A new model of diffuse interstitial pulmonary fibrosis in the rat

We have produced experimental diffuse interstitial pulmonary fibrosis in rats with a combination of low and repeated doses of paraquat plus continuous exposure to normobaric 74% O2 in the breathing air for several weeks. Pulmonary fibrosis was evaluated histologically and biochemically, through the determination of total collagen content in the lung. Our procedure is characterized by low initial mortality, the development of extensive distortion of the pulmonary architecture, and the presence of severe and diffuse interstitial fibrosis. The model was compared with bleomycin-induced pulmonary fibrosis in the same rat strain, in which the process is focal and leaves most of the lung unaffected. We conclude that lung damage produced by the combination of low doses of paraquat plus normobaric 74% O2 concentration in the breathing air is an adequate experimental model of diffuse interstitial pulmonary fibrosis as it occurs in many of the human cases of this condition.     

Severe acute oxidant exposure: morphological damage and aerobic metabolism in the lung

Groups of male rats were exposed to acute doses of oxygen, ozone, or paraquat which produced equivalent mortality (25-30%) over a 28 day post-exposure period. Quantitative evaluation of morphological changes indicated the primary response to be edema and inflammation with only slight fibrosis being apparent by the end of the observation period. Aerobic pulmonary metabolism was inhibited in lungs from animals exposed to oxygen and ozone as evidenced by decreased oxygen consumption; however, this was transient and O2 consumption returned to normal within 24 hours after removal from the exposure chamber. Conversely, treatment with paraquat caused an immediate, transient stimulation of O2 consumption. Glucose metabolism was unaltered by the gas exposures and, as previously reported, was initially stimulated by paraquat treatment. In vitro, only paraquat altered both O2 consumption and glucose metabolism when added to lung slice preparations; ozone had no effect. Oxygen did not alter O2 consumption but caused a slight biphasic response in glucose metabolism. Aerobic metabolism is relatively unchanged by these doses of oxygen and ozone which result in the death of 25-30% of all treated animals. Even though paraquat produces similar morphologic changes, it may represent a more severe metabolic insult than "equivalent" doses of oxygen or ozone. Also, if interstitial pulmonary fibrosis is a desired result of experimental exposure, rats may not be a suitable model for oxidant induced lung injury.     

The Enhancement of Paraquat Toxicity in Rats by 85% Oxygen: Lethality and Cell-Specific Lung Damage

When rats were dosed s.c. with paraquat or diquat and then exposed to air or 85% oxygen, the lethality of paraquat was enhanced approximately 10-fold by 85% oxygen exposure, whereas the lethality of diquat was enhanced only 2-fold. This increase in toxicity was not caused by an increase in the lung concentration of either bipyridyl.The lungs of rats which had been dosed with paraquat (2·5 and 20 mg/kg) or diquat (10 and 20 mg/kg) and exposed to air or 85% oxygen were examined morphologically at various times up to 24 h after dosing. By 24 h after dosing, the extent of damage appeared to be generally similar for those doses of paraquat that killed the same proportion of animals when combined with air or 85% oxygen. The combination of 20 mg paraquat/kg and air exposure caused alveolar epithelial Type I and Type II cell damage. Following 2·5 mg paraquat/kg and 85% oxygen exposure or 20 mg diquat/kg and 85% oxygen exposure the Type II alveolar epithelial cells were more severely damaged than the Type I epithelial and endothelial cells. In contrast, there was no cell damage after 1 or 2 days of exposure to 85% oxygen alone, and when lung damage did develop after 4 days of exposure, it was the capillary endothelial cells which were primarily affected. Thus the toxic effects of paraquat to the Type II alveolar epithelial cells are enhanced by exposure to oxygen.The ability of the lung to accumulate paraquat was measured in lung slices that had been taken from rats dosed with paraquat or diquat and exposed to air or 85% oxygen for 2, 8 or 24 h. Paraquat accumulation was inhibited at times after dosing when the alveolar epithelial cells appeared to be damaged. This is consistent with the hypothesis that paraquat is primarily accumulated by the alveolar epithelial cells.We have concluded that (i) the toxic effects of paraquat to the alveolar epithelial cells of the lung are markedly enhanced when paraquat-treated rats are exposed to 85% oxygen, and (ii) the combination of low concentrations of paraquat (2·5 mg/kg) and 85% oxygen or high concentrations of diquat (20 mg/kg) and 85% oxygen damages the Type II alveolar epithelial cells.     

Pulmonary artery remodeling and pulmonary hypertension after exposure to hyperoxia for 7 days. A morphometric and hemodynamic study.

This study shows by morphometric and hemodynamic techniques that exposure to hyperoxia at normobaric pressure causes rapid structural remodeling of rat pulmonary arteries and pulmonary hypertension. After 7 days of 90% O2, pulmonary artery cross-sectional area is reduced by a striking loss of intraacinar arteries (control, 13 +/- 1 sq mm; exposed, 8 +/- 1 sq mm; P less than 0.001), the ratio of arteries to alveoli being 4:100 in control rats and 2.5:100 after hyperoxia. The lumen of preacinar and intraacinar arteries is narrowed by a reduction of vessel external diameter (ED) and an increased medial wall thickness (MT). There is a significant reduction in the percent medial thickness [( 2 X 100 X MT]/ED) in both regions. The proportion of muscular and partially muscular intraacinar arteries increases at the expense of nonmuscular ones (P [chi 2] less than 0.01), and fully muscular arteries appear in the alveolar wall where they are not normally found. Intimal thickening occurs in 19% of alveolar duct and 34% of alveolar wall nonmuscular arteries. Right ventricular hypertrophy occurs, the ratio of the left ventricle plus the septum to the right ventricle being significantly reduced (control, 4.07 +/- 0.26; exposed, 3.23 +/- 0.10; P less than 0.02). After 3 days of 87% O2, pulmonary artery pressure is still normal (17.0 +/- 0.9 mmHg) but after 7 days it is significantly increased (26.2 +/- 0.9 mmHg; P less than 0.01), as is pulmonary vascular resistance (control, 0.033 +/- 0.003; exposed, 0.065 +/- 0.015 U/kg; P less than 0.05). Return to air breathing (after 7 days at 87% O2) causes pulmonary vasoconstriction and a further rise of the pulmonary artery pressure (to 38.3 +/- 3.3 mmHg after 60 minutes).     

Hypoxia of sleep apnoea: cardiopulmonary and cerebral changes after intermittent hypoxia in rats

Sleep apnoea (SA) is common, especially in elderly people. In severe cases, arterial P(O2) may be lowered for a third or more in a night of sleep. To simulate the degree and duration of severe SA we exposed rats in a normobaric environmental chamber to 10% O(2) for 4h daily for 56 days (intermittent hypoxia: IH group) and compared them with rats continuously exposed for 8 weeks (continuous hypoxia: CH group) and control rats breathing room air (normoxic: N group). We found significant cardiopulmonary and cerebral changes. Right ventricular hypertrophy developed in IH and to a greater extent in CH. Small peripheral lung vessels developed thicker walls (assessed by a new method), which reduced their lumen, more in CH than IH. Coronal brain sections were immunostained for the glucose-transporter 1 (GLUT1) and the vascular endothelial growth factor (VEGF). The percentages of immunoreactivity in the frontal and temporal cortex, hippocampus, accumbens and putamen were determined by image-capture analysis. We noted GLUT1 immunoreactivity of the capillaries was similarly increased in all regions after CH but less so after IH. However, there was a significant linear trend in GLUT1 reactivity from N to IH to CH (R(2) = 0.73, P = 0.007) that was also confirmed by analysis of variance. The extent of VEGF-stained neurones and glial cells was significantly increased in all regions after IH but not after CH. This suggests that the signals for angiogenesis were complete or arrested after CH. Our findings have implications for the elderly subjected to hypoxic episodes during sleep apnoea.     

Persistence of DNA damage in the freshwater mussel Unio pictorum upon exposure to ethyl methanesulphonate and hydrogen peroxide

An important endpoint in assessing pollution-related toxicity is genotoxicity. To obtain insight into the time-course of oxidative- and alkylation-induced DNA damage in the freshwater mussel, Unio pictorum, mussels were exposed for 24 hr to concentration gradients of pro-oxidant hydrogen peroxide (H(2)O(2)) and a mono-functional alkylating agent, ethyl methanesulfonate (EMS). DNA damage was assessed in haemocytes immediately upon exposure and over the recovery period of up to 72 days by means of comet and micronucleus assays. Following exposure to H(2)O(2), DNA damage as detected by the comet assay returned to control values after one day, except for the mussels exposed to the highest dose when damage was detectable for the next 3 days. In contrast, alkylation-induced DNA damage was detectable even after 72 days of recovery in de-chlorinated water, with a dose-response relationship observable throughout the whole recovery period. Micronucleus frequency was the highest on Day 3 after exposure to EMS; it decreased considerably by Day 7 and returned almost to the control levels 19 days after exposure, while no significant induction of micronuclei was observed in mussels exposed to H(2)O(2). Although the comet assay is considered a biomarker of recent genotoxic exposure, detecting DNA damage of shorter longevity than with the micronucleus assay, results presented here show that in the case of alkylation damage the comet assay reveals genotoxic exposure of U. pictorum in a dose-dependent manner even after 2 months.     

Diffuse and focal oxygen pneumonitis: A preliminary report on the threshold of pulmonary oxygen toxicity in man

Utilizing hyaline membranes and proliferative pneumonitis as evidence of pulmonary oxygen toxicity, the lung changes in 21 patients (19 injured, two inhaled smoke) who died after oxygen therapy are correlated with the intensity and duration of oxygen administration. Diffuse pneumonitis inducing hypoxaemia was found in 10 (or 11) subjects, and in nine of them it was associated with the breathing of high concentrations of oxygen (60 to 100%) for at least two days. In at least eight subjects the pneumonitis contributed to death, and two others who survived for weeks had extensively fibrosed lungs. The breathing of 40% oxygen for a sufficient time seems to be a threshold for dangerous lung effects, since one patient developed a diffuse pneumonitis and another a partly-diffuse partly-focal pneumonitis while exposed to this concentration. Those respiring oxygen concentrations between 25 and 40% for days developed either subclinical focal lung lesions or had no relevant lung changes.     

Effect of systemic hypoxia on GLUT4 protein expression in exercised rat heart

Altitude training is a common method used to enhance endurance performance in athletes. We have examined the interactive effect of exercise training and chronic hypoxic on glycogen storage and GLUT4 protein expression in cardiac muscles. Thirty-two male Sprague-Dawley rats were weight balanced and assigned to one of the following four groups: control, exercise, hypoxia, and hypoxia-exercise. Rats with hypoxic treatment (breathing 14% O(2) for 12 hr/d) were exposed under normobaric conditions. The training protocol consisted of swimming for two 3-hr periods per day for 4 weeks. Glycogen content, GLUT4 protein, and mRNA of all rats were determined 16 hr after treatments. Four-week exercise training without hypoxia significantly elevated myocardial glycogen level by 45%. The chronic hypoxic-exercise training elevated the myocardial glycogen level by 67% above control level, significantly greater than the exercise group. Chronic hypoxia, exercise training, and hypoxia-exercise training significantly elevated GLUT4 protein by 40-70% in cardiac muscles. Chronic hypoxia significantly elevates the GLUT1 protein level independent of exercise training. The new finding in this study was that GLUT4 gene expression in cardiac muscle can be stimulated by exercise training with hypoxia treatments. This molecular adaptation appears to be associated with the observed increase in glycogen storage of the muscle.     

Effects of paraquat aerosol on mouse lung

BALB/c mice were exposed to an aerosol of paraquat dichloride solution and were killed six hours, 1, 3, 7, 14 and 28 days later. Initial necrosis and sloughing of the bronchiolar and alveolar epithelia with intact endothelium were followed by type 2 pneumocyte hyperplasia, fibroblast proliferation, and increased synthesis of collagen. These results indicate that inhaled paraquat solution produces pulmonary fibrosis that is morphologically similar to the lesions produced by systemic administration.     

Effects of normobaric hyperoxia on water content in different organs in rats

Pulmonary oxygen toxicity is a dose-dependent effect on alveolar epithelial and endothelial cells resulting in pulmonary oedema. Any concomitant effects on systemic capillary endothelium would be expected to result in capillary leakage and an increase in the tissues' water content. Total tissue water (TTW) in different organs was therefore studied in freely moving rats exposed to 100% O2 at normobaric pressure for 24 or 48 h, and compared to air-breathing control rats. The TTW for the following tissues was measured: Trachea, left bronchus, left lung, left and right ventricle, left kidney, skin (left paw-hindlimb), skin (back of the rat), left brain, left eye and thigh muscle left side. There was a significant increase in TTW of the lung accompanied by pleural effusion after 48 h of oxygen exposure as expected in all exposed animals. There was a small increase in TTW of the paw only, and a small decrease or no change in other tissues after 24 and 48 h of exposure. We conclude that there is no evidence of systemic capillary dysfunction as measured by tissue water content after exposure to hyperoxia in a dosage causing pulmonary oedema.     

Emphysema alters the deposition pattern of inhaled particles in hamsters.

How does pulmonary emphysema affect aerosol deposition? Groups of awake hamsters with emphysema (intratracheal elastase, 0.2 mg/100 g body wt) and age-matched controls (intratracheal saline) were exposed for 30 minutes to an insoluble radioactive aerosol (0.45 mu aerodynamic diameter) at 30, 60, or 90 days after instillation. Immediately after exposure, the animals were sacrificed. The lungs were excised, dried at total lung capacity, and sliced into 1-mm thick sections. Each slice was cut into pieces, which were counted for radioactivity and weighed. Then a measure of the uniformity of deposition, the evenness index (EI), was calculated. With perfect uniformity, all EIs would be one. We found fewer particles in the emphysematous, as compared with the control, lungs at 60 or 90 days after elastase instillation. The deposited particles were distributed less uniformly throughout the emphysematous lungs than in the control lungs. In controls, the standard deviation (SD) of the EI distribution (mean 1.0) averaged 0.33 for the three times studied. In elastase animals, the SD increased to 0.48 at 30 days, and at 60 days and 90 days the distributions were no longer normally distributed. This increased heterogeneity of deposition was also manifested as a loss of the normal apex-base gradient observed in control animals, an increase in the amount of nonventilated parenchyma, enhanced airway deposition, and an altered lobar deposition pattern. Morphometric analysis showed an increase in the mean linear intercept (MLI) of emphysematous lungs as compared with control lungs. However, the author found no correlation between MLI, a measure of emphysema, and EI, a measure of deposition, quantified in the same lung pieces. It is concluded that the emphysematous lesions produced by elastase markedly alter the deposition of an inhaled submicrometric aerosol. Factors that may contribute to these changes include airway obstruction and differences in breathing pattern in emphysematous as compared with control animals.     

Timed effects of an oral adrenergic bronchodilator on pulmonary function and measurements of plasma and leukocyte cyclic AMP: divergence in duration of drug action and development of tolerance

The time course of response to initiation and withdrawal of treatment with terbutaline (5 mg orally, three times daily) was examined in eight normal subjects and 14 asthmatic patients. The various indices of response, examined simultaneously, yielded divergent estimates of the duration of drug action and the development of tolerance during continuous treatment. Bronchodilator responses were observed after each dose of terbutaline, but within 8 hr after a dose, pulmonary functions were similar to those observed in the absence of treatment. There was a suggestion of moderate tolerance to the bronchodilator effects of medication in that areas under the curve for increments in pulmonary function after terbutaline were lower during treatment than after the initial doses of medication; but the variations in magnitude of pulmonary response on different study days did not achieve statistical significance. Measurements of plasma cyclic AMP concentration suggested a much longer duration of drug action, with elevated levels observed 24 hr after a treatment dose; there was a progressive decrease in the plasma cyclic AMP responses to medication during the course of treatment. Conversely, leukocyte cyclic AMP responses to adrenergic stimulation were suppressed within 4 hr after the first dose of medication; the suppression persisted throughout treatment and for 1 to 3 days thereafter. These observations indicated that duration of drug action and induction of tolerance vary in different organ systems.     

Effects of buthionine sulfoximine on the development of ozone-induced pulmonary fibrosis

The capacity of reduced glutathione (GSH) to protect lung tissue against ozone-induced pulmonary fibrosis was investigated. Male B6C3F1 mice were exposed to 0, 0.2, 0.5, and 1.0 ppm ozone for 23 hr/day for 14 days. During exposures and/or for a period of 90 days after exposures, subgroups of mice at each exposure level were given drinking water containing 30 mM L-buthionine-S,R-sulfoximine (BSO) to lower in vivo levels of GSH. These BSO treatments reduced blood glutamylcysteine synthetase (GCS) activity (regulatory enzyme for GSH biosynthesis) and lung nonprotein sulfhydryl (NPSH) levels in nonexposed animals by approximately half. In contrast, ozone exposures increased blood GCS activity and lung NPSH levels in a concentration-dependent manner, with smaller increases in the BSO-treated mice. Immediately after exposures, an ozone-related inflammatory response was seen in lungs, but no histopathological signs of developing fibrosis were evident. Ninety days later, mice exposed to 1 ppm ozone and not treated with BSO had modest evidence of pulmonary fibrosis. Mice exposed to 1 ppm ozone and treated with BSO during this post-exposure period (regardless of BSO treatment during exposures) showed histopathological evidence of exacerbated pulmonary fibrosis, compared to similarly exposed mice not treated with BSO postexposure. These results indicated that interference with the body's normal defense mechanisms against oxidant damage, including suppression of GSH biosynthesis, exacerbates the subsequent development of pulmonary fibrosis.     

Effects of respiratory treatment with N-hexane on rat testis morphology. I. A light microscopic study

Testicular damage was induced in rats by respiratory treatment with n-hexane at a concentration of 5000 ppm. The earliest lesions were observed immediately after 24 hr of continuous treatment, and involved primary spermatocytes from the leptotene to the middle pachitene stages and spermatids at late stages of maturation; at the same time numerous exfoliated, injured germ cells reached the epididymis. After the 24-hr treatment was suspended, damage to the seminiferous epithelium increased for the first 7 days, while the epididymis showed also focal infiltration by inflammatory cells; recovery was completed from Days 14 to 30. Intermittent treatment (16 hr/day, 6 days/week) at the same concentration of 5000 ppm for up to 6 weeks induced progressive increases in testicular and epididymal lesions, which, after 5 weeks (when most animals began to show clinical symptoms of polyneuropathy), reached aplasia of the germinal epithelium involving also the spermatogonia. Recovery from clinical symptoms was not paralleled by a regression of testicular pathology. On the contrary, after interruption of the treatment, the testicular lesions became increasingly severe, up to complete atrophy of the seminiferous tubules, suggesting an irreversible sterility of the treated animals. Pair-fed controls did not show histological alterations of the testis or epididymis.     

The effect of continuous light exposure on the retina in albino and pigmented rats

The effect of exposure to continuous light on the electroretinogram of albino and pigmented rats was studied. Two series of animal groups, adult or new-born at the start of the exposure period, were given different light-dark regimes for different periods of time. Increase of the a- and b-wave threshold was only found in the albino rats exposed to continuous light. In none of the groups an effect on wave threshold of age at the start of the exposure or exposure duration was seen. Reduction of the amplitude of the a- and b-wave, and lengthening of the time to peak of both waves was seen in all groups exposed to the high light intensity, though the effects of overexposure were much stronger in the albino rats. Moreover the changes in ERG parameters in the albino rats after overexposure were strongest in the adult at the start of the exposure period animals. Morphological damage of the retina after exposure was only seen in albino rats after continuous light exposure.     

The use of [125I]polyvinyl pyrrolidone K. 60 in the quantitative assessment of the uptake of macromolecular substances by the intestine of the young rat

1. A method has been developed which allows the quantitative estimation of the uptake of labelled polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000 (K. 60) by the wall of the small intestine of young rats.2. Four hours after feeding a standard dose of [(125)I]PVP by stomach tube, the small intestine was thoroughly washed out, and the radioactivity of the intestinal wall measured. Under these conditions, the small intestine of animals less than 18 days old took up more than 50% of the radioactivity which had left the stomach. There was no increase in PVP uptake if the duration of absorption exceeded 4 hr. The PVP was taken up by the epithelial cells of the villus, and its intracellular localization has been demonstrated by fluorescence microscopy and can be related to vacuolation in the cells.3. In animals between 18 and 20 days old the uptake of PVP declined progressively, until, in animals more than 20 days old, less than 5% of the radioactivity was taken up by the intestinal wall.4. There is good agreement between the reported age of termination of antibody absorption in young rats and the age at which PVP uptake ceased in the present experiments. It is suggested that the loss of ability of the intestine to take up substances of high mol. wt. may be the factor which limits the duration of the period of antibody absorption in this species.     

Endogenous circadian rhythms in rats recovered from lateral hypothalamic lesions

Compared with intact controls, rats which have recovered spontaneous ingestion after lateral hypothalamic lesions show exaggerated nocturnal rhythms. Food intake was low and water intake negligible in the light part of a LD 12:12 cycle. The endogenous rhythms persisted in constant dark, and were clearly free running in constant light with periods of 25–26 hr. Animals with relatively asymmetric damage showed strong LL suppression of intake on the first day; animals with symmetric damage showed no LL suppression and the strongest free running rhythms; rats with the largest lesions showed a permanent LL suppression of fluid intake from Day 3 onward. The LL rhythms were rapidly reentrained with a restored LD cycle, with phase shifts of over 90°/24 hr. Recovered laterals which were previously blinded by orbital enucleation showed free running rhythms with periods close to 24 hr. The division of the 24 hr period into active (α) and quiescent (?) phases is much more sharply defined after the lesion. This is especially marked for drinking; feeding and activity rhythms are very similar. It is suggested that the recovered lateral is dependent upon endogenous oscillator(s) subserving motivated behaviors, and implications for the recovery of function and residual impairments are discussed.     

Characterization of pulmonary cellular influx differentials to known toxic agents between species

In this study, we have shown that chickens, frogs, and toads are resistant to acute pulmonary injury by a variety of toxic agents, (O₂, hyperbaric O₂, paraquat, and silica), that cause extensive acute injury in mammals. Acute pulmonary injury is defined as a massive influx of inflammatory cells, both interstitially and into the alveolar spaces, pulmonary edema, hemorrhage, and the presence of H₂O₂ and O ₂ ^– in the lavaged supernatant, occurring within 48 h. In some cases, chronic effects of the toxins were observed after 90 h., i.e., hemorrhage, fibrosis, and an accumulation of interstitial inflammatory cells. In all three nonmammal systems, isolated inflammatory cells failed to respond chemotactically in vitro to known mammalian chemotaxins. Pulmonary lavage of the exposed chickens, frogs, and toads also failed to produce inflammatory cells. Pulmonary edema was not detected in any of the animals by comparison of lung weight to total body weight. Intratracheal injections of silica for 2 weeks did produce chronic effects in chickens and frogs. Morphologically, the lungs showed signs of fibrosis and accumulation of interstitial inflammatory cells, but no intraalveolar cells. After 90 h of hyperbaric O₂, frogs exhibited a massive infiltration of interstitial inflammatory cells and hemorrhage. Elevated O₂ levels (100%) for 2 weeks under normal atmospheric conditions produced no changes in frog lungs or in the amount of inflammatory cells in the lungs. Intravenous injections of paraquat for up to 208 h failed to initiate an accumulation of pulmonary inflammatory cells or the development of pulmonary edema in chickens. There was also no detectable H₂O₂ or O₂ in the lavaged supernatant. It was not determined whether paraquat had a longer or more chronic effect on chickens. We suggest that the lack of an acute pulmonary inflammatory mechanism in chickens, frogs, and toads is in part responsible for the resistance of these animals to acute pulmonary injury by oxidizing mammalian toxins.     

Effects of chronic intermittent asphyxia on haematocrit, pulmonary arterial pressure and skeletal muscle structure in rats

Sleep-disordered breathing in humans is a common condition associated with serious cardiovascular and other abnormalities. The prevalence and pathogenesis of increased haematocrit and pulmonary hypertension is controversial and it has been suggested that these changes only occur in patients who also have daytime continuous hypoxaemia. The hypothesis tested here is that the chronic intermittent hypoxia and asphyxia associated with sleep-disordered breathing causes erythropoiesis and pulmonary hypertension and that this occurs in the absence of periods of continuous hypoxia. In humans and animals with obstructive sleep apnoea, there are abnormalities of upper airway muscle structure that have been ascribed to increased load placed on these muscles. An alternative hypothesis is that chronic intermittent hypoxia and asphyxia cause changes in upper airway muscle structure and function. To test these hypotheses, rats were exposed to intermittent hypoxia and asphyxia for 8 h per day for 5 weeks. This caused an increase in haematocrit, right ventricular weight and pulmonary arterial pressure. There were only slight changes in diaphragm, upper airway and limb muscle structure and force production but in general, muscle fatigability was increased. In conclusion chronic intermittent hypoxia and asphyxia cause an increase in haematocrit and pulmonary arterial pressure in the absence of periods of continuous hypoxia. Chronic intermittent hypoxia and asphyxia have little effect on skeletal muscle structure and force production but increase muscle fatigue. Increased upper airway muscle fatigue could lead to a vicious cycle of further compromise in upper airway patency and further hypoxia and asphyxia.     

Progressive pulmonary fibrosis in rats: a biochemical, cell kinetic, and morphologic analysis

The concomitant treatment of rats with bleomycin and hyperoxia results in synergistic development of pulmonary injury. We exposed rats to 70% oxygen for 72 hr following an intratracheal instillation of bleomycin (0.2 U/kg body wt). Animals were killed 15, 30, 60 and 90 days after treatment for hydroxyproline, cell kinetics, and histopathologic analysis. A 16% increase in hydroxyproline over controls was seen 15 days after treatment which was manifested by the proliferation phase of diffuse alveolar damage and an increase in cell labeling by tritiated thymidine. Thirty days after treatment the hydroxyproline remained elevated while lung injury appeared to be healing with a residual focal interstitial pneumonitis and a drop in cell labeling. Between 60 and 90 days, there was an additional significant increase in hydroxyproline to 44% over controls. Diffuse interstitial pneumonitis with fibrosis was observed. Cell labeling remained constant between 60 and 90 days. We conclude that the treatment of rats with bleomycin and hyperoxia results in slowly progressive pulmonary fibrosis. The increase in hydroxyproline in the chronic phase was not accompanied by an increase in cell proliferation, and therefore may have resulted from an increase in cellular production of hydroxyproline rather than increased number of cells producing collagen.