The acidic protein Chromogranin A (CGA) is the precursor of several regulatory peptides generated by specific proteolytic processes. Human recombinant CGA N-terminal fragment STA-CGA_1-78 (hrSTA-CGA_1-78), containing vasostatin-1 (CGA1-76) domain, exerts negative inotropic effect and counteracts the -adrenergic positive inotropic effect on the rat heart. We hypothesized an involvement of nitric oxide (NO)-dependent pathway in both cardiodepression and cardioprotection by hrSTA-CGA_1-78. We also hypothesized an involvement of adenosine A₁ receptor and protein kinase C (PKC) in cardioprotection by hrSTA-CGA_1-78. Therefore we evaluate whether i) the cardio-inhibition mediated by hrSTA-CGA_1-78 involves the G_i/0 proteins/NO-dependent signal transduction cascade; ii) hrSTA-CGA_1-78 induces ischemic preconditioning-like protective effects on the myocardium; iii) inhibition of either NO synthase (NOS), adenosine A₁ receptor or PKC affects hrSTA-CGA_1-78 protection. Using the isolated rat heart, we found that the reduction of left ventricular pressure (LVP), rate pressure product and +(LVdP/dt)max elicited by hrSTA-CGA_1-78 at 33nM is abolished by blocking G_i/0 proteins by PTx, by scavenging NO with hemoglobin, by blocking NOS activity with L-NMMA or L-NIO, soluble guanylate cyclase with ODQ, and PKG with KT5823. Data suggest the involvement of the G_i/0 proteins/NO-cGMP-PKG pathway in the hrSTA-CGA_1-78-dependent cardio-inhibition. When given before 30 min of ischemia, hrSTA-CGA_1-78 significantly reduced the size of the infarct from 64+/-4% to 32+/-3% of the left ventricular mass. This protective effect was abolished by either NOS inhibition or PKC blockade, and attenuated, but not suppressed, by the blockade of A₁ receptors. These results suggest that hrSTA-CGA_1-78 activity triggers two different pathways: one of these pathways is mediated by A₁ receptors, the other is mediated by NO release. As with repeated-brief preconditioning ischemias, hrSTA-CGA_1-78 may be considered a stimulus strong enough to trigger both pathways, which may converge on PKC.