- Email: [email protected]
An ecological perspective on avian nectarivory
Abstracts / Comparative Biochemistry and Physiology, Part B 126 (2000) S1-S108
SURFACTANT IN THE TUBULAR BIRD LUNG IN COMPARISON TO THE ALVEOLAR MAMMALIAN LUNG - SIMILARITIES AND DISSIMILARITIES W. Bernhard l, G. Rau 1, A. Gebert2, J. Hohlfeld3, A. D. Postle4, J. Freilaorst 1 Departments of Pediatric Pulmonologyt, Applied Anatomy2 and Pulmonology3, Hannover Medical School, Hannover, Germany - Child Health4, University of Southampton, Southampton, UK Background and aims: Surfactant in the mammalian lung possibly stabilizes small airways, in addition to preventing alveolar collapse at end-expiration. Compared with lung lavage surfactant, however, surfactant isolated from conductive airways cannot generate low minimal surface tension values (<5 mN/m) on surface area compression and contains lower amounts of surfactant proteins B and C, but has the same composition of phospholipid molecular species ~. As the lungs of birds are tubular rather than alveolar, avian surfactant is a good prototype of a material primarily designed to stabilize tubules instead of alveoli. We therefore investigated functional and biochemical parameters of avian ('tubular') surfactant in comparison to mammalian ('alveolar') surfactant. Methods: Surfaetant from chicken, duck and pig lungs was isolated by lavage. Static and dynamic surface tension functions were investigated using a pulsating bubble surfactometer (PBS) and a capillary surfactometer (CS). Surfaetant morphology was assessed by transmission electron microscopy. Molecular species of phosphatidylcholine (PC) and other phospholipids were measured by HPLC and ESIMS. Surfactant proteins SP-B and SP-C were determined by gel-filtration-HPLC. Results: Granular pneumocytes were present in the atrial walls leading to the air tubules of avian lungs. From there secreted surfaetant spreads into the air tubules and forms a (monomolecular) layer. Maximal surface tension of bird surfactant, measured in the PBS, was lower than that of porcine surfactant, but bird surfactant could not reach comparable minimal surface tension values. For instance, porcine surfactant easily generated values below 5 mN/m within 5 cycles at all concentrations, frequencies and temperatures tested. However, the avian and porcine surfactants demonstrated identical abilities to keep open the small tubule of the CS. These results suggest that avian surfactant has a more rapid adsorption, and a comparable ability to keep open tubular structures compared with porcine surfactant. Avian surfactant was enriched in dipalmitoyl-PC (PC16:0/16:0) compared with porcine surfactant, but contained less palmitoylmyristoyl-PC (PC16:0/14:0) and palmitoylpalmitoleoyl-PC (PC16:0/16:I). Avian surfactant contained considerably less PG and no measurable SP-C. Conclusion: Surfactant from avian lungs is inferior to mammalian surfactant with respect to minimal surface tension. However, it is superior with respect to adsorption and equally potent at stabilising airways. Avian surfactant is decreased in some biochemical components characteristic of mammalian surfactant, notably PC16:0/14:0, PC 16:0/16:1, PG and SP-C. These differences are in part consistant with parameters of conductive airway surfactantfrom pigs ~. 1: Bernhard, W. et al (1997) Am. J. Respir. Cell Mol. Biol. 17:41-50.
An ecological perspective on avian nectarivory Carol A. Beuchat Dept. of Physiology, University of Arizona, USA; and Dept. of Zoology, University of Cape Town, South Africa From an osmoregulatory point of view, it would seem that a common problem faced by avian nectarivores would be maintaining energy and electrolyte balance in the face of rates of water excretion that can be extreme. In fact, however, the magnitude of the challenge should wary with body size. To support metabolic requirements on nectar alone, consumption must scale in proportion to metabolism, with a slope (b) of about 0.75. For nectar of a given concentration, intake of water incidental to nectar consumption will thus scale as b = 0.75 as well. Total evaporative water loss scales in birds as b = 0.67. The consequence of these relationships is that larger birds must consume relatively less nectar, but their loss of water by evaporation will also be relatively less, with the result that a greater proportion of ingested water must be lost by way of the kidney. That is, the relative magnitude of the water load that must be managed by the kidney should increase with body size. However, solute reabsorption by the kidney, which is necessary for urinary dilution, should depend fundamentally on the rate of ATP production, so it should also scale as metabolism does, with b = 0.75. Consequently, large animals should have relatively lower solute transport capacity than small ones. So, with increasing body size, it should be increasingly more difficult to produce a dilute urine by salvaging electrolytes and other solutes from the renal filtrate before excretion. Because a greater fraction of the total water flux is leaving larger animals via the kidney, excretory solute loss will be greater as well. Taken together, these scaling relationships suggest that coping with the 9smoregulatory challenges associated with nectarivory is more difficult for animals of larger body size; that is, nectarivory should favor the evolution of small body size.
S 11
SURFACTANT IN THE TUBULAR BIRD LUNG IN COMPARISON TO THE ALVEOLAR MAMMALIAN LUNG - SIMILARITIES AND DISSIMILARITIES W. Bernhard l, G. Rau 1, A. Gebert2, J. Hohlfeld3, A. D. Postle4, J. Freilaorst 1 Departments of Pediatric Pulmonologyt, Applied Anatomy2 and Pulmonology3, Hannover Medical School, Hannover, Germany - Child Health4, University of Southampton, Southampton, UK Background and aims: Surfactant in the mammalian lung possibly stabilizes small airways, in addition to preventing alveolar collapse at end-expiration. Compared with lung lavage surfactant, however, surfactant isolated from conductive airways cannot generate low minimal surface tension values (<5 mN/m) on surface area compression and contains lower amounts of surfactant proteins B and C, but has the same composition of phospholipid molecular species ~. As the lungs of birds are tubular rather than alveolar, avian surfactant is a good prototype of a material primarily designed to stabilize tubules instead of alveoli. We therefore investigated functional and biochemical parameters of avian ('tubular') surfactant in comparison to mammalian ('alveolar') surfactant. Methods: Surfaetant from chicken, duck and pig lungs was isolated by lavage. Static and dynamic surface tension functions were investigated using a pulsating bubble surfactometer (PBS) and a capillary surfactometer (CS). Surfaetant morphology was assessed by transmission electron microscopy. Molecular species of phosphatidylcholine (PC) and other phospholipids were measured by HPLC and ESIMS. Surfactant proteins SP-B and SP-C were determined by gel-filtration-HPLC. Results: Granular pneumocytes were present in the atrial walls leading to the air tubules of avian lungs. From there secreted surfaetant spreads into the air tubules and forms a (monomolecular) layer. Maximal surface tension of bird surfactant, measured in the PBS, was lower than that of porcine surfactant, but bird surfactant could not reach comparable minimal surface tension values. For instance, porcine surfactant easily generated values below 5 mN/m within 5 cycles at all concentrations, frequencies and temperatures tested. However, the avian and porcine surfactants demonstrated identical abilities to keep open the small tubule of the CS. These results suggest that avian surfactant has a more rapid adsorption, and a comparable ability to keep open tubular structures compared with porcine surfactant. Avian surfactant was enriched in dipalmitoyl-PC (PC16:0/16:0) compared with porcine surfactant, but contained less palmitoylmyristoyl-PC (PC16:0/14:0) and palmitoylpalmitoleoyl-PC (PC16:0/16:I). Avian surfactant contained considerably less PG and no measurable SP-C. Conclusion: Surfactant from avian lungs is inferior to mammalian surfactant with respect to minimal surface tension. However, it is superior with respect to adsorption and equally potent at stabilising airways. Avian surfactant is decreased in some biochemical components characteristic of mammalian surfactant, notably PC16:0/14:0, PC 16:0/16:1, PG and SP-C. These differences are in part consistant with parameters of conductive airway surfactantfrom pigs ~. 1: Bernhard, W. et al (1997) Am. J. Respir. Cell Mol. Biol. 17:41-50.
An ecological perspective on avian nectarivory Carol A. Beuchat Dept. of Physiology, University of Arizona, USA; and Dept. of Zoology, University of Cape Town, South Africa From an osmoregulatory point of view, it would seem that a common problem faced by avian nectarivores would be maintaining energy and electrolyte balance in the face of rates of water excretion that can be extreme. In fact, however, the magnitude of the challenge should wary with body size. To support metabolic requirements on nectar alone, consumption must scale in proportion to metabolism, with a slope (b) of about 0.75. For nectar of a given concentration, intake of water incidental to nectar consumption will thus scale as b = 0.75 as well. Total evaporative water loss scales in birds as b = 0.67. The consequence of these relationships is that larger birds must consume relatively less nectar, but their loss of water by evaporation will also be relatively less, with the result that a greater proportion of ingested water must be lost by way of the kidney. That is, the relative magnitude of the water load that must be managed by the kidney should increase with body size. However, solute reabsorption by the kidney, which is necessary for urinary dilution, should depend fundamentally on the rate of ATP production, so it should also scale as metabolism does, with b = 0.75. Consequently, large animals should have relatively lower solute transport capacity than small ones. So, with increasing body size, it should be increasingly more difficult to produce a dilute urine by salvaging electrolytes and other solutes from the renal filtrate before excretion. Because a greater fraction of the total water flux is leaving larger animals via the kidney, excretory solute loss will be greater as well. Taken together, these scaling relationships suggest that coping with the 9smoregulatory challenges associated with nectarivory is more difficult for animals of larger body size; that is, nectarivory should favor the evolution of small body size.
S 11