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Biomedical subjects

D Massaro

Publications and source records attributed to D Massaro.

At least 73 records · Page 4Linked to original sources
PubMed1986

Hyperoxia reversibly suppresses development of bronchiolar epithelium.

The bronchiolar epithelium of rats is anatomically immature at birth. We now ask whether postnatal hyperoxia impairs the normal development of bronchiolar epithelium; and, if development is impaired, is the impairment permanent? To answer these questions, we exposed newborn rats to hyperoxia (greater than 95% O2, 1 atm) or air for 7 days and killed the rats at age 7 or 30 days. We used ultrastructural and morphometric means to assess maturation of the bronchiolar epithelium. Hyperoxia substantially diminished the postnatal increase in nuclear numerical density of bronchiolar Clara cells and ciliated cells. Hyperoxia also markedly delayed the rise in volume density of Clara cell secretory granules and rough endoplasmic reticulum but accelerated the increase in volume density of Clara and ciliated cell mitochondria. When rats exposed to hyperoxia from age 1 to 7 days were thereafter allowed to breathe air, by age 30 days all the differences were eliminated that were detected between the air- and O2-breathing groups at age 7 days. We conclude hyperoxia causes a marked but nonpermanent suppression of maturation of the bronchiolar epithelium.

Aging↗
PubMed1986

Dexamethasone protects against high-dose endotoxin without loss of tolerance to oxygen.

Endotoxin (500 micrograms/kg)-treated rats are very tolerant to hyperoxia (greater than 95% O2, 1 ATA). We have now attempted to determine if dexamethasone given to rats 1 h before a usually lethal dose of endotoxin would diminish endotoxin's lethality without substantially abrogating its capacity to confer tolerance to hyperoxia. Endotoxin (20 mg/kg) given alone killed 70-80% of air- or O2-breathing rats within 24 h; dexamethasone (0.6 mg) given 1 h before endotoxin decreased mortality at 24 h to 10-15%. About 90% of the rats that were alive 24 h after receiving dexamethasone plus endotoxin (20 mg/kg) survived 72 h of hyperoxia. Dexamethasone plus endotoxin (10 mg/kg) provided as much protection against pulmonary edema resulting from 72 h of hyperoxia as did 500 micrograms/kg endotoxin alone. Tolerance to hyperoxia produced by dexamethasone plus high-dose endotoxin was accompanied by a rise in the activity in the lung of antioxidant enzymes. We conclude that dexamethasone protects rats against the lethal effects of high doses of endotoxin without interfering with endotoxin's capacity to engender tolerance to hyperoxia.

Animals↗
PubMed1986

Dexamethasone increases superoxide dismutase activity in serum-free rat fetal lung organ cultures.

Dexamethasone (Dex) injected intraperitoneally to dams on gestational days 19 through 21 significantly enhances the normal late gestational rise of rat pulmonary superoxide dismutase activity. To study if Dex could act directly on lung cells to increase the activity of superoxide dismutase, rat fetal lung organ cultures were established from 21- or 22-day-old pups and maintained in serum free Waymouth 752/1 medium in 95% O2 for 72 h with and without 10 nM Dex in the medium. The cultures increased spontaneously in total superoxide dismutase activity from 17.5 +/- 3.1 to 33.5 +/- 6.2 U/mg DNA during this interval (+90%). The presence of 10 nM Dex caused an increase in enzyme activity to 40.1 +/- 9.3 U/mg DNA (+130%) demonstrating this hormone can act directly on the lung independent of the systemic metabolic consequences of corticosteroid administration. Dex decreased the rate of Cu,Zn superoxide dismutase synthesis (13.5 +/- 3.4 nmol Phe incorporated/mg DNA/h control vs 7.2 +/- 1.6, Dex) and seemed to also decrease the rate of enzyme degradation.

Animals↗
PubMed1985

Synthesis and binding of lactose-specific lectin by isolated lung cells.

Neonatal maturation of alveolar structure in rat lung temporally coincides with the peak activity of a beta-galactoside-specific endogenous lung lectin of the type that has been linked to developmental processes in other tissues. To learn more about the lung lectin we examined four cell types for their ability to synthesize and bind the lectin. Cultured lung fibroblasts and pulmonary artery endothelial cells synthesized and bound the lectin, alveolar macrophages bound but did not synthesize it, and alveolar epithelial type II cells neither bound nor synthesized it. Pulmonary macrophages made a different lactose-binding protein that did not agglutinate or bind trypsin-treated red blood cells, a property of lung lectin that is the means of its assay.

Amino Acids↗
PubMed1985

Mitogenic effect of endotoxin on lung and tolerance of rats to hyperoxia.

Treatment of rats with endotoxin, as late as 24 h after beginning exposure to greater than 95 O2 at 1 atm, increases survival at 72 h from 20-30% to greater than 95% (J. Clin. Invest. 65: 1104, 1980), whereas treatment with corticosteroids reduces survival (Toxicol. Appl. Pharmacol. 47: 367, 1979). Since endotoxin is mitogenic to some cells and glucocorticosteroids decrease DNA synthesis by lung cells, we asked 1) is endotoxin mitogenic to the lung, and, if so, 2) is the mitogenic effect required for endotoxin to produce tolerance to hyperoxia? We found endotoxin administered in vivo does have a mitogenic effect on the lung as indicated by an increased rate of DNA synthesis by lung slices; dexamethasone blocked this effect. However, although dexamethasone given alone markedly diminished survival in hyperoxia, dexamethasone did not impair the protection conferred to rats by endotoxin against the edemogenicity and lethality of hyperoxia. Furthermore, dexamethasone did not diminish the rise of antioxidant enzyme activity in the lungs of endotoxin-treated O2-exposed rats. We conclude endotoxin can produce tolerance to hyperoxia even when its mitogenic action on the lung is substantially diminished.

Animals↗
PubMed1985

Oxygen toxicity in rats. Varied effect of dexamethasone treatment depending on duration of hyperoxia.

The low rate of survival in patients with the adult respiratory distress syndrome (ARDS) may in part reflect a failure to consider that the lung's response to applied therapies may not be constant throughout the course of illness. To test this notion, we used hyperoxia to produce progressive lung damage in rats and administered dexamethasone at different times during O2 exposures of various lengths. Dexamethasone improved survival and decreased lung damage if given when exposure to hyperoxia was to be soon terminated; pulmonary inflammation was marked at the time at which the administration of dexamethasone led to increased survival. Dexamethasone worsened lung damage and diminished survival when given early during exposure to hyperoxia; inflammation was minimal early in the course of exposure to hyperoxia. These findings point to the need for a more analytical approach to research on therapy of ARDS; agents that are harmful at one time may be beneficial at another time.

Animals↗
PubMed1985

Postnatal development of alveoli. Regulation and evidence for a critical period in rats.

In many species, including humans, pulmonary alveoli are formed after birth by septal subdivision of the large gas-exchange saccules present at birth. In rats septation occurs mainly between the 4th and 14th postnatal days (Burri, P. H. 1974. Anat. Rec. 180:77-98), but little is known about the regulation of this process. We found that dexamethasone (0.1 micrograms daily) given to rats from age 4 to 13 d markedly impaired saccule septation to at least age 60 d and also diminished the extent of the increase of alveolar surface area (Sa). Underfeeding from birth to age 14 d did not diminish saccule septation but did result in diminished Sa. We conclude dexamethasone-treated rats have a critical period during which the gas-exchange saccules present at birth must be subdivided. Since Sa increased in dexamethasone-treated rats without a change in alveolar size, and, the enlargement of Sa was diminished in underfed rat pups without a deficit of saccule septation, we postulate new alveoli were formed by means other than septation of the large gas-exchange saccules present at birth. Furthermore, these various means of forming alveoli, and hence of increasing Sa, were differently regulated: dexamethasone decreased the enlargement of Sa brought about by both septation of the gas-exchange saccules present at birth and by other, as yet unidentified, means of forming alveoli; underfeeding did not diminish Sa increases produced by saccule septation but did decrease the extent of Sa enlargement due to the other means of forming alveoli.

Animals↗
PubMed1984

Postnatal development of the bronchiolar Clara cell in rats.

We studied aspects of perinatal rat bronchiolar Clara cell development. We found that the volume density (Vv) of glycogen areas decreased 10-fold between postnatal days 1 and 2 and that the Vv of secretory granules, rough endoplasmic reticulum (RER), and mitochondria increased markedly during the 1st postnatal wk. Compared with pups of dams allowed food ad libitum during gestation, pups from dams underfed during gestation had a higher Vv of glycogen areas for the first 2 postnatal days but a lower Vv of secretory granules and RER for the time studied (to age 7 days). Glucagon injected, in utero, into fetal rats at 21.5 days of gestation resulted in a 40% decrease in the Vv of the glycogen areas within 4 h. We conclude that 1) bronchiolar Clara cells are immature at birth and undergo marked early postnatal maturation, 2) prenatal events (maternal undernutrition) affect postnatal maturation of the Clara cells, and 3) exogenous glucagon leads to glycogen depletion in Clara cells of fetal rats of 21.5 days gestation.

Animals↗
PubMed1984

Adrenalectomy and surfactant in adult rats.

We examined the effect of adrenalectomy (ADX) on aspects of the surfactant system of adult rats. Five days after bilateral ADX, ADX rats had about 20% less disaturated phosphatidylcholine (DSPC) in lung lavage returns (airway DSPC) than sham-operated rats, but the amount of tissue DSPC was not different between the groups; airway DSPC formed 12.8 +/- 0.5% of total DSPC (airway + tissue) in ADX and 15.9 +/- 0.7% in sham-ADX rats. An ultrastructural morphometric analysis of alveolar type 2 cells did not reveal an effect of ADX on lamellar body volume density or surface-to-volume ratio. ADX rats had heavier lungs (not as a result of edema) than sham-ADX rats. Treatment of ADX rats with hydrocortisone returned the amount of DSPC toward normal and eliminated the increase of lung weight. ADX did not alter the recoil of saline-filled lungs but did slightly increase the recoil of air-filled lungs. We conclude that corticosteroid hormones influence the in vivo functioning of the surfactant system of adult rats, but this effect seems to be slight.

Adrenalectomy↗
PubMed1983

Food deprivation and surfactant in adult rats.

We sought to determine if fasting (80% reduction of food intake for 72 h) diminishes airway or tissue disaturated phosphatidylcholine (DSPC) relative to alveolar surface area, or alters the lung response to overventilation. The lungs of fasted rats were lighter, but the size and recoil of saline-filled lungs, and the alveolar surface area of lungs fixed in glutaraldehyde, were the same in fed and fasted rats. In their airways fed rats had 0.32 +/- 0.01 microgram DSPC/cm2 of alveolar surface; fasted rats had 0.28 +/- 0.02 microgram DSPC/cm2 (P less than 0.05) (surface area determined at 20 cmH2O transpulmonary pressure). Fasted rats had 13% less tissue DSPC/cm2 alveolar surface than fed rats (P less than 0.01). After 1 h of mechanically produced overventilation the unequal amounts of airway, but not tissue, DSPC were eliminated and pulmonary compliance was similar in both groups. We conclude food reduction decreases the quantity of airway and tissue DSPC/cm2 of alveolar surface but does not increase lung recoil of spontaneously breathing rats (Gail, Massaro, and Massaro, J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 42: 88-92, 1977) or overventilated rats.

Animals↗
PubMed1983

Morphologic evidence that large inflations of the lung stimulate secretion of surfactant.

We ventilated rats at normal tidal volume without periodic deep breaths, or with a 4-times tidal volume inflation every 5 min for 1 h. The volume density of lamellar bodies in alveolar type 2 cells was about one-third lower after 60 min of ventilation in sighed than in unsighed rats, and this effect of sighs was not blocked by bilateral cervical vagotomy. These morphologic data support previously reported biochemical studies indicating that large inflations are potent stimuli of surfactant secretion.

Animals↗
PubMed1983

Surfactant deficiency in rats without a decreased amount of extracellular surfactant.

Low volume ventilation without periodic large inflations leads to diminished alveolar stability and to the accumulation of increased amounts of airway disaturated phosphatidylcholine (DSPC) in large aggregates that sediment at 1,000 g; surfactant in this form lowers surface tension less rapidly than surfactant present in the 1,000-g supernatant fraction. These observations led to the present work in which we tested the notion that alveolar instability may develop in the presence of an undiminished quantity of total airway surfactant, if the amount of surfactant found in the 1,000-g supernatant fraction is diminished. Pulmonary compliance fell and the alveolar-arterial O2 gradient widened in normothermic rats during constant ventilation in the resting tidal volume range, and, in hyperthermic rats (approximately 39 degrees C) similarly ventilated but with the addition of periodic sighs. The total amount of airway DSPC was undiminished in each group, but in each less DSPC was present in the 1,000-g supernatant fraction compared with controls. Alveolar instability and hypoxemia also developed in hyperthermic rats during low volume ventilation without periodic sighs. Although the total amount of airway DSPC was decreased in these rats, enough remained to theoretically form a continuous monomolecular film over the entire alveolar surface at functional residual capacity; however, there was insufficient surfactant in the 1,000-g supernatant fraction to form such a continuous film. These findings demonstrate that the mode of ventilation, and moderate hyperthermia, may lead to decreased alveolar stability despite the presence of normal amounts of airway surfactant, and, by inference, indicate the extracellular form or state of surfactant has an important effect on alveolar stability.

Animals↗
PubMed1982

Protein synthesis by attached pulmonary macrophages. Effect of phagocytosis.

We studied the effect of phagocytosis of polystyrene latex beads on protein synthesis by pulmonary macrophages. To do this we determine the specific radioactivity of extracellular and intracellular free phenylalanine and of phenylalanine released from tRNA and used this information in calculating the rates of protein synthesis. Phagocytosis resulted in an increased rate of protein synthesis irrespective of which precursor specific radioactivity was used in the calculation. The rate of protein synthesis was increased per microgram polyribosomal RNA; but there was no increase in the amount of polyribosomal RNA in phagocytizing macrophages. The increase in the rate of protein synthesis (1.4-fold) was almost identical to the increase (1.3-fold) in the rate of ribosome transit in phagocytizing compared to nonphagocytizing macrophages. The decreased ribosome transit time during phagocytosis occurred without a fall in the average molecular weight of macrophage proteins. We conclude that phagocytosis increases the rate of protein synthesis in attached pulmonary macrophages and that this increased rate of synthesis can be accounted for almost completely by an increased rate of polypeptide chain elongation and/or termination.

Animals↗
PubMed1982

The effect of bacterial endotoxin on synthesis of (Cu,Zn)superoxide dismutase in lungs of oxygen-exposed rats.

Administration of bacterial endotoxin to rats exposed to greater than 95% O2 results in increased lung superoxide dismutase activity, decreased O2-induced lung damage, and a 3- to 4-fold improvement in survival rate (Frank, L., Yam, J., and Roberts, R. J. (1978) J. Clin. Invest, 61, 269-275). Antibodies to rat liver (Cu,Zn) superoxide dismutase were prepared and utilized to investigate the mechanism by which endotoxin treatment leads to increased lung superoxide dismutase activity. Assay of enzyme activity and of immunodetectable enzyme showed that the increased activity is due to an increase in the number of enzyme molecules rather than activation of existing enzyme. Compared to air controls, lung slices from rats exposed to greater than 95% O2 and treated with endotoxin have elevated rats of synthesis of (Cu,Zn)superoxide dismutase (51%) and of total protein (100%). Lung slices from untreated rats exposed to greater than 95% O2 have no such elevations. Endotoxin treatment thus appears to stimulate lung protein synthesis, leading to greater (Cu,Zn)superoxide dismutase activity due to an increased number of enzyme molecules.

Animals↗
PubMed1982

Surfactant secretion: evidence that cholinergic stimulation of secretion is indirect.

There is strong evidence that cholinergic agents stimulate the secretion of surfactant in vivo and in the isolated perfused lung and that they do not stimulate surfactant secretion in isolated type 2 alveolar cells. These observations suggest that in multicellular systems the cholinergic effect is indirect. In the present work we have accrued the following support for this hypothesis. 1) Propranolol blocked the in vivo stimulation of disaturated phosphatidylcholine (DSPC) secretion by pilocarpine. 2) Bilateral adrenalectomy decreased by 50% the in vivo stimulation of DSPC secretion by pilocarpine. 3) Bilateral vagotomy did not block the increased secretion of DSPC produced in vivo by periodic deep inflations. 4) Pilocarpine (10(-7) M) stimulated DSPC secretion in the isolated perfused lung, and this effect was blocked by indomethacin as well as by atropine. We conclude that cholinergic stimulation of the secretion of surfactant in rats is indirect, i.e., cholinergic agonists do not stimulate the secretion of surfactant by acting directly on type 2 alveolar cells.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1982

Studies on the regulation of secretion in Clara cells with evidence for chemical nonautonomic mediation of the secretory response to increased ventilation in rat lungs.

Using electron microscopy and morphometric methods to assess secretion, we previously found that two times tidal volume ventilation of isolated perfused rat lung stimulates secretion by bronchiolar Clara cells; this effect is not prevented by beta-adrenergic blockade (J. Clin. Invest. 1981. 67: 345-351.). In this study we used the isolated perfused rat lung and the anesthetized mechanically ventilated rat, to further study the mechanism by which large tidal volumes stimulate secretion by Clara cells. With the perfused lung we found (a) alpha-adrenergic inhibition did not block the secretory effect of ventilation at two times normal tidal volume; (b) indomethacin completely blocked the secretory action of two times tidal volume ventilation; (c) medium previously used to perfuse lungs ventilated at two times tidal volume, but not medium previously used to ventilate lungs at normal tidal volume, stimulated secretion by Clara cells when used to perfuse fresh lungs ventilated at tidal volume; (d) addition of prostacyclin to the fresh perfusate increased secretion by Clara cells of lungs ventilated at normal tidal volume. In anesthetized mechanically ventilated rats, sighs stimulated secretion by Clara cells; this increased secretion was inhibited by indomethacin but not by cholinergic blockade (bilateral vagotomy). These studies indicate that increased volume ventilation stimulates secretion by Clara cells in vivo and in vitro; they provide evidence that chemical nonadrenergic, noncholinergic mechanisms are involved in this secretion, and that prostaglandins may be the chemical messenger coupling the mechanico-secretory events.

Airway Resistance↗
PubMed1981

Proteolysis in the rat lung: hypoxia and evidence for an inhibitor of proteolysis.

We labeled proteins with [14C]phenylalanine in rats breathing air and assessed the rate of proteolysis in the isolated ventilated lung by measuring the accumulation of [14C]phenylalanine in the medium perfusing the lung. Ventilation with 0% O2 decreased the rate of proteolysis and the ATP content in the lung 60%. Medium from lungs ventilated with 0% O2, when used to perfuse lungs ventilated with 95% O2, decreased the rate of proteolysis 60% without lowering the ATP content of the lung. Correcting the pH of "used" medium or dialyzing used medium did not decrease its ability to inhibit proteolysis. Used medium from nonhypoxic lungs, or exogenous lactate (50 mM), diminished proteolysis only 20%. In a cell-free system the degradation by cathepsin D of radioactive lung proteins and radioactive hemoglobin was decreased by used medium from hypoxic lungs. We conclude that the hypoxic perfused lung releases a factor(s) that decreases the rate of proteolysis in nonhypoxic lungs and that this factor may be a protease inhibitor.

Adenosine Triphosphate↗