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Shunting and survival in alligators
Abstracts / Comparative Biochemistry and Physiology, Part B 126 (2000) $1-S108
F R E E - R A N G I N G O S T R I C H E S DO N O T E M P L O Y S E L E C T I V E BRAIN C O O L I N G A. Fuller 1, P.R. Kamerman 1, S.K. Maloney lg, G. Mitchell I and D. Mitchell 1 Department o f Physiology, IUniversity o f the Witwatersrand, Johannesburg, 2University o f Western Australia, Perth, Australia.
South Africa,
Birds maintain brain temperature ~ 1 °C below colonic (or eloacai) temperalaa'e at rest, and the gradient is increased during hyperthermia. A similar phenomenon is exhibited by mammals exposed to heat in a laboratory setting, and it is widely held that such brain cooling serves to protect the brain t~om thermal damage. However, in frce-ranging antelope in their natural habitat, selective brain cooling occurs only sporadicaUyand is evident during normothermia. Moreover, rather than being enhanced by physical activity, selective brain cooling is abolished during high-intensity exercise when brain temperature is highest. To date, no one has investigated the relationship between brain and core body temperatures in unrestrained birds in their natural environment. We used implanted miniature data loggers to measure brain (hypothalamie) and carotid arterial blood temperatures in three free-farting ostriches (Struthio camelus) in their natural habitat, every 5 min for one week. Measurements were made during summer and ostriches were subjected to a nychthemeral range of globe temperature o f - 30 °C (maximum 41 °(2). Arterial blood temperature exhibited a peak-to-trough amplitude of 4 °C, on average, with maximum temperatures between 09:00 and 16:00, and a trough near to 05:00. Bloodtemperatures were significantly correlated with globe (and air) temperatures (linear correlation, P < 0.0001). On average, brain temperature exceeded blood temperature by - 0.5 °C during the day, with the difference inca'easingto - 1 °C at night. Sporadic episodes of selective brain cooling occurred, but the duration and magnitude of such cooling was small, and unrelated to the environmental heat load. Unlike previous investigators who have compared brain temperature to colonic temlxxature, we compared brain temperature to the temperature of arterial blood supplying the brain. Ostriches, like mammals, maintained brain temperatures above arterial blood temperatures. However, unlike that of free-ranging antelope and zebras, carotid blood temperature was highly variable and influenced by the prevailing mieroelimate. Brain temperatures were confined within narrower limits than blood temperature, but selective brain cooling was not employed, even during hyperthermia. Our results do not support the conceptthat birds routinely employ selectivebrain cooling to survive in hot environments.
S H U N T I N G AND SURVIVAL IN A L L I G A T O R S Manuela N. Gardner and David R. Jones Department o f Zoology, University o f British Columbia
Unlike other reptiles, crocodilians have a completely divided heart, which prevents mixing o f blood within the heart. However, crocodilians have retained the ability to shunt right ventricular blood to the systemic circulation (pulmonary to systemic shunt) via the left aorta (LAo) which supplies the digestive organs. There has been some debate on the possible function o f shunting hypercapnic, hypoxie and acidic blood to the gut. We propose that during fasting, it might help to serve as a trigger to downregulate the gut. During feeding and digestion, right ventrieular blood may aid in the secretion o f the large amounts o f HCl. One group o f alligators had their LAo surgically tied off (cannot shunt) and the other group had sham surgeries performed on them (LAo intact). During fasting, serum glucose values, blood pH values and metabolic rates were similar in the two groups o f alligators, as were the rates o f weight loss. During feeding, growth rates, pH changes following feeding, plasma amino acids and chloride levels did not differ significantly. These results suggest that the ability to shunt right ventrieular blood to the digestive system during fasting and feeding is o f little consequence in captive animals.
$39
F R E E - R A N G I N G O S T R I C H E S DO N O T E M P L O Y S E L E C T I V E BRAIN C O O L I N G A. Fuller 1, P.R. Kamerman 1, S.K. Maloney lg, G. Mitchell I and D. Mitchell 1 Department o f Physiology, IUniversity o f the Witwatersrand, Johannesburg, 2University o f Western Australia, Perth, Australia.
South Africa,
Birds maintain brain temperature ~ 1 °C below colonic (or eloacai) temperalaa'e at rest, and the gradient is increased during hyperthermia. A similar phenomenon is exhibited by mammals exposed to heat in a laboratory setting, and it is widely held that such brain cooling serves to protect the brain t~om thermal damage. However, in frce-ranging antelope in their natural habitat, selective brain cooling occurs only sporadicaUyand is evident during normothermia. Moreover, rather than being enhanced by physical activity, selective brain cooling is abolished during high-intensity exercise when brain temperature is highest. To date, no one has investigated the relationship between brain and core body temperatures in unrestrained birds in their natural environment. We used implanted miniature data loggers to measure brain (hypothalamie) and carotid arterial blood temperatures in three free-farting ostriches (Struthio camelus) in their natural habitat, every 5 min for one week. Measurements were made during summer and ostriches were subjected to a nychthemeral range of globe temperature o f - 30 °C (maximum 41 °(2). Arterial blood temperature exhibited a peak-to-trough amplitude of 4 °C, on average, with maximum temperatures between 09:00 and 16:00, and a trough near to 05:00. Bloodtemperatures were significantly correlated with globe (and air) temperatures (linear correlation, P < 0.0001). On average, brain temperature exceeded blood temperature by - 0.5 °C during the day, with the difference inca'easingto - 1 °C at night. Sporadic episodes of selective brain cooling occurred, but the duration and magnitude of such cooling was small, and unrelated to the environmental heat load. Unlike previous investigators who have compared brain temperature to colonic temlxxature, we compared brain temperature to the temperature of arterial blood supplying the brain. Ostriches, like mammals, maintained brain temperatures above arterial blood temperatures. However, unlike that of free-ranging antelope and zebras, carotid blood temperature was highly variable and influenced by the prevailing mieroelimate. Brain temperatures were confined within narrower limits than blood temperature, but selective brain cooling was not employed, even during hyperthermia. Our results do not support the conceptthat birds routinely employ selectivebrain cooling to survive in hot environments.
S H U N T I N G AND SURVIVAL IN A L L I G A T O R S Manuela N. Gardner and David R. Jones Department o f Zoology, University o f British Columbia
Unlike other reptiles, crocodilians have a completely divided heart, which prevents mixing o f blood within the heart. However, crocodilians have retained the ability to shunt right ventricular blood to the systemic circulation (pulmonary to systemic shunt) via the left aorta (LAo) which supplies the digestive organs. There has been some debate on the possible function o f shunting hypercapnic, hypoxie and acidic blood to the gut. We propose that during fasting, it might help to serve as a trigger to downregulate the gut. During feeding and digestion, right ventrieular blood may aid in the secretion o f the large amounts o f HCl. One group o f alligators had their LAo surgically tied off (cannot shunt) and the other group had sham surgeries performed on them (LAo intact). During fasting, serum glucose values, blood pH values and metabolic rates were similar in the two groups o f alligators, as were the rates o f weight loss. During feeding, growth rates, pH changes following feeding, plasma amino acids and chloride levels did not differ significantly. These results suggest that the ability to shunt right ventrieular blood to the digestive system during fasting and feeding is o f little consequence in captive animals.
$39