The ultrastructural histochemistry and stereoscanning electron microscopy of the rodent and amphibian surfactant systems

Comparative Morphology of the Lungs and Skin of two Anura, Pelophylax nigromaculatus and Bufo gargarizans

The lungs and skin are important respiratory organs in Anura, but the pulmonary structure of amphibians remains unclear due to the lack of a suitable procedure. This study improved the procedure used for fixing lungs tissues and used light microscopy, transmission electron microscopy and scanning electron microscopy to reveal the differences in the lung and skin morphologies between Pelophylax nigromaculatus (P. nigromaculatus) and Bufo gargarizans (B. gargarizans). In P. nigromaculatus and B. gargarizans, the cystic lungs comprise a continuous outer pulmonary wall on which primary, secondary, and tertiary septa attach, and a number of regular lattices form from raised capillaries and the pulmonary epithelium on the surfaces of the pulmonary wall and septa. Each lattice in P. nigromaculatus consists of several elliptical sheets and flat bottom, and the septa are distributed with denser sheets and have a larger stretching range than the pulmonary wall. The lattice in B. gargarizans consists of thick folds and an uneven bottom with several thin folds, and the septa have more developed thick and thin folds than the pulmonary wall. However, the density of the pulmonary microvilli, the area of a single capillary, the thicknesses of the blood-air barrier, pulmonary wall and septum, and the lung/body weight percentage obtained for B. gargarizans were higher than those found for P. nigromaculatus. In P. nigromaculatus, the dorsal skin has dense capillaries and a ring surface structure with mucus layer on the stratum corneum, and the ventral skin is slightly keratinized. In B. gargarizans, the stratum corneum in both the dorsal and ventral skins is completely keratinized. A fine ultrastructure analysis of P. nigromaculatus and B. gargarizans revealed that the pulmonary septa are more developed than the pulmonary walls, which means that the septa have a stronger respiratory function. The more developed lungs are helpful for the adaptation of B. gargarizans to drought environments, whereas P. nigromaculatus has to rely on more vigorous skin respiration to adapt to a humid environment.

Atrial natriuretic peptide (ANP) system in the lung ofRana esculenta

The atrial natriuretic peptide (ANP)-system was examined in Rana esculenta lung with cytochemical and immunocytochemical methods. The results showed a cellular type that synthesizes the hormone and the presence of receptors in various components of the lung. The lung, therefore, produces ANP and at the same time is a target organ for the hormone. ANP may play an important physiological role in pulmonary function and in protecting against pulmonary edema.

Intraalveolar bubbles and bubble films: III. Vulnerability and preservation in the laboratory

BACKGROUND

Having confirmed (Scarpelli et al. 1996. Anat. Rec. 244:344-357 and 246:245-270) the discovery of intraalveolar bubbles and films as the normal anatomical infrastructure of aerated alveoli at all ages, we now address three questions. Why have these structures been so elusive? Visible in fresh lungs from the in vivo state, can they be preserved by known laboratory methods? Can they be preserved intact for study in tissue sections?

METHODS

Lungs of adult rabbits and pups were examined in thorax directly from the in vivo state to confirm normal bubbles both at functional residual capacity and at maximal volume; other lungs were permitted to deflate naturally to minimal volume. The fate of bubbles in situ (either intact, transected, or diced lung tissue) and of isolated bubbles was assessed (1) during conventional histopreparative processing, (2) during inflation-deflation after degassing, (3) after drying in air, (4) during and after quick freezing in liquid N2, and (5) after preservation in fixed and stained tissue sections prepared by a new double-impregnation procedure in which glutaraldehyde-fixed tissue was preembedded in agar, dehydrated and clarified chemically, embedded in paraffin, sectioned, and stained. Control studies included both blocking of bubble formation by rinsing the air spaces with Tween 20 prior to double impregnation and preparation of normal tissue without preembedding in agar.

RESULTS

(1) Each of the following procedures in conventional processing dislocated and disrupted bubbles and films: osmium tetroxide and glutaraldehyde:formaldehyde:tannic acid mixture fixation; chemical dehydration (70-100% ethanol) and clarification (xylene and acetone); and embedding in paraffin or epoxy resin. Transection and dicing of the tissue aggravated the untoward effects. In contrast, bubbles and films remained stable in either glutaraldehyde or formaldehyde, which, however, did not protect against the other agents. (2) Degassing destroyed all bubbles as expected; however, bubbles and films re-formed immediately with reinflation. (3) Topography of fixed bubbles and films was retained after air drying. The dry polygonal configuration reverted to spherical-oval either in saline solution or in 50% ethanol, whereas vulnerability to upgraded ethanol concentrations was unchanged. (4) Normal topography and shape appeared to be retained during quick freezing and after thawing. (5) Intraalveolar and intraductal bubbles and films were preserved and photographed in sections from tissue prepared by the double-impregnation procedure; they were not seen either when bubble formation had been blocked (double-impregnation procedure) or when preembedding in agar had been omitted.

CONCLUSIONS

(1) Whether or not fixed in glutaraldehyde or formaldehyde, preservation of intraalveolar and intraductal bubbles and films is not to be expected in tissue prepared by conventional histopreparative procedures, whereas product artifacts may be expected from bubble rupture in situ. (2) Degassing cannot be recommended for studies of alveolar structure-function interrelations because all natural bubbles are disrupted in the process, and bubble re-formation may not parallel their "natural history" in vivo. (3) Compared with glutaraldehyde or formaldehyde fixation, air drying offers no added protection against the untoward effects of conventional processing. (4) Quick-frozen tissue is equally at risk. (5) A new double-impregnation procedure does preserve bubbles and films during processing, sectioning, and staining.

An ultrastructural study of hydrogen peroxide production by cultured fetal and neonatal rat lung cells exposed to hyperoxia

Hydrogen peroxide production in organotypic cultures of fetal and newborn rat lung cells has been investigated using an ultrastructural histochemical method, in which the quantity and location of an electron-dense reaction product derived from the interaction of cerium chloride and hydrogen peroxide was detected. Hydrogen peroxide was present in fetal cell cultures exposed to hyperoxia (50% oxygen) compared to controls maintained in 10% oxygen. This increase could be limited by incubation of cultures with ascorbic acid and preincubation with dexamethasone. On the other hand, in newborn rat lung cell cultures, less hydrogen peroxide was identified in cultures including those exposed to hyperoxia (50% oxygen).

Surface active substances in the chinchilla tubotympanum. A biochemical study

It has been demonstrated that the eustachian tube and middle ear epithelium produce Tubal Surface Active Substances (TSAS), which facilitate the opening of the eustachian tube. In order to characterize the biochemical contents of chinchilla TSAS, the tubal washings were analyzed using 2-D thin layer chromatography. The results indicate that phosphatidylcholine was the predominant phospholipid, followed by sphingomyelin, phosphatidylinositol phosphatidylethanolamine, and phosphatidylserine. In comparison, pulmonary lavage showed phosphatidylcholine to be highest allowed by phosphatidylethanolamine and sphingomyelin. Phosphatidylcholine/phosphatidylethanolanim ratios were 5:1 in the tubal lavage, and 8:1 in the pulmonary lavage. Phosphatidylcholine/sphingomyelin ratios were 2:1 in the tubal lavage, and 67:1 in the pulmonary lavage. It is concluded that the biochemical content of TSAS is similar but not identical to that of pulmonary surfactants.

Lung of the tree frog, Hyla arborea L. A scanning and transmission electron microscopic study

Lungs of Hyla arborea L. were examined by scanning and transmission electron microscopy and morphometric methods. The lungs contain several interconnected folds in a netlike reticular arrangement of first, second and third order, mainly covered with pneumocytes. On the septa of first and second order, irregularly distributed small patches of ciliated epithelium devoid of goblet cells are located. Dome-shaped neuroepithelial bodies can be seen in the vicinity of ciliated epithelium. The pulmonary epithelium consists of one type of pneumocyte, which contain in their cytoplasm three kinds of bodies: lamellar, dense and multivesicular. The dense bodies are precursors of lamellar bodies (LBs), while the multivesicular bodies are incorporated into the LBs, being later secreted to the air space. The lining layer covering the internal lung surface contains numerous transformed LBs but tubular myelin figures are scarce. The surface of the lining layer is coated by a thin film. The air-blood barrier, consisting of three layers: epithelium, interstitial space and endothelium, is 0.6 micron thick.

Extramembraneous particles and structural variations of tubular myelin figures in rat lung surfactant

Tubular myelin figures of pulmonary surfactant were examined by electron microscopy after fixation in glutaraldehyde and postfixation in an osmium tetroxide-ferrocyanide mixture. Bilayered membranes were seen as parallel arrays or as lattices with spacings varying from about 36 to 50 nm. This method also produced good visualization of drumstick-like particles, 5 nm in diameter and about 15 nm in length. The particles were regularly spaced at intervals of 16 nm in rows along the rectangular angles of myelin membranes. Depending on the size of the tubules the particles contacted each other in the center of the tubules at low diameters (tubular diameter less than 40 nm) and formed a continuous filamentous central core, or they were separated from one another (tubular diameter greater than 40 nm). In the latter case the central core had a hollow appearance. Based on further findings employing tannic acid, lipid extraction with 2,2-dimethoxypropane, and a ruthenium red-osmium tetroxide technique for the demonstration of polyanionic proteins it is suggested that these particles are protein in nature and that they are involved in the formation and maintenance of the structure of tubular myelin. A new concept of the ultrastructure of tubular myelin figures is proposed.