Nitric Oxide Modulates Cardiac Performance in the Heart of Anguilla Anguilla

Abstract

Nothing is known about the effects of nitric oxide (NO) on cardiac performance in fish. Using an in vitro working heart preparation that generates physiological values of output pressure, cardiac output and ventricular work and power, we assessed the effects of NO on the cardiac performance of the eel Anguilla anguilla. We examined basal cardiac performance (at constant preload, afterload and heart rate), the effects of cholinergic stimulation and the Frank-Starling response (preload-induced increases in cardiac output at constant afterload and heart rate). The NO synthase (NOS) inhibitors N(G)-monomethyl-l-arginine (l-NMMA) and l-N(5)(1-iminoethyl)ornithine (l-NIO), the guanylate cyclase inhibitor 1H-(1,2,4)oxadiazolo-(4,3-a)quinoxalin-1-one (ODQ) and Triton X-100, a detergent that damages the endocardial endothelium, all increased stroke volume (V(S)) and stroke work (W(S)). In contrast, the endogenous NOS substrate l-arginine, tested before and after treatment with haemoglobin, the NO donor 3-morpholinosydnonimine, tested with and without the superoxide scavenger superoxide dismutase, and the stable cGMP analogue 8-bromoguanosine 3′,5′-cyclic monophosphate (8-Br-cGMP) decreased V(S) and W(S). Acetylcholine chloride produced a biphasic effect. At nanomolar concentrations, in 34 % of the preparations, it induced a NO-cGMP-dependent positive inotropism that required the integrity of the endocardial endothelium. Pretreatment with Triton X-100 or with NO-cGMP pathway inhibitors (l-NMMA, l-NIO, N(G)-nitro-l-arginine methyl ester, Methylene Blue and ODQ) abolished the positive effect of acetylcholine. In contrast, at micromolar concentrations, acetylcholine produced a negative effect that involved neither the endocardial endothelium nor the NO-cGMP pathway. Pre-treatment with l-arginine (10(−)(6)mol l(−)(1)) was without effect, whereas l-NIO (10(−)(5)mol l(−)(1)) significantly reduced the Frank-Starling response. Taken together, these three experimental approaches provide evidence that NO modulates cardiac performance in the eel heart.

The goldfish Carassius auratus: an emerging animal model for comparative cardiac research

“…The heart of C. auratus is a typical volume pump. Under basal conditions, CO values [11.85 mL/min/kg at 18 °C (Garofalo et al 2012 )] are similar to those of other teleosts [e.g., crucian carp: 8.4 mL/min/kg at 8 °C (Farrell and Stecyk 2007 ); European eel: 11.8 mL/min/kg (Peyraud-Waitzenegger and Soulier 1989 ), 10 mL/min/kg at 18 °C (Imbrogno et al 2001 ); rainbow trout: 15 mL/min/kg at 12 °C (Agnisola et al 2003 )]. It shows a marked sensitivity to filling pressure changes, as revealed by the elevated V s values (~ eightfold increase) reached in response to increasing preloads (Garofalo et al 2012 ).…”

“…Acetylcholine (ACh) negatively modulates HR and cardiac contractility [for extensive review, see (Vornanen 2017 )]. However, its effects are variable, being sometimes biphasic [ A. anguilla : (Imbrogno et al 2001 )], or different between atrium and ventricle [ Godus morhua : (Holmgren 1977 )]. In the isolated and perfused goldfish heart, exogenous ACh decreases both HR and contractility (Cameron and Brown 1981 ; Cameron 1979 ).…”

Hypoxic and Thermal Stress: Many Ways Leading to the NOS/NO System in the Fish Heart

“…In the avascular, or poorly vascularized, fish heart, the EE represents the major source of NO. The data from our laboratory reveal that this EE-derived NO is obligatory for the contractile effects elicited by many endoluminal chemical stimuli such as acetylcholine, angiotensin II, vasostatin-1, and β3-adrenoreceptor [32,[35][36][37].…”

“…This NO-dependent effect is related to contraction frequency, as the twitch duration is reduced by 25% at a frequency of 20 beats per min (bpm), but only by 5% at 80 bpm [31]. In eel [32], salmon [33], and goldfish [11], a tonic release of autocrine NO negatively modulates the basal mechanical performance of the heart. In addition, NO influences the Frank-Starling mechanism (salmon [33]; eel [34]; goldfish [11]), a fundamental cardiac trait that, in all vertebrates, allows the myocardium to increase stroke volume (SV), and consequent cardiac output (CO), in response to increased venous return (preload).…”

“…In the eurythermal eel A. anguilla, the NOS/NO-dependent modulation of the Frank-Starling response [32,34] is impaired by temperature changes [125]. Amelio and coworkers observed that the positive modulation elicited by the intracardiac NO release on the Frank-Starling response disappears when animals are acutely exposed at temperatures lower or higher than the acclimation one, both in the case of spring-and winter-like (acclimation temperature: 20 • C and 10 • C, respectively) conditions.…”