GODDARD, Adam C*; BATTIPROLU, Pavan K; RODNICK, Kenneth J; Idaho State University; Idaho State University; Idaho State University: Effects of Exogenous Glucose on Cardiac Oxygen Consumption and Lactate Release in Rainbow Trout (Oncorhynchus Mykiss)

Oxygen and energy substrates are key determinants of cardiac function. The importance of glucose under non-stimulated conditions has not been defined in fishes. We investigated the effect of glucose on ventricular oxygen consumption (VO₂) and lactate release in the basal state, and explored whether sex differences in cardiac metabolism exist in rainbow trout. Ventricles from 10-12 month old immature males and females (n = 4-7 per group) were excised and cut into uniform strips. Individual strips were incubated in Ringers solution containing 5 mM glucose, and saturated with 99.5% O₂:0.5% CO₂ at 15° C for 60 min. Strips were then placed in a respiration cell (2.5 ml) containing either: 1) glucose-free Ringers (glu-f), 2) 5 mM glucose (glu), 3) glu-f/20 mM 2,3-butanedione monoxime (BDM), a cardioplegic compound, or 4) glu-BDM, and saturated with 21% O₂:0.5% CO₂ at 15° C for 20 min. Oxygen consumption (VO2) and lactate release were measured. VO₂(~0.32 µmol g^-1min^-1) was similar between sexes and was not affected by glu and/or BDM. In the presence of glu, lactate release (nmol g^-1min^-1) was significantly higher in females than males (273 � 34 vs. 185 � 24, P<0.05). The addition of BDM to glu-f reduced lactate release in males (glu-f = 239 � 32 vs. glu-f BDM = 154 � 26, P<0.05) but not in females. However, BDM plus glu reduced lactate release in females (glu = 273 � 34 vs. glu-BDM = 190 � 24, P<0.05) but not in males. In conclusion, female ventricle strips may have a greater dependency on exogenous glucose for glycolysis and energy metabolism than males. The fact that BDM reduces lactate release in males and females suggests that intrinsic contractile activity involves glycolysis for energy production.