C-type natriuretic peptide (CNP), a member of the natriuretic peptide family, is expressed widely in central and peripheral tissues, with particularly abundant expression in vascular endothelial cells; however, the physiological function(s) of endothelial CNP has been uncertain. Recently, we demonstrated that, akin to other endothelium-derived autacoids such as nitric oxide (NO), CNP is a potent vasodilator that is released in response to endothelial stimuli (i.e. acetylcholine) and plays an important role in the regulation of vascular tone and local blood flow (Chauhan et al. 2003). In the present study we tested the hypothesis that, like NO, CNP also regulates leukocyte-endothelial interactions.

Intravital microscopy was employed to assess the effects of CNP on leukocyte activation in vivo in mice with high basal leukocyte activation (endothelial NO synthase knockout, eNOS^-/-) or under acute inflammatory conditions (induced by IL-1β or histamine). Male wild-type (WT) and eNOS^-/- mice (10–15g) were anesthetized with diazepam (6mg/kg;s.c.) and Hypnorm (0.7mg/kg fentanyl citrate & 20mg/kg fluanisone; i.m.). The mesenteric vascular bed was exteriorised and viewed with a light microscope. Mesenteries were superfused (2ml/min) with bicarbonate-buffered solution at 37°C (g/litre: NaCl 7.71; KCl 0.25; MgSO₄ 0.14; NaHCO 3 1.51; CaCl₂ 0.22 [pH 7.4], gassed with 5% CO₂/95% N₂). Post-capillary venules (diameter 20-50µm; length 100µm) were randomly chosen and leukocyte rolling/adhesion determined over a period of 60 s.

Superfusion of mesenteric vessels with CNP (10min) reduced basal leukocyte flux in eNOS^-/- mice in a concentration-dependent manner (control vs CNP: 19±2.6 vs 16±2.9, n=7; 25±6.8 vs 16±4.6, n=7, P<0.05 and 22±3.0 vs 7±2.2, n=9, P<0.01 for 0.1μM, 0.3μM and 1μM respectively). The effect of CNP was rapid in onset (within 5min) and completely reversed within 10min following washout. Similarly, cANF^4-23 (1μM), a selective agonist of natriuretic peptide receptor-C (NPR-C), attenuated leukocyte flux from 27±7.5 to 14±4.6 (n=6, P<0.05) whilst the vasodilator calcitonin gene-related peptide (10nM) had no effect (n=4, P>0.05). IL-1β (5ng i.p., 90min) elevated leukocyte flux in eNOS^-/- to 40±11.3 (n=6), which was reduced to 16±4.8 (n=6, P<0.05) in the presence of CNP (1μM). CNP (1μM) also attenuated leukocyte flux in WT animals treated with IL-1β (from 32±5.6 to 20±5.1, n=6, P<0.05) or histamine (100μM; from 31±5.8 to 21±4.8, n=8, P<0.05).

Thus, CNP is a novel modulator of acute inflammation characterised by enhanced leukocyte activation. These anti-inflammatory effects appear to be mediated, at least in part, via activation of NPR-C. Consequently, endothelial CNP is likely to maintain an anti-inflammatory/anti-atherogenic influence on the blood vessel wall and the CNP/NPR-C pathway is a novel target for therapeutic intervention in inflammatory cardiovascular disorders.

Chauhan, S.D. et al. (2003). Proc. Natl. Acad. Sci. USA., 100, 1426-1431.

This work was supported by The Wellcome Trust