Alterations in pulmonary surfactant after rapid arousal from torpor in the marsupial Sminthopsis crassicaudata.

Torpor in the dunnart, Sminthopsis crassicaudata, alters surfactant lipid composition and surface activity. Here we investigated changes in surfactant composition and surface activity over 1 h after rapid arousal from torpor (15-30 degrees C at 1 degrees C/min). We measured total phospholipid (PL), disaturated PL (DSP), and cholesterol (Chol) content of surfactant lavage and surface activity (measured at both 15 and 37 degrees C in the captive bubble surfactometer). Immediately after arousal, Chol decreased (from 4.1 +/- 0.05 to 2.8 +/- 0.3 mg/g dry lung) and reached warm-active levels by 60 min after arousal. The Chol/DSP and Chol/PL ratios both decreased to warm-active levels 5 min after arousal because PL, DSP, and the DSP/PL ratio remained elevated over the 60 min after arousal. Minimal surface tension and film compressibility at 17 mN/m at 37 degrees C both decreased 5 min after arousal, correlating with rapid changes in surfactant Chol. Therefore, changes in lipids matched changes in surface activity during the postarousal period.     

The effect of temperature on adrenergic receptors of alveolar type II cells of a heterothermic marsupial

Fat-tailed dunnarts, Sminthopsis crassicaudata, survive dramatic changes in body temperature during torpor without experiencing surfactant dysfunction. Adrenergic factors regulate surfactant secretion through beta(2)-adrenergic receptors on alveolar type II cells. Temperature has no effect on the secretory response of dunnart type II cells to adrenergic stimulation. We hypothesise that during torpor, dunnart type II cells up-regulate the number of adrenergic receptors present on type II cells to enable stimulation at lower concentrations of agonist. Here, we isolated type II cells from warm-active (35 degrees C) and torpid (15 degrees C) dunnarts and examined the effects of an in vitro temperature change on the number and activity of adrenergic receptors. Torpor did not affect the beta-adrenergic receptor number. However, we observed a significant decrease in adrenergic receptor number when cells from warm-active animals were incubated at 15 degrees C and when cells from torpid animals were incubated at 37 degrees C. cAMP production was significantly higher in type II cells from torpid dunnarts than warm-active dunnarts and this may contribute, in part, to the temperature insensitivity we have previously observed in the adrenergic regulation of surfactant secretion.     

The roles of cholesterol in pulmonary surfactant: insights from comparative and evolutionary studies

In most eutherian mammals, cholesterol (Chol) comprises approximately 8-10 wt.% or 14-20 mol.% of both alveolar and lamellar body surfactant. It is regarded as an integral component of pulmonary surfactant, yet few studies have concentrated on its function or control. Throughout the evolution of the vertebrates, the contribution of cholesterol relative to surfactant phospholipids decreases, while that of the disaturated phospholipids (DSP) increases. Chol generally appears to dominate in animals with primitive bag-like lungs that lack septation, in the saccular lung of snakes or swimbladders which are not used predominantly for respiration, and also in immature lungs. It is possible that in these systems, cholesterol represents a protosurfactant. Cholesterol is controlled separately from the phospholipid (PL) component in surfactant. For example, in heterothermic mammals such as the fat-tailed dunnart, Sminthopsis crassicaudata, and the microchiropteran bat, Chalinolobus gouldii, and also in the lizard, Ctenophorus nuchalis, the relative amount of Chol increases in cold animals. During the late stages of embryonic development in chickens and lizards, the Chol to PL and Chol to DSP ratios decrease dramatically. While in isolated lizard lungs, adrenaline and acetylcholine stimulate the secretion of surfactant PL, Chol secretion remains unaffected. This is also supported in isolated cell studies of lizards and dunnarts. The rapid changes in the Chol to PL ratio in response to various physiological stimuli suggest that these two components have different turnover rates and may be packaged and processed differently. Infusion of [3H]cholesterol into the rat tail vein resulted in a large increase in Chol specific activity within 30 min in the lamellar body (LB) fraction, but over a 48-h period, failed to appear in the alveolar surfactant fraction. Analysis of the limiting membrane of the lamellar bodies revealed a high (76%) concentration of LB cholesterol. The majority of lamellar body Chol is, therefore, not released into the alveolar compartment, as the limiting membrane fuses with the cell membrane upon exocytosis. It appears unlikely, therefore, that lamellar bodies are the major source of alveolar Chol. It is possible that the majority of alveolar Chol is synthesised endogenously within the lung and stored independently from surfactant phospholipids. The role of cholesterol in the limiting membrane of the lamellar body may be to enable fast and easy processing by maintaining the membrane in a relatively fluid state.     

Torpor-associated fluctuations in surfactant activity in Gould's wattled bat

The primary function of pulmonary surfactant is to reduce the surface tension (ST) created at the air-liquid interface in the lung. Surfactant is a complex mixture of lipids and proteins and its function is influenced by physiological parameters such as metabolic rate, body temperature and breathing. In the microchiropteran bat Chalinolobus gouldii these parameters fluctuate throughout a 24 h period. Here we examine the surface activity of surfactant from warm-active and torpid bats at both 24 degrees C and 37 degrees C to establish whether alterations in surfactant composition correlate with changes in surface activity. Bats were housed in a specially constructed bat room at Adelaide University, at 24 degrees C and on a 8:16 h light:dark cycle. Surfactant was collected from bats sampled during torpor (2535 degrees C). Alterations in the lipid composition of surfactant occur with changes in the activity cycle. Most notable is an increase in surfactant cholesterol (Chol) with decreases in body temperature [Codd et al., Physiol. Biochem. Zool. 73 (2000) 605-612]. Surfactant from active bats was more surface active at higher temperatures, indicated by lower ST(min) and less film area compression required to reach ST(min) at 37 degrees C than at 24 degrees C. Conversely, surfactant from torpid bats was more active at lower temperatures, indicated by lower ST(min) and less area compression required to reach ST(min) at 24 degrees C than at 37 degrees C. Alterations in the Chol content of bat surfactant appear to be crucial to allow it to achieve low STs during torpor.     

Development of the pulmonary surfactant system in two oviparous vertebrates

In birds and oviparous reptiles, hatching is often a lengthy and exhausting process, which commences with pipping followed by lung clearance and pulmonary ventilation. We examined the composition of pulmonary surfactant in the developing lungs of the chicken, Gallus gallus, and of the bearded dragon, Pogona vitticeps. Lung tissue was collected from chicken embryos at days 14, 16, 18 (prepipped), and 20 (postpipped) of incubation and from 1 day and 3 wk posthatch and adult animals. In chickens, surfactant protein A mRNA was detected using Northern blot analysis in lung tissue at all stages sampled, appearing relatively earlier in development compared with placental mammals. Chickens were lavaged at days 16, 18, and 20 of incubation and 1 day posthatch, whereas bearded dragons were lavaged at day 55, days 57-60 (postpipped), and days 58-61 (posthatched). In both species, total phospholipid (PL) from the lavage increased throughout incubation. Disaturated PL (DSP) was not measurable before 16 days of incubation in the chick embryo nor before 55 days in bearded dragons. However, the percentage of DSP/PL increased markedly throughout late development in both species. Because cholesterol (Chol) remained unchanged, the Chol/PL and Chol/DSP ratios decreased in both species. Thus the Chol and PL components are differentially regulated. The lizard surfactant system develops and matures over a relatively shorter time than that of birds and mammals. This probably reflects the highly precocial nature of hatchling reptiles.     

Torpor-associated fluctuations in surfactant activity in Gould’s wattled bat

The primary function of pulmonary surfactant is to reduce the surface tension (ST) created at the air–liquid interface in the lung. Surfactant is a complex mixture of lipids and proteins and its function is influenced by physiological parameters such as metabolic rate, body temperature and breathing. In the microchiropteran bat Chalinolobus gouldii these parameters fluctuate throughout a 24 h period. Here we examine the surface activity of surfactant from warm–active and torpid bats at both 24°C and 37°C to establish whether alterations in surfactant composition correlate with changes in surface activity. Bats were housed in a specially constructed bat room at Adelaide University, at 24°C and on a 8:16 h light:dark cycle. Surfactant was collected from bats sampled during torpor (25<T_b<28°C), and while active (T_b>35°C). Alterations in the lipid composition of surfactant occur with changes in the activity cycle. Most notable is an increase in surfactant cholesterol (Chol) with decreases in body temperature [Codd et al., Physiol. Biochem. Zool. 73 (2000) 605–612]. Surfactant from active bats was more surface active at higher temperatures, indicated by lower ST_min and less film area compression required to reach ST_min at 37°C than at 24°C. Conversely, surfactant from torpid bats was more active at lower temperatures, indicated by lower ST_min and less area compression required to reach ST_min at 24°C than at 37°C. Alterations in the Chol content of bat surfactant appear to be crucial to allow it to achieve low STs during torpor.     

A comparison of the molecular species compositions of mammalian lung surfactant phospholipids

While dipalmitoyl phosphatidylcholine (PC16:0/16:0) is essential for pulmonary surfactant function, roles for other individual molecular species of surfactant phospholipids have not been established. If any phospholipid species other than PC16:0/16:0 is important for surfactant function, then it may be conserved across animal species. Consequently, we have quantified, by electrospray ionisation mass spectrometry, molecular species compositions of phosphatidylcholine (PC), phosphatidylglycerol (PG) and phosphatidylinositol (PI) in surfactants from human, rabbit, rat and guinea pig lungs. While PC compositions displayed only relatively minor variations across the animal species studied, there were wide variations of PG and PI concentrations and compositions. Human surfactant PG and PI were enriched in the same three monounsaturated species (PG16:0/18:1, PG18:1/18:1 and PG18:0/18:1) with minimal amounts of PG16:0/16:0 or polyunsaturated species, while all animal surfactant PG contained increased concentrations of PG16:0/16:0 and PG16:0/18:2. Animal surfactant PIs were essentially monounsaturated except for a high content of PI18:0/20:4 (29%) in the rat. As these four surfactants all maintain appropriate lung function of the respective animal species, then all their varied compositions of acidic phospholipids must be adequate at promoting the processes of adsorption, film refinement, respreading and collapse characteristic of surfactant. We conclude that this effectively monounsaturated composition of anionic phospholipid molecular species is a common characteristic of mammalian surfactants.     

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.     

Ontogeny of the pulmonary surfactant and antioxidant enzyme systems in the viviparous lizard,Tiliqua rugosa

The antioxidant enzyme (AOE) system protects the lung from oxidative damage. The pulmonary surfactant (PS) system lowers the interfacial pressure within the lung, improving lung compliance and aiding lung clearance. In mammals, the AOE and PS systems develop in tandem during the final 10%-20% of gestation. Here, we investigated the development of these systems in the viviparous skink, Tiliqua rugosa. The content of total phospholipid (PL), disaturated phospholipid (DSP), and cholesterol (Chol) increased in lung washings from foetal lizards with advancing gestational age. Similarly, the relative saturation of the PLs increased throughout gestation, with mid-stage 40 foetuses having a DSP/PL equivalent to newborns and adults. Maternal lizards had significantly less total PL, DSP, and Chol than nongravid and newborn lizards; however, the relative composition did not differ from nongravid animals. This presumably results from compression of the lungs under the bulk of the developing foetus. The Chol/PL and Chol/DSP ratios declined early in development such that mid-stage 40 embryos had comparable ratios to both newborns and adults. Thus, it appears that the PS system matures in a similar manner in skinks and in mammals. However, the composition of surfactant is complete some weeks before parturition, probably to enable improved survivorship of the precocial young in the event of premature birth. Unlike the surfactant lipids, the AOEs, catalase, superoxide dismutase, and glutathione peroxidase did not differ appreciably throughout gestation. It appears therefore that like the surfactant lipids the AOE system is in readiness for air breathing throughout the latter stages of gestation, possibly in preparation for premature birth. Unlike mammals, the PS and AOE systems develop independently from one another.     

Eustachian tube surfactant is different from alveolar surfactant: determination of phospholipid composition of porcine eustachian tube lavage fluid.

Phosphatidylcholine (PC) is the main phospholipid in lung surfactant and, more specifically, dipalmitoyl PC (PC16:0/16:0) is the major surface-active component. Several studies have tentatively shown that eustachian tube lavage fluid (ETLF) contains surface-active material. The aim of the present study was to determine, using electrospray ionization mass spectrometry, whether the phospholipid molecular species composition of ETLF is similar to that of lung surfactant. PC was the main component of both ETLF and bronchoalveolar lavage fluid (BALF). The concentration of phosphatidylethanolamine was higher and phosphatidylglycerol was undetectable in ETLF compared with BALF. The molecular species composition of PC in ETLF was notably different from that of BALF, palmitoyloleoyl PC being the major component. Importantly, given its predominance in BALF PC, the concentration of PC16:0/16:0 was low in ETLF. As expected on the basis of this molecular species composition of PC, ETLF did not generate low surface tension values under dynamic compression in a pulsating bubble surfactometer.We conclude that the surfactant in ET is different from lung surfactant, and that low surface tension is not a major determinant of ETLF function.     

Alterations in surface activity of pulmonary surfactant in Gould's wattled bat during rapid arousal from torpor

The small microchiropteran bat, Chalinolobus gouldii, undergoes large daily fluctuations in metabolic rate, body temperature, and breathing pattern. These alterations are accompanied by changes in surfactant composition, predominantly an increase in cholesterol relative to phospholipid during torpor. Furthermore, the surface activity changes, such that the surfactant functions most effectively at that temperature which matches the animal's activity state. Here, we examine the surface activity of surfactant from bats during arousal from torpor. Bats were housed at 24 degrees C on an 8:16h light:dark cycle and their surfactant was collected during arousal (28相似文献   

Phospholipid molecular species of bronchoalveolar lavage fluid after local allergen challenge in asthma

Electrospray ionization mass spectrometry was used to quantify phosphatidylcholine (PC) and phosphatidylglycerol (PG) molecular species in bronchoalveolar lavage fluid (BALF) from control and mild asthmatic subjects after local allergen challenge. BALF was obtained from 5 control and 13 asthmatic subjects before and 24 h after segmental allergen and saline challenge. There were no differences in the ratio of total PC to total PG or in the molecular species composition of PC or PG between the asthmatic and control groups under basal conditions. Allergen challenge in asthmatic but not in control volunteers caused a significant increase in the PC-to-PG ratio because of increased concentrations of PC species containing linoleic acid (16:0/18:2 PC, 18:0/18:2 PC, and 18:1/18:2 PC). These molecular species were characteristic of plasma PC analyzed from the same subjects, strongly suggesting that the altered PC composition in BALF in asthmatic subjects after allergen challenge was due to infiltration of plasma lipoprotein, not to catabolism of surfactant phospholipid. Interactions between surfactant and lipoprotein infiltrate may contribute to surfactant dysfunction and potentiate disease severity in asthma.     

Lipidomics of cellular and secreted phospholipids from differentiated human fetal type II alveolar epithelial cells

Maturation of fetal alveolar type II epithelial cells in utero is characterized by specific changes to lung surfactant phospholipids. Here, we quantified the effects of hormonal differentiation in vitro on the molecular specificity of cellular and secreted phospholipids from human fetal type II epithelial cells using electrospray ionization mass spectrometry. Differentiation, assessed by morphology and changes in gene expression, was accompanied by restricted and specific modifications to cell phospholipids, principally enrichments of shorter chain species of phosphatidylcholine (PC) and phosphatidylinositol, that were not observed in fetal lung fibroblasts. Treatment of differentiated epithelial cells with secretagogues stimulated the secretion of functional surfactant-containing surfactant proteins B and C (SP-B and SP-C). Secreted material was further enriched in this same set of phospholipid species but was characterized by increased contents of short-chain monounsaturated and disaturated species other than dipalmitoyl PC (PC16:0/16:0), principally palmitoylmyristoyl PC (PC16:0/14:0) and palmitoylpalmitoleoyl PC (PC16:0/16:1). Mixtures of these PC molecular species, phosphatidylglycerol, and SP-B and SP-C were functionally active and rapidly generated low surface tension on compression in a pulsating bubble surfactometer. These results suggest that hormonally differentiated human fetal type II cells do not select the molecular composition of surfactant phospholipid on the basis of saturation but, more likely, on the basis of acyl chain length.     

The energetics of basking behaviour and torpor in a small marsupial exposed to simulated natural conditions

Limited information is available on basking behaviour in torpid mammals and its energetic consequences. We investigated the effects of physiological and behavioural strategies on the energetics of the fat-tailed dunnart (Sminthopsis crassicaudata). Metabolic rate and body temperature during torpor, basking and rest were measured over 24 h in response to simulated environmental conditions: (a) constant ambient temperature (T _a) of 15°C, (b) constant T _a of 15°C with access to a radiant heat lamp, (c) a T _a cycle (range 15–31°C), and (d) a T _a cycle with access to a radiant heat lamp. When a radiant heat source was provided, all dunnarts (n = 16) basked during all measurements, which resulted in energy savings of up to 74% during rest. Overall, torpor was used on 59% of measurements with a maximum duration of 16.2 h and reductions in metabolic rate of 90% compared to normothermic values. Torpid dunnarts actively moved from a shaded area to position themselves under the heat lamp with body temperatures as low as 17.5°C and thereby reduced rewarming costs by 66%. We demonstrated, for the first time in the laboratory, that torpid animals actively move to a heat source to bask, and that this behaviour results in considerable energy savings. Our finding supports the view that basking during normothermia and rewarming from torpor substantially reduces energetic requirements, which may be important for the survival of small dasyurids living on limited resources in the Australian arid zone.     

Control of pulmonary surfactant secretion: an evolutionary perspective

Pulmonary surfactant, a mixture consisting of phospholipids (PL) and proteins, is secreted by type II cells in the lungs of all air-breathing vertebrates. Virtually nothing is known about the factors that control the secretion of pulmonary surfactant in nonmammalian vertebrates. With the use of type II cell cultures from Australian lungfish, North American bullfrogs, and fat-tailed dunnarts, we describe the autonomic regulation of surfactant secretion among the vertebrates. ACh, but not epinephrine (Epi), stimulated total PL and disaturated PL (DSP) secretion from type II cells isolated from Australian lungfish. Both Epi and ACh stimulated PL and DSP secretion from type II cells of bullfrogs and fat-tailed dunnarts. Neither Epi nor ACh affected the secretion of cholesterol from type II cell cultures of bullfrogs or dunnarts. Pulmonary surfactant secretion may be predominantly controlled by the autonomic nervous system in nonmammalian vertebrates. The parasympathetic nervous system may predominate at lower body temperatures, stimulating surfactant secretion without elevating metabolic rate. Adrenergic influences on the surfactant system may have developed subsequent to the radiation of the tetrapods. Furthermore, ventilatory influences on the surfactant system may have arisen at the time of the evolution of the mammalian bronchoalveolar lung. Further studies using other carefully chosen species from each of the vertebrate groups are required to confirm this hypothesis.     

Hypoxic control of the development of the surfactant system in the chicken: evidence for physiological heterokairy

The surfactant system, a complex mixture of lipids and proteins, controls surface tension in the lung and is crucial for the first breath at birth, and thereafter. Heterokairy is defined as plasticity of a developmental process within an individual. Here, we provide experimental evidence for the concept of heterokairy, as hypoxia induces a change in the onset and rate of development of surfactant, probably via endogenous glucocorticoids, to produce individuals capable of surviving early hatching. Chicken eggs were incubated under normoxic (21% O(2)) conditions throughout or under hypoxic (17% O(2)) conditions from day 10 of incubation. Embryos were sampled at days 16, 18, and 20 and also 24 h after hatching. In a second experiment, dexamethasone (Dex), tri-iodothyronine (T(3)), or a combination (Dex + T(3)) was administered 24 and 48 h before each time point. Both hypoxia and Dex accelerated maturation of the surfactant lipids by increasing total phospholipid (PL), disaturated phospholipid (DSP), and cholesterol (Chol) in lavage at days 16 and 18. Maturation of surfactant lipid composition was accelerated, with day 16 %DSP/PL, Chol/DSP, and Chol/PL resembling the ratios of day 20 control animals. The effect of Dex + T(3) was similar to that of Dex alone. Hypoxia increased plasma corticosterone levels at day 16, while plasma T(3) levels were not affected. Hence, exposure to hypoxia during critical developmental windows accelerates surfactant maturation, probably by increasing corticosterone production. This internal modulation of the developmental response to an external stimulus is a demonstration of physiological heterokairy.     

Hibernation and torpor in tropical and subtropical bats in relation to energetics, extinctions, and the evolution of endothermy

Torpor, the most effective means of energy conservation available to endotherms, is still widely viewed as a specific adaptation in a few high-latitude, cold-climate endotherms with no adaptive function in warm regions. Nevertheless, a growing number of diverse terrestrial mammals and birds from low latitudes (0-30°), including species from tropical and subtropical regions, are heterothermic and employ torpor. Use of torpor is especially important for bats because they are small, expend large amounts of energy when active, rely on a fluctuating food supply, and have only a limited capacity for storage of fat. Patterns of torpor in tropical/subtropical bats are highly variable, but short bouts of torpor with relatively high body temperatures (T(b)) are most common. Hibernation (a sequence of multiday bouts of torpor) has been reported for free-ranging subtropical tree-dwelling vespertilionids, cave-dwelling hipposiderids, and house-dwelling molossids. The observed range of minimum T(b) is ～6-30 °C, and the reduction of energy expenditure through the use of torpor, in comparison to normothermic values, ranges from 50 to 99%. Overall, torpor in the tropics/subtropics has been reported for 10 out of the currently recognized 18 bat families, which contain 1079 species, or 96.7% of all bats. Although it is unlikely that all of these are heterothermic, the large majority probably will be. Frequent use of torpor, including hibernation in diverse groups of tropical/subtropical bats, suggests that heterothermy is an ancestral chiropteran trait. Although data especially from the field are still scarce, it is likely that torpor, highly effective in reducing requirements for energy and water even under warm conditions, plays a crucial role in the long-term survival of the majority of small tropical and subtropical bats. Discovering how bats achieve this provides numerous opportunities for exiting new research.     

Increased palmitoyl-myristoyl-phosphatidylcholine in neonatal rat surfactant is lung specific and correlates with oral myristic acid supply

Surfactant predominantly comprises phosphatidylcholine (PC) species, together with phosphatidylglycerols, phosphatidylinositols, neutral lipids, and surfactant proteins-A to -D. Together, dipalmitoyl-PC (PC16:0/16:0), palmitoyl-myristoyl-PC (PC16:0/14:0), and palmitoyl-palmitoleoyl-PC (PC16:0/16:1) make up 75-80% of mammalian surfactant PC, the proportions of which vary during development and in chronic lung diseases. PC16:0/14:0, which exerts specific effects on macrophage differentiation in vitro, increases in surfactant during alveolarization (at the expense of PC16:0/16:0), a prenatal event in humans but postnatal in rats. The mechanisms responsible and the significance of this reversible increase are, however, not understood. We hypothesized that, in rats, myristic acid (C14:0) enriched milk is key to lung-specific PC16:0/14:0 increases in surfactant. We found that surfactant PC16:0/14:0 in suckling rats correlates with C14:0 concentration in plasma chylomicrons and lung tissue triglycerides, and that PC16:0/14:0 fractions reflect exogenous C14:0 supply. Significantly, C14:0 was increased neither in plasma PC, nor in liver triglycerides, free fatty acids, or PC. Lauric acid was also abundant in triglycerides, but was not incorporated into surfactant PC. Comparing a C14:0-rich milk diet with a C14:0-poor carbohydrate diet revealed increased C14:0 and decreased C16:0 in plasma and lung triglycerides, respectively. PC16:0/14:0 enrichment at the expense of PC16:0/16:0 did not impair surfactant surface tension function. However, the PC profile of the alveolar macrophages from the milk-fed animals changed from PC16:0/16:0 rich to PC16:0/14:0 rich. This was accompanied by reduced reactive oxygen species production. We propose that nutritional supply with C14:0 and its lung-specific enrichment may contribute to decreased reactive oxygen species production during alveolarization.     

Development of the pulmonary surfactant system in non-mammalian amniotes

Pulmonary surfactant (PS) is a complex mixture of phospholipids, neutral lipids and proteins that lines the inner surface of the lung. Here, it modulates surface tension thereby increasing lung compliance and preventing the transudation of fluid. In mammals, the PS system develops towards the end of gestation, characterized by an increase in the saturation of phospholipids in lung washings and the appearance of surfactant proteins in amniotic fluid. Birth, the transition from in utero to the external environment, is a rapid process. At this time, the PS system is important in opening and clearing the lung of fluid in order to initiate pulmonary ventilation. In oviparous vertebrates, escape from an egg can be a long and exhausting process. The young commence pulmonary ventilation and hatching by 'pipping' through the eggshell, where they remain for some time, presumably clearing their lungs. This paper relates changes in the development of the pulmonary surfactant system within the non-mammalian amniotes in response to birth strategy, lung morphology and phylogeny in order to determine the conservatism of this developmental process. Total phospholipid (PL), disaturated phospholipid (DSP) and cholesterol (Chol) were quantified from lung washings of embryonic and hatchling chickens, bearded dragons (oviparous), sleepy lizards (viviparous), snapping turtles and green sea turtles throughout the final stages of incubation and gestation. In all cases, the pattern of development of the pulmonary surfactant lipids was consistent with that of mammals. PL and DSP increased throughout the latter stages of development and Chol was differentially regulated from the PLs. Maximal secretion of both PL and DSP occurred at 'pipping' in oviparous reptiles, coincident with the onset of airbreathing. Similarly, the amount of DSP relative to total PL was maximal immediately after the initiation of airbreathing in chickens. The relative timing of the appearance of the lipids differed between groups. In the oviparous lizard, surfactant lipids were released over a relatively shorter time than that of the sleepy lizard, turtles, birds and mammals. Thus, despite temporal differences and vastly different lung morphologies, birth strategies and phylogenies, the overall development and maturation of the PS system is highly conserved amongst the amniotes.     

Concurrent reductions in blood pressure and metabolic rate during fasting in the unrestrained SHR

Arctic ground squirrels (Spermophilus parryii) overwinter in hibernaculum conditions that are substantially below freezing. During torpor, captive arctic ground squirrels displayed ambient temperature (T(a))-dependent patterns of core body temperature (T(b)), metabolic rate (TMR), and metabolic fuel use, as determined by respiratory quotient (RQ). At T(a) 0 to -16 degrees C, T(b) remained relatively constant, and TMR rose proportionally with the expanding gradient between T(b) and T(a), increasing >15-fold from a minimum of 0.0115 +/- 0.0012 ml O(2). g(-1). h(-1). At T(a) 0-20 degrees C, T(b) increased with T(a); however, TMR did not change significantly from T(b) 0 to 12 degrees C, indicating temperature-independent inhibition of metabolic rate. The overall change in TMR from T(b) 4 to 20 degrees equates to a Q(10) of 2.4, but within this range of T(b), Q(10) changed from 1.0 to 14.1. During steady-state torpor at T(a) 4 and 8 degrees C, RQ averaged 0.70 +/- 0.013, indicating exclusive lipid catabolism. At T(a) -16 and 20 degrees C, RQ increased significantly to >0.85, consistent with recruitment of nonlipid fuels. RQ was negatively correlated with maximum torpor bout length. For T(a) values <0 degrees C, this relationship supports the hypothesis that availability of nonlipid metabolic fuels limits torpor duration in hibernating mammals; for T(a) values >0 degrees C, hypotheses linked to body temperature are supported. Because anterior body temperatures differ from core, overall, the duration torpor can be extended in hibernating mammals may be dependent on brain temperature.