In this study we tested the hypothesis that vasostatins could act as myocardial modulators in the mammalian heart. Using the Langendorff-perfused rat heart, the cardiac effects of the two recombinant human CGA N-terminal fragments STA-CGA1-78 and STA-CGA1-115, containing the vasostatin-1 (CGA 1-76) and vasostatin-2 (CGA 1-113) sequences, respectively, were evaluated at concentrations of 11 / 165 nM. Cardiac performance was evaluated by analyzing left ventricular pressure (LVP) and the rate pressure product (RPP: HR x LVP), used as indexes of contractile activity and cardiac work, respectively. Under basal conditions, STA-CGA1-78 at all concentrations tested elicited a dose-dependent negative inotropism (LVP variations ranging from -9.6% +/- 2 to -23% +/- 2.9) without affecting coronary pressure (CP). In contrast, STA-CGA1-115 increased CP at 110 and 165 nM without affecting inotropism. Both STA-CGA1-78 and STA-CGA1-115 counteracted the cardio-stimulatory effects of isoproterenol (ISO). The ISO-dependent positive chronotropism was unaffected by STA-CGA1-78, while being reduced by STA-CGA1-115. Both peptides abolished the ISO-induced positive inotropism without modifying either the beta-adrenergic-dependent coronary dilation or the ouabain-induced positive inotropism. The analysis of the percentage of variations of RPP in terms of EC50 values of ISO alone (-8.5 +/- 0.3; r2 = 0.88) and in presence of STA-CGA1-78 (11, or 33, or 65 nM: -7.7 +/- 0.15, r2 = 0.97; -7.7 +/- 0.15, r2 = 0.97; -7.8 +/- 0.78, r2 = 0.55, respectively) revealed a non-competitive type of antagonism of STA-CGA1-78. Taken together, these data suggest vasostatins as novel cardioregulatory peptides in mammals.

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.