Omapatrilat: a new tool for understanding metabolism of bradykinin at the endothelium level

Vasoactive peptides in cardiovascular (patho)physiology

Numerous vasoactive agents play an important physiological role in regulating vascular tone, reactivity and structure. In pathological conditions, alterations in the regulation of vasoactive peptides result in endothelial dysfunction, vascular remodeling and vascular inflammation, which are important processes underlying vascular damage in cardiovascular disease. Among the many vasoactive agents implicated in vascular (patho)biology, angiotensin II (Ang II), endothelin (ET), serotonin and natriuretic peptides appear to be particularly important because of their many pleiotropic actions and because they have been identified as potential therapeutic targets in cardiovascular disease. Ang II, ET-1, serotonin and natriuretic peptides mediate effects via specific receptors, which belong to the group of G-protein-coupled receptors. ET, serotonin and Ang II are primarily vasoconstrictors with growth-promoting actions, whereas natriuretic peptides, specifically atrial, brain and C-type natriuretic peptides, are vasodilators with natriuretic effects. Inhibition of vasoconstrictor actions with drugs that block peptide receptors, compounds that inhibit enzymes that generate vasoactive peptides or agents that increase levels of natriuretic peptides are potentially valuable therapeutic tools in the management of cardiovascular diseases. This review focuses on ET, natriuretic peptides and serotonin. The properties and distribution of these vasoactive agents and their receptors, mechanisms of action and implications in cardiovascular (patho)physiology will be discussed.

Matrix metalloproteinase 2-induced venous dilation via hyperpolarization and activation of K+ channels: relevance to varicose vein formation

BACKGROUND

Varicose veins are a common disorder of extensive venous dilation and remodeling with an as-yet unclear mechanism. Studies have shown increased plasma and tissue levels of matrix metalloproteinases (MMPs) in human varicose veins and animal models of venous hypertension. Although the effects of MMPs are generally attributed to extracellular matrix degradation, their effects on the mechanisms of venous contraction/relaxation are unclear. Our preliminary experiments have demonstrated that MMP-2 causes inhibition of phenylephrine-induced venous contraction. The purpose of this study was to determine whether MMP-induced inhibition of venous contraction involves an endothelium-dependent and/or -independent pathway.

METHODS

Circular segments of the inferior vena cava (IVC) were isolated from male Sprague-Dawley rats and suspended between two wire hooks in a tissue bath, and the effects of MMP-2 on phenylephrine- and KCl-induced contraction were measured. To study the role of endothelium-derived vasodilators, experiments were performed in the presence and absence of endothelium; N(G)-l-nitro-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis; indomethacin, an inhibitor of prostacyclin synthesis; cromakalim, an activator of adenosine triphosphate-sensitive K+ channels (K(ATP)); and iberiotoxin, a blocker of large-conductance Ca2+-dependent K+ channels (BK(Ca)) and smooth muscle hyperpolarization.

RESULTS

In endothelium-intact IVC segments, phenylephrine (10(-5) mol/L) caused significant contraction that slowly declined to 82.0% in 30 minutes. The addition of MMP-2 (1 microg/mL) caused a gradual decrease of phenylephrine contraction to 39.5% at 30 minutes. In endothelium-denuded IVC, MMP-2 induced a greater reduction of phenylephrine contraction, to 7.6%. In the presence of L-NAME (10(-4) mol/L), MMP-2 caused a marked decrease in phenylephrine contraction, to 4.4%. Large MMP-2-induced inhibition of phenylephrine contraction was also observed in IVC treated with L-NAME plus indomethacin. MMP-2 caused relaxation of phenylephrine contraction in IVC pretreated with cromakalim (10(-7) mol/L), an activator of K(ATP) channels. MMP-2-induced inhibition of phenylephrine contraction was abrogated in the presence of iberiotoxin (10(-8) mol/L), a blocker of BK(Ca). MMP-2 did not inhibit venous contraction during membrane depolarization by 96 mmol/L KCl, a condition that prevents outward K+ conductance and cell hyperpolarization.

CONCLUSIONS

MMP-2 causes significant IVC relaxation that is potentiated in the absence of endothelium or during blockade of endothelium-mediated nitric oxide and prostacyclin synthesis. The lack of effects of MMP-2 on KCl contraction and in iberiotoxin-treated veins suggests MMP-2-induced smooth muscle hyperpolarization and activation of BK(Ca) channels--a novel effect of MMP that may play a role in the early stages of venous dilation and varicose vein formation.