 were studied. It was found that both the microsomal chain elongation and desaturation of fatty acids were depressed in rats held at 1 ATA of He-O2 as compared to animals held at 1 ATA of air. When animals were exposed to an environment of 20 ATA of He-O2, the chain elongation of fatty acid was about the same as for rats held at 1 ATA of air and was two times greater than for the rats held at 1 ATA of He-O2. The desaturase activity was depressed as compared to the two groups of control animals held at 1 ATA of air and 1 ATA of He-O2.     

Does hyperbaric oxygen exposure affect high-intensity, short-duration exercise performance?

Hyperbaric oxygen (HBO) exposure involves the breathing of 100% oxygen under conditions of elevated atmospheric pressure and is used to increase the oxygen content of the plasma fraction of arterial blood. The purpose of this study was to determine the effects of acute HBO exposure on selected physiological responses and performance in response to maximal lower extremity or upper extremity short-term, high-intensity exercise. The study was performed with 2 separate experiments incorporating double-blinded and randomized protocols. In experiment 1, 9 subjects ran on a treadmill at a speed of 268 m x min(-1) with a predetermined grade. In experiment 2, 9 different subjects performed a repetitive bench press exercise. Both exercise protocols were designed to induce fatigue within 1-2 minutes. Within each experiment, subjects received either a 1-hour HBO exposure inspiring 100% O2 at 202.6 kPa (2.0 atmospheres absolute pressure [ATA]) or a 1-hour sham exposure inspiring ambient air at 121.5 kPa (1.2 ATA) before exercise. No significant differences (p > or = 0.05) were observed in postexercise blood lactate concentrations, peak heart rate, ratings of perceived exertion, or performance as determined by treadmill running time or number of completed lifts. Unlike other methods that elevate oxygen content of the blood, acute HBO exposure appears to have no significant effect on subsequent high-intensity running or lifting performance.     

The oxygenation of murine tumor isografts and human tumor xenografts by nicotinamide.

The changes in pO2 caused by nicotinamide in the FSaII mouse tumor and three different xenografts of human tumors, HP-56, FaDu, and EO1, grown subcutaneously in the legs of mice were studied. The tumor pO2, as measured with microelectrodes, began to rise soon after the host mice were injected intraperitoneally with 500 mg/kg nicotinamide, and it increased continuously for 100-120 min. The rate and magnitude of the increase in tumor pO2 was dependent on the tumor line and also on the tumor size. In FSaII tumors, the increase in pO2 caused by nicotinamide was relatively small in the well-oxygenated small tumors (173 +/- 5 mm3) compared with that in the larger tumors (515 +/- 25 mm3). The blood perfusion in FSaII tumors as measured with the laser Doppler method was also increased by nicotinamide. The growth delay in FSaII tumors induced by X irradiation was enhanced significantly by nicotinamide. It was concluded that the enhancement of radiation damage in the experimental tumors in mice by nicotinamide, as observed in the present study and reported by others, is due to an increase in intratumor pO2, possibly as a result of an increase in blood perfusion.