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The role of angiotensin II in regulating catecholamine secretion during hypoxia in rainbow trout Oncorhynchus mykiss
Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, Canada K1N 6N5
*Author for correspondence (e-mail: sfperry{at}science.uottawa.ca)
Accepted September 20, 2001
Experiments were performed in vivo on chronically cannulated adult rainbow trout (Oncorhynchus mykiss) to assess the involvement of serotonergic or muscarinic receptor stimulation or activation of the reninangiotensin system in eliciting catecholamine release during acute hypoxia during periods of nicotinic receptor desensitisation.Despite nicotinic receptor desensitisation induced by intravenous infusion of nicotine (1.3x105 mol kg1 h1), plasma catecholamine levels were increased to levels (adrenaline plus noradrenaline 125200 nmol l1) similar to those in control fish during severe hypoxia (4045 mmHg; 5.36.0 kPa). Blockade of serotonergic receptors using methysergide or of muscarinic receptors using atropine did not affect the ability of fish to elevate circulating catecholamine levels during hypoxia. However, selective blockade of the reninangiotensin system, using lisinopril to inhibit angiotensin-converting enzyme, prevented the elevation of both angiotensin II and circulating catecholamine levels in acutely hypoxic fish experiencing nicotinic receptor desensitisation. In fish possessing functional nicotinic receptors, angiotensin-converting enzyme blockade attenuated but did not prevent the elevation of plasma catecholamine levels during hypoxia. The results of this study indicate that the reninangiotensin system is activated during hypoxia and plays a role in eliciting catecholamine release that is secondary to activation of nicotinic receptors. However, under conditions of nicotinic receptor desensitisation, activation of the reninangiotensin system during hypoxia is a prerequisite for catecholamine release.
Key words: desensitisation, rainbow trout, Oncorhynchus mykiss, chromaffin cell, adrenaline, noradrenaline, hypoxia, catecholamine, nicotinic receptor, angiotensin II, serotonin, muscarinic receptor.
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