Pulmonary function in men after oxygen breathing at 3.0 ATA for 3.5 h.

As a pulmonary component of Predictive Studies V, designed to determine O2 tolerance of multiple organs and systems in humans at 3.0-1.5 ATA, pulmonary function was evaluated at 1.0 ATA in 13 healthy men before and after O2 exposure at 3.0 ATA for 3.5 h. Measurements included flow-volume loops, spirometry, and airway resistance (Raw) (n = 12); CO diffusing capacity (n = 11); closing volumes (n = 6); and air vs. HeO2 forced vital capacity maneuvers (n = 5). Chest discomfort, cough, and dyspnea were experienced during exposure in mild degree by most subjects. Mean forced expiratory volume in 1 s (FEV1) and forced expiratory flow at 25-75% of vital capacity (FEF25-75) were significantly reduced postexposure by 5.9 and 11.8%, respectively, whereas forced vital capacity was not significantly changed. The average difference in maximum midexpiratory flow rates at 50% vital capacity on air and HeO2 was significantly reduced postexposure by 18%. Raw and CO diffusing capacity were not changed postexposure. The relatively large change in FEF25-75 compared with FEV1, the reduction in density dependence of flow, and the normal Raw postexposure are all consistent with flow limitation in peripheral airways as a major cause of the observed reduction in expiratory flow. Postexposure pulmonary function changes in one subject who convulsed at 3.0 h of exposure are compared with corresponding average changes in 12 subjects who did not convulse.     

The effects of the inhibition of the renal carbonic anhydrase on the blood acid-base status in hypercapnic rats

Arterial blood acid-base status was measured in unanesthetized rats treated with benzolamide (a selective renal carbonic anhydrase inhibitor). These measurements were carried out in rats exposed to different levels of CO2 in air (0-10% CO2) for periods of up to 6 hr. In untreated rats the whole body buffer value showed a continuous increase and after 6 hr of exposure to hypercapnia its value was twice that measured initially. On the other hand, the whole body buffer value of benzolamide treated rats did not change during the 6 hr of exposure to hypercapnia. The whole body buffer value of normal rats, measured after 6 hr of hypercapnia is similar to that reported for chronic (3-5 days) hypercapnia in the normal dog. The whole body buffer value in benzolamide treated rats was similar to that reported for the normal dog and man, during acute CO2 exposures. It is suggested that mechanisms involving the renal carbonic anhydrase are responsible for the significant, rapid changes in the whole body buffer value that take place during the initial phase of acute exposure to CO2 in the rat. This may represent a mechanism of adaptation to burrow hypercapnic conditions.     

Respiratory adaptation to chronic hypercapnia in newborn rats

We asked 1) whether newborn rats respond to chronic hypercapnia with a persistent increase in ventilation and 2) whether changes in lung mass were accompanying the respiratory adaptation to chronic hypercapnia, as previously observed during neonatal chronic hypoxia. Five litters of rats were kept in 7% CO2 (with 21% O2) from day 1 to 7 after birth (CO2exp) and compared with six litters of control rats growing in normocapnia-normoxia (C). Body weight was similar between the two groups. Ventilation, measured by flow plethysmography, increased in CO2exp from day 2 and remained steadily elevated, and at day 7 it almost doubled (174%) the C value because of the large increase in tidal volume and mean inspiratory flow (192 and 189%, respectively) with no changes in respiratory frequency. Two days after return to normocapnia, ventilation was still 33% higher than in C; at this time, acute exposure to hypercapnia increased ventilation relatively less in the CO2exp than in C because of a lower increase in tidal volume. Neither the lung weight-to-body weight nor the heart weight-to-body weight ratios increased in CO2exp. We conclude that 1) chronic hypercapnia in newborn rats induces a steady increase in ventilation, which persists at least 2 days after return to normocapnia with a reduction in the acute response to CO2, and 2) hyperventilation per se is not the cause of the increased lung mass observed during chronic neonatal hypoxia.     

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.     

Optimization of oxygen tolerance extension in rats by intermittent exposure.

Optimization of oxygen tolerance extension by intermittent exposure was studied in groups of 20 rats exposed to systematically varied patterns of alternating oxygen and normoxic breathing periods at 4.0, 2.0, and 1.5 ATA. Oxygen periods of 20, 60, and 120 min were alternated with normoxic intervals that provided oxygen-to-normoxia ratios of 4:1, 2:1, 1:1, and 1:3. In general, median survival times had nearly linear relationships to increasing normoxic intervals with oxygen period held constant. Exceptions occurred at 4.0 and 2.0 ATA where a 5-min normoxic interval was too short for adequate recovery even with a 20-min oxygen period, and an oxygen period of 120 min was too long even with a normoxic interval of 30 min. These exceptions did not occur at 1.5 ATA. Survival time for many intermittent exposure patterns was equivalent to that for continuous exposure to an oxygen pressure definable as a time-weighted average of the alternating oxygen and normoxia periods. However, this predictive method underestimated the degree of protection achieved by several of the intermittent exposure patterns, especially those performed at 4.0 ATA. Results provided guidance for selection of intermittent exposure patterns for direct evaluation in humans breathing oxygen at 2.0 ATA. Definition of intermittent exposure patterns and conditions that produced prominent gains in oxygen tolerance can also facilitate the performance of future experiments designed to study potential mechanisms for oxygen tolerance extension by intermittent exposure. Heat shock and oxidation-specific stress proteins that are induced by exposure to oxidant injury are suggested for emphasis in such investigations.     

Therapeutic gain factors for fractionated radiation treatment of spontaneous murine tumors using fast neutrons, photons plus O2(1) or 3 ATA, or photons plus misonidazole

Therapeutic gain factors (TGFs) have been determined for three spontaneous tumors of the C3H mouse treated by photons + normobaric oxygen (O2(1) ATA), photons + hyperbaric oxygen (O2 3 ATA), photons + misonidazole, or fast neutrons. The tumors were early generation isotransplants of spontaneous tumors: MCaIV, a mammary carcinoma; FSaII, a fibrosarcoma; and SCCVII, a squamous cell carcinoma. The tumors, transplanted to the right leg, were 6 mm at start of treatment. Normal tissue responses studied were acute reaction of normal skin (all treatment modalities) and LD50 following irradiation of the upper abdomen (in test of photons + O2 at 1 or 3 ATA). Thus both the tumor and normal tissues would be classified as "acute responding." All subject tissues were at congruent to 34.5-35 degrees C at irradiation. Treatments were based on d(25)Be or p(43)Be fast neutron beams, 60Co and 137Cs photon beams. Treatments were given in 5 or 15 equal doses in 5 days. For photon treatments, TGFs (air/O2 3 ATA) were substantially and significantly larger than 1 for all three tumor systems treated at small or large doses per fraction when related to skin or abdominal tissue responses. The TGFs (air/O2 1 ATA) were greater than 1 at small doses per fraction for MCaIV and FSaII for skin as the normal tissue; the TGFs for all three tumors and at all doses per fraction would be greater than 1 when related to upper abdominal tissues. TGFs (O2 1 ATA/O2 3 ATA) for photon irradiation greater than 1 were found only for SCCVII and that obtained for both large and small doses per fraction. Misonidazole achieved impressive TGFs (air/air + miso or air/O2 1 ATA + miso); the drug was tested only at 10-12 Gy/fraction and relative to skin. RBEs(FN) for the three tumors were lower at 1.5-2 Gy(FN)/fraction than at 5-6 Gy(FN)/fraction, i.e. the opposite to that reported for normal tissue (RBE increases with decreasing dose per fraction). A TGF (relative to skin reaction) greater than 1 for fast neutron therapy was found only for SCCVII when treated at large doses/fraction; this was true for air or O2 1 ATA conditions.     

Fructose feeding and intermittent hypoxia affect ventilatory responsiveness to hypoxia and hypercapnia in rats.

We hypothesized that, in male rats, 10% fructose in drinking water would depress ventilatory responsiveness to acute hypoxia (10% O2 in N2) and hypercapnia (5% CO2 in O2) that would be depressed further by exposure to intermittent hypoxia. Minute ventilation (Ve) in air and in response to acute hypoxia and hypercapnia was evaluated in 10 rats before fructose feeding (FF), during 6 wk of FF, and after FF was removed for 2 wk. During FF, five rats were exposed to intermittent air and five to intermittent hypoxia for 13 days. Six rats given tap water acted as control and were exposed to intermittent air and subsequently intermittent hypoxia. In FF rats, plasma insulin levels increased threefold in the rats exposed to intermittent hypoxia and during washout returned to levels observed in rats exposed to intermittent air. During FF, ventilatory responsiveness to acute hypoxia was depressed because of decreased tidal volume (Vt) responsiveness. During washout, Ve decreased as a result of decreased Vt and frequency of breathing, and the ventilatory responsiveness to hypoxia in intermittent hypoxia rats did not recover. In all rats, the ventilatory responses to hypercapnia were decreased during FF and recovered after washout because of an increased Vt responsiveness. In the control group, hypoxic responsiveness was not depressed after intermittent hypoxia and was augmented after washout. Thus FF attenuated the ventilatory responsiveness of conscious rats to hypoxia and hypercapnia. Intermittent hypoxia interacted with FF to increase insulin levels and depress ventilatory responses to acute hypoxia that remained depressed during washout.     

Hypercapnia does not affect functional residual capacity enlargement induced by chronic hypoxia

To determine whether changes in partial pressure of CO2 participate in mechanism enlarging the lung functional residual capacity (FRC) during chronic hypoxia, we measured FRC and ventilation in rats exposed either to poikilocapnic (group H, F(I)O2 0.1, F(I)CO2 <0.01) or hypercapnic (group H+CO2, F(I)O2 0.1, F(I)CO2 0.04-0.05) hypoxia for the three weeks and in the controls (group C) breathing air. At the end of exposure a body plethysmograph was used to measure ventilatory parameters (V'(E), f(R), V(T)) and FRC during air breathing and acute hypoxia (10 % O2 in N2). The exposure to hypoxia for three weeks increased FRC measured during air breathing in both experimental groups (H: 3.0+/-0.1 ml, H+CO2: 3.1+/-0.2 ml, C: 1.8+/-0.2 ml). During the following acute hypoxia, we observed a significant increase of FRC in the controls (3.2+/-0.2 ml) and in both experimental groups (H: 3.5+/-0.2 ml, H+CO2: 3.6+/-0.2 ml). Because chronic hypoxia combined with chronic hypercapnia and chronic poikilocapnic hypoxia induced the same increase of FRC, we conclude that hypercapnia did not participate in the FRC enlargement during chronic hypoxia.     

In vivo binding of carbon monoxide to cytochrome c oxidase in rat brain

The possibility of binding of CO to cytochrome c oxidase (cytochrome a,a3) in brain cortex has been examined in vivo by reflectance spectrophotometry. During ventilation with CO-containing gases, cytochrome a,a3 absorption at 605 nm increased in the parietal cortex of anesthetized rats during carboxyhemoglobin (HbCO) formation. HbCO levels, measured by changes in absorption at 569-586 nm in vivo, correlated positively with arterial HbCO by CO oximetry. Arterial blood pressure and calculated O2 content varied inversely with HbCO. During CO exposure, decreases in blood pressure, O2 content, and cytochrome a,a3 oxidation level could be reversed partly at constant HbCO by compression to 3 atmospheres absolute (ATA). After removing CO from inspired gas at 3 ATA, optical and physiological parameters recovered completely to control values except for minor persistent elevations of HbCO. Difference spectra from parallel experiments at constant HbCO revealed absorption minima at 588-592 nm and 600-605 nm as a result of hyperbaric exposure. Spectral analysis of these components was consistent with partial dissociation of a cytochrome a3-CO complex and cytochrome a reoxidation with increasing dissolved O2 in hyperbaric conditions.     

Pressure increases oxygen affinity of whole blood and erythrocyte suspensions

Effect of hydrostatic pressure (HP) on whole blood (WB) or erythrocyte suspension hemoglobin (Hb) O2 affinity has been studied using newly developed techniques. O2 partial pressure at which hemoglobin is half-saturated with O2 (P50) measurements were made at 5 HP (1, 26, 51, 76, and 126 ATA) on thin films of human WB or erythrocytes at 37 degrees C. CO2 partial pressure of WB was either 28 or 57 Torr (film pH 7.51 or 7.31). HP increased affinity of erythrocytes and WB. For erythrocytes in tris(hydroxymethyl)aminomethane buffer, the ratio (r) of P50 (1 ATA)/P50 (51 ATA) was 1.089 (P less than 0.01) at pH 7.0. WB P50 decreased with HP at a rate of -3.3 X 10(-2) Torr X atm-1; change in P50 at higher HP vs. 1 ATA was highly significant (P less than 0.01). No effect of HP was seen on the CO2 Bohr coefficient. Inert gas choice, N2 vs. helium (He), had no effect. Measurement of decrease of P50 with HP at 76 ATA in hemolyzed WB gave an r of 1.15, as great or greater than that found in WB, indicates that Donnan equilibrium alteration is not involved. No effect of HP was found in WB on the ratio of P50 of erythrocytes with normal (5 mmol/l erythrocytes) 2,3-diphosphoglycerate (DPG) to P50 of erythrocytes with less than 5% of normal DPG; i.e., no effect of pressure was seen on the independent influence of DPG on P50. WB measurements of Hb O2 uptake under simulated physiological conditions are characterized by a net decrease in partial molal volume on oxygenation of 30-35 ml/mol Hb4.     

Diaphragmatic function during hypercapnia: neonatal and developmental aspects

The effect of acute hypercapnia on diaphragmatic force output was studied in 6 young (4-8 days) and 6 older (16-20 days) anesthetized, spontaneously breathing piglets. Diaphragmatic force output was assessed by analysis of the transdiaphragmatic pressure (Pdi) generated during phrenic nerve stimulation. Pdi was measured under base-line conditions (50% O2-50% N2) and after 10 min of hypercapnia induced by breathing 5, 10, or 15% CO2 balanced with N2 and 50% O2. Pdi was significantly less than base line during the 10 and 15% hypercapnic conditions in the young (P less than 0.05) but not the older piglets. End-expiratory lung volume was noted to decrease during 15% CO2 hypercapnia. Force output augmentation occurred at this lower end-expiratory lung volume and was significantly greater in the older piglet compared with its younger counterpart (P less than 0.05). When the effects of lung volume on Pdi were corrected for, there was no age-related difference in the response to 15% CO2 hypercapnia. We conclude that severe hypercapnia has a depressant effect on diaphragmatic force output in both young and older piglets, and a differential augmentation in diaphragmatic force-output gain occurs at lower end-expiratory lung volume between young and older piglets, with the greater output occurring in the more mature animal.     

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.     

Exhaustive exercise, animal stress, and environmental hypercapnia on motility of sperm of steelhead trout (Oncorhynchus mykiss)

Motility of salmonid sperm is inhibited by the presence of carbon dioxide (CO2) in vitro; however, whether this occurs in response to challenges to the adult in vivo is not known. To determine whether CO2 negatively impacts sperm function in vivo, mature males were exposed to exhaustive exercise as well as to acute stress, chronic stress, tricaine anesthesia and environmental hypercapnia and sperm motility and semen CO2 tensions and pH values assessed. Semen CO2 rose and pH decreased significantly only in response to exhaustive exercise and environmental hypercapnia (13 kPa CO2). These changes in semen CO2 and pH were associated with reductions in numbers of sperm becoming motile upon water activation. Chronic and acute stress and tricaine anesthesia were without effect on sperm motility or on semen CO2 or pH. The time course of CO2 inhibition and recovery was evaluated in vitro. At least 50 min was required to note 50% of the inhibitory effect of low CO2 tensions on motility when sperm were exposed to 1.6-3.1 kPa CO2. At higher CO2 levels sperm motility displayed 50% of the inhibitory effect of these tensions within about 30 min. Sperm recovered maximal motility within 1 h of being placed in a nominally CO2-free environment. This study demonstrates sperm vulnerability to not only in vitro CO2 exposure but also in vivo exposure during exhaustive exercise and as result of environmental hypercapnia.     

Effects of photoperiod and hibernation duration on the lifespan of Bombus terrestris

In this study the effects of photoperiod and hibernation duration on the lifespan of Bombus terrestris queens were examined. Hibernation durations of 2.0, 2.5, 3.0, 3.5 and 4.0 months were studied, as were photoperiods of 0 h light : 24 h dark (LD 0:24), LD 8:16, LD 16:8 and LD 24:0. The queens that hibernated for 2.5 months and were exposed to 1 week of LD 8:16 had the highest survival rate (89.3%); the lowest survival rate was found in queens that hibernated for 4.0 months and were reared at LD 24:0. Photoperiod and hibernation duration had significant effects on egg predation by founding queens, competition between queens and workers, and emergence of sexual queens. Hibernation durations of 2.5 and 3.0 months and a photoperiod of LD 8:16 resulted in a significantly longer lifespan of B. terrestris.     

Suppression of spermatogenesis by testosterone in adult male rats: effect on fertility, pregnancy outcome and progeny

The relationship between decreasing spermatogenic activity and fertility, pregnancy outcome and the progeny is poorly understood. To study this relationship a model where testosterone is given by a sustained release device is used. Adult male Sprague-Dawley rats received empty or testosterone-filled implants measuring 0.5, 1.0, 2.0, 3.0, 4.0 and 8.0 cm. On Day 90 and again on Day 104 each male was exposed to two females in proestrus. Twenty days later the females were killed. Corpora lutea, implantation sites, resorptions and live normal and abnormal fetuses were counted. Sperm counts in the caput-corpus region of the epididymis in the 3.0-, 4.0- and 8.0-cm testosterone treatment groups were 12.6%, 3.0% and 29.9% of control, while those in the caudal region were 19.8%, 4.0% and 50.8% of control, respectively. The number of females with spermatozoa in the vagina after breeding was significantly diminished only in animals treated with the 4.0-cm testosterone implants (control, 95.8%; 4.0-cm, 50%) while the number of pregnant females per sperm-positive females was markedly reduced in the females mated with both the 3.0-cm and 4.0-cm testosterone implants (control, 82.6%; 3.0-cm, 10.0%; 4.0-cm, 7.7%). There was no effect on the numbers of corpora lutea, on the incidence of pre- or post-implantation loss, malformations, or on the numbers of pups/litter. Individual animals with a decrease in caudal epididymal spermatozoal reserves to less than 5 million, however, are infertile. A decrease in epididymal spermatozoal reserves mediated by testosterone does not cause an increase in teratogenicity in the resultant progeny.     

Medullary CO2 chemoreceptor neuron identification by c-fos immunocytochemistry.

In a search for CO2 chemoreceptor neurons in the brain stem, we used immunocytochemistry to monitor the expression of neuronal c-fos, a marker of increased activity, after 1 h of exposure to CO2 in five groups of Sprague-Dawley rats (294 +/- 20 g): five air breathing controls, three breathing 10% CO2, three breathing 13% CO2, three breathing 15% CO2, and three breathing 15% CO2 and treated with morphine (10 mg/kg sc). After exposure the rats were anesthetized with pentobarbital sodium and perfused intracardially with 4% paraformaldehyde. The brain stem was removed and cryoprotected, and then 50-microns frozen sections were cut and immunostained for the fos protein. Brain stem fos-immunoreactive neurons were plotted and counted in the superficial 0.5 mm of the ventral medullary surface. Thirteen to 15% CO2 evoked fos-like immunoreactivity (FLI) in 321 +/- 146 neurons/rat. Significant CO2-induced labeling was confined within the superficial 150 microns: 67% of identified cells were less than 50 microns below the surface, greater than 90% between 1.0 and 3.0 mm from the midline, and approximately 60% in the rostral half of the medulla. Thirteen to 15% CO2 also evoked FLI in the area of the nucleus tractus solitarius but not in other medullary regions. Morphine (10 mg/kg sc) did not suppress high CO2-evoked FLI in either the ventral medullary surface or the nucleus tractus solitarius, although it eliminated excitement and hyperventilation. We suggest that respiratory CO2 chemoreceptor neurons can be identified in rats by their expression of c-fos after 1 h of hypercapnia.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Effects of hypoxia and hypercapnia on surfactant protein expression proliferation and apoptosis in A549 alveolar epithelial cells

During lung injury alveolar epithelial cells are directly exposed to changes in PO(2) and PCO(2). Integrity of alveolar epithelial type II cells (AECII) is critical in lung injury but the effect of hypoxia and hypercapnia on AECII function, viability and proliferation has not been clearly investigated. Aim of the present work was to determine the direct effect of hypoxia and hypercapnia on surfactant protein expression, proliferation and apoptosis of lung epithelial cells in vitro. A549 alveolar epithelia cells were subjected to hypoxia (1%O(2)-5% CO(2)) or hypercapnia (21% O(2-) 15% CO(2)) and expression of surfactant protein C was measured and compared to normal conditions (21% O(2)- 5% CO(2)). Cell cycle progression and apoptosis were measured by flow cytometric analysis. RESULTS: A549 alveolar epithelial cells produce surfactant proteins, including surfactant protein C, when cultured under normal conditions, which is reduced under hypoxic conditions. Specifically, pro-SpC expression is moderately decreased after 8 h of culture in hypoxia, and is completely attenuated after 48 h. Hypercapnia decreases pro-SpC expression only after 48 h of exposure. Stimulation with TNF-alpha partly reverses pSPC decrease observed under hypoxic and hypercapnic conditions. Hypoxic culture of A549 cells results in progressive arrest of cells in the G1 phase of the cell cycle and increased apoptosis first observed 4 h following exposure and peaking at 24 h. In contrast hypercapnia has no significant effect on alveolar epithelial cell proliferation or apoptosis. CONCLUSIONS: Taken together we can conclude that hypoxia rapidly and severely affects AECII function and viability while hypercapnia has an inhibitory effect on pro-SpC production only after prolonged exposure.     

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.     

A mathematical model of CO2 effect on cardiovascular regulation

The effect of changes in arterial CO2 tension on the cardiovascular system is analyzed by means of a mathematical model. The model is an extension of a previous one that already incorporated the main reflex and local mechanisms triggered by O2 changes. The new aspects covered by the model are the O2-CO2 interaction at the peripheral chemoreceptors, the effect of local CO2 changes on peripheral resistances, the direct central neural system (CNS) response to CO2, and the control of central chemoreceptors on ventilation and tidal volume. A statistical comparison between model simulation results and various experimental data has been performed. This comparison suggests that the model is able to simulate the acute cardiovascular response to changes in blood gas content in a variety of conditions (normoxic hypercapnia, hypercapnia during artificial ventilation, hypocapnic hypoxia, and hypercapnic hypoxia). The model ascribes the observed responses to the complex superimposition of many mechanisms simultaneously working (baroreflex, peripheral chemoreflex, CNS response, lung-stretch receptors, local gas tension effect), which may be differently activated depending on the specific stimulus under study. However, although some experiments can be reproduced using a single basal set of parameters, reproduction of other experiments requires a different combination of the mechanism strengths (particularly, a different strength of the local CO2 mechanism on peripheral resistances and of the CNS response to CO2). Starting from these results, some assumptions to explain the striking differences reported in the literature are presented. The model may represent a valid support for the interpretation of physiological data on acute cardiovascular regulation and may favor the synthesis of contradictory results into a single theoretical setting.