Fabiano E. Xavier

Participation of Prostacyclin in Endothelial Dysfunction Induced by Aldosterone in Normotensive and Hypertensive Rats

The aim of the present study was to analyze the possible involvement of vasoconstrictors prostanoids on the reduced endothelium-dependent relaxations produced by chronic administration of aldosterone in Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). For this purpose, acetylcholine (ACh) relaxations in aortic segments from both strains were analyzed in absence and presence of the cyclooxygenase-1 (COX-1) and COX-2 inhibitor indomethacin, the specific COX-2 inhibitor NS-398, the TP receptor antagonist (SQ 29 548), the thromboxane A2 (TXA2) synthase inhibitor furegrelate, and the prostacyclin (PGI2) synthesis inhibitor tranylcypromine (TCP). In addition, COX-2 protein expression was studied by Western blot analysis. Release of prostaglandin E2 (PGE2) and the metabolites of PGF2α, TXA2, and PGI2, 13,14-dihydro-15-keto PGF2a, TXB2, and 6-keto-PGF1α, respectively, were measured. Treatment with aldosterone did not modify blood pressure levels in any strain. However, aldosterone markedly reduced (P<0.05) ACh-induced relaxations in segments from both strains in a similar extent. Indomethacin, NS-398, SQ 29 548, and TCP enhanced (P<0.05) ACh relaxations in both strains treated with aldosterone. Aortic COX-2 protein expression was higher in both strains of rats treated with aldosterone. In normotensive animals, aldosterone increases the ACh-stimulated aortic production of 13,14-dihydro-15-keto PGF2a, PGE2, and 6-keto-PGF1α (P<0.05). In SHR, ACh only increased the 6-keto-PGF1α production (P<0.05). It could be concluded that chronic treatment with aldosterone was able to produce endothelial dysfunction through COX-2 activation in normotensive and hypertensive conditions. PGI2 seems to be the main factor accounting for endothelial dysfunction in hypertensive rats, whereas other prostanoids besides PGI2 appear to be involved in endothelial dysfunction under normotensive conditions.

Aldosterone induces endothelial dysfunction in resistance arteries from normotensive and hypertensive rats by increasing thromboxane A2 and prostacyclin

The present study was designed to assess whether cyclooxygenase‐2 (COX‐2) activation is involved in the effects of chronic aldosterone treatment on endothelial function of mesenteric resistance arteries (MRA) from Wistar‐Kyoto (WKY) and spontaneously hypertensive rats (SHR).

Time-dependent hyperreactivity to phenylephrine in aorta from untreated diabetic rats: role of prostanoids and calcium mobilization.

Diabetes alters vascular smooth muscle contractility. Changes in reactivity to phenylephrine (Phe) in aortas from controls and untreated 1- and 4-week streptozotocin (STZ)-induced diabetic rats were investigated. In 1-week diabetic (DB1) aortas, the maximum response (E(max)) and sensitivity (pD(2)) to Phe were similar to controls (CT1), but in 4-week diabetic (DB4) aortas, the E(max) for Phe was increased compared to CT4 aortas (E(max), DB4: 125+/-8.4% vs. CT4: 89.8+/-4.5%, P<.001). Endothelial denudation increased the response to Phe, and E(max) was increased in the DB4 aortas compared to CT4 (E(max), DB4: 156+/-4.2% vs. CT4: 125+/-3.8%, P<.001). Pretreatment of CT4 and DB4 aortas with indomethacin reduced E(max) and pD(2) for Phe. After indomethacin treatment, no differences in E(max) and pD(2) to Phe were observed in either group. SQ 29548 did not alter the Phe actions in CT4 aortas. However, in DB4 aortas, E(max) was reduced to control level. CT4 and DB4 aortas incubated in free-Ca(2+) solution plus Phe, contracted upon addition of CaCl(2), this response was increased in DB4 aortas. No changes were observed for acetylcholine (ACh) or sodium nitroprusside (SNP) responses. Nitric oxide (NO) release in response to Phe determined by acute L-NAME administration showed no differences in the percentage increase of the contraction in CT1 and DB1 aortas, but was enhanced in DB4 aortas. Results suggested that diabetes induces time-dependent changes in the vascular reactivity to Phe. This response is not related to a reduction of endothelium-derived NO but might be due to an increase in prostaglandin H(2) (PGH(2))/thromboxane A(2) (TxA(2)) and/or an enhanced extracellular Ca(2+) influx.

Endothelial dysfunction in cardiovascular and endocrine-metabolic diseases: an update

The endothelium plays a vital role in maintaining circulatory homeostasis by the release of relaxing and contracting factors. Any change in this balance may result in a process known as endothelial dysfunction that leads to impaired control of vascular tone and contributes to the pathogenesis of some cardiovascular and endocrine/metabolic diseases. Reduced endothelium-derived nitric oxide (NO) bioavailability and increased production of thromboxane A2, prostaglandin H2 and superoxide anion in conductance and resistance arteries are commonly associated with endothelial dysfunction in hypertensive, diabetic and obese animals, resulting in reduced endothelium-dependent vasodilatation and in increased vasoconstrictor responses. In addition, recent studies have demonstrated the role of enhanced overactivation of β-adrenergic receptors inducing vascular cytokine production and endothelial NO synthase (eNOS) uncoupling that seem to be the mechanisms underlying endothelial dysfunction in hypertension, heart failure and in endocrine-metabolic disorders. However, some adaptive mechanisms can occur in the initial stages of hypertension, such as increased NO production by eNOS. The present review focuses on the role of NO bioavailability, eNOS uncoupling, cyclooxygenase-derived products and pro-inflammatory factors on the endothelial dysfunction that occurs in hypertension, sympathetic hyperactivity, diabetes mellitus, and obesity. These are cardiovascular and endocrine-metabolic diseases of high incidence and mortality around the world, especially in developing countries and endothelial dysfunction contributes to triggering, maintenance and worsening of these pathological situations.

Ouabain‐induced hypertension alters the participation of endothelial factors in α‐adrenergic responses differently in rat resistance and conductance mesenteric arteries

This study compares the role of endothelial factors in α‐adrenoceptor contractile responses in mesenteric resistance (MRA) and superior (SMA) mesenteric arteries from ouabain‐treated (8.0 μg day−1, 5 weeks) and untreated rats. The role of the renin–angiotensin system was also evaluated. Ouabain treatment increased systolic blood pressure. In addition, ouabain reduced the phenylephrine response in SMA but did not alter noradrenaline responses in MRA. Endothelium removal or the nitric oxide synthase (NOS) inhibitor (L‐NAME, 100 μM) increased the responses to α‐adrenergic agonists in both vessels. After ouabain treatment, both endothelial modulation and the L‐NAME effect were increased in SMA, while only the L‐NAME effect was increased in MRA. Endothelial NOS expression remained unaltered after ouabain treatment. Indomethacin (10 μM) similarly reduced the noradrenaline contraction in MRA from both groups; in contrast, in SMA, indomethacin only reduced phenylephrine‐induced contractions in segments from untreated rats. Co‐incubation of L‐NAME and indomethacin leftward shifted the concentration–response curves for noradrenaline more in MRA from ouabain‐treated rats; tetraethylammonium (2 mM) shifted the noradrenaline curves further leftward only in MRA from untreated rats. Losartan treatment prevents the development of hypertension but not all vascular changes observed after ouabain treatment. In conclusion, a rise in endothelial NO and impaired prostanoid participation might explain the reduction in phenylephrine‐induced contraction in SMA after ouabain treatment. An increase in the modulatory effect of endothelial NO and impairment of endothelium‐dependent hyperpolarizing factor effect might explain why the ouabain treatment had no effect on noradrenaline responses in MRA.

Neurogenic nitric oxide release increases in mesenteric arteries from ouabain hypertensive rats.

Objectives We investigated whether chronic ouabain treatment changes the vasoconstrictor responses induced by electrical field stimulation (EFS) in endothelium-denuded rat superior mesenteric arteries and a possible role of neuronal nitric oxide (NO). Method Mesenteric arteries from untreated and ouabain-treated rats (≃8.0 μg/kg per day, for 5 weeks) were used in this study. Vascular reactivity was analyzed by isometric tension recording. Expression of the neuronal NO synthase isoform was analyzed by Western blot. Noradrenaline release was evaluated in segments incubated with [3H]noradrenaline. Results Systolic (SBP) and diastolic (DBP) blood pressure were higher in ouabain-treated rats than in untreated rats (SBP, untreated: 120 ± 3.5 mmHg versus ouabain-treated: 150 ± 4.7 mmHg, P < 0.01; DBP, untreated: 87 ± 3.0 mmHg versus ouabain-treated: 114 ± 2.6 mmHg, P < 0.001). EFS-induced vasoconstrictions were smaller in arteries from ouabain-treated rats than in those from untreated animals, while the EFS-induced [3H]noradrenaline release and the vasoconstriction induced by exogenous noradrenaline (1 nmol/l–10 μmol/l) remained unmodified. The non-selective NO synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (100 μmol/l), increased the EFS-induced vasoconstriction in mesenteric arteries from both groups, although the effect was more pronounced in segments from ouabain-treated rats. The selective neuronal NOS inhibitor, 7-nitroindazole (7-NI; 100 μmol/l) increased EFS-induced contraction only in segments from ouabain-treated rats. Neuronal NOS expression was greater in the mesenteric arteries from ouabain-treated rats than in those from untreated animals. Sodium nitroprusside (0.1 nmol/l–10 μmol/l) induced a similar vasodilatation in segments from both groups. Conclusions These results suggest that chronic ouabain treatment is accompanied by an increase in neuronal NO release that reduces EFS-induced vasoconstriction.

Endothelium modulates vasoconstrictor response to prostaglandin I2 in rat mesenteric resistance arteries: interaction between EP1 and TP receptors

Background and purpose:  Prostacyclin (PGI2) is usually described as an endothelium‐derived vasodilator, but it can also induce vasoconstriction. We studied the vasomotor responses to PGI2 in resistance arteries and the role of thromboxane (TP) and prostaglandin E2 (EP) receptors in this effect.

Contribution of the endothelin and renin-angiotensin systems to the vascular changes in rats chronically treated with ouabain.

Renin–angiotensin and endothelin systems are involved in the cardiovascular effects produced by treatment with ouabain. We recently demonstrated that the contractile response to phenylephrine is decreased in ouabain‐treated rats. The present study investigated whether endothelin‐1 (ET‐1) and angiotensin II (Ang II) contributes to the vascular changes observed in rats chronically treated with ouabain. Wistar rats were treated with ouabain (8.0 μg day−1, s.c. pellets for 5 weeks) alone or in combination with an endothelin type A receptor (ETA) antagonist, BMS182874 (40 mg kg−1 day−1, per gavage) or an angiotensin type 1 (AT1) receptor antagonist, losartan (15 mg kg−1 day−1, p.o.). Treatment with ouabain increased systolic blood pressure and treatment with either losartan or BMS182874 prevented the development of ouabain‐induced hypertension. The sensitivity and maximal response for phenylephrine were reduced in aortic rings from ouabain‐treated rats. Removal of the endothelium or in vitro exposure to an inhibitor of nitric oxide synthase (NOS), N‐nitro‐L‐arginine methyl ester (L‐NAME, 100 μM) increased the responses to phenylephrine, an effect that was more pronounced in aortas from ouabain‐treated rats. Endothelial NOS protein (eNOS) expression was increased after ouabain treatment. Treatment with BMS182874, but not with losartan, prevented the effects of ouabain on the reactivity of phenylephrine and in eNOS protein expression. Gene expression of pre–pro‐ET‐1 and ETA receptors was increased in aortic rings from ouabain‐treated rats. ETB receptor gene expression was not altered by ouabain treatment. In conclusion, our results suggest that endothelin and angiotensin systems play an important role in the development of ouabain‐induced hypertension. However, ET‐1, by activation of ETA receptors, but not Ang II, contributes to changes in vascular reactivity to phenylephrine induced by chronic treatment with ouabain.

Long-term ouabain treatment impairs vascular function in resistance arteries.

Background/Aims: The purpose of this study was to examine the cardiovascular effects of long-term ouabain treatment at different time points. Methods: Systolic blood pressure (SBP) was measured by tail-cuff method in male Wistar rats treated with ouabain (approx. 8.0 µg·day–1) or vehicle for 5, 10 and 20 weeks. Afterwards, vascular function was assessed in mesenteric resistance arteries (MRA) using a wire myograph. ROS production and COX-1 and COX-2, TNF-α, and IL-6 protein expression were investigated. Results: SBP was increased by ouabain treatment up to the 6th week and remained stable until the 20th week. However, noradrenaline-induced contraction increased only in MRA in rats treated with ouabain for 20 weeks. NOS inhibition and endothelium removal increased the noradrenaline response, but to a smaller magnitude in MRA in the ouabain group. Moreover, inhibition of COX-2 or incubation with superoxide dismutase restores noradrenaline-induced contraction in the 20-week ouabain group to control levels. ROS production as well as COX-2, IL-6 and TNF-α protein expression increased in MRA in this group. Conclusion: Although ouabain treatment induced hypertension in all groups, a larger noradrenaline induced contraction was observed over 20 weeks of treatment. This vascular dysfunction was related to COX-2-derived prostanoids and oxidative stress, increased pro- inflammatory cytokines and reduced NO bioavailability.

Ouabain at Nanomolar Concentration Promotes Synthesis and Release of Angiotensin II from the Endothelium of the Tail Vascular Bed of Spontaneously Hypertensive Rats

The effects of 1 nM ouabain (OUA) on the contractile actions of phenylephrine (PHE, 0.001–100 μg) and functional activity of the sodium pump (NKA) in isolated-perfused tail vascular beds from WKY and SHR were investigated. In preparations from SHR, perfusion with OUA in the presence of endothelium (E+) increased the sensitivity (pED50) of PHE (before: 2.14 ± 0.06 versus after: 2.47 ± 0.07; P < 0.05) without altering the maximal response (Emax). After endothelial damage, OUA reduced the Emax of PHE in SHR (before: 350 ± 29 versus after: 293 ± 25 mm Hg; P < 0.05). In SHR/E+, pretreatment with losartan (10 μM) or enalaprilat (1 μM) prevented the increased sensitivity to PHE induced by OUA. OUA increased NKA activity in SHR/E+ (before: 45 ± 6 versus after: 58 ± 5%, P < 0.05). Losartan (10 mg/Kg, i.v.) also abolished the increment in systolic and diastolic blood pressure induced by OUA (0.18 μg/Kg, i.v.) in anesthetized SHR. OUA did not alter the actions of PHE in either anesthetized WKY rats or vascular preparations. Results suggest that 1 nM OUA increased the vascular reactivity to PHE only in SHR/E+. This effect is mediated by OUA-induced activation of endothelial angiotensin converting enzyme that promotes the local formation of angiotensin II, which sensitizes the vascular smooth muscle to the actions of PHE.