Sulfhydryl group donors potentiate the hypotensive effect of acetylcholine in rats

Protective effect of N-acetylcysteine activated carbon release microcapsule on myocardial ischemia-reperfusion injury in rats

With the development of science and technology, and development of artery bypass, methods such as cardiopulmonary cerebral resuscitation have been practiced in recent years. Despite this, some methods fail to promote or recover the function of tissues and organs, and in some cases, may aggravate dysfunction and structural damage to tissues. The latter is typical of ischemia-reperfusion (IR) injury. Lipid peroxidation mediated by free radicals is an important process of myocardial IR injury. Myocardial IR has been demonstrated to induce the formation of large numbers of free radicals in rats, which promotes the peroxidation of lipids within unsaturated fatty acids in the myocardial cell membrane. Markers of lipid peroxidation include malondialdehyde, superoxide dismutase and lactic dehydrogenase. Recent studies have demonstrated that N-acetylcysteine (NAC) is able to dilate blood vessels, prevent oxidative damage, improve immunity, inhibit apoptosis and the inflammatory response and promote glutathione synthesis in cells. NAC also improves the systolic function of myocardial cells and cardiac function, prevents myocardial apoptosis, protects ventricular remodeling and vascular remodeling, reduces opiomelanocortin levels in the serum and increases the content of nitric oxide in the serum, thus improving vascular endothelial function. Therefore, NAC has potent pharmacological activity; however, the relatively fast metabolism of NAC, along with its large clinical dose and low bioavailability, limit its applications. The present study combined NAC with medicinal activated carbons, and prepared N-acetylcysteine activated carbon sustained-release microcapsules (ACNACs) to overcome the limitations of NAC. It was demonstrated that ACNACs exerted greater effective protective effects than NAC alone on myocardial IR injury in rats.

Role of oxidative stress in elevated blood pressure induced by high free fatty acids

The aim of the study is to investigate the possible mechanism of oxidative stress in the high free fatty acids (FFAs)-induced hypertension. Male Sprague-Dawley rat models were established and classified into three groups, namely the control group (NC group), the FFA group, and the N-acetylcysteine (NAC) group. Blood pressure (BP) was recorded. An organ chamber experiment was performed to determine endothelium-dependent/-independent vasodilation (EDV/EIV). Reactive oxygen species (ROS), nitrotyrosine, reduced glutathione hormone (GSH) and NO(2)(-)/NO(3)(-) levels were measured in plasma. Endothelial nitric oxide synthase (eNOS) mRNA expression in endothelial cells was evaluated by real-time PCR. The following results were observed: (1) In the FFA group, BP increased after 4 h infusion of Intralipid+heparin. In the NAC group, systolic and diastolic BP remained the same. (2) In the FFA group, the aortic rings tended to show impaired EDV in response to acetylcholine (ACh). There was no difference of EDV response in the NAC and NC groups. (3) In the FFA group, NO(2)(-)/NO(3)(-) levels were significantly reduced, and eNOS mRNA expression and activity were significantly decreased compared with the NC group. NAC administration increased eNOS mRNA expression and activity. (4) ROS and nitrotyrosine concentrations in the FFA group were higher than in the NC group, and GSH concentrations in the FFA group were lower than in the NC group. Elevated FFAs can induce elevated BP, potentially through FFA-induced impairment of EDV resulting from decreased eNOS mRNA expression and activity. Oxidative stress may also play an important role in potential mechanisms of this high FFA-induced elevated BP.

The effect of N-acetylcysteine and melatonin in adult spontaneously hypertensive rats with established hypertension

The attenuated nitric oxide (NO) formation and/or elevated production of reactive oxygen species are often found in experimental and human hypertension. We aimed to determine possible effects of N-acetylcysteine (1.5 g/kg/day) and N-acetyl-5-methoxytryptamine (melatonin, 10 mg/kg/day) in adult spontaneously hypertensive rats (SHR) with established hypertension. After a six-week-treatment, blood pressure was measured and NO synthase (NOS) activity, concentration of conjugated dienes, protein expression of endothelial NOS, inducible NOS and nuclear factor-kappaB (NF-kappaB) in the left ventricle were determined. Both treatments improved the NO pathway by means of enhanced NOS activity and reduced reactive oxygen species level as indicated by decreased conjugated diene concentrations and lowered NF-kappaB expression. N-acetylcysteine (but not melatonin) also increased the endothelial NOS protein expression. However, only melatonin was able to reduce blood pressure significantly. Subsequent in vitro study revealed that both N-acetylcysteine and melatonin lowered the tone of phenylephrine-precontracted femoral artery via NO-dependent relaxation. Nevertheless, melatonin-induced relaxation also involved NO-independent component which was preserved even after the blockade of soluble guanylate cyclase by oxadiazolo[4,3-a]quinoxalin-1-one. In conclusion, both N-acetylcysteine and melatonin were able to improve the NO/reactive oxygen species balance in adult SHR, but blood pressure was significantly lowered by melatonin only. This implies that a partial restoration of NO/reactive oxygen species balance achieved by the antioxidants such as N-acetylcysteine has no therapeutic effect in adult rats with established hypertension. The observed antihypertensive effect of melatonin is thus mediated by additional mechanisms independent of NO pathway.

Effect of chronic N-acetylcysteine treatment on the development of spontaneous hypertension

The imbalance between NO (nitric oxide) and ROS (reactive oxygen species) is an important factor in the development of hypertension. The aim of the present study was to determine the preventive and therapeutic effects of NAC (N-acetylcysteine) in SHRs (spontaneously hypertensive rats). Young and adult SHRs and WKY (Wistar-Kyoto) rats were treated with NAC (20 g/l in the drinking water). After 8 weeks of treatment, BP (blood pressure) and NOS (NO synthase) activity, conjugated dienes and GSH (reduced glutathione) in the kidney and left ventricle were determined. Protein expression of eNOS (endothelial NOS), inducible NOS and NF-kappaB (nuclear factor kappaB) were also determined in the left ventricle and kidney. Chronic NAC treatment partially attenuated the rise in BP in young SHRs (179+/-6 compared with 210+/-8 mmHg in untreated animals), but it had no significant effect on BP in adult SHRs. The antioxidant action of NAC, measured as a decrease of the concentration of conjugated dienes or inhibition of NF-kappaB expression, was greater in young than in adult SHRs. Similarly, eNOS protein expression was attenuated more in young than in adult SHRs, although NAC treatment increased NOS activity to a similar extent in both young and adult rats. In conclusion, both decreased ROS production and increased NOS activity appear to participate in the BP changes after NAC treatment in young SHRs. In adult SHRs with established hypertension, however, the secondary alterations (such as pronounced structural remodelling of resistance vessels) might attenuate the therapeutic effect of NAC.

Chronic N-Acetylcysteine Administration Prevents Development of Hypertension in N.OMEGA.-Nitro-L-Arginine Methyl Ester-Treated Rats: The Role of Reactive Oxygen Species

The aim of this study was to evaluate the production of superoxide anions as well as their role in the induction and/or maintenance of high blood pressure in rats with N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension. In the preventive study, we compared adult Wistar rats treated with L-NAME for 4 weeks with L-NAME-treated rats that were simultaneously given N-acetylcysteine (NAC) in their drinking water. Basal blood pressure, superoxide production, conjugated dienes concentration and NO synthase (NOS) activity were measured at the end of the experiment. Chronic NOS inhibition by L-NAME treatment increased blood pressure, enhanced superoxide production in the aorta and elevated the concentration of conjugated dienes in the heart and kidney. All these changes were prevented by simultaneous NAC administration, which augmented NOS activity in L-NAME-treated rats. In the therapeutic study, the effects of chronic NAC treatment were studied in rats with established hypertension which developed during 4 weeks of L-NAME administration. The blood pressure effects of chronic NAC treatment in established L-NAME hypertension were only moderate, although this treatment also restored NOS activity and lowered conjugated dienes in the heart and kidney. Since chronic NAC treatment had better preventive than therapeutic effects, it seems that reactive oxygen species play a more important role in the induction than in the maintenance of L-NAME hypertension.

N-Acetylcysteine ameliorates lipopolysaccharide-induced organ damage in conscious rats

Lipopolysaccharide is strongly associated with septic shock, leading to multiple organ failure. It can activate monocytes and macrophages to release proinflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and nitric oxide (NO). The present experiments were designed to induce endotoxin shock by an intravenous injection of Klebsiella pneumoniae lipopolysaccharide (LPS, 10 mg/kg) in conscious rats. Arterial pressure and heart rate (HR) were continuously monitored for 48 h after LPS administration. N-Acetylcysteine was used to study its effects on organ damage. Biochemical substances were measured to reflect organ functions. Biochemical factors included blood urea nitrogen (BUN), creatinine (Cre), lactic dehydrogenase (LDH), creatine phosphokinase (CPK), aspartate transferase (GOT), alanine transferase (GPT), TNF-alpha, IL-1 beta, methyl guanidine (MG), and nitrites/nitrates. LPS caused significant increases in blood BUN, Cre, LDH, CPK, GOT, GPT, TNF-alpha, IL-1 beta, MG levels, and HR, as well as a decrease in mean arterial pressure and an elevation of nitrites/nitrates. N-Acetylcysteine suppressed the release of TNF-alpha, IL-1 beta, and MG, but enhanced NO production. These actions ameliorate LPS-induced organ damage in conscious rats. The beneficial effects may suggest a potential chemopreventive effect of this compound in sepsis prevention and treatment.

Interaction between hemoglobin and glutathione in the regulation of blood flow in normal and septic pigs

BACKGROUND

Hemoglobin (Hb) induces vasoconstriction by heme group binding nitric oxide in an irreversible fashion. Recent in vitro studies indicate that the thiol groups in Hb reversibly bind nitric oxide and participate in trans-nitrosylation reactions with other thiols. Sepsis is a pathophysiologic state characterized by vasodilation mediated, at least in part, by an excessive release of nitric oxide. The role of nitrosothiols (RSNOs) in these changes is unknown.

OBJECTIVES

We tested the following in a porcine model of sepsis: (i) whether glutathione (GSH) reverses the hemodynamic effects of Hb; (ii) whether GSH induces an increase in blood flow in sepsis; (iii) whether RSNO plasma concentration increases in sepsis and is related to hypotension.

DESIGN

Nonrandomized animal controlled study.

SETTING

Animal research facility in a university hospital.

SUBJECTS

Anesthetized pigs were monitored with a pulmonary artery catheter and ultrasonic blood flow probes in the mesenteric artery and the portal vein for measurement of systemic, mesenteric, and portal blood flows (Q(TOT), Q(MES), and Q(POR), respectively). Four groups of pigs were studied: nonseptic, septic, nonseptic treated with Hb (stroma-free purified porcine hemoglobin), and septic treated with Hb (n = 6 in each group).

INTERVENTIONS

Sepsis was induced at 0 min by the administration of live Escherichia coli. Hb (400 mg/kg/hr) was administered at 240 mins, followed by glutathione (1 g iv).

MEASUREMENTS AND MAIN RESULTS

Hb induced a pressor response and a decrease in Q(TOT), Q(MES), and Q(POR). Glutathione reversed the effects of Hb on Q(MES) and Q(POR). In septic pigs not treated with Hb, GSH induced an increase in Q(POR). RSNO plasma concentration increased after the induction of sepsis and correlated significantly with blood pressure.

CONCLUSIONS

These results indicate the reversibility of the effects of Hb by GSH, probably by interactions between nitric oxide and the reduced sulfhydryl groups in Hb, and suggest a role of RSNOs in the cardiovascular changes of sepsis.

Endothelium-dependent vasorelaxation in inhibited by in vivo depletion of vascular thiol levels: role of endothelial nitric oxide synthase

Thiols like glutathione may serve as reducing cofactors in the production of nitric oxide (NO) and protect NO from inactivation by radical oxygen species. Depletion of thiol compounds reduces NO-mediated vascular effects in vitro and in vivo. The mechanisms underlying these actions are not clear, but may involve decreased synthesis of NO and/or increased degradation of NO. This study investigates the effect of glutathione depletion on the response to NO-mediated vasodilation induced by acetylcholine (Ach, 10 micrograms/kg), endothelial NO synthase (eNOS) activity and potential markers of vascular superoxide anion (O2.-) production in conscious chronically catheterized rats. Thiol depletion induced by buthionine sulfoximine (BSO, 1 g i.p. within 24 h) decreased the hypotensive effect of Ach by 30% (MAP reduction before BSO 27 +/- 3 mmHg, 19 +/- 3 mmHg after BSO, (mean +/- SEM), p < .05, n = 8). The impaired effect of Ach was associated with a significant reduction in eNOS activity (control: 7.7 +/- 0.8, BSO: 3.9 +/- 0.4 pmol/min/mg protein (p < .05), n = 6). In contrast, neither NADH/NADPH driven membrane-associated oxidases nor lucigenin reductase activity were significantly (p < .05) affected by BSO (BSO: 4415 +/- 123, control: 4105 +/- 455 counts/mg; n = 6) in rat aorta. It is concluded that in vivo thiol depletion results in endothelial dysfunction and a reduced receptor-mediated vascular relaxation. This effect is caused by reduced endothelial NO formation.

Effects of chronic N-acetylcysteine treatment on the actions of peroxynitrite on aortic vascular reactivity in hypertensive rats

BACKGROUND

Peroxynitrite (ONOO-), the product of superoxide and nitric oxide, seems to be involved in vascular alterations in hypertension.

OBJECTIVES

To evaluate the effects of ONOO- on endothelium-dependent and independent aortic vascular responsiveness, oxidized/reduced glutathione balance (GSSG/GSH), malondialdehyde aortic content, and the formation of 3-nitrotyrosine (3-NT), a stable marker of ONOO-, in N-acetylcysteine (NAC)-treated normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

RESULTS

In SHR only, NAC significantly reduced heart rate and systolic, but not diastolic, blood pressure. It also improved endothelium-dependent aortic relaxation in SHR, but not after exposure to ONOO-. Endothelium-dependent and independent aortic relaxations were markedly impaired by ONOO- in both strains of rat. NAC partially protected SHR against the ONOO- -induced reduction in endothelium-independent relaxation. Aortic GSSG/GSH ratio and malondialdehyde, which were higher in SHR than in WKY rats, showed a greater increase in SHR after exposure to ONOO-. NAC decreased GSSG/GSH and malondialdehyde in both strains of rat before and after exposure to ONOO-. The 3-NT concentration, which was similar in both strains of rat under basal conditions, was greater in SHR than in WKY rats after the addition of ONOO-, with a reduction only in NAC-treated SHR.

CONCLUSIONS

These findings suggest an increased vulnerability of SHR aortas to the effects of ONOO- as compared with those of WKY rats. The selective improvements produced by NAC, in systolic arterial pressure, heart rate, aortic endothelial function, ONOO- -induced impairment of endothelium-independent relaxation, aortic GSSG/GSH balance, malondialdehyde content and 3-NT formation in SHR suggest that chronic administration of NAC may have a protective effect against aortic vascular dysfunction in the SHR model of hypertension.

Effect of angiotensin-converting enzyme inhibitors and nitroxy groups on human coronary resistance vessels in vitro

We investigated the interaction between nitroxy groups and angiotensin-converting enzyme (ACE) inhibitors to assess the role of sulfhydryl groups and adenosine triphosphate (ATP)-sensitive potassium channels in vasodilation of human coronary resistance vessels in vitro. Coronary resistance vessels were resected from the right atrial appendage of 27 patients undergoing open heart surgery. The vessel ends were inserted into a microglass pipette with the internal pressure maintained at 40 mm Hg. Nitroglycerin did not change the vasoresponse, whereas nicorandil induced a concentration-dependent vasodilation that was not affected by methylene blue, but was markedly inhibited by glibenclamide. The ACE inhibitors, captopril, with a sulfhydryl group (1 x 10(-6) M), and enalaprilat, without a sulfhydryl group (1 x 10(-6) M), were added to either nitroglycerin or nicorandil to assess the incremental response of the sulfhydryl group to vasodilation. The addition of captopril or L-cysteine (1 x 10(-6) M) enhanced the activity of both nitroglycerin and nicorandil, whereas addition of enalaprilat did not. The responses of nicorandil and nitroglycerin to captopril and were similar. Cromakalim was not enhanced by L-cysteine or captopril. The response of nitroglycerin was not enhanced by captopril or L-cysteine after addition of N(G)-monomethyl-L-ARGININE (L-NMMA). Both nitroglycerin and nicorandil exhibited an increase in vasodilation in the presence of an ACE inhibitor containing a sulfhydryl group. The mechanism of the vasodilatory action in the coronary resistance vessels may involve the opening of an ATP-sensitive potassium channel and subsequent guanylate cyclase activation. These interactions have important clinical implications.

Cardiovascular effects of captopril and enalapril in obese Zucker rats

The effects of two weeks of oral administration of the angiotensin-converting enzyme inhibitors captopril (a sulphydryl-containing drug) and enalapril (which lacks the sulphydryl group) on skeletal muscle glucose uptake, arterial blood pressure, cardiac hypertrophy, proteinuria and aortic vascular reactivity in obese Zucker rats were evaluated. Captopril (50 mg kg(-1) once daily) and enalapril (10 mg kg(-1) did not modify body weight gain or food or water intake. Both drugs decreased systolic blood pressure (157+/-6, 133+/-4 and 136+/-3 mm Hg, in vehicle-, captopril- and enalapril-treated rats, respectively), blood glucose (172+/-8 vs. 151+/-7 and 158+/-5 mg dl(-1), respectively), proteinuria (46+/-10 vs. 17+/-2 and 18+/-2.5 mg dl(-1), respectively) and heart weight (2.17+/-0.03, 1.98+/-0.02 and 1.99+/-0.04 mg g(-1)of body weight, respectively). Plasma insulin concentration was significantly increased by enalapril (17+/-2 ng ml(-1) vs. 9+/-2) but not by captopril (12+/-1). In the absence of insulin, the diaphragms from captopril- or enalapril-treated rats showed a significantly higher glucose uptake than that of controls (31% and 30% vs. control group, respectively). The presence of insulin in the incubation medium did not stimulate peripheral glucose uptake in the control group but significantly increased glucose uptake in diaphragms from captopril- or enalapril-treated rats (enhancement of glucose uptake vs. control: 52% and 43%, respectively). Endothelium-intact aortic rings from control Zucker rats showed a poor relaxant response to acetylcholine (maximal relaxation of 38.4+/-4.7%). Captopril significantly improved the endothelium-dependent vascular relaxation responses to acetylcholine and the endothelium-independent relaxation to the nitric oxide donor sodium nitroprusside whereas enalapril did not modify these relaxant responses. Neither captopril nor enalapril significantly affected the vascular contractile responses to the vasoconstrictors noradrenaline or KCl. In conclusion, the angiotensin-converting enzyme inhibitors captopril and enalapril reversed insulin resistance and the associated cardiovascular complications (cardiac hypertrophy, hypertension and proteinuria) in the obese Zucker rat, an animal model of non-insulin-dependent (type II) diabetes mellitus. However, only captopril, but not enalapril, improved the impaired endothelium-dependent and independent relaxant responses in the isolated rat aorta.

Endothelial dysfunction in spontaneously hypertensive rats: consequences of chronic treatment with losartan or captopril

BACKGROUND

Hypertension is associated with endothelial dysfunction characterized by decreased endothelium-dependent relaxations and increased endothelium-dependent contractions. Angiotensin converting enzyme inhibitors and thromboxane A2 receptor antagonists decreased the endothelium dysfunction in hypertensive animals.

OBJECTIVE

To investigate the effects of prolonged treatment with losartan on endothelium-dependent and -independent relaxations and contractions in aortic rings from spontaneously hypertensive rats (SHR).

MATERIAL AND METHODS

Male SHR aged 16 weeks were treated for 12 consecutive weeks either with 10 mg/kg losartan per day or with 60 mg/kg captopril per day administered via their drinking water. The systolic blood pressure was evaluated basally and during week 12. At the end of the treatment period, the vascular reactivity in aortic rings was studies. A group of rats treated with captopril was studies as a reference group.

RESULTS

Losartan and captopril reduced the blood pressure significantly and comparably. Both drugs enhanced acetylcholine-induced relaxations and reduced the maximal contractile response to acetylcholine in the presence of NG-nitro-L arginine methyl ester (L-NAME). Contractile responses to phenylephrine, endothelin-l and U46619 were not affected by these treatments. Increased relaxing responses to superoxide dismutase were observed only in captopril-treated rats. Losartan reduced the contractile response to angiotensin II. By contrast this contractile response was elevated in rats treated with captopril.

CONCLUSIONS

Prolonged antihypertensive treatments with losartan and captopril decreased the endothelial dysfunction in aortic rings from SHR not only by enhancing NO-dependent relaxations but also by reducing the contractions in response to an endothelium-derived contracting factor. The results further confirm that an endothelium-derived contracting factor plays a role in vascular dysfunction in SHR and the relationships between this factor and angiotensin II.

The effects of intravenous antioxidants in patients with septic shock

Oxidative stress is implicated in septic shock. We investigated the effect of intravenous antioxidant therapy on antioxidant status, lipid peroxidation, hemodynamics and nitrite in patients with septic shock. Thirty patients randomly received either antioxidants (n-acetylcysteine 150 mg/kg for 30 min then 20 mg/kg/h plus bolus doses of 1 g ascorbic acid and 400 mg alpha-tocopherol) or 5% dextrose. Basal vitamin C was low and redox-reactive iron was elevated in all patients. In the 16 patients receiving antioxidants, vitamin C increased (p = .0002) but total antioxidant capacity was unaffected. Lipid peroxides were elevated in all patients but did not increase further in the patients receiving antioxidants. Plasma total nitrite also increased (p = .007) in the antioxidant group. Heart rate increased in patients receiving antioxidants at 60 min (p = .018) and 120 min (p = .004). Cardiac index also increased at 60 min (p = .007) and 120 min (p = .05). Systemic vascular resistance index decreased at 120 min in the antioxidant treated patients (p = .003). The effect of antioxidants on hemodynamic variables has not previously been reported. Antioxidant administration may be a useful adjunct to conventional approaches in the management of septic shock.

Effect of 2,3-dimercaptosuccinic acid on nephrosclerosis in the Dahl rat. I. Role of reactive oxygen species

2,3-Dimercaptosuccinic acid (DMSA), a sulfhydryl-containing chelator, has previously been shown to reduce mean blood pressure in lead-treated rats. In the present study we have demonstrated that DMSA (0.5% for 5 days every 2 weeks) also reduces mean blood pressure in the Dahl salt-sensitive (SS) rat. Six-week-old Dahl SS and salt resistant (SR) rats were placed on a 0.3% NaCl diet for two weeks, followed by an 8% NaCl diet for four weeks. Eight SS and 8 SR rats remained untreated while 8 SS and 8 SR rats were treated with DMSA. DMSA treatment ameliorated the mean blood pressure rise in the Dahl SS rats (141 +/- 5 vs. 120 +/- 4 mm Hg at 6 weeks, P < 0.001). Nephrosclerosis was severe in untreated SS rats but absent in treated SS rats as well as in both treated and untreated SR rats. Reactive oxygen species formation, as assessed by kidney cortex content of malondialdehyde (MDA) and immunohistochemical demonstration of nitrotyrosine (a byproduct of peroxynitrite) in interlobular arteries, was increased in Dahl SS rats, but abolished by DMSA (MDA 9.65 +/- 0.33 nmol/g wet wt, untreated SS, vs. 6.46 +/- 0.51, treated SS, P < 0.001). The anti-nephrosclerotic action of DMSA was clearly disproportionate to the reduction in blood pressure. We conclude that the effect of DMSA was related instead to the reactive oxygen species scavenging properties of the thiol groups.

Salivary thiol oxidase activity of Rhodnius prolixus

Cysteine and other thiol compounds can accelerate the unloading of nitric oxide (NO) from salivary nitrosyl-nitrophorins of the blood sucking bug Rhodnius prolixus. The dependence of NO unloading on cysteine concentration is biphasic, showing a maximum between 0.5 and 1 mM cysteine. The proposed mechanism of action for the unloading is a series of reactions where cysteine (at low concentrations) reacts with the heme group of nitrophorins to form cystine and superoxide. The superoxide then reacts with NO to form peroxynitrite, which decays to a mixture of nitrite and nitrate anions. At high cysteine concentrations, cysteine is converted to cystine and H2O and thus no removal of NO from nitrophorins is observed. The thiol oxidase activity of Rhodnius nitrophorins is similar to that observed before in plant peroxidases [Pichorner et al., Phytochemistry 31, 3371 (1992)]. The possible physiological significance of this reaction to probing and feeding by R. prolixus is discussed.

Endothelial dysfunction in preeclampsia. Part II: Reducing the adverse consequences of endothelial cell dysfunction in preeclampsia; therapeutic perspectives

Next to low-dose Aspirin there appear to be several new and promising pharmacologie approaches for reducing the adverse consequences of endothelial cell dysfunction in preeclampsia. Among these are selective thromboxane-A2 synthetase and/or thromboxane-A2 receptor antagonists, stable prostacyclin analogues, selective S(erotonin)2-receptor blockers, nitrovasodilators, glycoprotein IIb/IIIa antagonists, hirudin, and ticlopidine. Early-onset preeclampsia appears to be associated with certain disorders that are likely to provoke an arterial thrombotic process by impairing the normal endothelial cell-platelet interactions. Especially heterozygous hyperhomocysteinemia, protein S deficiency and anticardiolipin antibodies appear to be fairly common. The management of these 3 separate disease entities will be discussed.

Role of nitric oxide on papillary blood flow and pressure natriuresis

This study examined whether nitric oxide synthesis blockade or potentiation (with N omega-nitro-L-arginine methyl ester [L-NAME] or N-acetylcysteine, respectively) can shift the relations between sodium excretion, papillary blood flow, and renal perfusion pressure. Papillary blood flow was measured by laser Doppler flowmetry. A low dose of L-NAME (3.7 nmol/kg per minute) reduced papillary blood flow only at high arterial pressure (140 mm Hg), but it had no effect on pressure natriuresis. Infusion of 37 nmol/kg per minute L-NAME reduced cortical blood flow by 9% at all perfusion pressures studied, lowered papillary blood flow by 8% and 19% at 120 and 140 mm Hg, respectively, and blunted the pressure-natriuresis response. The administration of 185 nmol/kg per minute L-NAME reduced cortical blood flow by 30% and decreased papillary blood flow by 25% in the range of 100 to 140 mm Hg of arterial pressure. Blockade of nitric oxide synthesis with L-NAME at all doses studied reduced papillary blood flow only at high renal perfusion pressures, but papillary blood flow remained essentially unchanged at low perfusion pressures, thus restoring papillary blood flow autoregulation. N-Acetyl-cysteine (1.8 mmol/kg) increased papillary blood flow by 9% and shifted the relations between papillary blood flow, sodium excretion, and renal perfusion pressure toward lower pressures. This effect of N-acetylcysteine on papillary blood flow was blocked by subsequent L-NAME administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of captopril and enalapril on endothelial function in hypertensive patients

Endothelium-dependent vasodilation is impaired in patients with essential hypertension. The objective of this study was to determine whether long-term treatment with angiotensin-converting enzyme inhibitors improves endothelium-dependent vasodilation in forearm resistance vessels of patients with hypertension. Furthermore, since tissue thiols may be relevant to nitric oxide-mediated vasodilation, we queried whether an angiotensin-converting enzyme inhibitor with a sulfhydryl group preferentially augments endothelium-dependent vasodilation in these individuals. The study included 24 patients with essential hypertension (mean age, 45 +/- 2 years) and 20 normotensive subjects (mean age, 47 +/- 1 years). Methacholine chloride (0.3 to 10 micrograms/min) was infused via the brachial artery to assess endothelium-dependent vasodilation in forearm resistance vessels. Nitroglycerin (1 to 30 micrograms/min) was administered to evaluate endothelium-independent vasodilation. Forearm blood flow was determined by venous occlusion strain-gauge plethysmography. Forearm vascular function studies were performed in hypertensive patients before and 7 to 8 weeks after randomization to either captopril or enalapril, angiotensin-converting enzyme inhibitors with and without a sulfhydryl moiety, respectively. Normotensive subjects were studied on only one occasion. Before treatment, the forearm vasodilative response to methacholine was attenuated in hypertensive compared with normotensive subjects (P < .01). The effects of nitroglycerin on forearm blood flow did not differ significantly between the two groups. Both captopril and enalapril reduced mean blood pressure in the hypertensive subjects (12 +/- 2 versus 15 +/- 3 mm Hg, respectively; P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)