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The adrenal gland and the diving response in ducks (Anas platyrhynchos)

University of British Columbia

The extreme elevation in plasma levels of norepinephrine (NE) and epinephrine (EP) which occurs during forced diving of ducks (Anas platyrhynchos) was studied before and after denervation of the adrenal glands. Elevated PaCO₂, decreased arterial pH, decreased blood glucose as well as low PaO₂ have been described as causal factors in this response. These variables, as well as blood pressure, heart rate and breathing frequency were measured in ducks dived after breathing air or pure 0₂ to clarify and quantify the mechanism involved and its physiological function. Both NE and EP concentration increased by up to 2 orders of magnitude in the 4 minute dive period, but by a significantly lesser amount if the duck breathed 0₂, before the dive. While pH and PaCO₂ were well correlated with the changes in plasma NE and EP levels during both air and 0₂ dives, both pH and PaCO₂ changed more in the 0₂ trials, indicating that they are not the primary cause of the response. Plasma glucose levels were variable. PaO₂ values less than normal correlated well with increasing NE and EP concentrations, but at high PaO₂s, there was no correlation, suggesting that hypoxia is the permissive state for the full response. Compared with breathing air, breathing O₂ before the dive attenuated the diving bradycardia, eliminated the decrease in blood pressure normally observed during dives, and caused more extreme changes in pH, PaC0₂, and of course, PaO₂. Denervating the adrenals decreased the amounts of both catecholamines released during dives after breathing air and 0₂, EP significantly more than NE. Adrenal denervation per se did not cause a significant change in heart rate, blood pressure, arterial gas tensions, pH, or plasma glucose changes during dives although the operation caused increased variation in some of the parameters. In ducks, the cause for the catecholamine release is decreasing PaO₂ and full expression of the response is dependent on intact innervation of the adrenal gland, although there is a component that is unaffected by denervation. While possible roles for this response are discussed, the true physiological function of this response remains cast in shadows.

Text

2010-05-20

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http://hdl.handle.net/2429/24857

Zoology

University of British Columbia

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