Alveolar hyperoxic injury in rabbits receiving exogenous surfactant

We have previously demonstrated that instillation of a calf lung surfactant extract (CLSE) in rabbits after exposure to 100% O2 for 64 h mitigates the progression of lung pathology after return to room air (J. Appl. Physiol. 62: 756-761, 1987). In the present study, we investigated whether we could prevent or reduce the onset and development of hyperoxic lung injury by sequential instillations of CLSE during the hyperoxic exposure. Rabbits were exposed to 100% O2. CLSE (125 mg, approximately 170 mumol of phospholipid) was suspended in 10 ml of sterile saline and instilled intratracheally into their lungs, starting at 24 h in O2, a time at which no physiological or biochemical injury was detected, and at 24-h intervals thereafter. Control rabbits breathed 100% O2 and received either equal volumes of saline or no instillations at all. CLSE-instilled rabbits had higher arterial PO2 (Pao2) values throughout the exposure period and survived longer when compared with saline controls [120 +/- 4 vs. 102 +/- 4 (SE) h; n greater than or equal to 10; P less than 0.05]. At 72 h in O2, CLSE-instilled rabbits had significantly higher lavageable alveolar phospholipid levels (12.5 +/- 1.5 vs. 5 +/- 1 mumol/kg) and total lung capacities (41 +/- 2 vs. 25 +/- 3.5 ml/kg) and lower levels of alveolar protein (24 +/- 3 vs. 52 +/- 8 mg/kg), minimum surface tension (2 +/- 1 vs. 26.1 dyn/cm), and lung wet-to-dry weights (5.9 +/- 0.2 vs. 6.5 +/- 0.3). After 72 h in O2, lungs from both CLSE- and saline-instilled rabbits showed evidence of diffuse hyperoxic injury. However, atelectasis was less prominent in the former. We concluded that instillation of CLSE limits the onset and development of hyperoxic lung injury to the alveolar epithelium of rabbits.     

Lung expansion and the perialveolar interstitial pressure gradient

We have determined the combined effects of lung expansion and increased extravascular lung water (EVLW) on the perialveolar interstitial pressure gradient. In the isolated perfused lobe of dog lung, we measured interstitial pressures by micropuncture at alveolar junctions (Pjct) and in adventitia of 30- to 50-microns microvessels (Padv) with stopped blood flow at vascular pressure of 3-5 cmH2O. We induced edema by raising vascular pressures. In nonedematous lobes (n = 6, EVLW = 3.1 +/- 0.3 g/g dry wt) at alveolar pressure of 7 cmH2O, Pjct averaged 0.5 +/- 0.8 (SD) cmH2O and the Pjct-Padv gradient averaged 0.9 +/- 0.5 cmH2O. After increase of alveolar pressure to 23 cmH2O the gradient was abolished in nonedematous lobes, did not change in moderately edematous lobes (n = 9, EVLW = 4.9 +/- 0.6 g/g dry wt), and increased in severely edematous lobes (n = 6, EVLW = 7.6 +/- 1.4 g/g dry wt). Perialveolar interstitial compliance decreased with increase of alveolar pressure. We conclude that increase of lung volume may reduce perialveolar interstitial liquid clearance by abolishing the Pjct-Padv gradient in nonedematous lungs and by compressing interstitial liquid channels in edematous lungs.     

The effects of temperature change on lung liquid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs of 58-65 days of gestation were supported in vitro for 3 h, and lung liquid production rates were measured by a dye dilution technique. In 36 control preparations, incubated continuously at 37 degrees C, the average production rate in the first hour was 1.46 +/- 0.23 ml/h per kg body weight; there was no significant change over the following two h. In 36 further preparations the temperature was changed during the middle hour (ABA), with the following % reductions in production rates: at -1 degrees C (relative to 37 degrees C), 68.2 +/- 17.1%; -2 degrees C, 125.5 +/- 30.1% (reabsorption); -3 degrees C, 103.8 +/- 32.8% (reabsorption); -5 degrees C, 82.7 +/- 16.6%, -8 degrees C, 94.7 +/- 1.8 %; +2 degrees C, 100.7 +/- 12.6% (all significant, P less than 0.025-0.005). Slow recoveries followed a return to starting conditions, except after the increase in temperature, 10(-6) M amiloride abolished reabsorption, but not depression, during the maximal effects of temperature reduction (at -2 degrees C, n = 6); amiloride had no effect on control preparations (n = 6). These results suggest that: (a) reductions of 2-3 degrees C, as seen in the delivery room, abolish secretion, but not reabsorption of lung fluid; larger reductions stop both processes; (b) the reabsorptions seen after a fall in temperature depend on Na(+)-transport mechanisms; (c) lung liquid production was sensitive to a rise in temperature, so that fevers might adversely affect lung development, and (d) the fall in temperature at birth may be an important factor in the early reabsorption of lung liquid.     

Isoproterenol improves ability of lung to clear edema in rats exposed to hyperoxia.

Exposure of adult rats to 100% O(2) results in lung injury and decreases active sodium transport and lung edema clearance. It has been reported that beta-adrenergic agonists increase lung edema clearance in normal rat lungs by upregulating alveolar epithelial Na(+)-K(+)-ATPase function. This study was designed to examine whether isoproterenol (Iso) affects lung edema clearance in rats exposed to 100% O(2) for 64 h. Active Na(+) transport and lung edema clearance decreased by approximately 44% in rats exposed to acute hyperoxia. Iso (10(-6) M) increased the ability of the lung to clear edema in room-air-breathing rats (from 0.50 +/- 0.02 to 0.99 +/- 0. 05 ml/h) and in rats exposed to 100% O(2) (from 0.28 +/- 0.03 to 0. 86 +/- 0.09 ml/h; P < 0.001). Disruption of intracellular microtubular transport of ion-transporting proteins by colchicine (0. 25 mg/100 g body wt) inhibited the stimulatory effects of Iso in hyperoxia-injured rat lungs, whereas the isomer beta-lumicolchicine, which does not affect microtubular transport, did not inhibit active Na(+) transport stimulated by Iso. Accordingly, Iso restored the lung's ability to clear edema after hyperoxic lung injury, probably by stimulation of the recruitment of ion-transporting proteins (Na(+)-K(+)-ATPase) from intracellular pools to the plasma membrane in rat alveolar epithelium.     

Regional lung water and hematocrit determined by positron emission tomography

We have measured with positron emission tomography (PET) the regional distribution of extravascular lung water (EVLW) and hematocrit (HctL) in normal supine dogs. H2(15)O and C15O were used as total lung water (TLW) and intravascular water (IVW) compartment labels, respectively. An additional plasma volume label (68Ga-transferrin) was used to determine regional HctL. EVLW was calculated as the difference between TLW and IVW. In 13 dogs, EVLW was relatively constant along a gravity-dependent vertical gradient, although values in the most anterior regions were statistically less (P less than 0.05) than those in more posterior ones. The average value for EVLW (13 dogs) was 14.4 +/- 2.5 ml H2O/100 ml lung. When EVLW was compared with IVW on a regional basis, the EVLW/IVW ratio decreased significantly in a gravity-dependent direction from 1.95 +/- 0.28 to 0.88 +/- 0.18. In 7 dogs, no significant difference between HctL and systemic hematocrit (average ratio 1.01 +/- 0.08) was found nor was any significant variation of HctL within the lung detected. Thus, in contrast to gravimetric techniques, a hematocrit correction does not appear to be necessary when regional EVLW is studied by PET.     

Mitigation of pulmonary hyperoxic injury by administration of exogenous surfactant

We studied the effects of surfactant supplementation on the progression of lung injury in rabbits exposed to 100% O2 for 64 h and returned to room air for 24 h. At this time, rabbits not treated with surfactant exhibit a severe lung injury with hypoxemia, increased alveolar premeability to solute, decreased total lung capacity (TLC) and lung edema. For surfactant treatment, 125 mg of calf lung surfactant extract (CLSE), suspended in 6-8 ml of normal saline, were instilled intratracheally at 0 and 12 h posthyperoxic exposure. At 24 h postexposure, these CLSE-treated rabbits compared with saline controls had significantly higher amounts of lung phospolipids (34 +/- 4 vs. 4.5 +/- 0.6 mumol/kg body wt) and increased TLC (42 +/- 2 vs. 27 +/- 1 ml/kg), with significantly lower amounts of alveolar protein (36 +/- 3 vs. 56 +/- 3 mg/kg) and decreased lung wet weight-to-dry weight ratios (5.6 +/- 0.1 vs. 6.3 +/- 0.3). Surfactant supplementation also decreased the degree of lung atelectasis as reflected by the increase in arterial O2 partial pressure (PaO2) after breathing 100% O2 for 20 min (PaO2 = 460 +/- 31 vs. 197 +/- 52 Torr). These findings indicate that instillation of exogenous surfactant mitigates the progression of hyperoxic lung injury in rabbits.     

Comparison of tracheal mucous transport in rats, guinea pigs, rabbits, and dogs

Tracheal mucous transport was measured using similar techniques in several species. One- to 10-microliter quantities of 99mTc-macroaggregated albumin (99mTc-MAA) were instilled via oral intubation in the distal trachea of rats, rabbits, and dogs. Tracheostomies were used for the instillation in guinea pigs. All animals were anesthetized with halothane for the instillation and allowed to recover immediately in restrainers. Clearance of the 99mTc-MAA in rats and guinea pigs was measured by a slit-collimated NaI scanner. In rabbits and dogs a series of gamma-camera scintiphotos were taken. Clearance was faster and more efficient in dogs than in the other species. No significant differences existed among the rats, rabbits, and guinea pigs in the percentages of the originally deposited material remaining at the instillation site after 1 h (P greater than 0.2). Mean values and standard deviations were 83 +/- 23%, 81 +/- 22% and 70 +/- 20% for rats, guinea pigs, and rabbits, respectively. However, in the dogs a mean of 14 +/- 12% remained at the original site of deposition after only 25 min indicating much more rapid clearance. Mean leading-edge velocities were 9.8 +/- 2.1 (SD) for dogs, 3.2 +/- 1.1 for rabbits, 2.7 +/- 1.4 for guinea pigs, and 1.9 +/- 0.7 mm/min for rats. Clearance patterns qualitatively among the species. In dogs the material moved as a few discrete boluses, whereas in the other species the activity spread toward the larynx. The relatively slow mucous transport of rats, rabbits, and guinea pigs could have important implications in inhalation toxicological studies.     

Effects of crystalloid and colloid fluids on extravascular lung water in hypoproteinemic dogs

We compared the effect of crystalloid to colloid fluid infusion on extravascular lung water (EVLW) in hypoproteinemic dogs. Plasmapheresis was used to decrease plasma colloid osmotic pressure (COP) to less than 40% of its base-line level. Five animals were then infused with 0.9% sodium chloride (saline), five with 5% human serum albumin (albumin), and five with 6% hydroxyethyl starch (hetastarch) to increase the pulmonary arterial occlusive pressure by 10 Torr in comparison to the postplasmapheresis level for a 5-h study interval. On completion of the procedure, the lungs were harvested and EVLW measured by the blood-free gravimetric technique. Three to six times the volume of saline compared with albumin or hetastarch (P less than 0.001) was infused. In the saline animals, COP was decreased to 3.3 +/- 1.3 Torr, whereas COP was increased to 18.1 +/- 1.4 Torr in albumin animals (P less than 0.001) and 20.1 +/- 1.6 Torr in the hetastarch group (P less than 0.001). The saline-treated dogs developed gross signs of systemic edema. The EVLW was 8.1 +/- 0.9 ml/kg in saline animals compared with 5.3 +/- 2.1 ml/kg in the albumin (P less than 0.05) and 4.1 +/- 1.4 ml/kg in the hetastarch (P less than 0.01) groups. These data indicate that crystalloid fluid infusion during hypoproteinemia is associated with the development of both systemic and pulmonary edema.     

Postnatal glucocorticoids induce alpha-ENaC formation and regulate glucocorticoid receptors in the preterm rabbit lung

At birth, lung fluid clearance is coupled to Na+ transport through epithelial Na+ channels (ENaC) in the distal lung epithelium. We evaluated the effect of postnatal glucocorticoids (GC) on lung alpha-ENaC expression in preterm 29-day gestational age (GA) fetal rabbits. Postnatal treatment of 29-day GA fetuses with 0.5 mg/kg of dexamethasone (Dex) iv resulted in a 2- and 22-fold increase in lung alpha-ENaC mRNA expression compared with saline-treated fetuses after 8 and 16 h, respectively. Lung alpha-ENaC protein levels in Dex-treated fetuses were also elevated compared with saline-treated counterparts. The extravascular lung water (EVLW)/dry lung tissue weight ratios of 29-day GA fetuses treated with either saline or Dex decreased over 24 h compared with that observed at birth; however, at 24 h, the EVLW/dry lung tissue weight ratios of saline- and Dex-treated fetuses were similar. Dex-induced alpha-ENaC mRNA and protein levels were attenuated by glucocorticoid receptor (GCR) antagonist RU-486 in fetal distal lung epithelial cells isolated from 29-day GA fetuses, indicating that GC-dependent augmentation of lung alpha-ENaC requires the presence of functional GCR. Lung GCR mRNA expression and protein levels were elevated in 29-day GA fetuses compared with fetuses at earlier GA. Exposure of 29-day GA fetuses to Dex for 16 h caused a 2.1-fold increase in lung GCR mRNA expression, but GCR protein levels were decreased in Dex-treated fetuses after 24 h. We conclude that postnatal treatment of preterm 29-day GA fetal rabbits with GC results in an elevation of lung alpha-ENaC accompanied by an autoregulation of pulmonary GCR.     

Ca(2+)-dependent stimulation of alveolar fluid clearance in near-term fetal guinea pigs

We investigated the importance of changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) for amiloride-sensitive alveolar fluid clearance (AFC) in late-gestational guinea pigs. Fetal guinea pigs of 61, 68, and 69 days (term) gestation were investigated under normal conditions and after oxytocin-induced preterm labor. AFC or alveolar fluid secretion was measured using an impermeable tracer technique. At 61 days gestation there was net secretion of fluid into the lungs, and at birth the lungs cleared 49 +/- 7% of the instilled fluid volume over 1 h. Induction of preterm labor with oxytocin induced AFC at 61 days gestation. When present, AFC was inhibited or reversed to net fluid secretion by amiloride (10(-3) M). Inhibition of membrane Ca(2+) channels by verapamil (10(-4) M) or depletion of intracellular Ca(2+) by thapsigargin (10(-5) M) reduced AFC when net AFC was evident. Amiloride lacked an inhibitory effect on AFC when instilled with verapamil or thapsigargin. The results indicate that AFC via amiloride-sensitive pathways develops during late gestation, and that inducing preterm labor precociously may activate such pathways. Our results suggest that Ca(2+) may act as a second messenger in mediating catecholamine-stimulated AFC.     

Alveolar and lung liquid clearance in anesthetized rabbits

Alveolar and lung liquid clearance were studied over 8 h in intact anesthetized ventilated rabbits by instillation of either isosmolar Ringer lactate (2 ml/kg) or autologous plasma (2 or 3 ml/kg) into one lower lobe. The half time for lung liquid clearance of the isosmolar Ringer lactate was 3.3 h and that for plasma clearance was 6 h. In the plasma experiments, the alveolar protein concentration after 1 h was 5.2 +/- 0.8 g/dl, which was significantly greater than the initial instilled protein concentration of 4.3 +/- 0.7 g/dl (P less than 0.05). Thus alveolar protein concentration increased by 21 +/- 12% over 1 h, which matched clearance from the entire lung of 19 +/- 11% of the instilled volume. Overall the rate of alveolar and lung liquid clearance in rabbits was significantly faster than in prior studies in dogs and sheep. The fast alveolar liquid clearance rate in rabbits was not due to higher endogenous catecholamine release, because intravenous and alveolar (5 x 10(-5) M) propranolol did not slow the clearance. Also, beta-adrenergic therapy with alveolar terbutaline (10(-5) or 10(-4) M) did not increase the alveolar or lung liquid clearance rates. Phloridzin (10(-3) M) did not slow alveolar liquid clearance. However, amiloride (10(-4) M) inhibited 75% of the basal alveolar liquid clearance in rabbits, thus providing evidence that alveolar liquid clearance in rabbits depends primarily on sodium-dependent transport. This rabbit study provides further evidence for important species differences in the basal rates of alveolar liquid and solute clearance as well as the response to beta-adrenergic agonists and ion transport inhibitors.     

Response of antioxidant enzymes to intermittent and continuous hyperbaric oxygen

Rats and guinea pigs were exposed to O2 at 2.8 ATA (HBO) delivered either continuously or intermittently (repeated cycles of 10 min of 100% O2 followed by 2.5 min of air). The O2 time required to produce convulsions and death was increased significantly in both species by intermittency. To determine whether changes in brain and lung superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSHPx) correlated with the observed tolerance, enzyme activities were measured after short or long HBO exposures. For each exposure duration, one group received continuous and one intermittent HBO; O2 times were matched. HBO had marked effects on these enzymes: lung SOD increased (guinea pigs 47%, rats 88%) and CAT and GSHPx activities decreased (33%) in brain and lung. No differences were seen in lung GSHPx or brain CAT in rats or brain SOD in either species. In guinea pigs, but less so in rats, the observed changes in activity were usually modulated by intermittency. Increases in hematocrit, organ protein, and lung DNA, which may also reflect ongoing oxidative damage, were also slowed with intermittency in guinea pigs. Intermittency benefited both species by postponing gross symptoms of toxicity, but its modulation of changes in enzyme activities and other biochemical variables was more pronounced in guinea pigs than in rats, suggesting that there are additional mechanisms for tolerance.     

Capillarity and oxygen diffusion distances of the soleus muscle of guinea pigs and rats. Effects of hyperthyroidism

The relationship between capillarity and oxidative capacity in the soleus muscle of rats and guinea pigs injected with triiodothyronine (T3) or with saline for up to 4 weeks was studied. The rats' soleus weight and FCSA were not affected by T3, but the guinea pigs that received T3 had smaller muscle weight and FCSA than the controls. The activities of cytochrome c oxidase and citrate synthase were significantly (41 and 65%) higher in the T3 than in the control rats. T3 administration did not affect the activities of these enzymes in the soleus of the guinea pigs. Capillary density (CD) was higher in T3 rats (892 +/- 80 vs 622 +/- 54 caps/mm2), and in T3 guinea pigs (1219 +/- 95 vs 739 +/- 142 caps/mm2). The higher CD in T3 rats was due to growth of new microvessels, while in the T3 guinea pigs it was due to a reduction in FCSA. Mean and maximal diffusion distances evaluated by the closest individual method were reduced by 2.02 and 3.37 microns in rats, and by 3.73 and 6.16 microns in guinea pigs. The magnitude of the reduction in diffusion distances brought about by the increased capillary density was partially offset by a concomitant change in the capillary arrangement from an ordered (hexagonal), towards a random distribution. These results seem to indicate that skeletal muscle capillarity is not necessarily determined by the oxidative capacity of the fibers.     

Ovalbumin sensitization alters the ventilatory responses to chemical challenges in guinea pigs.

Patients with chronic bronchial asthma show a depressed ventilatory response to hypoxia (DVH), but the underlying mechanism remains unclear. We tested whether DVH existed in ovalbumin (Ova)-treated guinea pigs, an established animal model of asthma. Twelve guinea pigs were exposed to Ova (1% in saline) or saline aerosol (control) for 5 min, 5 days/wk, for 2 wk. After completing aerosol exposure, the animals were anesthetized and exposed to systemic hypoxia. Ova treatment had no effects on animal body weight, baseline cardiorespiratory variables, or arterial blood O2 and CO2 tensions, but it attenuated the ventilatory response to hypoxia (10 breaths of pure N2) by 65% (P < 0.05). When the animals were subjected to intracarotid injections of sodium cyanide (20 microg) and doxapram (2 mg) to selectively stimulate carotid chemoreceptors, the ventilatory responses were reduced by 50% (P < 0.05) and 74% (P < 0.05), respectively. In contrast, Ova exposure failed to affect the ventilatory response to CO2 (7% CO2-21% O2-balance N2 for 5 min; P > 0.05). Furthermore, the apneic response evoked by stimulating bronchopulmonary C fibers (PCFs) with right atrial injection of capsaicin (5 microg) was markedly increased in the Ova-sensitized group (5.02 +/- 1.56 s), compared with the control group (1.82 +/- 0.45 s; P < 0.05). These results suggest that Ova sensitization induces a DVH in guinea pigs, which probably results from an attenuation of the carotid chemoreceptor-mediated ventilatory excitation and an enhancement of the PCF-mediated ventilatory inhibition.     

The effects of furosemide and bumetanide on lung liquid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs of 61 +/- 3 days of gestation were supported in vitro for 3 h, and lung liquid secretion rates were measured by a dye dilution technique based on Blue Dextran 2000. Ten preparations that had received no treatment showed an average secretion rate of 1.12 +/- 0.28 mL.kg-1 body weight.h-1 during the first hour, and there were no significant changes over the following 2 h. In studies of 54 fetal lungs, furosemide, bumetanide, control ethanol carrier, or saline alone were placed in the supporting medium during the middle hour of the 3-h incubations (ABA design). Furosemide at 10(-3) M reduced secretion 83.4 +/- 16.8%; at 10(-4) and 10(-5) M it produced smaller reductions. Bumetanide at 10(-3) M usually produced reabsorption (129.9 +/- 23.0% reduction), at 10(-4) M it reduced secretion 30.9 +/- 11.8%, but at 10(-5) M it was ineffective. Control carrier and saline were without effect. The ability of the loop diuretics to produce reabsorption of fluid in some preparations suggests the unmasking of an active reabsorptive process. The results also suggest that lung liquid secretion in the fetal guinea pig, as in the sheep, is dependent on a Na+ and Cl- cotransport system.     

Respiratory failure after endotoxin infusion in sheep: lung mechanics and lung fluid balance

Infusion of Escherichia coli endotoxin (0.12-1.5 micrograms/kg) into unanesthetized sheep causes transient pulmonary hypertension and several hours of increased lung vascular permeability, after which sheep recover. To produce enough lung injury to result in pulmonary edema with respiratory failure, we infused larger doses of E. coli endotoxin (2.0-5.0 micrograms/kg) into 11 chronically instrumented unanesthetized sheep and continuously measured pulmonary arterial, left atrial and aortic pressures, dynamic lung compliance, lung resistance, and lung lymph flow. We intermittently measured arterial blood gas tensions and pH, made interval chest radiographs, and calculated postmortem extravascular bloodless lung water-to-dry lung weight ratio (EVLW/DLW). Of 11 sheep 8 developed respiratory failure; 7 died spontaneously 6.3 +/- 1.1 h, and one was killed 10 h after endotoxin infusion. All sheep that had a premortem room air alveolar-arterial gradient in partial pressure of O2 (PAo2-Pao2) greater than 42 Torr (58 +/- 5 (SE) Torr) died. Of eight sheep that had radiographs made, six developed radiographically evident interstitial or interstitial and alveolar edema. Pulmonary artery pressure rose from base line 22 +/- 2 to 73 +/- 3 cmH2O and remained elevated above baseline levels until death. There was an initial fourfold decrease in dynamic compliance and sixfold increase in pulmonary resistance; both variables remained abnormal until death. EVLW/DLW increased with increasing survival time after endotoxin infusion, suggesting that pulmonary edema accumulated at the same rate in all fatally injured sheep, regardless of other variables. The best predictor of death was a high PAo2-Pao2. The marked increase in pulmonary resistance and decrease in dynamic compliance occurred too early after endotoxin infusion (15-30 min) to be due to pulmonary edema. The response to high-dose endotoxin in sheep closely resembles acute respiratory failure in humans following gram-negative septicemia. Respiratory failure and death in this model were not due to pulmonary edema alone.     

Repeated antigen challenge induces airway hyperresponsiveness with tissue eosinophilia in guinea pigs

To test the hypothesis that the development of airway hyperresponsiveness (AHR) lasting greater than or equal to 3 days after the last antigenic exposure required repeated mediator release, we compared dose-response changes in lung resistance (RL) to acetylcholine (ACh) in animals sensitized with 1% ovalbumin (OA), 4% Bordatella pertussis aerosol and subsequently challenged with 0.5% OA aerosol twice weekly for 4-6 wk vs. animals receiving saline aerosol instead of OA. Despite antihistamine pretreatment, each OA challenge produced cyanosis and inspiratory indrawing. Blood gas analysis in six guinea pigs revealed an immediate fall in arterial PO2 (PaO2) from 104.3 +/- 4.9 to 35.4 +/- 2.2 Torr after a 1-min exposure to aerosolized OA. ACh dose-response measurements of RL 3 days after the last OA challenge demonstrated a leftward shift and an increased magnitude of response. These differences were less marked at 7 days, and by 14 days after the last OA challenge, ACh dose-response curves were not different from those of control guinea pigs. Sensitization without repeated antigen challenge did not cause hyperresponsiveness. Morphometric analysis showed significantly increased numbers of eosinophils in the epithelium of airways in hyperresponsive guinea pigs, without neutrophil infiltration or alterations in epithelium and airway wall areas. We conclude that repeated antigenic challenge, but not sensitization alone, causes prolonged AHR in guinea pigs, which is associated with tissue eosinophilia.     

Ion transport regulation of lung liquid secretion in foetal lambs.

To test the hypothesis that liquid formation in the foetal lung reflects the balance between Cl- secretion and Na+ absorption by the respiratory tract epithelium, we studied the independent and combined effects of selective ion transport inhibitors on basal production of lung liquid in foetal lambs. We prepared 19 foetal lambs (gestation 125 +/- 4, term = 147 days) with chronic indwelling catheters for subsequent measurement of luminal liquid production over time (JV). Using an impermeant tracer technique, we measured JV before and after tracheal instillation of 2 different inhibitors of ion transport: bumetanide, a Na(+)-K(+)-2Cl- co-transport inhibitor, and amiloride, a Na+ transport inhibitor. In 7 foetuses we sequentially added bumetanide (10(-4) M) and 2 different concentrations of amiloride (10(-6) M, 10(-4) M) to the liquid within the lung lumen. After we gave bumetanide, JV decreased from 12 +/- 4 ml/h to 0 +/- 5 ml/h and subsequently increased during the 2 periods of amiloride exposure (10(-6) M: 6 +/- 5 ml/h; 10(-4) M: 7 +/- 7 ml/h). In 5 control studies we gave bumetanide, followed by only amiloride vehicle. JV for all time periods in the control studies was similar to the experimental group, demonstrating no effect of amiloride. In 5 foetuses we administered the 2 concentrations of amiloride before bumetanide. There was no change in JV with either concentration of amiloride (baseline: 13 +/- 2 ml/h; 10(-6) M amiloride: 15 +/- 5 ml/h; 10(-4) M amiloride: 13 +/- 6 ml/h).(ABSTRACT TRUNCATED AT 250 WORDS)     

Airflow obstruction after substance P aerosol: contribution of airway and pulmonary edema.

We have studied the effects of aerosolized substance P (SP) in guinea pigs with reference to lung resistance and dynamic compliance changes and their recovery after hyperinflation. In addition, we have examined the concomitant formation of airway microvascular leakage and lung edema. Increasing breaths of SP (1.5 mg/ml, 1.1 mM), methacholine (0.15 mg/ml, 0.76 mM), or 0.9% saline were administered to tracheostomized and mechanically ventilated guinea pigs. Lung resistance (RL) increased dose dependently with a maximum effect of 963 +/- 85% of baseline values (mean +/- SE) after SP (60 breaths) and 1,388 +/- 357% after methacholine (60 breaths). After repeated hyperinflations, methacholine-treated animals returned to baseline, but after SP, mean RL was still raised (292 +/- 37%; P less than 0.005). Airway microvascular leakage, measured by extravasation of Evans Blue dye, occurred in the brain bronchi and intrapulmonary airways after SP but not after methacholine. There was a significant correlation between RL after hyperinflation and Evans Blue dye extravasation in intrapulmonary airways (distal: r = 0.89, P less than 0.005; proximal: r = 0.85, P less than 0.01). Examination of frozen sections for peribronchial and perivascular cuffs of edema and for alveolar flooding showed significant degrees of pulmonary edema for animals treated with SP compared with those treated with methacholine or saline. We conclude that the inability of hyperinflation to fully reverse changes in RL after SP may be due to the formation of both airway and pulmonary edema, which may also contribute to the deterioration in RL.     

Influence of ketamine and propranolol on plasma renin activity (PRA) in female rabbits and guinea pigs.

1. Plasma renin activity was measured in non pregnant rabbits and guinea pigs under Ketamine-induced general anesthesia after pretreatment either with Propranolol or with a Placebo. Study was performed using a radio-immunoassay for angiotensin I. 2. Twenty minutes after the beginning of the observation period, renin activity in rabbits who had received Placebo alone (11.47 +/- 2.35 ng/ml/h) or associated with Ketamine (11.36 +/- 2.54 ng/ml/h) was similar. However, enzyme activity was significantly lower (P less than 0.001) when Propranolol was associated with Ketamine (3.97 +/- 0.58 ng/ml/h) or with Placebo (4.10 +/- 0.55 ng/ml/h). 3. In the same way, renin activity was significantly higher (P less than 0.001) in guinea pigs without Propranolol than in those who had received this drug. 4. These findings indicate that stress induced by general anesthesia with Ketamine or by simple manipulation of animals (Placebo) was accompanied by an excessive increase in plasma renin activity. Propranolol maintained the level of this enzyme activity within normal limits.