Effect of nitro-L-arginine on electrical and mechanical responses to acetylcholine in the superior mesenteric artery from stroke-prone hypertensive rat

Hyaluronidase 1 Deficiency Preserves Endothelial Function and Glycocalyx Integrity in Early Streptozotocin-Induced Diabetes

Hyaluronic acid (HA) is a major component of the glycocalyx involved in the vascular wall and endothelial glomerular permeability barrier. Endocytosed hyaluronidase HYAL1 is known to degrade HA into small fragments in different cell types, including endothelial cells. In diabetes, the size and permeability of the glycocalyx are altered. In addition, patients with type 1 diabetes present increased plasma levels of both HA and HYAL1. To investigate the potential implication of HYAL1 in the development of diabetes-induced endothelium dysfunction, we measured endothelial markers, endothelium-dependent vasodilation, arteriolar glycocalyx size, and glomerular barrier properties in wild-type and HYAL1 knockout (KO) mice with or without streptozotocin (STZ)-induced diabetes. We observed that 4 weeks after STZ injections, the lack of HYAL1 1) prevents diabetes-induced increases in soluble P-selectin concentrations and limits the impact of the disease on endothelium-dependent hyperpolarization (EDH)-mediated vasorelaxation; 2) increases glycocalyx thickness and maintains glycocalyx structure and HA content during diabetes; and 3) prevents diabetes-induced glomerular barrier dysfunction assessed using the urinary albumin-to-creatinine ratio and urinary ratio of 70- to 40-kDa dextran. Our findings suggest that HYAL1 contributes to endothelial and glycocalyx dysfunction induced by diabetes. HYAL1 inhibitors could be explored as a new therapeutic approach to prevent vascular complications in diabetes.

Deficiency of NG2+ cells contributes to the susceptibility of stroke-prone spontaneously hypertensive rats

AIMS

The purpose of this study is to investigate whether the NG2(+) cells, a class of oligodendrocyte progenitor cells, is involved in the pathophysiology of stroke in stroke-prone spontaneously hypertensive rat (SHR-SP).

METHODS

SHR-SP, SHR, Wistar-Kyoto rats (WKY), and C57BJ/6 mice were used. Immunohistochemistry was conducted to evaluate the number of NG2(+) cells in frozen brain sections. Demyelination was evaluated by Sudan black staining and serum level of myelin basic protein. Middle cerebral artery occlusion (MCAO) was performed to prepare experimental stroke model.

RESULTS

The number of NG2(+) cells was significantly decreased in infarct core and increased in penumbra in WKY rats after MCAO. In brain sections of 6-month-old SHR-SP, the number of NG2(+) cells was significantly (P < 0.01) less than that in age-matched SHR and WKY rats. However, this phenomenon was not observed in 3-month-old rats. Demyelination was found in 6-month-old SHR-SP but not in 3-month-old SHR-SP. Pharmacological treatment of cuprizone in mice induced demyelination and enlargement of cerebral infarction after MCAO.

CONCLUSION

The decline of NG2(+) cells may cause demyelination and contribute to the susceptibility of SHR-SP to ischemic brain injury.

Exacerbation by nicotine of the cyclosporine A-induced impairment of beta-adrenoceptor-mediated renal vasodilation in rats

Nicotine is implicated in smoking-related renovascular impairment and worsening of existing nephropathies. In the present study, we investigated whether nicotine aggravates the deleterious effect of the immunosuppressant drug cyclosporine A (CsA) on renal vasodilation induced by the beta-adrenoceptor agonist isoprenaline. Bolus isoprenaline (0.03-8.0 micromol) elicited dose-dependent vasodilation of phenylephrine-preconstricted perfused kidneys that was attenuated by infusion at 5 mL/min of nicotine (5 x 10(-4) mol/L) or CsA (2 micromol/L). Further, chronic administration of nicotine (0.4 mg/kg per day) or CsA (20 mg/kg per day) for 3 weeks reduced isoprenaline-induced vasodilation and elevated plasma urea and creatinine concentrations, effects that were magnified when both nicotine and CsA were administered concurrently. The role of endothelial and smooth muscle signalling in the acute nicotine/CsA renovascular interaction was investigated. Vasodilation caused by 0.25 micromol isoprenaline was attenuated by 6 micromol/L propranolol and 10 mmol/L tetraethylammonium (TEA), potentiated by 100 micromol/L hexamethonium and 7 micromol/L diclophenac, and virtually abolished in 80 mmol/L KCl-preconstricted tissues. N(G)-Nitro-L-arginine (L-NNA; 200 micromol/L), methylene blue (10 micromol/L), 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propane-sulphonate (CHAPS; 0.2% for 30 s), nifedipine (750 nmol/L), atropine (1 micromol/L) and SQ22536 (an adenylyl cyclase inhibitor; 3 x 10(-5) mol/L) had no effect on isoprenaline responses. Nicotine (5 x 10(-4) mol/L) reduced isoprenaline-induced vasodilation and this effect was potentiated by concurrent CsA (2 micromol/L) infusion. Nicotine-induced impairment of the vasodilator response to isoprenaline was reduced by hexamethonium and potentiated by L-NNA, methylene blue, CHAPS and nifedipine. Alternatively, CsA exacerbation of the nicotine-isoprenaline interaction was abolished by propranolol, L-NNA, methylene blue, CHAPS, L-arginine, TEA and nifedipine. 5. In summary, nicotine and CsA produce additive impairment of kidney function and beta-adrenoceptor-mediated renovascular control, nitric oxide (NO)-cGMP signalling tonically restrains nicotine-induced impairment of isoprenaline vasodilation and the endothelial NO-K+ pathway modulates the aggravating effect of CsA on nicotine-isoprenaline interactions.

Role of caveolar compartmentation in endothelium-derived hyperpolarizing factor-mediated relaxation: Ca2+ signals and gap junction function are regulated by caveolin in endothelial cells

BACKGROUND

In endothelial cells, caveolin-1, the structural protein of caveolae, acts as a scaffolding protein to cluster lipids and signaling molecules within caveolae and, in some instances, regulates the activity of proteins targeted to caveolae. Specifically, different putative mediators of the endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation are located in caveolae and/or regulated by the structural protein caveolin-1, such as potassium channels, calcium regulatory proteins, and connexin 43, a molecular component of gap junctions.

METHODS AND RESULTS

Comparing relaxation in vessels from caveolin-1 knockout mice and their wild-type littermates, we observed a complete absence of EDHF-mediated vasodilation in isolated mesenteric arteries from caveolin-1 knockout mice. The absence of caveolin-1 is associated with an impairment of calcium homeostasis in endothelial cells, notably, a decreased activity of Ca2+-permeable TRPV4 cation channels that participate in nitric oxide- and EDHF-mediated relaxation. Moreover, morphological characterization of caveolin-1 knockout and wild-type arteries showed fewer gap junctions in vessels from knockout animals associated with a lower expression of connexins 37, 40, and 43 and altered myoendothelial communication. Finally, we showed that TRPV4 channels and connexins colocalize with caveolin-1 in the caveolar compartment of the plasma membrane.

CONCLUSIONS

We demonstrated that expression of caveolin-1 is required for EDHF-related relaxation by modulating membrane location and activity of TRPV4 channels and connexins, which are both implicated at different steps in the EDHF-signaling pathway.

The diacylglycerol lipase inhibitor RHC-80267 potentiates the relaxation to acetylcholine in rat mesenteric artery by anti-cholinesterase action

The diacylglycerol lipase inhibitor 1,6-bis(cyclohexyloximinocarbonylamino) hexane (RHC-80267) was tested for its effect on acetylcholine-evoked relaxation in rat mesenteric artery. In artery contracted with either noradrenaline or KCl, RHC-80267 (0.1-10 muM) potentiated the relaxation evoked by acetylcholine. The effect of RHC-80267 was not affected by nitric oxide synthase inhibition or by inhibitors of protein kinase C or of phospholipase A(2). The diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol did not change the relaxation to acetylcholine. RHC-80267 did not affect the relaxation evoked by carbachol, by the nitric oxide donor SNAP (S-nitroso-N-acetylpenicillamine) or by the K(+) channel opener cromakalim. Neostigmine, a cholinesterase inhibitor, produced the same effect as RHC-80267 on acetylcholine-evoked relaxation. When tested on cholinesterase in brain homogenate, RHC-80267 concentration-dependently inhibited cholinesterase activity with an IC(50) of 4 muM. These results indicate that the potentiation of acetylcholine-evoked responses by RHC-80267 in rat mesenteric artery is caused by the inhibition of the cholinesterase activity in the vascular wall.

Comparative Study of the Antihypertensive Activity of Marrubium Vulgare and of the Dihydropyridine Calcium Antagonist Amlodipine in Spontaneously Hypertensive Rat

Water extract of Marrubium vulgare is widely used as antihypertensive treatment in folk medicine. We have compared the effect of 10-week-long treatment with amlodipine or Marrubium water extract on systolic blood pressure (SBP), cardiovascular remodeling and vascular relaxation in spontaneously hypertensive rats (SHR). Both treatments produced similar decrease in SBP. Amlodipine treatment reduced left ventricle, aortic and mesenteric artery weight. Marrubium treatment had a significant antihypertrophic effect in aorta only. Relaxation to acetylcholine (ACh) of mesenteric artery was improved by Marrubium but not by amlodipine treatment. These results demonstrate that, in addition to its antihypertensive effect, Marrubium water extract improved the impaired endothelial function in SHR.

[Endothelium-derived factors in hypertensive blood vessels, especially nitric oxide and hypertension]

Endothelium-dependent relaxation (EDR) in the blood vessels of spontaneously hypertensive rats (SHR) and the role of nitric oxide (NO) in the initiation of hypertension are reviewed. EDR was impaired in blood vessels of SHR depending on age and degree of hypertension when compared with those of normotensive rats. The cause of the impairment varied among the type of blood vessels: a decrease in the production of NO and endothelium-derived relaxing factor (EDRF) and an increase in the production of endothelium-derived contracting factor (EDCF) are the main causes of the impairment in large arteries, while a decrease in endothelium-dependent hyperpolarization and increased release of EDCF are the main causes of the impairment in small arteries. Interactions among these endothelium-derived factors and changes in the interactions are also causes of impairment. Superoxide may be involved in the impairment of EDR by destroying NO. The endothelium depresses smooth muscle contraction, including spontaneous tone developed in vascular smooth muscle, and the depressing effect of the endothelium is impaired in the preparations from SHR. The endothelium of blood vessels of SHR are structurally injured as demonstrated by scanning electron microscopy. Antihypertensive treatment prevented these functional and structural changes. Chronic treatment with inhibitors of NO production in normotensive rats impaired EDR and elevated blood pressure. The impairment of EDR is a secondary change due to continued hypertension, and early initiation of antihypertensive therapy is recommended.

Effects of benidipine and candesartan on kidney and vascular function in hypertensive Dahl rats

We examined the effect of the dihydropyridine calcium channel blocker (CCB) benidipine, the angiotensin II type 1 receptor blocker (ARB) candesartan, and the combination of these drugs on blood pressure and kidney and vascular function in rats with salt-induced hypertension. Dahl salt-sensitive (DS) rats were fed with a high-salt (8% NaCl) diet from 7 weeks of age. Benidipine (1, 3 mg/kg), candesartan (1, 3 mg/kg), benidipine (3 mg/kg) combined with candesartan (3 mg/kg), or vehicle was administered orally after the start of the feeding. Relaxant responses to acetylcholine (an endothelium-dependent vasodilator) and sodium nitroprusside (an endothelium-independent vasodilator) were measured to examine the vascular function. DS rats fed the high-salt diet showed an increase in systolic blood pressure (SBP), which was accompanied by glomerular sclerosis and an increase in urinary albumin excretion. Relaxant responses to acetylcholine and sodium nitroprusside were impaired in superior mesenteric arterial rings from the hypertensive DS rats. SBP was significantly lower in all of the drug-treated groups than in the vehicle-treated group. The antihypertensive effect of benidipine at 3 mg/kg was more potent than that of candesartan at 3 mg/kg. The albuminuria was significantly decreased in the benidipine and benidipine plus candesartan groups, but not in the candesartan group. The level of SBP in the benidipine plus candesartan group was lower than that by either drug alone. In addition, benidipine alone and benidipine plus candesartan inhibited the glomerular sclerosis and the impairment of relaxant responses in the arteries. These results demonstrate that benidipine is more effective than candesartan in lowering blood pressure and preventing the impairment of kidney and vascular function in salt-sensitive hypertensive rats. In addition, the results suggest that combination therapy with benidipine and an ARB decreases blood pressure more effectively than either drug alone and may be useful for the treatment of hypertension.

Cellular target of voltage and calcium-dependent K(+) channel blockers involved in EDHF-mediated responses in rat superior mesenteric artery

1. We have investigated the cellular target of K(+) channel blockers responsible for the inhibition of the EDHF-mediated relaxation in the rat mesenteric artery by studying their effects on tension, smooth muscle cell (SMC) membrane potential and endothelial cell Ca(2+) signal ([Ca(2+)](endo)). 2. In arteries contracted with prostaglandin F(2 alpha) (2.5 - 10 microM), relaxation evoked by ACh (0.01 - 3 microM) was abolished by a combination of charybdotoxin (ChTX, 0.1 microM) plus apamin (Apa, 0.1 microM) and was inhibited by 68+/-6% (n=6) by 4-aminopyridine (4-AP, 5 mM). 3. ACh(0.001 - 3 microM) increased [Ca(2+)](endo) and hyperpolarized SMCs with the same potency, the pD(2) values were equal to 7.2+/-0.08 (n=4) and 7.2+/-0.07 (n=9), respectively. SMCs hyperpolarization to ACh (1 microM) was abolished by high K(+) solution or by ChTX/Apa. It was decreased by 66+/-5% (n=6) by 4-AP. 4. The increase in [Ca(2+)](endo) evoked by ACh (1 microM) was insensitive to ChTX/Apa but was depressed by 58+/-16% (n=6) and 27+/-4% (n=7) by raising external K(+) concentration and by 4-AP, respectively. 5. The effect of 4-AP on [Ca(2+)](endo) was not affected by increasing external K(+) concentration. In Ca-free/EGTA solution, the transient increase in [Ca(2+)](endo) evoked by ACh (1 microM) was abolished by thapsigargin (1 microM) and was decreased by 75+/-7% (n=5) by 4-AP. 6. These results show that inhibition of EDHF-evoked responses by 4-AP may be attributed to a decrease in the Ca(2+) release activated by ACh in endothelial cells. The abolition of SMCs hyperpolarization to ACh by ChTX/Apa is not related to an interaction with the [Ca(2+)](endo).

Pharmacological evidence of hypotensive activity of Marrubium vulgare and Foeniculum vulgare in spontaneously hypertensive rat

The hypotensive effects of the water extract of Marrubium vulgare L. and Foeniculum vulgare L. were investigated in spontaneously hypertensive rats (SHR) and in normotensive Wistar-Kyoto rats (WKY). Oral administration of Marrubium or Foeniculum extract lowered the systolic blood pressure of SHR but not of WKY. In SHR, Foeniculum but not Marrubium treatment increased water, sodium and potassium excretion. Ex vivo as well as in vitro, Marrubium extract inhibited the contractile responses of rat aorta to noradrenaline and to KCl (100 mM). Inhibition was greater in aorta from SHR compared to WKY and was not affected by the NO synthase inhibitor N-nitro-L-arginine. Vascular effects of Foeniculum extract were less pronounced than those of Marrubium and were blocked by N-nitro-L-arginine. These results indicate that hypotensive activity of Marrubium and Foeniculum extracts seems to be mediated through different pathways: Foeniculum appeared to act mainly as a diuretic and a natriuretic while Marrubium displayed vascular relaxant activity.

Does a low-salt diet exert a protective effect on endothelial function in normal rats?

Sodium restriction is often used as an adjunct in the treatment of conditions characterized by endothelial dysfunction, such as hypertension and heart or kidney disease. However, the effect of sodium restriction on endothelial function is not known. Therefore, male Wistar rats were studied after a fixed salt diet had been maintained (low-salt group: 0.05% NaCl, n = 10; normal-salt group: 0.3% NaCl, n = 10) for 6 weeks. Blood pressure and sodium excretion values were measured once a week. Subsequently the rats were killed, the aorta was removed, and rings were cut. Endothelium-independent (sodium nitrite [SN]) and endothelium-dependent (acetylcholine [ACh]) vasodilator responses were assessed in the presence of indomethacin (a cyclo-oxygenase inhibitor) and in the presence or absence of NG-monomethyl-L-arginine (L-NMMA; a competitive inhibitor of nitric oxide [NO] synthase). Endothelium-independent vasodilatation was not different for the two salt groups. Endothelium-dependent vasodilatation, on the other hand, was different. The response to ACh was almost completely abolished by L-NMMA in the normal-salt group, whereas vasodilatation was partially preserved during L-NMMA in the low-salt group. Accordingly, the L-NMMA-sensitive contribution to ACh-dependent vasodilatation was smaller in the low-salt group. Thus, salt restriction induced a non-NO and non-prostaglandin-dependent vasodilating pathway. By exclusion this could be endothelium-derived hyperpolarizing factor, a pathway of vasculoprotective potential. Accordingly, the relative contributions of the different vasoactive endothelial pathways were affected by salt intake. Further research will be needed to clarify the nature and importance of this non-NO, non-prostaglandin-dependent pathway in the clinical setting as well.

Factors involved in the time course of response to acetylcholine in mesenteric arteries from spontaneously hypertensive rats

The time course of the response to prolonged application of acetylcholine in mesenteric arteries from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY) was compared. Only a relaxing response, which was blocked by N(omega)-nitro-L-arginine (L-NOARG), was observed after the prolonged application of a low concentration of acetylcholine (10(-8) M) in both preparations; the response was impaired in SHRSP preparations. Prolonged application of a high concentration of acetylcholine (10(-5) M) induced a second contractile response after a first relaxing response in SHRSP preparations under basal conditions and in WKY preparations in the presence of L-NOARG. This contractile response was attenuated by indomethacin. In the presence of a combination of apamin and charybdotoxin, the relaxing response to the high concentration of acetylcholine was reduced and a contractile response, which was abolished by indomethacin, appeared. In the presence of all of these blockers, a contractile response, which was blocked by cyclo(D-alpha-aspartyl-L-propyl-D-valyl-L-leucyl-D-tryptophyl) (BQ-123), was observed in preparations from WKY but not in preparations from SHRSP. Results indicate that prolonged application of acetylcholine in rat mesenteric arteries induces the release of endothelium-derived relaxing, contracting, hyperpolarizing factors and endothelin-1, and that the mode of action differs between preparations from WKY and SHRSP.

Lacidipine prevents endothelial dysfunction in salt-loaded stroke-prone hypertensive rats

Endothelium-dependent vasorelaxation is defective in hypertensive rats, especially in conduit arteries. In the stroke-prone spontaneously hypertensive rat, impaired endothelium-dependent vasorelaxation appears to contribute to the pathogenesis of stroke independent of blood pressure. Because treatment with lacidipine, a long-acting calcium channel blocker, protects against stroke and cardiovascular remodeling in this model, we investigated the effect of this treatment on endothelium-dependent vasorelaxation in the aorta. Stroke-prone rats were exposed to a salt-rich diet (1% NaCl in drinking water) with or without lacidipine (1 mg. kg(-1). d(-1)) for 6 weeks. A high-sodium diet (1) increased systolic blood pressure, aortic weight, and wall thickness and plasma renin activity (P<0.05); (2) markedly reduced nitric oxide (NO)-mediated, endothelium-dependent relaxation of aortic rings to acetylcholine and the sensitivity to the relaxing effect of S-nitroso-N-acetylpenicillamine, an NO donor (P<0.001); and (3) induced an elevation of preproendothelin-1 mRNA levels in aortic tissue (P<0.01) without affecting endothelial NO synthase mRNA levels. Lacidipine treatment prevented the salt-dependent functional and structural alterations of the aorta, including the overexpression of the preproendothelin-1 gene, and increased endothelial NO synthase mRNA levels in aortic tissue (P<0.01). In conclusion, lacidipine protects stroke-prone hypertensive rats against the impairment of endothelium-dependent vasorelaxation evoked by a salt-rich diet, and this effect may contribute to its beneficial effect against end-organ damage and stroke.