Nitroxyl anion exerts redox-sensitive positive cardiac inotropy in vivo by calcitonin gene-related peptide signaling

Abstract

Nitroxyl anion (NO(-)) is the one-electron reduction product of nitric oxide (NO( small middle dot)) and is enzymatically generated by NO synthase in vitro. The physiologic activity and mechanism of action of NO(-) in vivo remains unknown. The NO(-) generator Angeli's salt (AS, Na(2)N(2)O(3)) was administered to conscious chronically instrumented dogs, and pressure-dimension analysis was used to discriminate contractile from peripheral vascular responses. AS rapidly enhanced left ventricular contractility and concomitantly lowered cardiac preload volume and diastolic pressure (venodilation) without a change in arterial resistance. There were no associated changes in arterial or venous plasma cGMP. The inotropic response was similar despite reflex blockade with hexamethonium or volume reexpansion, indicating its independence from baroreflex stimulation. However, reflex activation did play a major role in the selective venodilation observed under basal conditions. These data contrasted with the pure NO donor diethylamine/NO, which induced a negligible inotropic response and a more balanced veno/arterial dilation. AS-induced positive inotropy, but not systemic vasodilatation, was highly redox-sensitive, being virtually inhibited by coinfusion of N-acetyl-l-cysteine. Cardiac inotropic signaling by NO(-) was mediated by calcitonin gene-related peptide (CGRP), as treatment with the selective CGRP-receptor antagonist CGRP(8-37) prevented this effect but not systemic vasodilation. Thus, NO(-) is a redox-sensitive positive inotrope with selective venodilator action, whose cardiac effects are mediated by CGRP-receptor stimulation. This fact is evidence linking NO(-) to redox-sensitive cardiac contractile modulation by nonadrenergic/noncholinergic peptide signaling. Given its cardiac and vascular properties, NO(-) may prove useful for the treatment of cardiovascular diseases characterized by cardiac depression and elevated venous filling pressures.

Figure 1

(A) Hemodynamic response to AS in a conscious dog. Abscissa is in min. There was a rapid decline in left ventricular systolic pressure (LV ESP) and left ventricular preload (LV EDP, left ventricular end-diastolic pressure; LV EDD, left ventricular end-diastolic dimension) that occurred within 5–10 min of bolus infusion ^H(B), and persisted for at least 35 min of sustained AS infusion. Systemic vascular resistance (SVR) was unchanged. Ventricular contractility (Ees, slope of end-systolic pressure–dimension relation; D_EDV relation slope) also rose rapidly and markedly and remained elevated throughout drug infusion. (B) Representative pressure–dimension loops before (Left) and after (Right) AS infusion. There was an increase in Ees (dotted line at upper left) and decline in chamber volume. (C) Similar results for heart with hexamethonium-induced autonomic blockade (Right).

Figure 2

(A) Mean ± SEM for % change in hemodynamics for AS (black bars, n = 9) vs. AS in the presence of preload-volume restoration (white bars, n = 4). HR, heart rate; dPdt/EDV, slope of dP/dt_max-end-diastolic dimension; Pes, end-systolic pressure; Tau, time constant of pressure decay; Ped, end-diastolic pressure; Ea, arterial elastance; EDV, enol-diastolic volume. *, P < 0.05 vs. baseline; †, P < 0.01 vs. baseline; ‡, P < 0.01 vs. nitroxyl alone. (B and C) Cardiac function curves showing stroke volume (B) and maximal rate of pressure rise (C) at two different end diastolic volumes. Control curves (●) were significantly shifted upward after AS infusion (○).

Figure 3

(A) Pressure–dimension loops before (Left) and after (Right) infusion of DEA/NO, a NO donor. Unlike AS, the NO donor did not significantly alter contractility. However, there was a decline in systemic resistance reflected by widening of the loop with less preload change. (B) Summary results (n = 3) show the lack of contractile increase (Ees or D_EDV) with DEA/NO, but arterial resistance (SVR) decreased by 25% .

Figure 4

(A) Example of inotropic response to AS (NO⁻) before and after administration of the CGRP receptor-blocking peptide CGRP-(8–37). The blocking peptide effectively eliminated the inotropic response to AS. (B) Summary data for two measures of LV contractility showing inhibition of AS-induced positive inotropy by CGRP-(8–37) (n = 5). The blocking peptide did not produce significant inotropic effects per se.