Seven freshwater turtles Trachemys scripta were instrumented with flow probes and cannulated for blood pressure measurements. The turtles were warmed from 24 to 34°C, and cooled down to 24°C, with and without atropine. Animals exhibited a hysteresis of heart rate and blood flow to both the pulmonary and systemic circulations, which was not cholinergically mediated. Blood pressure remained constant during both warming and cooling, while systemic resistance decreased during heating and increased during cooling, indicating a barostatic response. There was a large right-to-left (R-L) shunt during warming and cooling in untreated animals, which remained relatively constant. Atropinisation resulted in a large L-R shunt, which decreased during warming and increased during cooling. Nevertheless, heating rates were the same in untreated and atropinised animals, and cooling rates were significantly longer in atropinised animals, indicating that shunt patterns contribute little to heat exchange.

No abstract

Bos indicus cattle are better adapted to tropical conditions than Bos taurus breeds and in part this may be related to differences in lipid and carbohydrate metabolism during heat stress. Bos indicus and Bos taurus cattle were subjected to heat stress and blood samples obtained to measure metabolism. Heat stress decreased feed intake and increased plasma non-esterifi ed fatty acids (NEFA) in Bos taurus but not in Bos indicus cattle. Also, Bos indicus appear to be more insulin resistant than Bos taurus cattle and this may explain some of the differences between breeds.

Exposure of the dogfish to rapidly induced hypoxia caused an initial, large reduction in heart rate to 32 % of its initial normoxic value. When of inspired water reached its lowest level, heart rate increased to 65 % of its normoxic value and this rate was maintained until was returned to normal. Bilateral section of the branchial and pharyngeal branches of either cranial nerve IX or cranial nerve X had no significant effect on the cardiac response to rapidly induced hypoxia. Bilateral section of the pharyngeal and branchial branches of both of these cranial nerves abolished the initial large reduction in heart rate in response to rapidly induced hypoxia; heart rate fell steadily to 40 % of its initial normoxic value after 3 min. Bilateral section of cranial nerves V and VII had a similar effect, with heart rate reaching 62 % of its normoxic value, 3 min after exposure to rapidly induced hypoxia. When the four cranial nerves were bilaterally sectioned together, there was no significant change in heart rate after 3 min exposure to rapidly induced hypoxia. It is concluded that the oxygen receptors responsible for the brady-cardia elicited in dogfish by environmental hypoxia are innervated by cranial nerves, V, VII, IX and X and that if receptors in the C.N.s. are involved in the response, their role is minimal.