Resistance to endotoxic shock in mice lacking natriuretic peptide receptor-A

Abstract

Background and purpose: Excessive production of nitric oxide (NO) by inducible NO synthase (iNOS) is thought to underlie the vascular dysfunction, systemic hypotension and organ failure that characterize endotoxic shock. Plasma levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are raised in animal models and humans with endotoxic shock and correlate with the associated cardiovascular dysfunction. Since both NO and natriuretic peptides play important roles in cardiovascular homeostasis via activation of guanylate cyclase-linked receptors, we used mice lacking natriuretic peptide receptor (NPR)-A (NPR1) to establish if natriuretic peptides contribute to the cardiovascular dysfunction present in endotoxic shock.

Experimental approach: Wild-type (WT) and NPR-A knockout (KO) mice were exposed to lipopolysaccharide (LPS) and vascular dysfunction (in vitro and in vivo), production of pro-inflammatory cytokines, and iNOS expression and activity were evaluated.

Key results: LPS-treated WT animals exhibited a marked fall in mean arterial blood pressure (MABP) whereas NPR-A KO mice maintained MABP throughout. LPS administration caused a greater suppression of vascular responses to the thromboxane-mimetic U46619, ANP, acetylcholine and the NO-donor spermine-NONOate in WT versus NPR-A KO mice. This differential effect on vascular function was paralleled by reduced pro-inflammatory cytokine production, iNOS expression and activity (plasma [NO(x)] and cyclic GMP).

Conclusions and implications: These observations suggest that NPR-A activation by natriuretic peptides facilitates iNOS expression and contributes to the vascular dysfunction characteristic of endotoxic shock. Pharmacological interventions that target the natriuretic peptide system may represent a novel approach to treat this life-threatening condition.

Figure 1

Change in mean arterial blood pressure (MABP) in WT and NPR-A KO mice treated with LPS (12.5 mg·kg⁻¹) or saline (both i.v.) for 16 h. Data are represented as mean ± standard error of the mean, n = 9; *P < 0.05 versus WT (across the whole time period). WT, wild-type; KO, knockout; NPR-A, natriuretic peptide receptor-A; LPS, lipopolysaccharide.

Figure 2

Plasma NO_x (A) and cGMP (B) levels in WT and NPR-A KO mice treated with LPS (12.5 mg·kg⁻¹) or saline (both i.v.) for 16 h. Data are represented as mean ± standard error of the mean, n = 7; *P < 0.05 versus corresponding saline control, #P < 0.05 versus LPS-treated WT. cGMP, cyclic GMP; WT, wild-type; KO, knockout; LPS, lipopolysaccharide; NPR-A, natriuretic peptide receptor-A.

Figure 3

Plasma IL-1β (A), IFNγ (B), TNFα (C) and IL-10 (D) in WT and NPR-A KO mice treated with LPS (12.5 mg·kg⁻¹) or saline (both i.v.) for 16 h. Data are represented as mean ± standard error of the mean, n = 6–7; *P < 0.05 versus corresponding saline control, #P < 0.05 versus LPS-treated WT. IL, interleukin; IFNγ, interferon- γ; TNF-α, tumour necrosis factor-α; WT, wild-type; KO, knockout; NPR-A, natriuretic peptide receptor-A; LPS, lipopolysaccharide.

Figure 4

Expression of iNOS protein in lung (A and B) and aorta (C and D) from WT and NPR-A KO mice treated with LPS (12.5 mg·kg⁻¹; i.v.) for 16 h. Protein expression was analysed by Western blot (A and C) and quantified by densitometry (B and D). Data are represented as mean ± standard error of the mean, n = 5 (lung); n = 4 (aorta); *P < 0.05 versus WT. iNOS, inducible nitric oxide synthase; WT, wild-type; KO, knockout; NPR-A, natriuretic peptide receptor-A; LPS, lipopolysaccharide.

Figure 5

Concentration-response curves to U46619 in aortic rings from WT (A) and NPR-A KO (B) mice treated with LPS (12.5 mg·kg⁻¹) or saline (both i.v.) for 16 h. Contraction is expressed as mean ± standard error of the mean tension in g; *P < 0.05 versus saline-treated animals (across the entire curve), n = 7. WT, wild-type; KO, knockout; NPR-A, natriuretic peptide receptor-A; LPS, lipopolysaccharide.

Figure 6

Concentration-response curves to ANP in aortic rings from WT (A) and NPR-A KO (B) mice treated with LPS (12.5 mg·kg⁻¹) or saline (both i.v.) for 16 h. Relaxation is expressed as mean ± standard error of the mean percentage reversal of U46619-induced tone; *P < 0.05 versus saline-treated animals (across the entire curve), n = 9. ANP, atrial natriuretic peptide; WT, wild-type; KO, knockout; NPR-A, natriuretic peptide receptor-A; LPS, lipopolysaccharide.

Figure 7

Concentration-response curve to ACh in aortic rings from WT (A) and NPR-A KO (B) mice treated with LPS (12.5 mg·kg⁻¹) or saline (both i.v.) for 16 h. Relaxation is expressed as mean ± standard error of the mean percentage reversal of U46619-induced tone; *P < 0.05 versus saline-treated animals (across the entire curve), n = 5. WT, wild-type; KO, knockout; NPR-A, natriuretic peptide receptor-A; LPS, lipopolysaccharide.

Figure 8

Concentration-response curve to SPER-NO in aortic rings from WT (A) and NPR-A KO (B) mice treated with LPS (12.5 mg·kg⁻¹) or saline (both i.v.) for 16 h. Relaxation is expressed as mean ± standard error of the mean percentage reversal of U46619-induced tone; *P < 0.05 versus saline-treated animals (across the entire curve), n = 5. SPER-NO, spermine-NONOate; WT, wild-type; KO, knockout; NPR-A, natriuretic peptide receptor-A; LPS, lipopolysaccharide.

Figure 9

Concentration-response curve to forskolin in aortic rings from WT (A) and NPR-A KO (B) mice treated with LPS (12.5 mg·kg⁻¹) or saline (both i.v.) for 16 h. Relaxation is expressed as mean ± standard error of the mean percentage reversal of U46619-induced tone; *P < 0.05 versus saline-treated animals (across the entire curve), n = 5. WT, wild-type; KO, knockout; NPR-A, natriuretic peptide receptor-A; LPS, lipopolysaccharide.