69.5 Saturday, Jan. 5 Control of branchial artery tone in Antarctic fish EGGINTON, S; University of Birmingham, UK email@example.com
We examined potential vasomotor control mechanisms in Antarctic fishes, compared with teleosts of different phylogenetic relatedness from both cold and temperate environments. In general, vascular constrictor activity showed a modest α and β adrenergic tonus, but with greater potency for cholinergic and serotonergic vasoconstriction, in Antarctic notothenioids and both related and phylogenetic sister group species from warmer waters around New Zealand. This unusual pattern of control appears to be primarily a consequence of evolutionary lineage rather than low environmental temperature, but may be modified according to functional demand e.g. a pelagic species showed a dominance of vasodilatation over vasoconstriction. Prostanoid vasodilators were effective in reducing vascular tone, but a variety of potential nitrodilators all failed to elicit a response (though they were active in trout vessels). Polar and temperate northern hemisphere species, phylogenetically distant from each other and the nototheniids, showed both similarities and differences making simple inferences about phenotype vs. genotype difficult. In light of a reduced importance for the classical adrenergic and nitroergic vascular control, maintenance of adequate cardiovascular control at extremely low temperatures likely involves compensation by a variety of other vasoactive substances. In addition, each species possessed a unique pattern of vascular innervation that partially differentiated between nototheniids and non-nototheniids, while functional consequences for oxygen delivery to locomotory muscle also involve changes in microvascular structure. We conclude there is little evidence for cold adaptation of branchial artery contractility, and mechanisms of vascular control likely reflect phylogeny rather than thermal history.