The role of atrial natriuretic peptide to attenuate inflammation in a mouse skin wound and individually perfused rat mesenteric microvessels.

We tested the hypothesis that the anti-inflammatory actions of atrial natriuretic peptide (ANP) result from the modulation of leukocyte adhesion to inflamed endothelium and not solely ANP ligation of endothelial receptors to stabilize endothelial barrier function. We measured vascular permeability to albumin and accumulation of fluorescent neutrophils in a full-thickness skin wound on the flank of LysM-EGFP mice 24 h after formation. Vascular permeability in individually perfused rat mesenteric microvessels was also measured after leukocytes were washed out of the vessel lumen. Thrombin increased albumin permeability and increased the accumulation of neutrophils. The thrombin-induced inflammatory responses were attenuated by pretreating the wound with ANP (30 min). During pretreatment ANP did not lower permeability, but transiently increased baseline albumin permeability concomitant with the reduction in neutrophil accumulation. ANP did not attenuate acute increases in permeability to histamine and bradykinin in individually perfused rat microvessels. The hypothesis that anti-inflammatory actions of ANP depend solely on endothelial responses that stabilize the endothelial barrier is not supported by our results in either individually perfused microvessels in the absence of circulating leukocytes or the more chronic skin wound model. Our results conform to the alternate hypothesis that ANP modulates the interaction of leukocytes with the inflamed microvascular wall of the 24 h wound. Taken together with our previous observations that ANP reduces deformability of neutrophils and their strength of attachment, rolling, and transvascular migration, these observations provide the basis for additional investigations of ANP as an anti-inflammatory agent to modulate leukocyte-endothelial cell interactions

Atrial natriuretic peptide: an essential physiological regulator of transvascular fluid, protein transport, and plasma volume

Atrial natriuretic peptide (ANP) acts acutely to reduce plasma volume by at least 3 mechanisms: increased renal excretion of salt and water, vasodilation, and increased vascular permeability. Authors of a study in this issue of the JCI performed a knockout of the receptor for ANP in vascular endothelia in order to distinguish the effects of ANP-dependent increases in vascular permeability from those of other endocrine actions of ANP in the regulation of plasma volume. The knockout mice exhibited reduced vascular permeability to plasma protein, resulting in chronically increased plasma volume, arterial hypertension, and cardiac hypertrophy. Renal excretion and vasodilation did not account for these changes. Thus ANP-induced increases in endothelial permeability may be critical to the ability of ANP to lower arterial blood pressure

Determination of Microvessel Permeability and Tissue Diffusion Coefficient of Solutes by Laser Scanning Confocal Microscopy

Interstitium contains a matrix of fibrous molecules that creates considerable resistance to water and solutes in series with the microvessel wall. On the basis of our preliminary studies, by using laser-scanning confocal microscopy and a theoretical model for interstitial transport, we determined both microvessel solute permeability (P) and solute tissue diffusion coefficient (D) of alpha-lactalbumin (Stokes radius 2.01 nm) from the rate of tissue solute accumulation and the radial concentration gradient around individually perfused microvessel in frog mesentery. P(alpha-lactalbumin) is 1.7 +/- 0.7(SD) x 10(-6) cm/s (n = 6). D(t)/D(free) for alpha-lactalbumin is 27% +/- 5% (SD) (n = 6). This value of D(t)/D(free) is comparable to that for small solute sodium fluorescein (Stokes radius 0.45 nm), while p(alpha-lactalbumin) is only 3.4% of p(sodium fluorescein). Our results suggest that frog mesenteric tissue is much less selective to solutes than the microvessel wall

Dynamics of neutrophil extravasation and vascular permeability are uncoupled during aseptic cutaneous wounding

Transport of macromolecules and transmigration of leukocytes across vascular endothelium are regulated by a tight molecular junction, but the mechanisms by which these two inflammatory events are differentially controlled in time and magnitude during aseptic cutaneous wounding remain elusive. A real-time fluorescence imaging technique was developed to simultaneously track influx of Alexa 680-labeled albumin and genetically tagged enhanced green fluorescent protein-neutrophils [polymorphonuclear neutrophils (PMN)] within the wound bed. Vascular permeability increased approximately threefold more rapidly than the rate of PMN influx, reaching a maximum at 12 h, on the order of ∼0.15% per minute versus ∼0.05% per minute for PMN influx, which peaked at 18 h. Systemic depletion of PMN with antibody blocked their extravasation to the wound but did not alter the increase in vascular permeability. In contrast, pretreatment with antiplatelet GPIb decreased permeability by 25% and PMN influx by 50%. Hyperpermeability stimulated by the endothelium-specific agonists VEGF or thrombin at 24 h postwounding was completely inhibited by blocking Rho-kinase-dependent signaling, whereas less inhibition was observed at 1 h and neutrophil influx was not perturbed. These data suggest that in aseptic wounds, the endothelium maintains a tight junctional barrier to protein leakage that is independent of neutrophil transmigration, partially dependent on circulating platelets, and associated with Rho-kinase-dependent signaling