Dichloroacetate selectively improves cardiac function and metabolism in female and male rainbow trout

Abstract

Cardiac tissue from female rainbow trout demonstrates a sex-specific preference for exogenous glucose and glycolysis, impaired Ca(2+) handling, and a greater tolerance for hypoxia and reoxygenation than cardiac tissue from male rainbow trout. We tested the hypothesis that dichloroacetate (DCA), an activator of pyruvate dehydrogenase, enhances cardiac energy metabolism and Ca(2+) handling in female preparations and provide cardioprotection for hypoxic male tissue. Ventricle strips from sexually immature fish with very low (male) and nondetectable (female) plasma sex steroids were electrically paced in oxygenated or hypoxic Ringer solution with or without 1 mM DCA. In the presence of 5 mM glucose, aerobic tissue from male trout could be paced at a higher frequency (1.79 vs. 1.36 Hz) with lower resting tension and less contractile dysfunction than female tissue. At 0.5 Hz, DCA selectively reduced resting tension below baseline values and lactate efflux by 75% in aerobic female ventricle strips. DCA improved the functional recovery of developed twitch force, reduced lactate efflux by 50%, and doubled citrate in male preparations after hypoxia-reoxygenation. Independent of female sex steroids, reduced myocardial pyruvate dehydrogenase activity and impaired carbohydrate oxidation might explain the higher lactate efflux, compromised function of the sarcoplasmic reticulum, and reduced mechanical performance of aerobic female tissue. Elevated oxidative metabolism and reduced glycolysis might also underlie the beneficial effects of DCA on the mechanical recovery of male cardiac tissue after hypoxia-reoxygenation. These results support the use of rainbow trout as an experimental model of sex differences of cardiovascular energetics and function, with the potential for modifying metabolic phenotypes and cardioprotection independent of sex steroids.

Keywords: cardiac; dichloroacetate; glucose; hypoxia; lactate; rainbow trout; sex differences.

Fig. 1.

A: effects of varying contraction frequencies (0.2–2.0 Hz) on isometric twitch force (F) and resting tension in ventricle strips from male and female rainbow trout. The original recording of twitch force production in trout ventricle strips from one fish of both sexes showed a decrease in absolute twitch force and increase in resting tension (female fish only) at higher frequencies. The temporal scale at each frequency was varied to capture at least two contraction cycles. After the equilibration period (60 min at 0.5 Hz), ventricle strips from both sexes contracted for 15 min (or until steady performance at a specific frequency was observed) at each frequency tested. All ventricle strips contracted at increasing pacing frequencies until we observed mechanical dysfunction. B: effects of pretreatment with ryanodine (Ryn; 10 μM) on ventricle strips from both sexes. Values are means ± SE; n = 6–7 independent data points for male and female preparations. *P < 0.05 and **P < 0.01 vs. the initial value.

Fig. 2.

Effects of pretreatment with dichloroacetate (DCA; 1 mM) or sodium cyanide (NaCN; 2 mM) on F under aerobic conditions and after hypoxia-reoxygenation. Control strips either remained glucose free (Gf) or received 5 mM glucose (G). The presence (+) and absence (−) of specific compounds in the incubation medium are shown. Absolute F_max (in mN) was not significantly different between male (6.18 ± 0.78) and female (5.88 ± 1.08) preparations during the 60-min equilibration period. Values are means ± SE; n = 6–9 independent data points for male and female preparations. *P < 0.05 and **P < 0.01 vs. controls; †P < 0.05 and §P < 0.01 vs. male preparations with glucose and no DCA under hypoxia-reoxygenation.

Fig. 3.

Effects of pretreatment with DCA (1 mM) or NaCN (2 mM) on lactate efflux under aerobic conditions and after hypoxia-reoxygenation. Control strips remained glucose free or received 5 mM glucose. Values are means ± SE; n = 6–9 independent data points per treatment for male and female preparations. *P < 0.05 vs. male preparations under identical treatment conditions; §P < 0.01 vs. controls within each sex; †P < 0.05 within each sex.

Fig. 4.

Effects of pretreatment with DCA (1 mM) or NaCN (2 mM) on citrate levels in initial samples of ventricular tissue and ventricle strips from both sexes under aerobic conditions and after hypoxia-reoxygenation. Control strips either remained glucose free or received 5 mM glucose. Values are means ± SE; n = 6–9 independent data points per treatment for for male and female preparations. *P < 0.05 and **P < 0.01 vs. the initial value; †P < 0.001 vs. glucose controls under a similar oxygenation state.