ORIGINAL PAPER S.F. Perry á C.J. Montpetit á J. McKendry P.R. Desforges á K.M. Gilmour á C.M. Wood K.R. Olson The effects of endothelin-1 on the cardiorespiratory physiology of the freshwater trout Oncorhynchus mykiss ) and the marine dog®sh Squalus acanthias ) Accepted: 28 May 2001 / Published online: 9 August 2001 Ó Springer-Verlag 2001 Abstract The aim of the present study was to evaluate the eects of endothelin-1-elicited cardiovascular events on respiratory gas transfer in the freshwater rainbow trout Oncorhynchus mykiss) and the marine dog®sh Squalus acanthias). In both species, endothelin-1 666 pmol kg ±1 ) caused a rapid within 4 min) reduc- tion ca. 30±50 mmHg) in arterial blood partial pres- sure of O 2 . The eects of endothelin-1 on arterial blood partial pressure of CO 2 were not synchronised with the changes in O 2 partial pressure and the responses were markedly dierent in trout and dog®sh. In trout, ar- terial CO 2 partial pressure was increased transiently by 1.0 mmHg but the onset of the response was delayed and occurred 12 min after endothelin-1 injection. In contrast, CO 2 partial pressure remained more-or-less constant in dog®sh after injection of endothelin-1 and was increased only slightly 0.1 mmHg) after 60 min. Pre-treatment of trout with bovine carbonic anhydrase 5 mg ml ±1 ) eliminated the increase in CO 2 partial pressure that was normally observed after endothelin-1 injection. In both species, endothelin-1 injection caused a decrease in arterial blood pH that mirrored the changes in CO 2 partial pressure. Endothelin-1 injection was associated with transient trout) or persistent dog®sh) hyperventilation as indicated by pronounced increases in breathing frequency and amplitude. In trout, arterial blood pressure remained constant or was decreased slightly and was accompanied by a transient increase in systemic resistance, and a temporary reduction in cardiac output. The decrease in cardiac output was caused solely by a reduction in cardiac frequency; cardiac stroke volume was unaected. In dog®sh, arterial blood pressure was lowered by 10 mmHg at 6±10 min after endothelin-1 injection but then was rapidly restored to pre-injection levels. The decrease in arterial blood pressure re¯ected an increase in branchial vascular resistance as determined using in situ perfused gill preparations) that was accompanied by simultaneous decreases in systemic resistance and cardiac output. Cardiac frequency and stroke volume were reduced by endothelin-1 injection and thus both variables contributed to the changes in cardiac output. We conclude that the net consequences of endothelin-1 on arterial blood gases result from the opposing eects of reduced gill functional surface area caused by vasoconstriction) and an increase in blood residence time within the gill caused by decreased cardiac output. Keywords Catecholamines á Cardiac output á Ventilation á Endothelin-1 á Carbonic anhydrase Abbreviations CA carbonic anhydrase á ET-1 endothelin-1 á f H cardiac frequency á f R ventilation respiration) frequency á G DIFF diusion conductance á H SV cardiac stroke volume á P a arterial blood pressure á P CA caudal artery pressure á P DA dorsal aortic pressure á PaCO 2 á arterial blood á PCO 2 á PaO 2 arterial PO 2 á pHa arterial pH á _ Q cardiac output á R G branchial vascular resistance á R S systemic vascular resistance á Vent. Amp. ventilation amplitude J Comp Physiol B 2001) 171: 623±634 DOI 10.1007/s003600100213 Communicated by L.C.-H. Wang S.F. Perry &) á C.J. Montpetit á J. McKendry á P.R. Desforges Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, Canada K1N 6N5 E-mail: sfperry@science.uottawa.ca Tel.: +1 613-5625800 ext 6005 Fax: +1-613-5625486 K.M. Gilmour Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6 C.M. Wood Department of Biology, McMaster University, 1280 Main Street W., Hamilton, Ontario, Canada L8S 4K1 K.R. Olson Indiana University School of Medicine, South Bend Center, University of Notre Dame, Notre Dame, IN 46556-5607, USA