Septic shock is systemic inflammatory condition secondary to an infectious process leading to systemic hypotension and reduced vasoconstriction to several agonists with great production of nitric oxide (NO). Plasma concentration of C-type natriuretic peptide (CNP) is increased in animal models and patients in sepsis. The present study aimed to evaluate the contractile response induced by phenylephrine (PE) and the effect of CNP on this response in the isolated aorta from rats submitted to sepsis by ligation and puncture model (CLP). All the experimental protocols used in this study are approved by the Ethics Committee of the University of São Paulo (#144/2011). Male rats (35 days old) were anaesthetized with tribromoethanol (250 mg/Kg, ip). They were submitted to catheterization of femoral artery and vein 24h before the surgery to sepsis induced by CLP (16G needle) or sham-surgery (control rats, CO). The mean arterial pressure (MAP) of the rats was measured 4h after the surgery following PE administration (10-10 a 10-8 mol/Kg or saline, iv). The aortic rings were isolated from CO and CLP rats, for in vitro experiments of vascular reactivity. It was performed cumulative concentration-effect curves to PE (10-10 a 10-5 mol/L) with (E+) or without (E-) endothelium, in the absence or in the presence of CNP (10-8 mol/L). The aortic endothelial cells were used for flow cytometry studies. The cytosolic concentration of NO ([NO]c) was measured by using DAF-2/DA (10-5 mol/L). It was evaluated the maximum effect (Emax) and potency (pD2) of the PE. The MAP was higher in CO rats (74.3±0.3 mmHg, n=13) than in CLP rats (49.5±0.8 mmHg, n=15, P<0.05) 4h after the surgery, and the heart rate was enhanced in both groups as compared to the basal levels. Intravenous administration of PE increased the MAP and reduced the heart rate in both groups. PE induced contractile response in aortic rings from CO and CLP. It was reduced in CLP E+ group (Emax: 733±63,2g/g; pD2: 6,89±0,06, n=5, P<0.05) compared to CLP E- (Emax: 1468,3±181,7g/g; pD2: 7,51±0,31, n=8, P<0.05) and CO E+(Emax: 1231,4±106,4g/g; pD2: 7,32±0,10, n=11, P<0.05). CNP presented a negatively modulation in this PE response, only in E+ (CO Emax: 723,6±154,6g/g; pD2: 6,92±0,09; CLP Emax: 284,39±9,3g/g; pD2: 6,32±0,09, n=4, P<0.05). In the endothelial cells, the increase of [NO]c was higher in CLP (2706,3±325,8U, n= 4, P<0.05) than in CO rat aortic endothelial cells (1794,8±38,5U, n=4). Taken together, the results indicate that the vasoconstriction to PE is decreased in septic rat aorta, which should be due the enhanced production of NO in the endothelial cells. PE-induced contractile response is negatively modulated by CNP in intact-endothelium CO and CLP rat aortas.