Regulation of solute and water balance in primitive fishes

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Endocrine control of solute and water balance is a life sustaining process in all organisms. It requires the coordinated action of a number of different physiological systems through the interaction of a multitude of hormones. Hormones such as angiotensin II, C-type natriuretic peptide, bradykinin and arginine vasotocin are all involved in solute and water regulation in mammals. Research has shown that these hormones also exist, and have physiological function, in the phylogenetically ancient elasmobranch fish. The proposed research programme will examine the role these hormones play in the regulation of renal, cardiovascular and gastro-intestinal physiology of elasmobranch fish. In addition, molecular characterisation of key transport proteins for urea and ammonia will provide new information on nitrogen balance in elasmobranchs. Furthermore, the role ureolytic bacteria may play in nitrogen metabolism in these primitive fish will be examined. The proposed research is significant as it aims to provide an evolutionary framework for solute transport mechanisms in vertebrates and a physiological understanding of how hormone systems regulate similar physiological functions in elasmobranch fish. Additional research is proposed to examine calcium transport and the endocrine regulation of this key ion in a second primitive fish, the lake sturgeon. These freshwater cartilaginous fish present a unique model in terms of calcium regulation. Molecular characterisation of transport mechanisms in addition to hormonal regulation of this ion will aid in our understanding of calcium metabolism in these fish and therefore the proposed research will aid in the mitigation of potential impacts in the documented declines of environmental calcium may have on this threatened species. Therefore, information gained from this proposed research programme can be used not only in the context of industry as this fundamental research underpins more advanced and innovative research in the development of therapeutics in the pharmaceutical industry but also from the context of conservation physiology for the protection of threatened species such as the lake sturgeon.