INFLUENCE OF HYPOXIA AND ADRENALINE ADMINISTRATION ON CORONARY BLOOD-FLOW AND CARDIAC-PERFORMANCE IN SEAWATER RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

To investigate the relationship between cardiac performance and corona ry perfusion, cardiovascular variables (Q, Vs, fH, PDA) and coronary b lood flow (q(cor)) were measured in rainbow trout (Oncorhynchus mykiss ) (1.2-1.6 kg) before and after adrenergic stimulation (1.0 mu g kg(-1 ) adrenaline) under conditions of (1) normoxia, (2) hypoxia (approxima te Pwo(2) 12 kPa) and (3) 2.5 h after returning to normoxia. q(cor) fo r resting fish under normoxic conditions was 0.14+/-0.02 ml min(-1) kg (-1) (approximately 0.85 % of Q). When exposed to hypoxia, although ba th resting Q and q(cor) increased, q(cor) increased to a greater degre e (Q by 17 % and q(cor) by 36 %). During hypoxia, maximum adrenaline-s timulated h was comparable to that observed for normoxic fish. However , because Q was elevated in resting hypoxic fish, the capacity of hypo xic fish to increase Q above resting levels was 50 % lower than that m easured in normoxic fish. Although maximum qcor in adrenaline-injected hypoxic trout was greater than that measured in normoxic trout, post- injection increases in q(cor) (above resting levels) were not differen t between the two groups. Two and a half hours after hypoxic exposure, resting Q was still elevated (11%) above normoxic levels, and the abi lity to increase and when adrenergically stimulated was not fully rest ored. These results suggest (1) that resting q(cor) in salmonids is ap proximately 1 % of Q, (2) that increases in q(cor) may be important in maintaining cardiovascular performance during hypoxic conditions, (3) that interactions between alpha-adrenergic constriction and metabolic ally related vasodilation of the coronary vasculature are important in determining q(cor) in fish, (4) that exposure of fish to moderate env ironmental hypoxia reduces the scope for adrenergically mediated incre ases in h, and (5) that periods of recovery in excess of several hours are required before cardiovascular performance returns to pre-hypoxic levels.