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Biomedical subjects

D Massaro

Publications and source records attributed to D Massaro.

At least 55 records · Page 3Linked to original sources
PubMed1989

New "rest period" protocol for inducing tolerance to high O2 exposure in adult rats.

We report a new protocol for inducing marked tolerance to prolonged exposure to hyperoxia in adult rats that entails the use of a single "rest period" between exposures to a usually lethal concentration of O2. Exposure of adult rats to greater than 95% O2 for 48 h followed by a rest in air, or a rest even in 50-75% O2, consistently resulted in 100% survival with evidence of only slight pulmonary edema during continuation of exposure to greater than 95% O2 for 3-7 more days (7-day survival for rats rested in room air for 24 h = 23/23; for rats rested in 50-75% O2 for 24 h = 27/27; for continuously O2-exposed control rats = 0/11). Induction of tolerance to hyperoxia was associated with significant increases in the lungs' antioxidant enzyme activities during the reexposure to greater than 95% O2 following the rest period. The molecular means by which the events in this protocol lead to increased lung antioxidant enzyme activity is only partially known, but because of the marked tolerance produced, the elucidation of the mechanisms must be important to our understanding of tolerance to hyperoxia.

Animals↗
PubMed1989

Alveolar dimensions and number: developmental and hormonal regulation.

We used three-dimensional reconstruction 1) to determine the effect of treating rats with dexamethasone, from age 4 to 13 days, on alveolar volume (v) and number (Na) and 2) to determine if v, Na, or both change between age 14 and 60 days. At age 14 days, v, Na, and gas exchange surface area (Sa) were (2.7 +/- 0.3) x 10(4) microns3, (20.2 +/- 2.1) x 10(6), and 832 +/- 29 cm2, respectively, in diluent-treated rats; in dexamethasone-treated 14-day-old rats the same parameters were (7.5 +/- 1.1) x 10(4) microns3, (9.9 +/- 1.6) x 10(6), and 733 +/- 16 cm2, respectively. At age 60 days, v, Na, and Sa were (7.1 +/- 0.4) x 10(4) microns3, (60.8 +/- 4.1) x 10(6), and 4,495 +/- 187 cm2 in diluent-treated rats and in rats treated with dexamethasone from age 4 to 13 days, v, Na, and Sa at age 60 days were (15.9 +/- 2.4) x 10(4) microns3, (25.8 +/- 3.8) x 10(6), and 3,424 +/- 203 cm2. We conclude that treatment with dexamethasone from age 4 to 13 days (the period of normal septation) resulted in larger alveoli at age 14 and 60 days, and in diluent- and dexamethasone-treated rats the increase in Sa between age 14 and 60 days is due, at least in part, to the formation of new alveoli.

Aging↗
PubMed1989

Rat lung Cu,Zn superoxide dismutase. Isolation and sequence of a full-length cDNA and studies of enzyme induction.

The synthesis of Cu,Zn SOD by rat lung increases spontaneously in the fetus in late gestation and during exposure of neonatal and adult rats to greater than 95% O2. To explore the regulation of these increases, we measured rat lung Cu,Zn SOD synthesis and activity. We also cloned and sequenced a rat lung Cu,Zn SOD cDNA that was used to measure Cu,Zn SOD mRNA concentration. We found that (a) under normal gestational and postgestational conditions the synthesis of this enzyme was regulated pretranslationally; (b) the increased synthesis that occurs under hyperoxia (greater than 95% O2), was pretranslationally mediated in otherwise unmanipulated neonatal rats but translationally controlled in hyperoxic adult rats; and (c) in lungs of rats made tolerant to greater than 95% O2 by allowing 24 h rest in air after an initial 48 h in greater than 95% O2, the increased Cu,Zn SOD synthesis that occurred during the second period of hyperoxia was regulated pretranslationally. We conclude Cu,Zn SOD gene expression in the lung is developmentally regulated under normal conditions and in response to an oxidant challenge. Tolerance, whether endogenous or induced, appears to require the accumulation of increased amounts of Cu,Zn SOD mRNA.

Aging↗
PubMed1988

Sequence of a full-length cDNA for rat lung beta-galactoside-binding protein: primary and secondary structure of the lectin.

A full-length cDNA for rat lung beta-galactoside lectin (subunit Mr approximately 14,000, lectin 14K) was cloned and the nucleotide sequence determined. The deduced amino acid sequence agrees with the amino acid composition and direct amino acid sequence analysis of purified rat lung lectin peptides. We found that the amino-terminal alanine is blocked with an acetyl group. Comparison of the amino acid sequence with other proteins shows a high degree of homology only with other vertebrate lectin sequences, supporting the suggestion that these lectins may constitute a unique class of vertebrate proteins. The amino acid composition and sequence of lectin peptides, the sequence of lectin cDNA, and isoelectric focusing of purified lectin indicate that rat lung lectin 14K is composed predominantly of a single protein. In addition, rat uterus lectin 14K was found to be the same protein as that present in lung. We characterized the secondary and tertiary structure of rat lung lectin 14K by circular dichroism, by analytical ultracentrifugation, and by computer analysis of its primary structure. Results of these experiments suggest that lectin 14K is primarily a hydrophilic protein with an asymmetric, elongated structure consisting of approximately equal amounts of alpha helix, beta sheet, beta turn, and random coil. We found that Cys-2 and Cys-130 react most rapidly with iodoacetamide; one or both of these residues may be primarily responsible for the thiol requirement of lectin activity.

Amino Acid Sequence↗
PubMed1988

Regulation of the synthesis of superoxide dismutases in rat lungs during oxidant and hyperthermic stresses.

Heat shock proteins are induced at normal temperatures by oxidants and during reoxygenation following hypoxia. We now report cyanide-resistant O2 consumption increased 30-50% in rat lungs exposed to heat shock or reoxygenation following hypoxia. The synthesis of Cu,Zn superoxide dismutase, but not Mn superoxide dismutase, was increased in rat lung slices by in vivo hyperthermia (39 degrees C), by in vitro heat shock (41 degrees C), and during incubation of lung slices with the Cu chelator diethyldithiocarbamate, which decreased the activity of Cu,Zn superoxide dismutase. The heat shock-induced increase in Cu,Zn superoxide dismutase developed 2 h later than the induction of heat shock proteins and was not blocked by actinomycin D. The rates of synthesis of both superoxide dismutases were decreased 50% by hypoxia and failed to increase during reoxygenation. During hypoxia the activity of Cu,Zn superoxide dismutase decreased about 50%, but the activity of Mn superoxide dismutase remained unchanged. We conclude that hyperthermia increases the synthesis of Cu,Zn superoxide dismutase, the synthesis of Cu,Zn superoxide dismutase and Mn superoxide dismutase are not coordinately regulated by hyperthermia or by the oxidant stress produced by lowering the activity of Cu,Zn superoxide dismutase, and the synthesis of heat shock proteins and Cu,Zn superoxide dismutase are regulated at different levels of gene expression.

Amino Acids↗
PubMed1988

Development of bronchiolar epithelium: time course of response to oxygen and recovery.

Hyperoxia (greater than 95% O2) reversibly suppresses the early postnatal development of rat bronchiolar epithelium. We now show that blunting of the normal increase in nuclear numerical density per centimeter cubed of Clara and ciliated cells becomes apparent within 24 h of exposure to O2 (age 2 days) and reaches a maximum on the last day of hyperoxia (age 7 days). The intergroup differences began to disappear within 48 h after removal from O2. During air breathing, Clara cell mitosis increased sixfold between the ages of 1 and 2 days and returned to day 1 values by age 7 days. During O2 breathing, Clara cell mitosis increased threefold between age 1 and 2 days, returned to day 1 values by day 4, but exhibited a second peak 24 h post-O2 (day 8) not present in unexposed pups. The onset of differences in the volume of Clara cell organelles and glycogen was variable, but the differences were partly or completely eliminated 48 h post-O2 exposure. We conclude hyperoxia reversibly impairs mitosis by Clara cells.

Animals↗
PubMed1988

Postnatal undernutrition slows development of bronchiolar epithelium in rats.

The lung's small conducting airways are sites of dysfunction early in the course of chronic lung diseases that are prevalent in humans; furthermore, there is evidence that aspects of childhood environment may adversely influence small airway function in adulthood. Because there is considerable early postnatal morphological maturation of the bronchiolar epithelium in rats, these considerations led to the present study in which we assessed the effect of early postnatal undernutrition in rats on the anatomic development of the bronchiolar epithelium. We found undernutrition, produced by increasing rat litter size shortly after birth, led to delayed development of the mitochondria and rough endoplasmic reticulum of bronchiolar Clara cells. Of particular interest, underfeeding resulted in considerably diminished mitosis by Clara cells, decreased nuclear numerical density of bronchiolar ciliated cells, evidence of diminished conversion of Clara cells to ciliated cells, and an abnormal cellular composition of the small airway epithelium that persisted well beyond the period of underfeeding. We conclude that early neonatal events can have long-term effects on the bronchiolar epithelium.

Aging↗
PubMed1987

Mitogenic response of rat lung to endotoxin exposure.

Adult rats exposed to hyperoxia are protected from lung injury by treatment with bacterial endotoxin. Experiments were undertaken to determine whether endotoxin treatment produces a mitogenic effect on the lung. Endotoxin treatment caused a significant (P less than .05) loss of body weight (8%) in rats exposed to either air or greater than 95% O2 for 24 hr. Therefore, experiments were also undertaken in which both saline- and endotoxin-treated rats were starved for the duration of the experiments to make equal any nutritional imbalance. The rate of DNA synthesis in lung slices from fed rats treated with endotoxin did not differ from that of saline-treated controls. In contrast, lung DNA synthesis in starved rats treated with endotoxin increased 50%. The effect of endotoxin treatment was similar in rats breathing air or greater than 95% O2, and lung protein synthesis generally paralleled lung DNA synthesis. These results indicate that endotoxin does exert a mitogenic effect on the lung and this effect can be masked by the nutritional imbalance resulting from endotoxin administration.

Animals↗
PubMed1987

Developmental regulation of rat lung Cu,Zn-superoxide dismutase.

In the present investigation we found that lung Cu,Zn-superoxide dismutase (SOD) activity (units/mg of DNA) increases steadily in the rat from birth to adulthood. The specific activity (units/micrograms of enzyme) of Cu,Zn-SOD was unchanged from birth to adulthood, excluding enzyme activation as a mechanism responsible for the increase in enzyme activity. Lung synthesis of Cu,Zn-SOD peaked at 1 day before birth and decreased thereafter to adult values. Calculations, based on rates of Cu,Zn-SOD synthesis and the tissue content of the enzyme, indicated that lung Cu,Zn-SOD activity increased during development owing to the rate of enzyme synthesis exceeding its rate of degradation by 5-10%. These calculations were supported by measurements of enzyme degradation in the neonatal (half-life, t1/2, = 12 h) and adult lung (t1/2 = greater than 100 h); the difference in half-life did not reflect the rates of overall protein degradation in the lung, since these rates were not different in lungs from neonatal and adult rats. We did not detect differences in the Mr or pI of Cu,Zn-SOD during development, but the susceptibility of the enzyme to inactivation by heat or copper chelation decreased with increasing age of the rats. We conclude that the progressive increase in activity of Cu,Zn-SOD is due to a rate of synthesis that exceeds degradation of the enzyme. The data also suggest that increased stabilization of enzyme conformation accounts for the greater half-life of the enzyme in lungs of adult compared with neonatal rats.

Animals↗
PubMed1987

Rat lung lectin synthesis, degradation and activation. Developmental regulation and modulation by dexamethasone.

Soluble lectins are widely distributed cell-agglutinating proteins. Their activity is developmentally regulated in several tissues, including the lung, but virtually nothing is known about the mechanisms of the developmental regulation or the turnover of these proteins. We studied mechanisms that might be responsible for the developmentally regulated changes in the activity of a lectin (beta-galactoside-binding protein) found in the lung, and determined if its activity or turnover could be modulated by treatment of rat pups with a glucocorticosteroid hormone (dexamethasone). Our studies on the activity and turnover of the lectin indicated that the peak of lectin activity (units/mg of protein) that occurred at age 12 days appeared to be brought about by two means: an increase in the activity of the lectin molecule itself (units/micrograms of lectin) that occurred at age 8 days, and 1.5-fold increase in the absolute rate of lectin synthesis at age 11 days. The decline in lectin activity was associated with a decrease in its rate of synthesis, return to the baseline extent of activation, and an increased rate of degradation. Treatment of rat pups with dexamethasone diminished the peak of lectin activity (units/mg of protein) by about 25%. This effect of dexamethasone was due, at least in part, to the complete prevention of activation of the lectin molecule (units/micrograms of lectin) and a premature increase in the rate of lectin degradation. Perhaps the normal fall in lectin activity after age 11 days is caused by mechanisms induced by the increase in serum corticosteroid that occurs at that age.

Animals↗
PubMed1987

PO2-dexamethasone interactions in fibroblast growth and antioxidant enzyme activity.

Fetal rat lung fibroblasts were cultured in a gas phase of 20% O2, 5% CO2 (PO2 measured, 150 Torr) or 2% oxygen, 5% CO2 (PO2 measured, 25 Torr) with or without 100 nM dexamethasone (Dex). Superoxide dismutase (SOD) activity per cell increased spontaneously during 4 days of incubation at both PO2, but catalase (CAT) activity tended to fall during this time and glutathione peroxidase (GPx) activity showed no consistent trend during this interval. Cells cultured at a low PO2 had a lower protein content and SOD activity compared with air controls. Dex inhibited cell proliferation and enhanced intracellular accumulation of protein at the low PO2 but prevented the increase in protein content without affecting cell multiplication at a PO2 of 150 Torr. SOD activity per cell was enhanced by Dex at a low PO2 but reduced in 20% O2, 5% CO2. An increase in CAT and GPx activity per cell resulted on exposing fibroblasts to Dex in the presence of low PO2. These results show that Dex affects the growth and antioxidant enzyme activity of fetal lung fibroblasts, and this action of Dex can be modulated by changing the ambient PO2.

Animals↗
PubMed1987

Differences in CuZn superoxide dismutase induction in lungs of neonatal and adult rats.

The failure of adult rats to survive prolonged exposure to greater than 95% O2 is generally ascribed to the inability of their lungs to increase antioxidant enzyme synthesis in response to the oxidant challenge. We studied the synthesis rate of the antioxidant enzyme CuZn superoxide dismutase (CuZn SOD) in lungs of adult and neonatal rats exposed to conditions that alter the lung's oxidant-to-antioxidant balance. Lung CuZn SOD synthesis in the adult was significantly increased after 24 h of hyperoxia but fell to control levels after further exposure, whereas in neonatal lungs an increased rate of synthesis of CuZn SOD was found only after 72 h of hyperoxia. The adult lung responded to two in vitro oxidant stresses, [diethyldithiocarbamate exposure and heat (42 degrees C)] with increases in CuZn SOD synthesis twice the magnitude of those in the neonatal lung. These data indicate that the adult lung is at least as capable as the neonatal lung of increasing its synthesis of CuZn SOD in response to an oxidative stress. However, the inability of the adult lung to maintain an increased rate of CuZn SOD synthesis during in vivo hyperoxia may contribute to the poor tolerance of the adult lung to greater than 95% O2.

Aging↗
PubMed1986

Postnatal development of pulmonary alveoli: modulation in rats by thyroid hormones.

We studied the effect of thyroid hormones on the postnatal development of the gas exchange region of rat lungs. Treatment with triiodothyronine (T3, 0.1 microgram . g body wt-1 . day-1) accelerated the increase of the surface-to-volume ratio (S/V) and surface area (Sa) and decrease of the mean chord length (Lm) of the gas exchange structures of pups killed at age 7 days. Propylthiouracil (PTU, 100 micrograms twice daily) from age 1 to 13 days, with death at age 14 days, diminished the rise of S/V and Sa and the fall of Lm compared with diluent-injected pups. Providing drinking water with 0.01% PTU to dams from gestation day 20 (term 22 days) to postnatal day 14 also diminished the rise of S/V and fall of Lm. Treatment of pups nursed by dams drinking 0.01% PTU with thyroxine (0.1 microgram/g body wt) every other day from age 1 to 13 days significantly diminished the effect of PTU on S/V, Sa, and Lm. We conclude thyroid hormones can modulate the postnatal architectural development of the gas exchange region of the rat lung.

Animals↗
PubMed1986

Development of bronchiolar epithelium in rats.

We used ultrastructural and morphometric means to examine aspects of the regulation of the maturation of rat bronchiolar Clara cells and the development of the epithelium of small conducting airways in the perinatal period. We found the nuclear numerical density per cubed centimeter (Nvn) of Clara cells fell and the Nvn of ciliated cells increased from birth to age 60 days, the prenatal administration of a glucocorticosteroid (dexamethasone) to dams caused a 35% decrease in the Nvn of ciliated cells present at birth but did not alter the Nvn of Clara cells, the administration of dexamethasone to pups from postnatal days 1 to 6 did not alter the Nvn of bronchiolar Clara or ciliated cells present at age 7 days but did diminish the total number of lung cells as assessed by measurements of lung DNA, the administration of dexamethasone to dams from gestation days 18 to 20 or from gestation days 20 to 22 did not alter the volume density of Clara cell glycogen, secretory granules, rough endoplasmic reticulum, or mitochondria of pups at gestation day 21.5 or on the day of birth, and glucagon, epinephrine, and 8-bromoadenosine 3',5'-cyclic monophosphate resulted in a decrease of Clara cell glycogen when individually incubated in vitro for 4 h with bronchiolar tissue from rat fetuses 21.5 days of age.

Animals↗
PubMed1986

Dexamethasone accelerates postnatal alveolar wall thinning and alters wall composition.

The gas exchange region of newborn rats is composed of large thick-walled gas exchange saccules that become subdivided by septum formation between ages 4 and 14 days. Dexamethasone given daily from age 4 to 13 days irreversibly prevents septation. We now asked if dexamethasone (0.1 micrograms) given daily from age 4 to 13 days accelerates alveolar wall thinning and alters wall composition. Compared with controls, within 2 days dexamethasone-treated pups had a 20% thinner gas exchange wall, a 35% lower volume density (Vv) and absolute volume of interstitial fibroblasts, and a 45% greater Vv of type II cells. At age 14 days the volumes of type I cells, fibroblasts, and acellular matrix were approximately 35% less in dexamethasone-treated pups, but the volumes of type II and endothelial cells did not exhibit significant intergroup differences. We conclude dexamethasone accelerates alveolar wall thinning and suggest dexamethasone diminishes replication of fibroblasts more rapidly than it diminishes division of type II, impairs conversion of type II to I, and does not decrease replication of endothelial cells.

Animals↗
PubMed1986

Perinatal anatomic development of alveolar type II cells in rats.

We studied the perinatal development of rat alveolar type II cells. The volume density (Vv) of lamellar bodies increased twofold from gestational day 21.5 to postnatal day 1 and 1.6-fold between age 1 and 60 days. The Vv of glycogen areas fell sharply between late gestation and postnatal day 1; this decrease was greater in pups delivered from dexamethasone- compared with diluent-treated dams. In utero administration of glucagon to fetuses on gestational day 21.5 caused a decline in the Vv of glycogen areas within 4 h. Pups from dams underfed in late gestation had a higher Vv of glycogen areas and a lower Vv of lamellar bodies on the first 2 postnatal days compared with pups from dams allowed food ad libitum. We conclude that rat alveolar type II cells are somewhat immature at birth; prenatal maternal underfeeding slows the pre- and postnatal maturation of alveolar type II cells; and 3) exogenous glucagon causes a fall in the Vv of glycogen areas in type II cells of fetal rats at gestational day 21.5.

Animals↗