Respiration Physiology. 77 (1989) 351-364 Elsevier 351 RESP 01570 Evidence that hypoxemia promotes catecholamine release during hypercapnic acidosis in rainbow trout (Salmo gairdneri) Steve F. Perry ~, R. Kinkead ~, P. Gallatlgher 2 and D.J. Randall 2 tDepartment of Biology. Unitm,sity of Ottawa, 30 Somerset St. E.. Ottawa. Ontario KIN 6N5, Canada and 2Deparunent of Zoology. Univer~y of British Columbia. 6270 University Blvd., Vancouver, British Columbia. ,, Canada (Accepted for publication 6 May 1989) Abstract. The concentrations of plasma catecholamines, epinephrine and norepinephrine, were monitored in rainbow trout ($almo gairdner 0 after acute (30 rain) exposure to various levels of extcrna~ hypercapnia (water Pco, (Pwco2) = 0-1 !.3 Tort) under normoxic (water Po2 (Pwo2) = 153 + I.I Ton) or hyperoxic (Pwo, - 653 + 27.0 Torr) conditions. Whole blood pH decreased to a similar extent as a function ofexternai carbon dioxide tensions in both the normoxic and hyperoxic hypercapnic groups. Arterial oxygen content, however, declined only during normoxic hyperc~pnia. Similarly, plasma catecholamines (primarily epinephrine) increased only during normoxic hypercapnia in proportion to the severity of the whole blood acidosis. Epinephrine levels were elevated 10-fold from 0.70 + 0.06 nM to 7.06 + 3.7 nM at the highest concentration of external CO, (I 1.3 Tort) whereas norepinephrine increased 3-fold from 0.56 + 0.07 nM to 1.62 ± 0.40 nM. The absence ofcatecholamine release into the circulation during hyperoxic hypercapnia was not due to inhibition of the 'catecholamine-releasing process' by abnormally elevated arterial oxygen tensions (Pao~ = ~ 400 Ton') because acutely anaemic and thus hypoxemic fish (haematocrit = 4.9 + 0.7%) displayed identical elevations of plasma catecholamines under both normoxic and hyperoxic conditions. The results of these experiments demonstrate that a~lerial hypoxemia, rather than blood acidosis per se, is the proximate stimulus causing catecholamine mobilization in rainbow trout during short-term environmental hypercapnia. Acidosis; Blood; CatecholawJnes; Fish; Hypercapnia; Hypoxemia The circulating levels of catecholamines, epinephrine and/or norepinephrine, increase during numerous experimentally-induced stresses in fish including imposed environ- mental disturbances (e.g. hypoxia, hypercapnia, air-exposure) and after severed types of exercise regimes. The mobilization of catecholamines is thought to be important in compensating the deleterious effects of stress on gas transfer and acid-base balance (see review by Perry and Wood, 1989). In table 1, we have compiled plasma catecholamine Correspondence address: Steve F. Perry, Department of Biology, University of Ottawa, 30 Somerset St. E., Ottawa, Ontario KIN 6N5, Canada 0034-5687/89/$03.50 © 1989 Elsevier Science Publishers B.V. (Biomedical Division)