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First published online January 5, 2005
Journal of Experimental Biology 208, 223-232 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01362

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Activation of the newly discovered cyclostome renin–angiotensin system in the river lamprey Lampetra fluviatilis

J. Anne Brown^1,*, Christopher S. Cobb^1,, Susan C. Frankling¹ and J. Cliff Rankin^2,

¹ School of Biological and Chemical Sciences, Hatherly Laboratories, University of Exeter, Prince of Wales Road, Exeter, EX4 4PS, UK
² Aquatic Biology Research Centre, Institute of Biology, University of Southern Denmark – Odense University, Hindsholmvej 11, DK-5300 Kerteminde, Denmark

^* Author for correspondence (e-mail: J.A.Brown{at}exeter.ac.uk)

Accepted 27 October 2004

This study describes the first investigations of the physiological signals involved in activating the newly discovered cyclostome renin–angiotensin system (RAS) and its role in the river lamprey Lampetra fluviatilis. Experimental manipulation showed that volume depletion (removal of 40% blood volume) rapidly activated the RAS of lampreys acclimated to water at 576 mOsm kg^–1 (21 p.p.t.), significantly increasing plasma angiotensin concentrations after 30 min and 60 min. In agreement with these results, a rapid change in environmental salinity (758 mOsm kg^–1 to freshwater (FW) and FW to 605 mOsm kg^–1), resulted in a rapid decrease and increase in plasma [angiotensin], respectively. Intraperitoneal (i.p.) injection of FW-acclimated river lampreys with 1% body mass by volume of nominally isosmotic saline (120 mmol l^–1 NaCl; 233 mOsm kg^–1) resulted in a significant decrease in the plasma angiotensin concentration within 15 min. In contrast, i.p. injection of hyperosmotic saline (4 mol l^–1 NaCl) at 1% body mass by volume, which significantly increased plasma osmolality, had no significant effect on plasma [angiotensin], suggesting that volume/pressure receptors and osmoreceptors interact in regulating the lamprey RAS. These results indicate an important role for volume/pressor receptors, as in teleosts, but with an additional osmoreceptor mechanism, such that circulatory [angiotensin] is determined by interaction of volume/pressure and osmoreceptors and their relative sensitivities. The volume/pressure sensitivity is in keeping with the recent evidence of a vasoconstrictor action of homologous lamprey angiotensin and provides evidence that the fundamental role of the RAS in maintaining volume and pressure is an ancient function conserved over 500 million years of vertebrate evolution.

Key words: renin–angiotensin system, river lamprey, Lampetra fluviatilis, plasma angiotensin, salinity adaptation, volume regulation

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