Sex differences in cardiac function and glucose metabolism in immature rainbow trout (Oncorhynchus mykiss)

My dissertation addresses sex differences in cardiac function and glucose metabolism in rainbow trout (Oncorhychus mykiss). Specifically, I evaluated male and female trout heart for: (1) the role of exogenous glucose, glycolysis and the sarcoplasmic reticulum (SR) for steroid-enhanced contractility; (2) metabolism and performance at different oxygenation levels; (3) metabolic energy modulation and intracellular Ca2+ regulation; and (4) glycogen content, form and distribution. I studied primarily sexually immature male and female trout (chapters 1--4); however, chapter 1 also deals with sexually maturing males.;Results from chapter 1 provide new evidence that glucose by itself is considered as 'metabolic inotrope' in vitro (maturing males > immature males > immature females). Females show an absolute requirement for exogenous glucose to maintain cardiac function. The presence of glucose and an active glycolytic pathway are crucial prerequisites for increased isometric force production (F) of ventricle strips following exposures to testosterone and 17beta-estradiol, but not epinephrine or elevated extracellular calcium. Males have higher capacity for SR Ca2+ storage and release than females. Sexual maturity appear to promote cardiac glucose metabolism and SR function in male trout.;Data from chapter 2 suggest that ventricle tissue in males has a higher capacity for aerobic and lipid metabolism, shows greater inotropic responses to exogenous glucose and octanoate, and sustain F longer than females under hyperoxia with glucose present. In contrast, females prefer glycolysis for ATP production, and sustain F better following severe hypoxia-reoxygenation.;Findings from chapter 3 show that ventricle tissue in females have inherently higher hypoxia tolerance, reduced mitochondrial function, less extensive SR and depend predominantly on Ca2+ via reverse mode Na +/Ca2+ exchanger as a source of intracellular Ca 2+ under hyperoxia. Conversely, males have higher initial citrate levels and more extensive SR.;Finally, chapter 4 extends the recurring theme of sex differences to ventricular glycogen content (males > females), hydrochloric acid soluble form (males > females) and the distribution (between sexes, males have higher glycogen in the epicardium and females in the endocardium).;In conclusion, sex differences in trout cardiac performance in vitro involve glucose metabolism, metabolic energy regulation coupled with intracellular Ca2+ homeostasis and SR function.