Malnutrition impairs alveolar fluid clearance in rat lungs

Inadequate nutrition complicates the clinical course of critically ill patients, and many of these patients develop pulmonary edema. However, little is known about the effect of malnutrition on the mechanisms that resolve alveolar edema. Therefore, we studied the mechanisms responsible for the decrease in alveolar fluid clearance in rats exposed to malnutrition. Rats were allowed access to water, but not to food, for 120 h. Then, the left and right lungs were isolated for the measurement of lung water volume and alveolar fluid clearance, respectively. The rate of alveolar fluid clearance was measured by the progressive increase in the concentration of Evans blue dye that was instilled into the distal air spaces with an isosmolar 5% albumin solution over 1 h. Malnutrition decreased alveolar fluid clearance by 38% compared with controls. Amiloride (10(-3) M) abolished alveolar fluid clearance in malnourished rats. Either refeeding for 120 h following nutritional deprivation for 120 h or an oral supply of sodium glutamate during nutritional deprivation for 120 h restored alveolar fluid clearance to 91 and 86% of normal, respectively. Dibutyryl-cGMP, a cyclic nucleotide-gated cation channel agonist, increased alveolar fluid clearance in malnourished rats supplied with sodium glutamate. Terbutaline, a beta(2)-adrenergic agonist, increased alveolar fluid clearance in rats under all conditions (control, malnutrition, refeeding, and glutamate-treated). These results indicate that malnutrition impairs primarily amiloride-insensitive and dibutyryl-cGMP-sensitive alveolar fluid clearance, but this effect is partially reversible by refeeding, treatment with sodium glutamate, or beta-adrenergic agonist therapy.     

Effect of alveolar hypoxia on pulmonary fluid filtration in in situ dog lungs

We have studied the effect of alveolar hypoxia on fluid filtration characteristics of the pulmonary microcirculation in an in situ left upper lobe preparation with near static flow conditions (20 ml/min). In six dogs (group 1), rate of edema formation (delta W/delta t, where W is weight and t is time) was assessed over a wide range of vascular pressures under two inspired O2 fraction (FIO2) conditions (0.95 and 0.0 with 5% CO2-balance N2 in both cases). delta W/delta t was plotted against vascular pressure, and the best-fit linear regression was obtained. There was no significant difference (paired t test) in either threshold pressure for edema formation [18.3 +/- 1.8 and 17.1 +/- 1.2 (SE) mmHg, respectively] or the slopes (0.067 +/- 0.008 and 0.073 +/- 0.017 g.min-1. mmHg-1.100g-1, respectively). In another seven dogs (group 2), delta W/delta t was obtained at a constant vascular pressure of 40 mmHg under four FIO2 conditions (0.95, 0.21, 0.05, and 0.0, with 5% CO2-balance N2). Delta W/delta t for the four conditions averaged 0.60 +/- 0.11, 0.61 +/- 0.11, 0.61 +/- 0.10, and 0.61 +/- 0.10 (SE) g.min-1.mmHg-1.100g-1, respectively. No significant differences (ANOVA for repeated measures) were noted. We conclude that alveolar hypoxia does not alter the threshold for edema formation or delta W/delta t at a given microvascular pressure.     

Pulmonary venous pressure increases during alveolar hypoxia in isolated lungs of newborn pigs.

The purpose of this study was to determine whether pulmonary venous pressure increases during alveolar hypoxia in lungs of newborn pigs. We isolated and perfused with blood the lungs from seven newborn pigs, 6-7 days old. We maintained blood flow constant at 50 ml.min-1.kg-1 and continuously monitored pulmonary arterial and left atrial pressures. Using the micropuncture technique, we measured pressures in 10 to 60-microns-diam venules during inflation with normoxic (21% O2-69-74% N2-5-10% CO2) and hypoxic (90-95% N2-5-10% CO2) gas mixtures. PO2 was 142 +/- 21 Torr during normoxia and 20 +/- 4 Torr during hypoxia. During micropuncture we inflated the lungs to a constant airway pressure of 5 cmH2O and kept left atrial pressure greater than airway pressure (zone 3). During hypoxia, pulmonary arterial pressure increased by 69 +/- 24% and pressure in small venules increased by 40 +/- 23%. These results are similar to those obtained with newborn lambs and ferrets but differ from results with newborn rabbits. The site of hypoxic vasoconstriction in newborn lungs is species dependent.     

Endogenous plasma proteins in edematous lungs and alveolar fluid in rabbits

In this study, we compared two methods of differentiating hydrostatic and permeability types of pulmonary edema. The first method entailed measurement of protein concentrations directly in samples of alveolar fluid (AF); the second method was an indirect technique in which protein concentration in extravascular extracellular water (EVECW) was calculated on the basis of separate measurements of the quantity of protein in the lung and the volume of EVECW. The concentration of albumin (Alb) and gamma-G-globulin was measured in EVECW and alveolar fluid in excised edematous rabbit lungs. Edema was caused by elevation of left ventricular end-diastolic pressure to 25 Torr (hydrostatic edema, HE) or by intravenous oleic acid, 0.09 ml/kg (permeability edema, PE). The volume of distribution of Na+ was utilized as a measure of EVECW in the lung. Protein concentration in EVECW and AF relative to plasma (EV/PL and AF/PL, respectively) was compared in the two types of edema. The EV/PL was 0.61 +/- 0.12 (SD) for Alb in He compared with 1.18 +/- 0.47 in PE (P less than 0.02). The AF/PL was 0.54 +/- 0.12 and 1.25 +/- 0.33 in HE and PE, respectively (P less than 0.001). There was good correlation between EV/PL and AF/PL for Alb (r = 0.74, P less than 0.001) but not for gamma-G-globulin. Thus EV/PL for Alb, AF/PL for Alb, and gamma-G-globulin all differentiated hydrostatic from permeability edema.     

Influence of hypoxia on 5-lipoxygenase pathway in rat alveolar macrophages

The effect of hypoxia was studied on the ionophore A23187-induced leukotriene production by rat alveolar macrophages. The production of LTB4 and LTC4 decreased with reducing oxygenation without change of cell viability. The synthesis of 5-HETE increased during hypoxia and the total production of LTB4, LTC4 and 5-HETE, the major metabolites of the 5-lipoxygenase pathway in rat alveolar macrophages, was equal during normoxia and hypoxia. Arachidonate release and LTA4-converting into LTB4 and LTC4 was unaffected by hypoxia. LTB4- and LTC4-degradating activities were not affected by hypoxia. These results suggest that LTA4 synthase reaction of leukotrienes biosynthesis might be suppressed by hypoxia.     

Degradation and reutilization of alveolar phosphatidylcholine by rat lungs

We have shown previously that phospholipids instilled through the trachea are removed from the air spaces in isolated rat lungs by a process that is stimulated by beta-adrenergic agonists. In this study, we evaluated the fate of radiolabeled lipid vesicles [50% [3H]dipalmitoyl phosphatidylcholine (DPPC), 25% phosphatidylcholine (PC), 15% cholesterol, and 10% phosphatidylglycerol (PG)]. Vesicles were instilled through the trachea of anesthetized rats, and the lungs removed for perfusion. The percent of instilled 3H that could not be removed from lungs by extensive lung lavage increased progressively; at 3 h this fraction was 25.8 +/- 0.63% (mean +/- SE; n = 8). The percent of dpm in the lung homogenate accounted for by PC decreased progressively while dpm in lyso-PC, unsaturated PC, and aqueous soluble metabolites [choline, choline phosphate, glycerophosphorycholine, and cytidine 5'-diphosphate (CDP) choline (CDP-choline) increased. The dpm in microsomal and lamellar body fractions isolated from lung homogenates also increased progressively with time of perfusion. The presence of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) significantly stimulated both uptake of DPPC and the appearance of radioactivity in metabolites and subcellular organelles. This effect of 8-BrcAMP was not due to stimulation of phospholipase A activity. These results indicate that exogenous phospholipids instilled into the air spaces of rat lungs are internalized and degraded by a process that is stimulated by cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of interstitium in clearance of alveolar fluid in normal and injured lungs

We investigated the contribution of the pulmonary interstitial space to the removal of alveolar fluid and solute. We prepared anesthetized sheep for the collection of lung lymph. A balloon-tipped catheter was advanced into a lower lung lobe, and 20 ml Ringer lactate solution (RL) were instilled in one group. Other groups received 20 ml RL with 4 mg/ml Evans blue dye (EB) or 10 micrograms/kg phorbol myristate acetate (PMA) or both. Instillation of 20 ml RL and EB resulted in an increase in lymph flow over RL alone, presumably by an osmotic mechanism. After 4 h, small perivascular fluid cuffs, which contained little EB, were present, and 1.9% of the instilled EB was removed by the lymphatics. An average of 9.2 ml of excess water remained in the lung. Instillation of RL, EB, and PMA resulted in an increase in lymph flow and large perivascular fluid cuffs, which contained large amounts of EB. Lymphatic removal of the instilled EB accounted for 1.2% of the total amount instilled. An average of 19.1 ml water was present in the lung after 4 h. We conclude that alveolar instillation of PMA results in epithelial and endothelial membrane injury and that when lung injury is present interstitial fluid reservoirs may be important sites of alveolar fluid accumulation and important routes of fluid removal from the air space.     

Transport properties of alveolar epithelium measured by molecular hetastarch absorption in isolated rat lungs.

To evaluate the transport properties of the alveolar epithelium, we instilled hetastarch (Het; 6%, 10 ml, 1 - 1 x 10(4) kDa) into the trachea of isolated rat lungs and then measured the molecular distribution of Het that entered the lung perfusate from the air space over 6 h. Het transport was driven by either diffusion or an oncotic gradient. Perfusate Het had a unique, bimodal molecular weight distribution, consisting of a narrow low-molecular-weight peak at 10-15 kDa (range, 5-46 kDa) and a broad high-molecular-weight band (range 46-2,000 kDa; highest at 288 kDa). We modeled the low-molecular-weight transport as (passive) restricted diffusion or osmotic flow through a small-pore system and the high-molecular-weight transport as passive transport through a large-pore system. The equivalent small-pore radius was 5.0 nm, with a distribution of 150 pores per alveolus. The equivalent large-pore radius was 17.0 nm, with a distribution of one pore per seven alveoli. The small-pore fluid conductivity (2 x 10(-5) ml. h(-1). cm(-2). mmHg(-1)) was 10-fold larger than that of the large-pore conductivity.     

Effect of colchicine on secretion of alveolar surfactant in intact and regenerating rat lungs

Electron microscopy showed that colchicin in a total dose of 0.6 mg/100 g body weight of noninbred male white rats inhibited alveolar surfactant secretion into the alveolar lumen in both intact and regenerating lungs. This was associated with a partial or complete alveolar collapse. In the course of inhibition of surfactant secretion, on the apical surface of type II alveolocytes there was an activation of surfactant secretion by way of exocytosis into the interstitial space in the basal part of the cells. Disintegration of the collagenous and elastic fibers as well as disturbance of the membranes occurred in the areas where the material of lipid character and products of its metabolism appeared. A hypothesis is suggested about the possible role of such a disturbance in the character and level of alveolar surfactant secretion in the development of lung abnormality under the effect of the factors inactivating the cytoplasmatic micro tubules.     

Hydrophilic solute transport across rat alveolar epithelium

Diffusional fluxes of a series of hydrophilic nonelectrolytes (molecular radii ranging from 0.15 to 0.57 nm) were measured across the alveolocapillary barrier in the isolated perfused fluid-filled rat lung. Radiolabeled solutes were lavaged into the distal air spaces of isolated Ringer-perfused lungs, and apparent permeability-surface area products were calculated from the rates of isotope appearance in the recirculating perfusate. These data were used to estimate theoretical equivalent pore radii in the alveolar epithelium, with the assumption of diffusive flow through water-filled cylindrical pores. The alveolar epithelium is best characterized by two pore populations, with small pores (radius 0.5 nm) occupying 98.7% of total pore area and larger pores (radius 3.4 nm) occupying 1.3% of total pore area. Net water flow out of the alveolar space was measured by including an impermeant solute (dextran) in the lavage fluid and measuring its concentration in the alveolar space as a function of time. Under control conditions, net water flow averaged 167 nl/s. When 24 microM terbutaline was added to the perfusate, net water flow increased significantly to 350 nl/s (P less than 0.001). Terbutaline had no effect on the fluxes of either glycerol (which traverses the small pore pathway) or sucrose (which traverses the large pore pathway). These findings indicate that the intact mammalian alveolar epithelium is complex and highly resistant to the flow of solutes and water.     

Platelet activating factor (PAF-acether) is released into rat pulmonary alveolar fluid as a consequence of hypoxia

Hypoxia provokes pulmonary constriction and because PAF-acether is a very strong pulmonary constrictor, we looked for PAF-acether in lung alveolar lavage (LAL) with a biological method based on the measurement of rabbit platelet aggregation. We first demonstrated a PAF-acether secretion during bronchoalveolar lavage with sterile isotonic NaCl (pH 7.2). PAF-acether secretion was completely suppressed with isotonic NaCl containing 5 mM EDTA but lyso-PAF-acether was still present (1.9 +/- 0.55 nmoles). Upon hypobaric hypoxia, PAF-acether was detected in LAL (1.05 +/- 0.25 10(-2)nmoles). The amount of lyso-PAF-acether increased by 6 times (12.1 +/- 4.1 nmoles). These results are given for 10(4) nmoles phospholipids of LAL. They indicate that alveolar macrophages might be activated by hypobaric hypoxia, so they produce PAF-acether in the alveole. Such a process could be involved in the well-known bronchoconstriction accompanying hypoxia.     

Effects of hypoxia on leukotriene activity and vasomotor tone in isolated sheep lungs

To determine whether hypoxic pulmonary vasoconstriction was associated with release of sulfidopeptide leukotrienes (SPLTs) from the lung, we measured SPLT activity by bioassay (guinea pig ileum) and radioimmunoassay in lymph, perfusate, and bronchoalveolar lavage (BAL) fluid from sheep lungs (n = 20) isolated and perfused in situ with a constant flow of autologous blood (100 ml.kg-1.min-1) containing indomethacin (60 micrograms/ml). The protocol consisted of three periods, each at least 1 h in duration. In experimental lungs, inspired O2 concentration (FIO2) was 28.2% in periods 1 and 3 and 4.2% in period 2. In control lungs, FIO2 was 28.2% throughout. Hypoxia increased pulmonary arterial pressure but did not alter peak tracheal pressure, lung lymph flow, or weight gain measured during the last 30 min of each period. SPLT activity was greatest in lung lymph and least in BAL fluid. Hypoxia did not alter SPLT activity in any fluid. Similar results were obtained in lungs not treated with indomethacin (n = 15). These data do not support the hypothesis that hypoxic pulmonary vasoconstriction is mediated by SPLTs.     

Effects of hypoxia and cold acclimation on thermoregulation in the rat.

The effects of hypoxia (inspired O2 fraction = 0.12) on thermoregulation and on the different sources of thermogenesis were studied in rats before and after periods of 1-4 wk of cold acclimation. Measurements of metabolic rate (VO2) and body temperature (Tb) were made at 5-min intervals, and shivering activity was recorded continuously in groups of rats subjected to three protocols. In protocol 1, rats were exposed to normoxia to an ambient temperature (Ta) of 5 degrees C for 2 h. In protocol 2, at Ta of 5 degrees C, rats were exposed for 30 min to normoxia, then for 45 min to hypoxia, and finally for 30 min to normoxia. In protocol 3, in the non-cold-acclimated (NCA) rats, Ta was decreased from 30 to 5 degrees C in steps of 5 degrees C and of 30-min duration while in cold-acclimated (CA) rats at 5 degrees C for 4-wk, Ta was increased from 5 to 30 degrees C in steps of 5 degrees C and of 30-min duration. Recordings were made in normoxia and in hypoxia on different days in the same animals. The results showed that 1) in NCA rats, cold exposure in normoxia induced increases in VO2 and shivering that were proportional to the decrease in Ta; 2) in CA rats in normoxia, for a given Ta, VO2 and Tb were higher than in NCA rats, whereas shivering was generally lower; and 3) in both NCA and CA rats, hypoxia induced a transient decrease in shivering and a sustained decrease in nonshivering thermogenesis associated with a marked decrease in Tb that was about the same in NCA and CA rats. We speculate that hypoxia acts on Tb control to produce a general inhibition of thermogenesis. Nonshivering thermogenesis is markedly sensitive to hypoxia, especially demonstrable in CA rats; a recovery or even an increase in shivering can compensate for the decrease in nonshivering thermogenesis.     

Effects of hypobaric hypoxia on the oxidative capacity of the extensor digitorum longus motor units in the rat

The fiber number, fiber type distribution, and succinate dehydrogenase activity were investigated from the fast-twitch extensor digitorum longus muscle of male rats exposed to 7 weeks of hypobaric hypoxia. The oxidative metabolic capacity of the motoneurons in the extensor digitorum longus neuron pool was also determined from quantitative histochemical analyses. The fiber number and oxidative enzyme activity of the muscle were not changed by hypoxia. An increase in the percentage of fast-twitch oxidative (FO) fibers and a concemitant decrease in the percentage of fast-twitch (F) fibers were observed in the hypoxic muscle. On the other hand, the oxidative capacity of small-to medium-sized alpha motoneurons (25–45 m average soma diameter) was increased. The increase in the oxidative capacity of small- to medium-sized motoneurons and the type shift of muscle fibers from F (low-oxidative) to FO (high-oxidative) indicate that hypoxia enhances the oxidative capacity of particular motor units in the neuron pool.