Effect of iron oxide nanoparticles on vascular function and nitric oxide production in acute stress-exposed rats.

We investigated whether polyethylene glycol-coated Fe3O4 nanoparticles (IONs), acute stress and their combination modifies vascular functions, nitric oxide synthase (NOS) activity, mean arterial pressure (MAP) as well as hepcidin and ferritin H gene expressions in Wistar-Kyoto rats. Rats were divided into control, ION-treated rats (1 mg Fe/kg i.v.), repeated acute air-jet stress-exposed rats and IONs-and-stress co-exposed rats. Maximal acetylcholine (ACh)-induced and sodium nitroprusside (SNP)-induced relaxations in the femoral arteries did not differ among the groups. IONs alone significantly elevated the N?-nitro-L-arginine methyl ester (L-NAME)-sensitive component of ACh-induced relaxation and reduced the sensitivity of vascular smooth muscle cells to SNP. IONs alone also elevated NOS activity in the brainstem and hypothalamus, reduced NOS activity in the kidneys and had no effect in the liver. Acute stress alone failed to affect vascular function and NOS activities in all the tissues investigated but it elevated ferritin H expression in the liver. In the ION-and-stress group, NOS activity was elevated in the kidneys and liver, but reduced in the brainstem and hypothalamus vs. IONs alone. IONs also accentuated air-jet stress-induced MAP responses vs. stress alone. Interestingly, stress reduced ION-originated iron content in blood and liver while it was elevated in the kidneys. In conclusion, the results showed that 1) acute administration of IONs altered vascular function, increased L-NAME-sensitive component of ACh-induced relaxation and had tissue-dependent effects on NOS activity, 2) ION effects were considerably reduced by co-exposure to repeated acute stress, likely related to decrease of ION-originated iron in blood due to elevated decomposition and/or excretion.

High concentration of uric acid failed to affect endothelial function of small mesenteric arteries, femoral arteries and aortas from aged Wistar-Kyoto rats.

It is known that a high level of uric acid (UA) in plasma, hyperuricemia (HU), is associated with the increased risk of cardiovascular diseases (CVDs). Endothelial damage has been suggested as a potential mechanism involved in HU-induced CVDs, especially in patients with the accumulation of other cardiovascular risk factors. However, the role of UA in the pathogenesis of endothelial dysfunction is still a matter of debate. It is unclear whether UA is a causative risk factor in endothelial dysfunction, an inert marker or an endothelium-protective molecule with respect to its antioxidant properties. Of note, only a few studies have been conducted to investigate the effect of UA on vascular endothelium-dependent relaxation. Therefore, we have studied the acute in vitro effects of high UA concentrations on the endothelial function of arteries isolated from aged rats. Experiments were performed in small mesenteric arteries (SMAs), femoral arteries and thoracic aortas isolated from 68-week-old and 57-week-old male Wistar-Kyoto rats. Vascular reactivity was investigated in isometric conditions using the wire myograph and organ chamber. Acetylcholine (ACh) was used to investigate endothelium-dependent vasorelaxation. Then, UA was added to the myograph or organ chamber at 600 µmol/l (arteries from 68-week-old rats) or 1200 µmol/l (arteries from 57-week-old rats) and incubated for 1 h, and this was followed by determining the ACh concentration-response curve. UA had no significant effect on ACh-induced vasorelaxation and pD2 values in all investigated groups. Likewise, no significant differences in noradrenaline- (SMAs), serotonin- (femoral arteries) and phenylephrine-induced (aortas) vasoconstriction were observed after UA pre-incubation. In conclusion, high concentrations of UA administered acutely failed to affect endothelial function and did not provoke endothelial dysfunction in resistant mesenteric arteries, medium-sized and large arteries from aged rats.

The peroxisome proliferator-activated receptor gamma agonist pioglitazone improves nitric oxide availability, renin-angiotensin system and aberrant redox regulation in the kidney of pre-hypertensive rats.

The peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-dependent nuclear receptor. It plays an important role in kidney physiology, where it might contribute to arterial blood pressure regulation and hypertension development by modulation of several signaling pathways. In our study we focused on the effect of PPARγ agonist pioglitazone on changes in the nitric oxide synthase (NOS) expression and activity, the renin-angiotensin system (RAS) cascade, and redox homeostasis signaling pathways in the renal cortex of young pre hypertensive rat models. Young (5-weeks old) spontaneously hypertensive (SHR) and borderline hypertensive (BHR) rats were treated by pioglitazone (PIO, 10 mg/kg/day) during 10 days. Blood pressure (BP) was determined by plethysmography method. Changes in lipid profile were detected in plasma with standard kits using biochemical analyser. Gene expression has been detected by qRT-PCR and protein level was determined using Western blot analysis. Superoxide dismutase (SOD) and catalase (CAT) activities were determined spectrophotometrically and the total enzyme activity of NOS was measured using a radioactive assay based on conversion of [3H] L-arginine to [3H] L- citrulline. Administration of pioglitazone decreased BP in BHR and slowed down the development of BP increase in young SHR animals. For NOS, activation by PPARγ correlated with increase in gene and protein expression of NOS isoforms and in total enzyme activity both in BHR and SHR. In the AT1R/Nox pathway, the treatment did not significantly influence mRNA expression of the p22phox subunit of NADPH oxidase (Nox) and AT1R, but up-regulated the 'pro-vasodilatatory' Mas and AT2R receptors in both BHR and SHR groups. Pioglitazone treatment affected redox regulation. Increase in gene expression of nuclear factor E2-related factor 2 (Nrf2) and SOD isoforms correlated with SOD and CAT enzyme activities. The group treatment-to-control ratios, BHR Pioglitazone to BHR control and SHR Pioglitazone to SHR control for gene expression increased by 10% to 230%. The largest effect of PPARγ has been observed in SOD1, SOD3 and the Mas receptor gene treatment-to-control ratios. The most prominent differences between BHR and SHR were observed in SOD1 and Mas receptor expressions, with large effects of opposite sign in BHR versus SHR. Our data indicate that an increase of NO release activates signaling in the renal cortex of pre-hypertensive rats after pioglitazone treatment. Improvement of NO availability, AT2R, Mas receptors and aberrant redox regulation is thought to be the major correlated mechanisms mediating the BP decrease affected by the PPARγ agonist treatment. We also observed that the most sensitive tissue responses to PPARγ-dependent activation of Nrf2 have been primarily found in the kidney of young hypertensive animals.

Corrigendum to "(-)-Epicatechin Prevents Blood Pressure Increase and Reduces Locomotor Hyperactivity in Young Spontaneously Hypertensive Rats".

[This corrects the article DOI: 10.1155/2016/6949020.].

(-)-Epicatechin Prevents Blood Pressure Increase and Reduces Locomotor Hyperactivity in Young Spontaneously Hypertensive Rats.

This study investigated the effects of subchronic (-)-epicatechin (Epi) treatment on locomotor activity and hypertension development in young spontaneously hypertensive rats (SHR). Epi was administered in drinking water (100 mg/kg/day) for 2 weeks. Epi significantly prevented the development of hypertension (138 ± 2 versus 169 ± 5 mmHg, p < 0.001) and reduced total distance traveled in the open-field test (22 ± 2 versus 35 ± 4 m, p < 0.01). In blood, Epi significantly enhanced erythrocyte deformability, increased total antioxidant capacity, and decreased nitrotyrosine concentration. In the aorta, Epi significantly increased nitric oxide (NO) synthase (NOS) activity and elevated the NO-dependent vasorelaxation. In the left heart ventricle, Epi increased NOS activity without altering gene expressions of nNOS, iNOS, and eNOS. Moreover, Epi reduced superoxide production in the left heart ventricle and the aorta. In the brain, Epi increased nNOS gene expression (in the brainstem and cerebellum) and eNOS expression (in the cerebellum) but had no effect on overall NOS activity. In conclusion, Epi prevented the development of hypertension and reduced locomotor hyperactivity in young SHR. These effects resulted from improved cardiovascular NO bioavailability concurrently with increased erythrocyte deformability, without changes in NO production in the brain.

Blood pressure regulation in stress: focus on nitric oxide-dependent mechanisms.

Stress is considered a risk factor associated with the development of various civilization diseases including cardiovascular diseases, malignant tumors and mental disorders. Research investigating mechanisms involved in stress-induced hypertension have attracted much attention of physicians and researchers, however, there are still ambiguous results concerning a causal relationship between stress and long-term elevation of blood pressure (BP). Several studies have observed that mechanisms involved in the development of stress-induced hypertension include increased activity of sympathetic nervous system (SNS), glucocorticoid (GC) overload and altered endothelial function including decreased nitric oxide (NO) bioavailability. Nitric oxide is well known neurotransmitter, neuromodulator and vasodilator involved in regulation of neuroendocrine mechanisms and cardiovascular responses to stressors. Thus NO plays a crucial role in the regulation of the stress systems and thereby in the BP regulation in stress. Elevated NO synthesis, especially in the initial phase of stress, may be considered a stress-limiting mechanism, facilitating the recovery from stress to the resting levels via attenuation of both GC release and SNS activity as well as by increased NO-dependent vasorelaxation. On the other hand, reduced levels of NO were observed in the later phases of stress and in subjects with genetic predisposition to hypertension, irrespectively, in which reduced NO bioavailability may account for disruption of NO-mediated BP regulatory mechanisms and accentuated SNS and GC effects. This review summarizes current knowledge on the role of stress in development of hypertension with a special focus on the interactions among NO and other biological systems affecting blood pressure and vascular function.

Short-term administration of alibernet red wine extract failed to affect blood pressure and to improve endothelial function in young normotensive and spontaneously hypertensive rats.

As wine polyphenols were shown to possess many positive effects in mammals, including improvement of vascular function, this study investigated the effect of the Slovak Alibernet red wine extract (AWE) on blood pressure and vascular function in young normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Six weeks old, male, WKY and SHR were treated with AWE for three weeks at the dose of 24.2 mg/kg/day. Blood pressure (BP), determined by tail-cuff plethysmography, was significantly elevated in SHR vs. WKY and AWE failed to affect it. Lipid peroxidation was evaluated by determination of thiobarbituric acid-reactive substances. Vascular function was assessed in rings of the femoral artery using Mulvany-Halpern's myograph. Maximal endothelium-dependent acetylcholine (ACh)-induced relaxation was reduced in control SHR vs. WKY rats by approximately 9.3 %, which was associated with a significant decrease of its NO-independent component. AWE failed to affect maximal ACh-induced relaxation, both its NO-dependent and independent components, compared to controls of the same genotype. AWE however reduced lipid peroxidation in the left ventricle of both WKY and SHR and in the liver of SHR. In conclusion, three-week administration of AWE failed to reduce BP and to improve endothelial function in the femoral arteries of both genotypes investigated.

Endothelial dysfunction in femoral artery of the hypertensive rats is nitric oxide independent.

This study examined nitric oxide (NO) production, oxidative load and endothelium-dependent relaxation (NO-dependent and NO-independent) in adult male borderline hypertensive (BHR) and spontaneously hypertensive (SHR) rats as compared to normotensive Wistar-Kyoto (WKY) rats. Systolic blood pressure (BP) was determined by tail-cuff. NO production was determined by conversion of [(3)H]-L-arginine. Conjugated dienes (CD) and concentrations of thiobarbituric acid-reactive substances (TBARS) were measured for assessment of oxidative load. Vascular function was investigated in rings of the femoral artery (FA) using a wire myograph. BP of WKY, BHR and SHR was 106+/-2, 143+/-3 and 191+/-3 mm Hg, respectively (p<0.01 for each). Significant left ventricle (LV) hypertrophy and elevated levels of CD and TBARS in the LV were present in BHR and SHR as compared to WKY. NO production was elevated significantly in the aorta of BHR and SHR vs. WKY as well as in the LV of SHR vs. WKY. Acetylcholine (ACh)-induced relaxation of the FA was reduced significantly in both BHR and SHR vs. WKY. The NO-dependent component of ACh-induced relaxation had increasing tendency in hypertensive groups and it correlated positively with BP. The NO-independent component of vasorelaxation was reduced significantly in BHR and SHR vs. WKY and it correlated negatively with BP. In conclusion, the results showed that endothelial dysfunction in the experimental model of borderline hypertensive and hypertensive rats is NO-independent. The results suggest that borderline hypertension represents a risk of other cardiovascular disorders which is qualitatively similar to that of fully developed hypertension.

[Assessment of vascular reactivity by wire myograph]. / Stanovenie cievnej reaktivity pomocou drôtikového myografu.

This paper describes the methodology and application of a wire myograph which has been used for the measurement of vascular reactivity. In an earlier years (pre-1970s) most of the information about the mechanical, morphological and pharmacological properties of vascular smooth muscle was confined only to larger arteries (mainly aorta). Whereas information about smaller arteries was purely inferred from perfusion experiments and histological examination. However, after mid-1970s Prof. Mulvany and Prof. Halpern developed and introduced an astonishing technique, a wire myography, to study the contractile responses of an isolated small resistance arteries (approximately 100-300 microm in internal diameter). This work describes some of the principles used in the investigation of the vessels, based on the use of the small vessel dual wire myograph. A dual myograph allows us simultaneous testing of two vessels. The technique allows segments of small arteries to be mounted as the ring preparations to the myograph chamber, and providing measurements of isometric responses. On the other hand, there are other techniques including an isobaric and isotonic mounting of arteries have been developed to date. The myograph has been used for the investigation of a variety of small and larger arteries and other tubular structures from a wide range of species. In the second part of this report we show an experimental example concerning measurement of endothelial functionality by technique described therein before.

Accurate normalization factor for wire myography of rat femoral artery.

Wire myograph is a device for the in vitro investigation of both, active and passive properties of arteries. Arteries from a variety of animal species, pathological states, and vascular beds were investigated using this method. We focus on the normalization procedure which is aimed to standardize experimental settings and, in part, to simulate physiological conditions. During normalization, it is determined the internal circumference of a vessel stretched to a tension that corresponds to the transmural pressure of 100 mm Hg (IC100). Once it is determined, the internal circumference is traditionally set to (0.9 IC100). However, this constant 0.9, called also the normalization factor (NF), was experimentally determined for rat small mesenteric arteries only. Therefore, the aim of our work was to show the influence of different NFs on the passive tension and reactivity of both, rat femoral arteries (FA) and the first branches of superior mesenteric arteries (MA). We found out that the maximal active wall tension of the FA was achieved at the NF value of 1.1, and that of the MA at 0.9. Considering the values of the active wall tension we suggest that higher reactivity and better signal-to-noise ratio in FA can be achieved when the NF is set at least to 1.0.

[Endothelial (dys)function in the experimental model of primary hypertension]. / Endotelová (dys)funkcia v experimentálnom modeli esenciálnej hypertenzie.

A number of vascular diseases, including hypertension, are characterised by endothelial dysfunction caused by alterations in the production and action of the endothelium-derived relaxing (EDRFs) and/or endothelium-derived contracting (EDCFs) factors. The spontaneously hypertensive rat (SHR) is one of the most widely studied animal models for human essential hypertension. Several similarities between human primary hypertension and hypertension in the SHR have been pointed out in both the pathophysiology and the clinical course of the hypertensive disease. In human hypertension as well as in SHR, endothelium-dependent relaxation may be attenuated and this endothelial dysfunction contributes to the increased peripheral resistance. However, various results concerning endothelium-dependent relaxation, including impairment, no change and improvement have been reported in experimental hypertension. Endothelial dysfunction in hypertension has been linked to decrease in NO bioavailability, reflecting the impaired generation of NO and/or the enhanced inactivation of NO by reactive oxygen species. There is evidence that increased vascular oxidative stress is present in SHR. Thus, it has been proposed that oxidative inactivation of NO may account for the endothelial dysfunction seen in SHR. On the other hand, several studies demonstrate elevated basal NO synthesis in SHR rats which may be an adapting mechanism, preventing them from excessive blood pressure elevation. However, the role of NO in hypertension in SHR and in humans remains still controversial. We hypothesize that the vascular bed studied, the effect of age as well as methodological aspects, such as "precontraction" with different vasoconstrictors as well as antioxidants added to the solution for determination of the vasoreactivity may contribute to the discrepancies among studies. Nevertheless, the involvement of endothelial function in hypertension remains subject of debate and further research is needed to complete our knowledge on the role of NO, reactive oxygen species and other endothelial factors in the regulation of vascular and cardiac function.

[The role of endothelium and nitric oxide in the regulation of vascular tone]. / Uloha endotelu a oxidu dusnatého v regulácii cievneho tonusu.

Vascular system is a large complex of tubes with different diameters which are able to perceive changes of endogenous milieu, to integrate and modulate signals of intercellular communication and to respond and adapt by a local production of different kinds of mediators affecting vascular structure and function. For a long time, it has been assumed that the main determinant of vasomotor function was the nervous system and the monolayer of endothelial cells was only a physical barrier between the vessel wall and blood. However, the first publications in 1960s and 70s indicated that endothelium is not only a passive barrier. Endothelium features autocrine, paracrine and endocrine activities. Vascular endothelium plays an important role in the regulation of vascular tone, blood pressure and blood flow beside central regulation of nervous system. The existence of endothelium-derived relaxing factor (EDRF) was found out by Furchgott and Zawadzki (1980) who showed that acetylcholine induced relaxation of the rabbit aorta only in the presence of intact endothelium. Nowadays, nitric oxide (NO), previously known as EDRF, is considered one of the crucial endothelium-derived vasorelaxing substances participating in the regulation of basal vascular tone, vascular resistance and thus in the regulation of blood pressure. Arterial bed is dilated continuously as a consequence of constant production of NO. Any damage of endothelium modifies regulatory functions of endothelial cells. These conditions are characterised as endothelial dysfunction associated with imbalance between vasodilating and vasoconstricting factors, pro- and anticoagulation factors and factors stimulating and inhibiting growth and proliferation of cells. However, cellular mechanisms which are involved in the development of endothelial dysfunction, are still not well-known.

Crowding-induced alterations in vascular system of Wistar-Kyoto rats: role of nitric oxide.

The aim of this study was to determine the effect of chronic crowding on the cardiovascular system of Wistar-Kyoto (WKY) rats. Rats were randomly divided into the control (480 cm(2) per rat) or crowded (200 cm(2) per rat) group for eight weeks. Body weight, blood pressure (BP), heart rate and plasma nitrate/nitrite levels of the crowded rats were not different from controls at the end of the experiment. Plasma corticosterone exhibited an increasing trend (5.7+/-1.8 vs. 12.6+/-3.7 ng/ml, p=0.08) while blood glucose was significantly reduced in the crowded rats in comparison with the controls. Nitric oxide (NO) synthase activity and nitrate/nitrite levels of the crowded rats were significantly elevated in the aorta by 80 % and 20 %, respectively, but unchanged in the left ventricle. Moreover, acetylcholine-induced relaxation was significantly increased in the crowded rats in both the femoral artery (61+/-5 % vs. 76+/-5 %, p<0.001) and mesenteric artery (51+/-6 % vs. 72+/-7 %, p<0.001). In conclusion, results suggest that chronic crowding may increase vasorelaxation and vascular NO production in normotensive rats. This may be considered as an adapting mechanism preventing the development of the stress-related elevation of BP. Additionally, results also suggest caution in the housing of rats because an inappropriate crowding may affect results of the experiment significantly.

Vascular function and nitric oxide production in chronic social-stress-exposed rats with various family history of hypertension.

The study investigated the effect of chronic crowding stress on vascular function and nitric oxide (NO) production in rats with various family history of hypertension. Wistar (W), wBHR (offspring of W dams and spontaneously hypertensive sires), sBHR (offspring of spontaneously hypertensive dams and W sires) and spontaneously hypertensive rats (SHR) were used. Twelve-week-old males were divided into the control or crowded group for eight weeks. Basal blood pressure (BP, determined by tail-cuff plethysmography) of W, wBHR, sBHR and SHR rats was 112 +/- 3, 129 +/- 2, 135 +/- 2 and 187 +/- 3 mmHg, respectively. Crowding increased BP and reduced aortic NO synthase activity only in sBHR and SHR rats, without alterations in hypothalamic NO production. Acetylcholine-induced vasorelaxation of the femoral artery of stress-exposed rats was improved in W, unaltered in wBHR and sBHR and reduced in SHR. Crowding reduced serotonin-induced vasoconstriction in W and wBHR rats but had no effect in sBHR and SHR rats. In conclusion, the results suggest that crowded offspring of normotensive mothers were able to modify their vascular function in order to maintain BP at normal levels. On the other hand, offspring of hypertensive mothers were unable of effective adaptation of vascular function in stressful conditions resulting in gradual development of hypertension.

Effect of blood pressure on L-NAME-sensitive component of vasorelaxation in adult rats.

The aim of this study was to investigate nitric oxide (NO) production and L-NAME-sensitive component of endothelium-dependent vasorelaxation in adult normotensive Wistar-Kyoto rats (WKY), borderline hypertensive rats (BHR) and spontaneously hypertensive rats (SHR). Blood pressure (BP) of WKY, BHR and SHR (determined by tail-cuff) was 111+/-3, 140+/-4 and 184+/-6 mm Hg, respectively. NO synthase activity (determined by conversion of [(3)H]-L-arginine) was significantly higher in the aorta of BHR and SHR vs. WKY and in the left ventricle of SHR vs. both BHR and WKY. L-NAME-sensitive component of endothelium-dependent relaxation was investigated in the preconstricted femoral arteries using the wire myograph during isometric conditions as a difference between acetylcholine-induced relaxation before and after acute N(G)-nitro-L-arginine methyl ester pre-treatment (L-NAME, 10(-5) mol/l). Acetylcholine-induced vasorelaxation of SHR was significantly greater than that in WKY. L-NAME-sensitive component of vasorelaxation in WKY, BHR and SHR was 20+/-3 %, 29+/-4 % (p<0.05 vs. WKY) and 37+/-3 % (p<0.05 vs. BHR), respectively. There was a significant positive correlation between BP and L-NAME-sensitive component of relaxation of the femoral artery. In conclusion, results suggest the absence of endothelial dysfunction in the femoral artery of adult borderline and spontaneously hypertensive rats and gradual elevation of L-NAME-sensitive component of vasorelaxation with increasing blood pressure.

Chronic low-dose L-NAME treatment increases nitric oxide production and vasorelaxation in normotensive rats.

N(G)-nitro-L-arginine methyl ester (L-NAME) is a non-specific nitric oxide (NO) synthase inhibitor, commonly used for the induction of NO-deficient hypertension. The aim of this study was to investigate the effect of chronic low-dose administration of L-NAME on NO production, vascular function and structure of the heart and selected arteries of rats. Adult male Wistar rats were treated with L-NAME in the dose of approximately 1.5 mg/kg/day in drinking water for 8 weeks. Basal blood pressure (BP) of rats (determined by tail-cuff) was 112+/-3 mm Hg. The low-dose administration of L-NAME significantly elevated BP measured on the third and sixth week of treatment vs. controls by approximately 9 % and 12 %, respectively. After this period, BP of L-NAME-treated rats returned to the control values. The relative left ventricular mass, heart fibrosis and collagen III/collagen I ratio were not affected by L-NAME. Similarly, there were no alterations in the cross-sectional area and wall thickness/diameter ratio of the aorta and the femoral artery of L-NAME-treated rats. NO synthase activity (determined by conversion of [(3)H]-L-arginine to [(3)H]-L-citrulline) was not altered in the hypothalamus of L-NAME-treated rats. Interestingly, chronic low-dose L-NAME treatment significantly elevated NO synthase activity in the left ventricle and aorta, increased endothelium-dependent acetylcholine-induced vasorelaxation and reduced serotonin-induced vasoconstriction of the femoral artery. The data suggest that chronic low-dose L-NAME treatment can increase NO production and vasorelaxation in normotensive rats without negative structural changes in the cardiovascular system.

Vascular effects of red wine polyphenols in chronic stress-exposed Wistar-Kyoto rats.

Present study investigated the effect of red wine polyphenolic compounds (Provinols) on blood pressure (BP), nitric oxide synthase (NOS) activity and vascular function in Wistar-Kyoto (WKY) rats exposed to chronic social stress produced by crowding. Adult male rats were divided into four groups: control (480 cm(2)/rat), Provinols-treated (20 mg/kg/day, 480 cm(2)/rat), crowded (200 cm(2)/rat) and crowded treated with Provinols (20 mg/kg/day, 200 cm(2)/rat) for 8 weeks. No differences in BP were observed among the groups at the end of experiment, however, reduced BP was observed in Provinols-treated rats after 3 weeks of treatment. NOS activity in the aorta was significantly elevated in crowded rats, while Provinols alone had no effect on nitric oxide (NO) production. Acetylcholine-induced relaxation of the femoral artery was significantly improved in stressed and Provinols-treated rats vs. control, without significant changes in their noradrenaline-induced vasoconstriction. Interestingly, Provinols blunted the elevation of NO production and vasorelaxation during crowding. Increased endothelium-dependent vasorelaxation and NO synthesis in crowded rats may represent the adaptation mechanisms, resulting in unaltered blood pressure in stress-exposed normotensive rats. This study further demonstrated that elevated release of NO during chronic stress may be prevented by Provinols. Thus, Provinols might maintain equilibrium between endothelium-derived vasoconstrictor and vasodilator factors in stress.