BATTIPROLU, Pavan K; RODNICK, Kenneth J; Idaho State University: Gender And Maturity Differences In Cardiac Performance Under Glucose And Glucose-Free Conditions In Rainbow Trout (Oncorhynchus mykiss)

The heart of teleost fish is omnivorous in its preference for metabolic fuels. However, the importance of glucose to contractile performance and the possibility that gender-related differences in cardiac metabolism exist have not been established. Our objective was to determine the inotropic effects of extracellular glucose in rainbow trout. Ventricles from 10-12 month old mature (n=12) and immature males (n=13), and immature females (n=16) were excised; four strips were cut and were attached to isometric force transducers, incubated in glucose-free Ringers for 1 h at 14�C, and electrically-stimulated to contract at 0.5 Hz. Strips were then treated with 1, 2, 5, or 10 mM glucose for 1 h. Basal tension, contraction force and post rest potentiation (PRP) after 5 min were measured. Results: In the absence of glucose basal tension decreased in mature males and increased in immature males and females. With the addition of a physiological concentration (5 mM) of glucose, basal tension was maintained in all fish and yet force productions was significantly higher in mature males (49%) when compared to immature males (25%) and females (23%). At 10 mM glucose, basal tension decreased in mature males and increased in immature males and females. PRPs were higher in strips that received glucose (5 mM) when compared to glucose-free strips. Conclusion: Depending on sex and maturity of the fish, a specific concentration of glucose was required to maintain basal tension. Glucose promoted 1) more contractility in mature males than in immature fish and 2) calcium storage in the SR. These results highlight the importance of available substrate, gender and maturity differences to studies of trout cardiac performance.