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Control of heart rate in voluntarily diving ducks

University of British Columbia

Heart rate in response to natural and induced changes in power output as well as the autonomic nervous control of heart rate were investigated in ducks diving voluntarily. Adult lesser scaup (Aythya affinis), were trained to dive in an indoor tank to obtain food. Heart rate was monitored using telemetry, and was determined for some or all of the following phases of a dive: predive, descent, feeding, ascent and postdive. Heart rate was found to be unaffected by changes in power output during the various dive phases. Power output by the ducks during a dive was decreased when the duck's buoyancy was reduced 41% by injecting 0.10 kg mercury (Hg) into a small bag implanted in the duck's peritoneal cavity. Calculated mechanical power output during the feeding phase of the dive was reduced 61% by the addition of Hg. Heart rate was collected before the addition of Hg, with the Hg in place and after the removal of the Hg. No significant differences in diving heart rate were observed between ducks with or without Hg in the bag. However leg beat frequency during the feeding phase was significantly reduced after filling the bag, concluding that the level of power output during diving in ducks has little influence on heart rate. To study the autonomic control of heart rate, adult lesser scaup {Aythya affinis), were injected with the (3-adrenergic agonist isoproterenol (N=3), the muscarinic blocker atropine, the (3-adrenergic blocker nadolol and a combination of both atropine and nadolol (N=5). An injection of saline was used as a control treatment. The reduction in heart rate normally seen during the dive was abolished with atropine demonstrating the importance of parasympathetic control of cardiovascular changes during diving. Nadolol reduced heart rate during all phases of the dive; predive, dive and postdive, whereas after isoproterenol heart rate was increased during all phases of the dive indicating that sympathetic output to the heart does not collapse during diving. The increase in heart rate as a result of injection of isoproterenol was not as high during the dive compared with the other phases of the dive cycle. These results suggest that a partial accentuated antagonism is present in ducks so the parasympathetic system predominates in the control of heart during diving despite the maintenance of efferent sympathetic influences to the heart.

Thesis/Dissertation

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2009-04-28

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http://hdl.handle.net/2429/7634

Zoology

University of British Columbia

UBCV

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