Enhancement of cytosolic calcium, prostacyclin and nitric oxide by bradykinin and the ACE inhibitor ramiprilat in porcine brain capillary endothelial cells

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Rapakinin, an anti-hypertensive peptide derived from rapeseed protein, dilates mesenteric artery of spontaneously hypertensive rats via the prostaglandin IP receptor followed by CCK(1) receptor

The anti-hypertensive peptide Arg-Ile-Tyr, which was isolated based on its inhibitory activity (IC(50)=28microM) for angiotensin I-converting enzyme (ACE) from the subtilisin digest of rapeseed protein, exhibited vasorelaxing activity (EC(50)=5.1microM) in an endothelium-dependent manner in the mesenteric artery of spontaneously hypertensive rats (SHRs). We named the peptide rapakinin. ACE inhibitors are reported to induce nitric oxide (NO)-dependent vasorelaxation by elevating the endogenous bradykinin level; however, the vasorelaxation induced by 10microM of rapakinin was blocked only insignificantly by HOE140 or N(G)-nitro-l-arginine methyl ester (l-NAME), antagonists of bradykinin B(2) receptor and an inhibitor of NO synthase, respectively. On the other hand, the vasorelaxation induced by 10microM rapakinin was significantly blocked by indomethacin and CAY10441, a cyclooxygenase (COX) inhibitor and an antagonist of the IP receptor, respectively. The vasorelaxing activity of rapakinin was also blocked by lorglumide, an antagonist of the cholecystokinin (CCK) CCK(1) receptor, although rapakinin has no affinity for the IP and CCK(1) receptors. The vasorelaxation induced by 10microM iloprost, an IP receptor agonist, was also blocked by lorglumide, suggesting that CCK-CCK(1) receptor system is activated downstream of the PGI(2)-IP receptor system. The anti-hypertensive activity of rapakinin after oral administration in SHRs was also blocked by CAY10441 and lorglumide. These results suggest that the anti-hypertensive activity of rapakinin might be mediated mainly by the PGI(2)-IP receptor, followed by CCK-CCK(1) receptor-dependent vasorelaxation.

Interaction of Endothelial Nitric Oxide and Angiotensin in the Circulation

Discovery of the unexpected intercellular messenger and transmitter nitric oxide (NO) was the highlight of highly competitive investigations to identify the nature of endothelium-derived relaxing factor. This labile, gaseous molecule plays obligatory roles as one of the most promising physiological regulators in cardiovascular function. Its biological effects include vasodilatation, increased regional blood perfusion, lowering of systemic blood pressure, and antithrombosis and anti-atherosclerosis effects, which counteract the vascular actions of endogenous angiotensin (ANG) II. Interactions of these vasodilator and vasoconstrictor substances in the circulation have been a topic that has drawn the special interest of both cardiovascular researchers and clinicians. Therapeutic agents that inhibit the synthesis and action of ANG II are widely accepted to be essential in treating circulatory and metabolic dysfunctions, including hypertension and diabetes mellitus, and increased availability of NO is one of the most important pharmacological mechanisms underlying their beneficial actions. ANG II provokes vascular actions through various receptor subtypes (AT1, AT2, and AT4), which are differently involved in NO synthesis and actions. ANG II and its derivatives, ANG III, ANG IV, and ANG-(1-7), alter vascular contractility with different mechanisms of action in relation to NO. This review article summarizes information concerning advances in research on interactions between NO and ANG in reference to ANG receptor subtypes, radical oxygen species, particularly superoxide anions, ANG-converting enzyme inhibitors, and ANG receptor blockers in patients with cardiovascular disease, healthy individuals, and experimental animals. Interactions of ANG and endothelium-derived relaxing factor other than NO, such as prostaglandin I2 and endothelium-derived hyperpolarizing factor, are also described.

Cyclic ADP ribose-mediated Ca2+ signaling in mediating endothelial nitric oxide production in bovine coronary arteries

The present study tested the hypothesis that cyclic ADP ribose (cADPR) serves as a novel second messenger to mediate intracellular Ca2+ mobilization in coronary arterial endothelial cells (CAECs) and thereby contributes to endothelium-dependent vasodilation. In isolated and perfused small bovine coronary arteries, bradykinin (BK)-induced concentration-dependent vasodilation was significantly attenuated by 8-bromo-cADPR (a cell-permeable cADPR antagonist), ryanodine (an antagonist of ryanodine receptors), or nicotinamide (an ADP-ribosyl cyclase inhibitor). By in situ simultaneously fluorescent monitoring, Ca2+ transient and nitric oxide (NO) levels in the intact coronary arterial endothelium preparation, 8-bromo-cADPR (30 microM), ryanodine (50 microM), and nicotinamide (6 mM) substantially attenuated BK (1 microM)-induced increase in intracellular [Ca2+] by 78%, 80%, and 74%, respectively, whereas these compounds significantly blocked BK-induced NO increase by about 80%, and inositol 1,4,5-trisphosphate receptor blockade with 2-aminethoxydiphenyl borate (50 microM) only blunted BK-induced Ca2+-NO signaling by about 30%. With the use of cADPR-cycling assay, it was found that inhibition of ADP-ribosyl cyclase by nicotinamide substantially blocked BK-induced intracellular cADPR production. Furthermore, HPLC analysis showed that the conversion rate of beta-nicotinamide guanine dinucleotide into cyclic GDP ribose dramatically increased by stimulation with BK, which was blockable by nicotinamide. However, U-73122, a phospholipase C inhibitor, had no effect on this BK-induced increase in ADP-ribosyl cyclase activity for cADPR production. In conclusion, these results suggest that cADPR importantly contributes to BK- and A-23187-induced NO production and vasodilator response in coronary arteries through its Ca2+ signaling mechanism in CAECs.

Enalapril attenuates angiotensin II-induced atherosclerosis and vascular inflammation

Angiotensin converting enzyme (ACE) inhibitors prevent a wide variety of key events underlying atherogenesis. Whether these actions depend solely on reduction of angiotensin II (Ang II) generation is still to be determined. This study was undertaken to determine whether enalapril, an ACE inhibitor, prevents atherosclerosis and vascular inflammation induced by Ang II in apolipoprotein E-deficient (apoE-KO) mice. Subcutaneous infusion of Ang II (1.44 mg/(kg day)) for 4 weeks increased blood pressure and accelerated atherosclerosis development in the carotid arteries. The expression of the endothelial adhesion molecules E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), as well as the chemokines monocyte chemotactic protein-1 (MCP-1) and macrophage-colony stimulating factor (M-CSF) was up-regulated in the aortas of Ang II-treated mice. Enalapril co-treatment (25 mg/(kg day), in drinking water) prevented the development of atherosclerosis without affecting blood pressure or circulating cholesterol. In addition to preventing the Ang II-induced over-expression of adhesion molecules and chemokines in the aorta, enalapril up-regulated the expression of peroxisome proliferator-activated receptors (PPARs)-alpha and -gamma, potential anti-inflammatory transcription factors. In the aortic arch, a lesion-prone site, the co-treatment with enalapril reduced the percentage of arterial wall occupied by macrophages and foam cells, medial sclerosis and elastin reduplication. Together, these data suggest an important role for Ang II-independent mechanisms in the antiatherogenic and anti-inflammatory effects of ACE inhibitors.

The cardioprotective effect of dual metallopeptidase inhibition: respective roles of endogenous kinins and natriuretic peptides

The objective of the present study was to assess the cardioprotective effect of dual NEP–ACE inhibition in relation to endogenous cardiac bradykinin (BK), its active metabolite des-Arg9-BK, endogenous brain natriuretic peptides (BNP), and cGMP. Rats were treated with the dual metallopeptidase inhibitor, omapatrilat, or the ACE inhibitor, ramipril, for 7 d (1 mg·kg–1·d–1). Hearts were then isolated and subjected to a zero-flow ischemia and reperfusion (except controls), in the absence or presence of either a B2-receptor antagonist (Hoe-140), a B1-receptor antagonist (Lys-Leu8-des-Arg9-BK), or the GC-A/GC-B-receptor antagonist (HS-142-1). Chronic omapatrilat and ramipril increased the amount of endogenous BK collected upon reperfusion, but only ramipril increased that of des-Arg9-BK. Only omapatrilat increased both peak BNP and peak cGMP upon reperfusion, those increases being blocked by Hoe-140. Chronic omapatrilat (but not ramipril) decreased the total noradrenaline and lactate dehydrogenase release during the reperfusion period. Importantly, only omapatrilat improved the functional recovery of the ischemic reperfused heart, with a reduced left ventricular end-diastolic pressure, and improved developed left ventricular pressure. All cardio protective effects of omapatrilat were blocked by Hoe-140 and by HS-142-1, but not by the B1-receptor antagonist. In conclusion, a chronic treatment with a dual metallopeptidase inhibitor demonstrated a cardioprotective action not observed with an ACE inhibitor in a context of severe ischemia in rat isolated hearts, which was mediated by both endogenous BK and BNP.Key words: ACE inhibitors, omapatrilat, bradykinin, natriuretic peptide, ischemia, reperfusion.

Urotensin II is a nitric oxide-dependent vasodilator and natriuretic peptide in the rat kidney

Recent studies have indicated that urotensin II (UII), a cyclic peptide, is vasoactive and may be involved in cardiovascular dysfunctions. It remains unknown, however, whether UII plays a role in the control of renal vascular tone and tubular function. In the present study, a continuous infusion of synthetic human UII (hUII) into the renal artery (RA) in anesthetized rats was found to increase renal blood flow (RBF) and urinary water and sodium excretion (UV and UNaV) in a dose-dependent manner. At a dose of 20 ng. kg-1. min-1, it increased RBF by 20% and UV and UNaV by 94 and 109%, respectively. Nitric oxide (NO) synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) completely abolished hUII-induced increases in RBF and water/sodium excretion. In isolated, pressurized, and phenylephrine-precontracted small RA with internal diameter of approximately 200 microm, hUII produced a concentration-dependent vasodilation with a maximal response of 55% at 1.5 microM. l-NAME significantly blocked this hUII-induced vasodilation by 60%. In denuded RA, hUII had neither vasodilator nor vasoconstrictor effect. With the use of 4,5-diaminofluorescein diacetate-based fluorescence imaging analysis of NO levels, hUII (1 microM) was shown to double the NO levels within the endothelium of freshly dissected small RA, and l-NAME blocked this UII-induced production of endothelial NO. These results indicate that UII produces vasodilator and natriuretic effects in the kidney and that UII-induced vasodilation is associated with increased endothelial NO in the RA.

Bradykinin-induced proinflammatory signaling mechanisms

Intravital microscopic techniques were used to examine the mechanisms underlying bradykinin-induced leukocyte/endothelial cell adhesive interactions (LECA) and venular protein leakage (VPL) in single postcapillary venules of the rat mesentery. The effects of bradykinin superfusion to increase LECA and VPL were prevented by coincident topical application of either a bradykinin-B(2) receptor antagonist, a cell-permeant superoxide dismutase (SOD) mimetic or antioxidant, or inhibitors of cytochrome P-450 epoxygenase (CYPE) or protein kinase C (PKC) but not by concomitant treatment with either SOD, a mast cell stabilizer, or inhibitors of nitric oxide synthase, cyclooxygenase, xanthine oxidase, NADPH oxidase, or platelet-activating factor. Immunoneutralizing P-selectin or intercellular adhesion molecule-1 (ICAM-1) completely prevented bradykinin-induced leukocyte adhesion and emigration but did not affect VPL. On the other hand, stabilization of F-actin with phalloidin prevented bradykinin-induced leukocyte emigration and VPL but did not alter leukocyte adhesion. These data indicate that bradykinin induces LECA in rat mesenteric venules via a B(2)-receptor-initiated, CYPE-, oxidant- and PKC-mediated, P-selectin- and ICAM-1-dependent mechanism. Bradykinin also produced VPL, an effect that was initiated by stimulation of B(2) receptors and involved CYPE and PKC activation, oxidant generation, and cytoskeletal reorganization but was independent of leukocyte adherence and emigration.

Simultaneous in situ monitoring of intracellular Ca2+ and NO in endothelium of coronary arteries

We developed an in situ assay system to simultaneously monitor intracellular Ca(2+) concentration ([Ca(2+)](i), fura 2 as indicator) and nitric oxide (NO) levels [4,5-diaminofluorescein as probe] in the intact endothelium of small bovine coronary arteries by using a fluorescent microscopic imaging technique with high-speed wavelength switching. Bradykinin (BK; 1 microM) stimulated a rapid increase in [Ca(2+)](i) followed by an increase in NO production in the endothelial cells. The protein tyrosine phosphatase inhibitor phenylarsine oxide (PAO; 10 microM) induced a gradual, small increase in [Ca(2+)](i) and a slow increase in intracellular NO levels. Removal of extracellular Ca(2+) and depletion of Ca(2+) stores completely blocked BK-induced increase in NO production but had no effect on PAO-induced NO production. However, a further reduction of [Ca(2+)](i) by application of BAPTA-AM or EGTA with ionomycin abolished the PAO-induced NO increase. These results indicate that a simultaneous monitoring of [Ca(2+)](i) and intracellular NO production in the intact endothelium is a powerful tool to study Ca(2+)-dependent regulation of endothelial nitric oxide synthase, which provides the first direct evidence for a permissive role of Ca(2+) in tyrosine phosphorylation-induced NO production.

Bradykinin increases permeability by calcium and 5-lipoxygenase in the ECV304/C6 cell culture model of the blood-brain barrier

The blood-brain barrier (BBB) was modelled in this study using ECV304 cells in co-culture with rat C6 glioma cells, which resulted in elevated transendothelial electrical resistance (TEER). The inflammatory mediator bradykinin (1 microM) was studied and found to induce a fall in TEER; the link between this change and intracellular free calcium concentration ([Ca(2+)](i)) was then examined. 1 microM bradykinin produced a peak-plateau increase in [Ca(2+)](i). The peak showed desensitization and was dose dependent (over 0.1 nM to 1 microM). The [Ca(2+)](i) increase was blocked by the B(2) antagonist HOE 140 (1 microM) without effect from a B(1) agonist and antagonist. The plateau response was abolished in Ca(2+)-free solution containing 2 mM EDTA, and also by the Ca(2+) channel blockers lanthanum, La(3+) (10 microM), and SKF 96365 (100 microM). The store Ca(2+)ATPase inhibitor thapsigargin (1 microM) abolished the peak response. The putative phospholipase C inhibitors, U73122 (20 microM) and ETH-18-OCH(3) (100 microM), unexpectedly increased [Ca(2+)](i); after their application, bradykinin was ineffective. Agents without effect on Ca(2+) responses to bradykinin included the phospholipase A(2) (PLA(2)) inhibitor aristolochic acid (0.5 mM), cyclooxygenase inhibitor indomethacin (100 microM), 5-lipoxygenase inhibitor nordihydroguaiaretic acid, NDGA (100 microM), calphostin C (0.5 microM), L-NAME (1 mM) and nifedipine (10 microM). The fall in TEER from bradykinin was blocked by HOE 140, U73122 and thapsigargin combined with La(3+), and also by aristolochic acid and NDGA, but not indomethacin, calphostin C or L-NAME. U73122 increased TEER while ETH-18-OCH(3) reduced it. Thus bradykinin reduced TEER through B(2) receptor-linked release of Ca(2+) from thapsigargin-sensitive stores, leading to activation of PLA(2) and metabolism of arachidonic acid by 5-lipoxygenase.

Plasma kallikrein localisation in human blood vessels

Immunoreactive plasma kallikrein/prekallikrein was detected in the endothelial cells and the smooth muscle cells of the arteries examined. The most intense overall immunolabelling of plasma kallikrein/prekallikrein was visualized in the medium to small size arteries. The endothelial cells of the pulmonary artery and the smooth muscle cells of the supracallosal artery showed the highest intensity of plasma kallikrein/prekallikrein labelling. The least defined labelling occurred in the tunica adventitia. The renal vein was the only blood vessel that showed no trace of immunoreactive plasma kallikrein/prekallikrein. The question arises as to the mechanisms that could be involved in the in vivo conversion of plasma kallikrein/prekallikrein into the active enzymatic molecule. The experiments indicate that a bacterial elastase cleaves the Arg371-Ile372 scissile bond within a disulphide bridge of the prekallikrein molecule. This is the bond that is cleaved also during activation of prekallikrein by trypsin-like proteinases. Functionally, the endogenous activation of plasma prekallikrein is of considerable importance, both in the regulation of blood flow and blood pressure and in the causation of septic shock. The incidental finding at histology, of patchy atheromatous disease in the coronary, vertebral and supracallosal arteries, assisted in elucidating the role of plasma kallikrein/prekallikrein in the commonest disease affecting human blood vessels. Intense labelling for plasma kallikrein was observed in the endothelial cells, foamy macrophages, inflammatory cells and fibroblasts within the thickened intima of the plaque as well as in smooth muscle cells of the underlying tunica media. The intense immunolabelling of plasma kallikrein/prekallikrein in these regions suggest that these may be induced by atheromatous disease.

Endogenous endothelial nitric oxide synthase-derived nitric oxide is a physiological regulator of myocardial oxygen consumption

Our objective was to determine the precise role of endothelial nitric oxide synthase (eNOS) as a modulator of cardiac O2 consumption and to further examine the role of nitric oxide (NO) in the control of mitochondrial respiration. Left ventricle O2 consumption in mice with defects in the expression of eNOS [eNOS (-/-)] and inducible NOS [iNOS (-/-)] was measured with a Clark-type O2 electrode. The rate of decreases in O2 concentration was expressed as a percentage of the baseline. Baseline O2 consumption was not significantly different between groups of mice. Bradykinin (10(-4) mol/L) induced significant decreases in O2 consumption in tissues taken from iNOS (-/-) (-28+/-4%), wild-type eNOS (+/+) (-22+/-4%), and heterozygous eNOS(+/-) (-22+/-5%) but not homozygous eNOS (-/-) (-3+/-4%) mice. Responses to bradykinin in iNOS (-/-) and both wild-type and heterozygous eNOS mice were attenuated after NOS blockade with N-nitro-L-arginine methyl ester (L-NAME) (-2+/-5%, -3+/-2%, and -6+/-5%, respectively, P<0.05). In contrast, S-nitroso-N-acetyl-penicillamine (SNAP, 10(-4) mol/L), which releases NO spontaneously, induced decreases in myocardial O2 consumption in all groups of mice, and such responses were not affected by L-NAME. In addition, pretreatment with bacterial endotoxin elicited a reduction in basal O2 consumption in tissues taken from normal but not iNOS (-/-)-deficient mice. Our results indicate that the pivotal role of eNOS in the control of myocardial O2 consumption and modulation of mitochondrial respiration by NO may have an important role in pathological conditions such as endotoxemia in which the production of NO is altered.

Potassium supplement upregulates the expression of renal kallikrein and bradykinin B2 receptor in SHR

High potassium intake is known to attenuate hypertension, glomerular lesion, ischemic damage, and stroke-associated death. Our recent studies showed that expression of recombinant kallikrein by somatic gene delivery reduced high blood pressure, cardiac hypertrophy, and renal injury in hypertensive animal models. The aim of this study is to explore the potential role of the tissue kallikrein-kinin system in blood pressure reduction and renal protection in spontaneously hypertensive rats (SHR) on a high-potassium diet. Young SHR were given drinking water with or without 1% potassium chloride for 6 wk. Systolic blood pressure was significantly reduced beginning at 1 wk, and the effect lasted for 6 wk in the potassium-supplemented group compared with that in the control group. Potassium supplement induced 70 and 40% increases in urinary kallikrein levels and renal bradykinin B2 receptor density, respectively (P < 0.05), but did not change serum kininogen levels. Similarly, Northern blot analysis showed that renal kallikrein mRNA levels increased 2.7-fold, whereas hepatic kininogen mRNA levels remained unchanged in rats with high potassium intake. No difference was observed in beta-actin mRNA levels in the kidney or liver of either group. Competitive RT-PCR showed a 1.7-fold increase in renal bradykinin B2 receptor mRNA levels in rats with high potassium intake. Potassium supplement significantly increased water intake, urine excretion, urinary kinin, cAMP, and cGMP levels. This study suggests that upregulation of the tissue kallikrein-kinin system may be attributed, in part, to blood pressure-lowering and diuretic effects of high potassium intake.

Na+-Ca2+ exchange and its implications for calcium homeostasis in primary cultured rat brain microvascular endothelial cells

1. The role of Na+-Ca2+ exchange in the regulation of the cytosolic free Ca2+ concentration ([Ca2+]i) was studied in primary cultured rat brain capillary endothelial cells. [Ca2+]i was measured by digital fluorescence imaging in cells loaded with fura-2. 2. ATP (100 microM) applied for a short period of time (6 s) caused a rise in [Ca2+]i from 127 +/- 3 (n = 290) to 797 +/- 25 nM, which then declined to the resting level, with a t time required for [Ca2+]i to decline to half of peak [Ca2+]i) of 5.4 +/- 0.09 s. This effect was independent of external Ca2+ and could be abolished by previously discharging the Ca2+ pool of the endoplasmic reticulum with thapsigargin (1 microM). 3. Application of thapsigargin (1 microM) or cyclopiazonic acid (10 microM) to inhibit the Ca2+-ATPase of the endoplasmic reticulum 6 s prior to ATP application did not influence the peak [Ca2+]i but greatly reduced the rate of decline of [Ca2+]i, with t values of 15 +/- 1.6 and 23 +/- 3 s, respectively. 4. In the absence of external Na+ (Na+ replaced by Li+ or N-methylglucamine) the basal [Ca2+]i was slightly elevated (152 +/- 6 nM) and the restoration of [Ca2+]i after the ATP stimulation was significantly slower (t , 7.3 +/- 0.46 s in Li+ medium, 8.12 +/- 0.4 s in N-methylglucamine medium). 5. The external Na+-dependent component of the [Ca2+]i sequestration was also demonstrated in cells stimulated by ATP subsequent to addition of cyclopiazonic acid; in a Na+-free medium [Ca2+]i remained at the peak level in 88 % of the cells after stimulation with ATP. 6. Addition of monensin (10 microM) in the presence of external Na+ increased the resting [Ca2+]i to 222 +/- 9 nM over approximately 1 min and subsequent removal of extracellular sodium resulted in a further increase in [Ca2+]i to a peak of 328 +/- 11 nM, which was entirely dependent on external Ca2+. 7. These findings indicate that a functional Na+-Ca2+ exchanger is present at the blood-brain barrier, which plays a significant role in shaping the stimulation-evoked [Ca2+]i signal and is able to work in reverse mode under pharmacological conditions.

Pathophysiology of the kallikrein-kinin system in mammalian nervous tissue

The nervous system and peripheral tissues in mammals contain a large number of biologically active peptides and proteases that function as neurotransmitters or neuromodulators in the nervous system, as hormones or cellular mediators in peripheral tissue, and play a role in human neurological diseases. The existence and possible functional relevance of bradykinin and kallidin (the peptides), kallikreins (the proteolytic enzymes), and kininases (the peptidases) in neurophysiology and neuropathological states are discussed in this review. Tissue kallikrein, the major cellular kinin-generating enzyme, has been localised in various areas of the mammalian brain. Functionally, it may assist also in the normal turnover of brain proteins and the processing of peptide-hormones, neurotransmitters, and some of the nerve growth factors that are essential for normal neuronal function and synaptic transmission. A specific class of kininases, peptidases responsible for the rapid degradation of kinins, is considered to be identical to enkephalinase A. Additionally, kinins are known to mediate inflammation, a cardinal feature of which is pain, and the clearest evidence for a primary neuronal role exists so far in the activation by kinins of peripherally located nociceptive receptors on C-fibre terminals that transmit and modulate pain perception. Kinins are also important in vascular homeostasis, the release of excitatory amino acid neurotransmitters, and the modulation of cerebral cellular immunity. The two kinin receptors, B2 and B1, that modulate the cellular actions of kinins have been demonstrated in animal neural tissue, neural cells in culture, and various areas of the human brain. Their localisation in glial tissue and neural centres, important in the regulation of cardiovascular homeostasis and nociception, suggests that the kinin system may play a functional role in the nervous system.

Acute ACE inhibition causes plasma extravasation in mice that is mediated by bradykinin and substance P

The use of angiotensin-converting enzyme (ACE) has been associated with the occurrence of adverse effects, including cough and angioneurotic edema. Accumulation of kinins has been suggested to play a major role in these adverse effects of ACE inhibitor, although conclusive evidence for such a role is lacking. We investigated whether ACE inhibition increases plasma extravasation in mice (Swiss, C57Bl/6J, and J129Sv/Ev strains) via inhibition of bradykinin metabolism and stimulation of neurogenic inflammatory mechanisms. Intravenous captopril and enalapril increased the extravasation of Evans blue dye in all tissues examined (trachea, stomach, duodenum, and pancreas). This effect was evident 15 minutes after drug administration. The particulate dye Monastral blue identified the sites of captopril-induced leakage in the microvasculature. Pretreatment with the bradykinin B2 receptor antagonist Hoe 140 or with the tachykinin NK1 receptor antagonist SR 140333 inhibited captopril-evoked increase in plasma extravasation. In mice in which the gene encoding the bradykinin B2 receptor was disrupted by gene targeting, neither bradykinin nor captopril increased plasma extravasation. Pretreatment with Hoe 140 did not reduce the hypotensive response induced by captopril. The present findings suggest that ACE inhibition increases kinin levels in tissues and/or plasma. These increased kinin levels increase microvascular leakage in mouse airways and digestive tract via the release of tachykinins from terminals of primary sensory neurons. Exaggerated kinin production and the subsequent stimulation of peptide release from sensory nerves may be involved in adverse effects of ACE inhibitors.

Endothelial Ca2+ waves preferentially originate at specific loci in caveolin-rich cell edges

Stimulation of endothelial cells (ECs) with ATP evoked an increase in intracellular Ca2+ concentration ([Ca2+]i). In a single bovine aortic EC, the [Ca2+]i rise started at a specific peripheral locus and propagated throughout the entire cell as a Ca2+ wave. The initiation locus was constant upon repeated stimulation with ATP or other agonists (bradykinin and thrombin). The Ca2+ wave was unaffected by the removal of extracellular Ca2+, demonstrating its dependence on intracellular Ca2+ release. Microinjection of heparin into the cell inhibited the ATP-induced Ca2+ responses, indicating that the Ca2+ wave is at least partly mediated by the inositol 1,4, 5-trisphosphate receptor. Immunofluorescence staining revealed that caveolin, a marker protein for caveolae, is distributed heterogeneously in the cell and that Ca2+ waves preferentially originate at caveolin-rich cell edges. In contrast to caveolin, internalized transferrin and subunits of the clathrin-associated adaptor complexes such as adaptor protein-1 and -2 were diffusely distributed. Disruption of microtubules by Colcemid led to redistribution of caveolin away from the edges into the perinuclear center of the cell, and the ATP-induced [Ca2+]i increase was initiated on the rim of the centralized caveolin. Thus, caveolae may be involved in the initiation of ATP-induced Ca2+ waves in ECs.

Neutral endopeptidase and angiotensin-converting enzyme inhibitors increase nitric oxide production in isolated canine coronary microvessels by a kinin-dependent mechanism

Bradykinin is a substrate for both neutral endopeptidase 24.11 (NEP) and angiotensin-converting enzyme (ACE). Our previous studies showed that ACE inhibitors can stimulate nitric oxide production in coronary microvessels, which is mediated by local kinins. Whether inhibition of NEP also can affect local vascular NO production has not been established. To determine the role of NEP in the control of NO production, coronary microvessels were isolated from seven mongrel dogs. Two NEP inhibitors, phosphoramidon and thiorphan, and an ACE inhibitor, ramiprilat, were used. Nitrite, the metabolite of NO in aqueous solution, was measured by using the Griess reaction. Phosphoramidon and thiorphan (10(-6) M) increased nitrite production from 80 +/- 6 to 136 +/- 6 and 144 +/- 7 pmol/mg, respectively. Ramiprilat (10(-8) M) increased nitrite production from 78 +/- 6 to 155 +/- 7 pmol/mg wet weight. The effect of these agents on nitrite release was blocked by L-NAME, which inhibits NO synthase, HOE-140, which blocks bradykinin B2-receptor, and dichloroisocoumarin, which blocks kinin-forming enzymes. These results clearly indicate that inhibition of kinin metabolism by using neutral endopeptidase inhibitors increases NO production from coronary microvessels. Thus neutral endopeptidase plays an important role in local kinin-modulated NO production in the coronary microcirculation and NEP inhibitors may be useful clinical tools in treatment of cardiovascular disease.

Kinin receptors in human vascular tissue: their role in atheromatous disease

Using samples of many human blood vessels, obtained at autopsy and specific antibodies directed to peptide sequences of the kinin B1 and B2 receptors, we demonstrate the localisation of these receptors within the human vascular system using standard immunolabelling techniques. In large elastic arteries and veins, kinin receptors are present only in the endothelial cells whereas in all muscular arteries and arterioles, these receptors are present in both the endothelial and smooth muscle cells. The identification of kinin receptors in human blood vessels confirms that kinins may modulate both vascular permeability and contractility. The incidental finding at histology, of patchy atheromatous disease in the coronary, femoral, vertebral and pericallosal arteries, assisted in elucidating the role of these receptors in the commonest disease affecting human blood vessels. Intense labelling for B1 receptors was observed in the endothelial cells, foamy macrophages, inflammatory cells and fibroblasts within the thickened intima of the plaque as well as in smooth muscle cells of the underlying tunica media. Immunoreactive B2 receptors were also observed in these cells but with reduced intensity. The intense immunolabelling of B1 receptors in these regions suggest that these may be induced by atheromatous disease and may have therapeutic importance for the B1 receptor antagonists.

Distribution of bradykinin B2 receptors in sheep brain and spinal cord visualized by in vitro autoradiography

Bradykinin B2 receptors were localized in the sheep brain and spinal cord by quantitative in vitro autoradiography using a radiolabelled and specific bradykinin B2 receptor antagonist analogue, 3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3,Thi5,D-Tic 7,Oic8]bradykinin, (HPP-HOE 140). This radioligand displays high affinity and specificity for bradykinin B2 receptors. The respective K(i) values of 0.32, 1.37 and 156 nM were obtained for bradykinin, HOE140 and D-Arg[Hyp3,D-Phe7,Leu8]bradykinin competing for radioligand binding to lamina II of sheep spinal cord sections. Using this radioligand, we have demonstrated the distribution of bradykinin B2 receptors in many brain regions which have not been previously reported. The highest density of bradykinin B2 receptors occur in the pleoglial periaqueductal gray, oculomotor and trochlear nuclei and the circumventricular organs. Moderate densities of receptors occur in the substantia nigra, particularly the reticular part, the posterior thalamic and subthalamic nuclei, zona incerta, the red and pontine nuclei, some of the pretectal nuclei and in discrete layers of the superior colliculus. In the hindbrain, moderate levels of bradykinin B2 receptor binding occur in the nucleus of the solitary tract, and in spinal trigeminal, inferior olivary, cuneate and vestibular nuclei. Laminae II, X and dorsal root ganglia display the most striking binding densities in the spinal cord, while the remainder of the dorsal and ventral horn display a low and diffuse density of binding. Bradykinin B2 receptors are extensively distributed throughout the sheep brain and spinal cord, not only to sensory areas but also to areas involved in motor activity.

Expression of nitric oxide synthase in the cerebral microvasculature after traumatic brain injury in the rat

Reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd) histochemistry and nitric oxide synthase (NOS) immunocytochemistry were performed on sections of brain after moderate traumatic brain injury. There was a pronounced increase in NADPHd reactivity and an induction of the endothelial NOS (eNOS) isoform in microvessels surrounding the cortical contusion by 24 h post-injury. This altered microvascular state may contribute to barrier breakdown and hyperemia which characterize traumatic brain injury.

Vasomotor and permeability effects of bradykinin in the cerebral microcirculation

All components of an intracerebral kallikrein-kinin system have been described. Thus, bradykinin (BK) acting from the parenchymal site as well as from the blood site may influence cerebral microcirculation. BK is a potent dilator of extra- and intraparenchymal cerebral arteries when acting from the perivascular site. The vasomotor effect of BK is mediated by B2 receptors which appear to be located at the abluminal membrane of the endothelial cell. The effect of BK is mediated by NO. prostanoids, free radicals, H2O2 or leukotrienes depending on the animal species and on the location of the artery. Selective opening of the blood-brain barrier for small tracers (Na(+)-fluorescein; MW, 376) has been found in cats during cortical superfusion or intraarterial application of BK. This leakage is mediated by B2 receptors located at the luminal and abluminal membrane of the endothelial cells. Formation of brain edema has been found after ventriculo-cisternal perfusion or interstitial infusion of BK. This can be explained by increase of vascular permeability and cerebral blood flow due to arterial dilation thus enhancing driving forces for the extravasation. An increase of the BK concentration in the interstitial space of the brain up to concentrations which induce extravasation, dilatation and oedema formation has been found under several pathological conditions. Thus, BK may be involved in oedema formation after cold lesion, concussive brain injury, traumatic spinal cord and ischemic brain injury. The mediator role of BK in brain edema is further supported by therapeutic results. Brain swelling due to cold lesion or ischemia could be diminished by treatment with kallikrein-inhibitors. Similarly, dilatation of cerebral arterioles after concussive brain injury was reduced by blockade of B2 receptors. Thus, all criteria favour BK as one mediator of vasogenic oedema.

Bradykinin dilates rat middle cerebral artery and its large branches via endothelial B2 receptors and release of nitric oxide

Ring segments of rat middle cerebral artery (MCA) were prepared for measurement of isometric force and precontracted with 10(-4) M uridine triphosphate (UTP). Concentration-effect curves (CEC) were constructed for bradykinin (BK, 10(-8)(-10)(-1) M) in segments with functionally intact (E+) or denuded (E-) endothelium. E- segments did not dilate to BK. The BK receptor was characterized by application of specific B1 or B2 antagonists [des-Arg4-Leu8] BK (10(-5) M) and [D-Arg4-Hyp3-Thi5-D-Tic7-Oic8] BK (HOE140, 3 x 10(-7) M), respectively, or B2 agonist [des-Arg9] BK (10(-8)-10(-4) M). Involvement of nitric oxide (NO) was tested with NG-nitro-L-arginine (LNNA, 10(-4) M). BK induced concentration-dependent relaxation with a maximal effect (Emax) of 40.86 +/- 1.50% at 10(-4) M and a pD2 (-log10 EC50) of 6.818 +/- 0.044. This relaxation could be prevented with HOE140 or LNNA, but was not influenced by [des-Arg(9)-Leu] BK. [des-Arg9] BK did not induce any effect. These results demonstrate that BK induced relaxation via endothelial B2 receptors and release of NO in isolated rat MCA.

Pathway across blood-brain barrier opened by the bradykinin agonist, RMP-7

The route taken by lanthanum (MW 139) across cerebral endothelium was delineated when the blood-brain barrier was opened by RMP-7, a novel bradykinin agonist. Balb C mice were infused through a jugular vein with LaCl3 with or without RMP-7 (5 micrograms/kg). Ten minutes later, the brains were fixed with aldehydes and processed for electron microscopy. The patency of the junctions between endothelial cells was estimated by counting the number of junctions penetrated by LaCl3. Tracer penetrated the junctions in about 25% of microvessels in vehicle infused, control mice and about 58% in the RMP-7 group, where more junctions per vessel were also penetrated. The LaCl3 then penetrated the basal lamina in about 20% of all microvessels in the RMP-7 group, versus 0.50% in the control group. From the basal lamina, the tracer entered perivascular spaces in about 13% of all microvessels in the RMP-7 group and about 0.07% in the controls. Very few endocytic pits or vesicles in the RMP-7 group were labeled, so LaCl3 did not cross endothelium by transcytosis. The increased number of tight junctions penetrated by tracer and its spread into periendothelial basal lamina and interstitial clefts indicated, therefore, a paracellular route of exudation in the RMP-7 treated animals.

Nitric oxide. An important signaling mechanism between vascular endothelium and parenchymal cells in the regulation of oxygen consumption

BACKGROUND

Nitric oxide (NO) is known to be an inhibitor of mitochondrial function. However, the physiological significance of endothelium-derived NO in the control of tissue respiration is not established.

METHODS AND RESULTS

Tissue O2 consumption by skeletal muscle slices of the triceps brachii of normal dogs was measured with a Clark-type O2 electrode/tissue bath system at 37 degrees C. S-Nitroso-N-acetylpenicillamine (SNAP), carbachol (CCh), or bradykinin (BK) decreased tissue O2 consumption by 12 +/- 3% to 55 +/- 8%, 15 +/- 6% to 36 +/- 11%, or 21 +/- 5% to 42 +/- 4% at doses of 10(-7) to 10(-4) mol/L, respectively. The effects of both CCh and BK but not SNAP were eliminated by nitro-L-arginine (NLA, 10(-4) mol/L), consistent with SNAP decomposing to release NO and both CCh and BK stimulating endogenous NO production from L-arginine. Oxygen consumption was also decreased by 8-bromo-cGMP. The mitochondrial uncoupler dinitrophenol blocked the effects of 8-bromo-cGMP but only slightly altered those of SNAP, indicating that the major site of action of NO is the mitochondria. In normal, chronically instrumented, resting conscious dogs, blockade of NO synthase by NLA increased mean arterial pressure by 28 +/- 2.5 mm Hg and hind limb vascular resistance by 114 +/- 12% and decreased blood flow by 39 +/- 3%. Most important, NLA also increased O2 uptake by 55 +/- 9% in hind limb skeletal muscle (P < .05), associated with decreases in PO2 and O2 saturation and an increase in reduced hemoglobin in hind limb venous blood.

CONCLUSIONS

Our results indicate that NO release from vascular endothelial cells appears to play an important physiological role in the regulation of tissue mitochondrial respiration in skeletal muscle and perhaps other organ systems.