Nifedipine increases microvascular permeability via a direct local effect on postcapillary venules

Myocardial oedema: pathophysiological basis and implications for the failing heart

Myocardial fluid homeostasis relies on a complex interplay between microvascular filtration, interstitial hydration, cardiomyocyte water uptake and lymphatic removal. Dysregulation of one or more of these mechanisms may result in myocardial oedema. Interstitial and intracellular fluid accumulation disrupts myocardial architecture, intercellular communication, and metabolic pathways, decreasing contractility and increasing myocardial stiffness. The widespread use of cardiac magnetic resonance enabled the identification of myocardial oedema as a clinically relevant imaging finding with prognostic implications in several types of heart failure. Furthermore, growing experimental evidence has contributed to a better understanding of the physical and molecular interactions in the microvascular barrier, myocardial interstitium and lymphatics and how they might be disrupted in heart failure. In this review, we summarize current knowledge on the factors controlling myocardial water balance in the healthy and failing heart and pinpoint the new potential therapeutic avenues.

Hypoxia-reoxygenation-induced endothelial barrier failure: role of RhoA, Rac1 and myosin light chain kinase

Hypoxia-reoxygenation induces loss of endothelial barrier function and oedema formation, which presents a major impediment for recovery of the organ. The integrity of the endothelial barrier is highly dependent on its contractile machinery and actin dynamics, which are precisely regulated by Rho GTPases. Perturbed activities of these Rho-GTPases under hypoxia-reoxygenation lead to derangement of the actin cytoskeleton and therefore may affect the integrity of the endothelial barrier. The aim of the present study was to analyse the role of these GTPases in regulating endothelial barrier function during hypoxia-reoxygenation in cultured porcine aortic endothelial cells and isolated perfused rat hearts. Hypoxia-reoxygenation induced an increase in albumin permeability of endothelial monolayers accompanied by an activation of the endothelial contractile machinery, derangement of the actin cytoskeleton and loss of VE-cadherin from cellular junctions. Inhibition of contractile activation with ML-7 partially protected against hypoxia-reoxygenation-induced hyperpermeability. Likewise, reoxygenation caused an increase in RhoA and a reduction in Rac1 activity accompanied by enhanced stress fibre formation and loss of peripheral actin. Inhibition of RhoA/rho kinase (Rock) signalling with RhoA or Rock inhibitors led to a complete depolymerisation and derangement of the actin cytoskeleton and worsened hypoxia-reoxygenation-induced hyperpermeability. Activation of Rac1 using a cAMP analogue, 8-CPT-O-Me-cAMP, which specifically activates Epac/Rap1 signalling, restored peripheral localisation of actin and VE-cadherin at cellular junctions and abrogated reoxygenation-induced hyperpermeability. Similar results were reproduced in isolated saline-perfused rat hearts. These data show that activation of Rac1 but not the inhibition of RhoA preserves endothelial integrity against reoxygenation-induced loss of barrier function.

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 approximately 0.15% per minute versus approximately 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.

Changes in the rat subcutaneous connective tissue after saline and histamine injection in relation to fluid storage and excretion

An experimental design was developed for morphometric analysis of the subcutaneous connective tissue after the subcutaneous injection of 0.1 ml of saline or a histamine solution (0.01, 0.1 or 1% histamine dihydrochloride in saline). The subcutaneous connective tissue of 4-week-old rats, originally 170.0 +/- 13.6 mum in thickness, swelled 5.2-fold at 15 min, 3.0-fold at 2 h, and 1.2-fold at 6 h after the injection of saline. The total cross sectional area of both blood and lymphatic vessels increased when compared to that at pre-injection (0.0186 +/- 0.0030 mm(2) in 6-mm-long specimen), 1.4-fold at 15 min, 2.2-fold at 2 h, and 1.1-fold at 6 h post-injection, while the total number of these vessels increased 1.1-fold at 2 h. The total cross sectional area of lymphatic vessels (0.0006 +/- 0.0002 mm(2) in 6-mm-long specimen) alone surged 7.7-fold at 15 min, 4.8-fold at 2 h, and 7.3-fold at 6 h. Collagen fibers were respectively highly, moderately, and mildly disorganized in arrangement at 15 min, 2 h, and 6 h after the saline injection. Histamine elicited an earlier, longer, and more pronounced vasodilatation, particularly at high concentrations. The transvascular permeability of Evans blue increased depending on the concentration of histamine. These findings indicate that the subcutaneous connective tissue has the ability to expand and store a considerable amount of fluid and reversibly returns to normal steady-state conditions by increasing fluid excretion into the blood and lymphatic vessels. It was also strongly suggested that the blood vessels are deeply involved in the excretion and volume regulation of the tissue fluid.