BATTIPROLU, P.K.; RODNICK, K.J.*; IDAHO STATE UNIV: Evidence for Sex Differences in Glucose-Mediated Cardiac Contractility in Rainbow Trout (Oncorhynchus mykiss)

The heart of the rainbow trout is hypoxia-intolerant, may experience variations in oxygen availability and is omnivorous in its preference for metabolic fuels. However, the importance of exogenous glucose, oxygen and sex differences for contractile performance has not been established. We determined whether extracellular glucose (5 mM) promotes cardiac contractility in male and female trout, and measured lactate release under oxygenated (PO₂ = 640 mm Hg) and hypoxic conditions (PO₂ = 20 mm Hg). METHODS: Ventricles from 10-12 month old immature males (n=8), and females (n=10) were excised. Four strips were cut, attached to isometric force transducers and electrically stimulated at 0.5 Hz under glucose-free/oxygenated conditions for 1 h at 14�C. Strips either 1) remained glucose-free/oxygenated; 2) were changed to hypoxia, or 3 and 4) were treated with glucose for 1 h (oxygenated or hypoxia). Percent original twitch force (F) and lactate release were calculated. RESULTS: Under glucose/oxygenated conditions, F was significantly higher in males compared with females (145 � 3% vs.125 � 4%; P<0.05). In contrast, glucose did not promote contractility in both sexes under hypoxic conditions. Lactate release (nmoles g-1 min-1) was higher in females under oxygenated (with glucose, 275 � 18; without glucose, 180 � 14 vs. males with glucose, 71 � 20; males without glucose, 46 � 15; P<0.05) and hypoxic conditions (females with glucose, 401 � 24; females without glucose, 421 � 25 vs. males with glucose, 244 � 20; males without glucose, 232 � 21; P<0.05). CONCLUSION: Glucose promoted contractility more in males and it appears that females may rely more on glycolysis for energy production under oxygenated and hypoxic conditions. Funded by NIH P20RR16454.