Pulmonary design in a microchiropteran bat (Pipistrellus subflavus) during hibernation

The role of endogenous H2S formation in reversible remodeling of lung tissue during hibernation in the Syrian hamster

During hibernation, small mammals alternate between periods of metabolic suppression and low body temperature ('torpor') and periods of full metabolic recovery with euthermic temperatures ('arousal'). Previously, we demonstrated marked structural remodeling of the lung during torpor, which is rapidly reversed during arousal. We also found that cooling of hamster cells increased endogenous production of H(2)S through the enzyme cystathionine-β-synthase (CBS). H(2)S suppresses the immune response and increases deposition of collagen. Therefore, we examined inflammatory markers and matrix metalloproteinase (MMP) activity in relation to CBS expression and H(2)S levels in lungs of euthermic and hibernating Syrian hamsters. Lung remodeling during torpor was confirmed by a strong increase in both collagenous and non-collagenous hydroxyproline content. The number of leukocytes in lung was unchanged in any phase of hibernation, while adhesion molecules VCAM-1 and ICAM-1, and the inflammatory marker NF-κB (P65) were modestly upregulated in torpor. Gelatinase activity was decreased in lungs from torpid animals, indicating inhibition of the Zn(2+)-dependent MMP-2 and MMP-9. Moreover, expression of CBS and tissue levels of H(2)S were increased in torpor. All changes normalized during arousal. Inhibition of gelatinase activity in torpor is likely caused by quenching of Zn(2+) by the sulphide ion of H(2)S. In accord, inhibition of CBS normalized gelatinase activity in torpid animals. Conversely, NaHS decreased the gelatinase activity of euthermic animals, which was attenuated by excess Zn(2+). Similar results were obtained on the activity of the Zn(2+)-dependent angiotensin converting enzyme. Our data indicate that increased production of H(2)S through CBS in hamster lungs during torpor contributes to remodeling by inhibition of gelatinase activity and possibly by suppression of the inflammatory response. Although administration of H(2)S is known to induce metabolic suppression in non-hibernating mammals ('suspended animation'), this is the first report implying endogenous H(2)S production in natural hibernation.

Functional and structural optimization of the respiratory system of the batTadarida brasiliensis(Chiroptera, Molossidae): does airway geometry matter?

We studied structure and function of the respiratory system in the bat Tadarida brasiliensis and compared it with those of two species of rodents, Abrothrix andinus and A. olivaceus. Tadarida brasiliensis had lower resting oxygen consumption, but higher maximum oxygen consumption and aerobic scope, than the rodents. The blood–gas barrier of the bat was thinner and its relative lung size was larger; however,alveolar surface density was similar among the three species. In consequence, T. brasiliensis has an oxygen diffusion capacity two or three times higher than that of the rodents. In Tadarida brasiliensis the characteristics of the lung were accompanied by geometrical changes in the proximal airway, such as high physical optimization as a consequence of small variations in the symmetry and the scaling ratio of the bronchial diameters. These may constitute an efficient way to save energy in respiratory mechanics and are the first report of airway adjustments to decrease entropy generation in bats.

Periodic fluctuations in the pulmonary surfactant system in Gould's wattled bat (Chalinolobus gouldii)

Pulmonary surfactant is a mixture of phospholipids, neutral lipids, and proteins that controls the surface tension of the fluid lining the lung. Surfactant amounts and composition are influenced by such physiological parameters as metabolic rate, activity, body temperature, and ventilation. Microchiropteran bats experience fluctuations in these parameters throughout their natural daily cycle of activity and torpor. The activity cycle of the microchiropteran bat Chalinolobus gouldii was studied over a 24-h period. Bats were maintained in a room at constant ambient temperature (24 degrees C) on an 8L : 16D cycle. Diurnal changes in the amount and composition of surfactant were measured at 4-h intervals throughout a 24-h period. The C. gouldii were most active at 2 a.m. and were torpid at 2 p.m. Alveolar surfactant increased 1.5-fold immediately after arousal. The proportion of disaturated phospholipid remained constant, while surfactant cholesterol levels increased 1.5-fold during torpor. Alveolar cholesterol in C. gouldii was six times lower than in other mammals. Cholesterol appears to function in maintaining surfactant fluidity during torpor in this species of bat.

A morphometric study of the lungs of different sized bats: correlations between structure and function of the chiropteran lung

1. The lungs of four species of bats, Phyllostomus hastatus (PH, mean body mass, 98 g), Pteropus lylei (PL, 456 g), Pteropus alecto (PA, 667 g), and Pteropus poliocephalus (PP, 928 g) were analysed by morphometric methods. These data increase fivefold the range of body masses for which bat lung data are available, and allow more representative allometric equations to be formulated for bats. 2. Lung volume ranged from 4.9 cm3 for PH to 39 cm3 for PP. The volume density of the lung parenchyma (i.e. the volume proportion of the parenchyma in the lung) ranged from 94% in PP to 89% in PH. Of the components of the parenchyma, the alveoli composed 89% and the blood capillaries about 5%. 3. The surface area of the alveoli exceeded that of the blood-gas (tissue) barrier and that of the capillary endothelium whereas the surface area of the red blood cells as well as that of the capillary endothelium was greater than that of the tissue barrier. PH had the thinnest tissue barrier (0.1204 microns) and PP had the thickest (0.3033 microns). 4. The body mass specific volume of the lung, that of the volume of pulmonary capillary blood, the surface area of the blood-gas (tissue) barrier, the diffusing capacity of the tissue barrier, and the total morphometric pulmonary diffusing capacity in PH all substantially exceeded the corresponding values of the pteropid species (i.e. PL, PA and PP). This conforms with the smaller body mass and hence higher unit mass oxygen consumption of PH, a feature reflected in the functionally superior gas exchange performance of its lungs. 5. Morphometrically, the lungs of different species of bats exhibit remarkable differences which cannot always be correlated with body mass, mode of flight and phylogeny. Conclusive explanations of these pulmonary structural disparities in different species of bats must await additional physiological and flight biomechanical studies. 6. While the slope, the scaling factor (b), of the allometric equation fitted to bat lung volume data (b = 0.82) exceeds the value for flight VO2max (b = 0.70), those for the surface area of the blood-gas (tissue) barrier (b = 0.74), the pulmonary capillary blood volume (b = 0.74), and the total morphometric lung diffusing capacity for oxygen (b = 0.69) all correspond closely to the VO2max value. 7. Allometric comparisons of the morphometric pulmonary parameters of bats, birds and non-flying mammals reveal that superiority of the bat lung over that of the non-flying mammal.(ABSTRACT TRUNCATED AT 400 WORDS)

Scanning and transmission electron microscopic study of the tracheal air sac system in a grasshopper Chrotogonus senegalensis (Kraus)--Orthoptera: Acrididae: Pyrgomorphinae

The morphology of the trachea-air sac system in a species of grasshopper Chrotogonus senegalensis has been studied by using scanning and transmission electron microscopes. Capacious air sacs were formed as dilatations along the primary tracheal trunks. Narrower secondary trachea arose either directly from the primary trachea that bypassed the air sacs or from the air sacs themselves. At or close to the organ or tissue supplied with air, the secondary trachea gave rise to the notably smaller tertiary trachea that penetrated the tissue, giving rise terminally to the extremely small tracheoles that indent some cells. The trachea and the air sacs were basically made up of an inner cuticular lining, helical taenidial rings, and an overlying epithelial cell cover. The air sacs may be important in efficient ventilation of the respiratory system. The supply of air directly to the tissue cells was viewed as an exemplary efficient design when compared to that prevailing in the nontracheate air-breathing animals, where the vascular system is interposed between the respiratory organ and the target tissue cells. A similarity in the general morphological design of the insect and avian respiratory systems has been observed, mainly in respect to the presence of the air sacs and that of the respiratory shunts. This, together with the reported functional features like the unidirectional mode of ventilation, has been interpreted as a classic case of structural and functional convergent evolution leading to the evolution of similar and comparably efficient respiratory systems capable of providing the large amount of oxygen demanded by flight.