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Pharmacological blockade of the dive response: effects on heart rate and diving behaviour in the harbour seal (Phoca vitulina)

Nicole M. Elliott¹, Russel D. Andrews^1,*, and David R. Jones^1,2

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

View larger version (29K): [in a new window]   Fig. 1. Effect of intravenous injection of specific agonists on heart rate (fH) before and after blockade with the appropriate antagonist in one seal. Each data point represents the mean fH for the preceding 10 s interval. Arrows denote the time of injection of agonists. (A) 1-phenylephrine hydrochloride (0.06 µg kg-1) alone and after S.C. injection of the muscarinic antagonist methoctramine (0.23 mg kg-1). (B) Phenylephrine (0.06 µg kg-1) alone and after oral administration of the 1-adrenergic antagonist prazosin (0.24 mg kg-1). (C) Isoproterenol hydrochloride (0.01 µg kg-1) alone and after the oral administration of ß1-adrenergic antagonist metoprolol (4 mg kg-1). Control saline injections caused no significant effect on fH.

View larger version (34K): [in a new window]   Fig. 2. Mean heart rate (fH) ± S.E.M. during (A) post-dive surface intervals and (B) dives in control and pharmacologically blocked harbour seals (N=5). Heart rate data from control groups were combined to give the mean fH indicated by the horizontal lines, although statistical analyses were performed on controls for each data set. * indicates values significantly different from the control group within dive states (P<0.05). For each treatment, the dive fH was significantly lower than the surface interval fH. , seals treated with -adrenergic blocker; ß, seals treated with ß-adrenergic blocker; mu+, seals treated with muscarinic and -adrenergic blockers combined; mu+ß, seals treated with muscarinic and ß-adrenergic blockers combined.

View larger version (33K): [in a new window]   Fig. 3. Heart rate (fH) profiles before, during and after voluntary dives in (A) -adrenergic- and ß-adrenergic-blocked harbour seals and in (B) muscarinic-, muscarinic- plus -adrenergic-, and muscarinic- plus ß-adrenergic-blocked seals. Control data for the two oral drugs (A) and for the three injected groups (B) were combined, although statistical analyses were performed on controls for each data set. Arrows denote the beginning and end of the dive. Each data point represents the mean fH for the preceding 5 s interval. For each treatment, mean fH during two dives (approximately 120 s) were averaged for each animal. Data from all seals (N=5) were then combined to give the means ± S.E.M. illustrated. The data were normalized so that dives of different lengths ended at the same time.

View larger version (27K): [in a new window]   Fig. 4. (A) Mean surface interval and (B) dive durations ± S.E.M. in control and pharmacologically blocked harbour seals (N=5). Note that the time scales for each graph are different. , seals treated with -adrenergic blocker; ß, seals treated with ß-adrenergic blocker; mu+, seals treated with muscarinic and -adrenergic blockers combined; mu+ß, seals treated with muscarinic and ß-adrenergic blockers combined.

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