PERFORMANCE OF THE ISOLATED RAINBOW-TROUT HEART PERFUSED UNDER SELF-CONTROLLED CORONARY PRESSURE CONDITIONS - EFFECTS OF HIGH AND LOW-OXYGEN TENSION, ARACHIDONIC-ACID AND INDOMETHACIN

The effects of arachidonic acid (AA) and indomethacin (IM) on performa nce, oxygen consumption and lactate release of the trout heart were st udied in vitro TPa s m(-3) using a perfusion system, which allowed the evaluation of the integrated function of ventricle and coronary syste m by continuously setting the input coronary flow and pressure proport ional to the pressure and flow output of the heart. The heart was work ing against a fixed resistance, A reduction of input oxygen partial pr essure (P-O2) from 175 torr (high P-O2) to 76 torr (low P-O2) increase d the coronary flow (from 0.51 ml min(-1) kg(-1) to 1.21 ml min(-1) kg (-1), respectively) due to a strong reduction in coronary resistance ( from 0.60 TPa s m(-3) to 0.19 TPa s m(-3) respectively). Oxygen consum ption by the heart was significantly reduced from 20.7 ml min(-1) g(-1 ) at high P-O2 to 4.6 ml min(-1) g(-1) at low P-O2. while lactate prod uction was increased from 42 mu mol h(-1) g(-1) to 42 mu mol h(-1) g(- 1), indicating a higher contribution of anaerobic respiration to mecha nical work. Mechanical efficiency was significantly higher at low than at high P-O2. Exogenous AA caused a depression of inotropism and a re duction in the aerobic metabolic rate (by 25 35%). which was not accom panied by increased lactate production. IM enhanced the depression of both inotropism and aerobic metabolism, The effect of AA and IM on the heart were amplified at low P-O2.