Christopher B. Daniels

Body Temperature Alters the Lipid Composition of Pulmonary Surfactant in the Lizard Ctenophorus nuchalis

In any 24-h period the body temperature (Tb) of the central Australian agamid lizard, Ctenophorus nuchalis, may vary from 13 to 45 degrees C; the mean preferred Tb is 37 degrees C. We have analyzed surfactant-type lipids in lizards that underwent rapid changes in Tb from 37 degrees C to 14, 19, 27, or 44 degrees C. Lipids were extracted from lung lavage and lamellar body fractions, and phospholipids and cholesterol components were measured. There was no change in either the total amount or relative proportions of the different classes of phospholipids, but cooling increased the cholesterol content of lavage. An increase in the cholesterol: phospholipid ratio was evident within 2 h of cooling to 19 degrees C and was maintained for at least 48 h. The ratio increased from 8% at 37 degrees C, to 15% after 4 h at 19 degrees C, and 18% after 4 h at 14 degrees C. Possibly the increase in cholesterol promotes fluidity and absorption of surfactant within the alveoli of lizards with low Tb. Cold lizards collapse their lungs during prolonged periods of apnea and the surfactant may prevent the epithelial walls from adhering.

Pulmonary-type surfactants in the lungs of terrestrial and aquatic amphibians.

We examined the composition and function of pulmonary surfactants in amphibians inhabiting aquatic and terrestrial habitats with particular regard to the influences of (1) variations in body temperature, (2) external hydrostatic pressure and (3) breathing pattern. Two fully aquatic salamanders, and the completely terrestrial cane toad Bufo marinus (all maintained at 21-23 degrees C) were selected. Whereas one of the salamanders (Siren intermedia) possessed gills and lungs, Amphiuma tridactylum only possessed lungs. We determined the amounts of cholesterol (Chol), disaturated phospholipids (DSP) and total phospholipid (PL) in lavage of all three species, and also determined the types of phospholipids of B. marinus and A. tridactylum. DSP lowers surface tension at the air-water interface in the lung, while Chol and unsaturated phospholipids assist spreading and maintain the DSP in its disordered, liquid-crystalline state at high lung volumes. All three species had significant amounts of pulmonary-type surfactant. The two aquatic salamanders had identical ratios of both Chol/PL and DSP/PL both of which in turn were nearly twice those of B. marinus. All three species had similar Chol/DSP ratios. Aquatic salamanders sustain high external hydrostatic pressures exerted by the aquatic environment and tend to collapse their lungs during expiration. We hypothesize that these salamanders might require a DSP-rich surfactant to prevent the epithelial surfaces from adhering and large amounts of Chol to keep the DSP fluid. The terrestrial B. marinus has less DSP, suggesting a surfactant which is fluid over a large range of temperatures. Possibly, cane toads do not require a DSP rich surfactant as they neither collapse their lungs on deflation, nor experience external hydrostatic pressures promoting lung collapse. The PL profile of B. marinus lavage was similar to that of other frogs and mammals, containing phosphatidylcholine (PC) as the predominant phospholipid together with substantial amounts of phosphatidylglycerol (PG). On the other hand, although A. tridactylum exhibited high levels of PC, it contained phosphatidylinositol (PI) in place of PG, a pattern typical of reptiles and birds.

A comparison of the surfactant associated lipids derived from reptilian and mammalian lungs

The lungs of the central netted dragon Ctenophorus nuchalis are bag-like, with most of the gas exchange region located in the anterior third. Although the faveoli are much larger than the mammalian alveoli, the lizard at 37 degrees C has approximately 70 times more surfactant phospholipid per unit area of respiratory surface than does a similar sized mammal. However, when expressed as per wet lung weight, lizards and rats possessed similar amounts of phospholipids. Dipalmitoylphosphatidylcholine was the principal phospholipid in both species. However, major differences existed in the phospholipid, neutral lipid and fatty acid profiles. Whereas the lizard contained neither phosphatidylglycerol nor phosphatidylethanolamine it had more cholesterol, esterified cholesterol, acylglycerides and unsaturated fatty acids. Although the ratio of saturated:unsaturated fatty acids was similar in rats and lizards, palmitic acid predominated in the former. The composition of lizard surfactant suggests that it would adsorb rapidly at reduced body temperature.

The composition and function of the pulmonary surfactant system during metamorphosis in the tiger salamander Ambystoma tigrinum.

Mammalian lungs secrete a mixture of surface-active lipids (surfactant), which greatly reduces the surface tension of the fluid coating the inner lung surface, thereby reducing the risk of collapse upon deflation and increasing compliance upon inflation. During foetal lung maturation, these lipids become enriched in the primary and active ingredient, a disaturated phopholipid. However, disaturated phospholipids exist in their inactive gellike form at temperatures below 37°C and thus are inappropriate for controlling surface tension in the lungs of many ectotherms. We examined the development of the composition and function of the surfactant system of the tiger salamander (Ambystoma tigrinum) during metamorphosis from the fully aquatic larva (termed stage I) through an intermediate air-breathing larval form (stage IV) to the terrestrial adult (stage VII). Biochemical analysis of lung washings from these three life stages revealed a decrease in the percentage of disaturated phospholipid per total phospholipid (23.03 versus 15.92%) with lung maturity. The relative cholesterol content remained constant. The increased level of phospholipid saturation in the fully aquatic larvae may reflect their generally higher body temperature and the higher external hydrostatic compression forces exerted on the lungs, compared to the terrestrial adults. Opening pressure (pressure required for initial lung opening) prior to lavage decreased from larval to adult salamanders (7.96 versus 4.69 cm H2O), indicating a decrease in resistance to opening with lung development. Opening pressure increased after lavage in older aquatic (stage IV) larvae (5.36 versus 9.80 cm H2O) and in the adults (4.69 versus 7.65 cm H2O), indicating that the surfactant system in salamanders may have an antiglue function which prevents apposing epithelial surfaces from adhering together.

Breathing in long necked dinosaurs; did the sauropods have bird lungs?

Abstract 1. 1. The 30 tonne herbivorous sauropod dinosaur Mamenchisaurus hochuanensis had specific problems in ventilating its lungs because of the physical characteristics of its llm long trachea. 2. 2. We modelled the breathing dynamics of this animal given the choice of either a mammalian or reptilian level of metabolism coupled with either a mammalian-type bellows lung or an avian air-sac type respiratory system of “cross current” gas exchange. 3. 3. We developed a mathematical model for ventilation based on air flow in long tubes which enables the use of allometric estimations to be greatly restricted. 4. 4. The model illustrates that bellows lungs or high metabolic rates cannot be served by very long tracheas. 5. 5. The greater efficiency and less work of breathing associated with the avian lung coupled with a reptilian level of metabolism represent the most likely combination of oxygen and carbon dioxide exchange variables which could function for an animal with such a long neck and such a great body mass. 6. 6. It is possible that a reptilian level of metabolism may have provided endothermic homeothermy for the super-large sauropods because of the small surface area to volume ratio.

Physiological diving adaptations of the australian water skink Sphenomorphus quoyii

Abstract 1. 1. Both the small riparian skink Sphenomorphus quoyii and its completely terrestrial relative Ctenotus robustus respond to forced submergence with instantaneous bradycardia. 2. 2. The strength of the bradycardia was affected by water temperature and fear. Dives into hot (30°C) water produced weak and erratic bradycardia compared to dives into cold (19.5°C) water. For S. quoyii the strongest bradycardia occurred when submergence took place in water at a lower temperature than the pre-dive body temperature. 3. 3. Upon emergence both species of skink exhibited elevated heart rates and breathing rates while heating from 19.5 to 30°C, compared to heating at rest. The increased heart and breathing rates probably act to replenish depleted oxygen stores and remove any lactate. Increased heart and ventilation rates are not indicators of physiological thermoregulation in this case. 4. 4. Both lizard species exhibited higher heart rates and ventilation frequencies during heating than cooling. 5. 5. Compared to its terrestrial relative, S. quoyii does not appear to possess any major thermoregulatory, ventilatory or cardiovascular adaptations to diving. However, very small reptiles may be generally preadapted to use the water to avoid predators.

Heating and cooling rates in air and during diving of the Australian water skink, Sphenomorphus quoyii

Abstract 1. 1. Heating and cooling rates of a semiaquatic skink (Sphenomorphus quoyii) and a related terrestrial one (Ctenotus robustus) were measured in air and during diving. 2. 2. In air, all lizards cooled faster than they heated; all cooled faster in water than in air. 3. 3. Dead water skinks in air heated as rapidly as they cooled; in water dead lizards cooled at similar rates to live ones during diving. 4. 4. In air, adult S. quoyii had higher τ values when heating and cooling than did Ctenotus despite the greater surface area to volume ratio of the former. 5. 5. Juvenile S. quoyii had smaller t values than either of the other two groups. 6. 6. During diving, τ values were similar for all these groups. 7. 7. It would seem that physiological thermoregulation is ineffective in altering heat exchange in these small lizards when submerged. 8. 8. In air, cooling occurs more rapidly than predicted from body size and may be influenced physiologically.