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Pharmacological blockade of the dive response: effects on heart rate and diving behaviour in the harbour seal (Phoca vitulina)
1 Department of Zoology, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z4
2 Peter-Wall Institute for Advanced Studies, University of British Columbia,
Vancouver, British Columbia, Canada V6T 1Z2
* Present address: Institute of Marine Science, University of Alaska Fairbanks
and Alaska SeaLife Center, Seward, AK 99664, USA
Author for correspondence (e-mail:
jones{at}zoology.ubc.ca)
While diving, harbour seals (Phoca vitulina) manage their oxygen
stores through cardiovascular adjustments, including bradycardia, a concurrent
reduction in cardiac output, and peripheral vasoconstriction. At the surface,
post-dive tachycardia facilitates rapid reloading of oxygen stores. Although
harbour seals can tolerate >20 min of submergence, the majority of their
natural dives are only 2-6 min and are usually followed by surface intervals
that are <1 min, so they spend approximately 80% of their time submerged.
Given that harbour seals meet their ecological needs through repetitive short
aerobic dives, we were interested in the functional role, if any, of the dive
response during these short dives. During voluntary diving in an 11 m deep
tank, the cardiovascular responses to submergence of five harbour seals were
manipulated using specific pharmacological antagonists, and the effects on
diving behaviour were observed. Effects of pharmacological blockade on heart
rate were also examined to assess the autonomic control of heart rate during
voluntary diving. Heart rate was recorded using subcutaneous electrodes and
data loggers, while diving behaviour was monitored using a video camera. The
muscarinic blocker methoctramine blocked diving bradycardia, the
-adrenergic blocker prazosin blocked diving vasoconstriction, and the
ß-adrenergic blocker metoprolol blocked post-dive tachycardia. Heart-rate
analysis indicated that diving bradycardia is primarily modulated by the
vagus, while post-dive tachycardia results from parasympathetic withdrawal as
well as increased sympathetic stimulation of the heart. None of the
pharmacological blockers had any effect on average dive or surface interval
duration. Seals maintained a high percentage of time spent diving in all
treatments. Thus, harbour seals do not appear to need the dive response during
short dives in order to maintain an efficient dive strategy.
Key words: diving, diving physiology, dive response, diving behaviour, heart rate, bradycardia, harbour seal, Phoca vitulina, methoctramine, metoprolol, prazosin, sympathetic system, parasympathetic system
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