Exercise training improves aortic endothelium-dependent vasorelaxation and determinants of nitric oxide bioavailability in spontaneously hypertensive rats.

The present study examined in vitro vasomotor function and expression of enzymes controlling nitric oxide (NO) bioavailability in thoracic aorta of adult male normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) that either remained sedentary (Sed) or performed 6 wk of moderate aerobic exercise training (Ex). Training efficacy was confirmed by elevated maximal activities of both citrate synthase (P = 0.0024) and beta-hydroxyacyl-CoA dehydrogenase (P = 0.0073) in the white gastrocnemius skeletal muscle of Ex vs. Sed rats. Systolic blood pressure was elevated in SHR vs. WKY (P < 0.0001) but was not affected by Ex. Despite enhanced endothelium-dependent relaxation to 10(-8) M ACh in SHR vs. WKY (P = 0.0061), maximal endothelium-dependent relaxation to 10(-4) M ACh was blunted in Sed SHR (48 +/- 12%) vs. Sed WKY (84 +/- 6%, P = 0.0067). Maximal endothelium-dependent relaxation to 10(-4) M ACh was completely restored in Ex SHR (93 +/- 9%) vs. Sed SHR (P = 0.0011). N(omega)-nitro-l-arginine abolished endothelium-dependent relaxation in all groups (P 相似文献   

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.     

Endothelium-dependent vasorelaxation to the AMPK activator AICAR is enhanced in aorta from hypertensive rats and is NO and EDCF dependent

Activation of AMP-activated protein kinase (AMPK) induces vasorelaxation in arteries from healthy animals, but the mechanisms coordinating this effect are unclear and the integrity of this response has not been investigated in dysfunctional arteries of hypertensive animals. Here we investigate the mechanisms of relaxation to the AMPK activator 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR) in isolated thoracic aorta rings from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Although AICAR generated dose-dependent (10(-6)-10(-2) M) relaxation in precontracted WKY and SHR aortic rings with (E(+)) or without (E(-)) endothelium, relaxation was enhanced in E(+) rings. Relaxation in SHR E(+) rings was also enhanced at low [AICAR] (10(-6) M) compared with that of WKY (57 ± 8% vs. 3 ± 2% relaxation in SHR vs. WKY E(+)), but was similar and near 100% in both groups at high [AICAR]. Pharmacological dissection showed that the mechanisms responsible for the endothelium-dependent component of relaxation across the dose range of AICAR are exclusively nitric oxide (NO) mediated in WKY rings, but partly NO dependent and partly cyclooxygenase (COX) dependent in SHR vessels. Further investigation revealed that ACh-stimulated COX-endothelium-derived contracting factors (EDCF)-mediated contractions were suppressed by AICAR, and this effect was reversed in the presence of the AMPK inhibitor Compound C in quiescent E(+) SHR aortic rings. Western blots demonstrated that P(Thr(172))-AMPK and P(Ser(79))-acetyl-CoA carboxylase (indexes of AMPK activation) were elevated in SHR versus WKY E(+) rings at low AICAR (～2-fold). Together these findings suggest that AMPK-mediated inhibition of EDCF-dependent contraction and elevated AMPK activation may contribute to the enhanced sensitivity of SHR E(+) rings to AICAR. These results demonstrate AMPK-mediated vasorelaxation is present and enhanced in arteries of SHR and suggest that activation of AMPK may be a potential strategy to improve vasomotor dysfunction by suppressing enhanced endoperoxide-mediated contraction and enhancing NO-mediated relaxation.     

Endothelium-derived relaxing factors in the kidney of spontaneously hypertensive rats

Acetylcholine (ACh)-induced vasodilation is mainly due to endothelium-derived nitric oxide (EDNO) and hyperpolarizing factor (EDHF). To explore the mechanisms underlying attenuated endothelium-dependent vasodilation in hypertensive arteries, we measured the EDNO released from isolated kidneys of spontaneously hypertensive rats (SHR) using a sensitive chemiluminescence assay system of NO. ACh-induced renal vasodilation was significantly smaller in SHR than in the normotensive control, Wistar-Kyoto rats (WKY). However, ACh-induced NO release did not differ between SHR and WKY (10⁻⁷ M: SHR +37 ± 2 [SE] vs. WKY +32 ± 4 fmol/min/g kidney). Perfusion with a 20 mEq/L high-K⁺ buffer, which is reported to inhibit action of EDHF, significantly reduced ACh-induced vasorelaxation in WKY but not in SHR, resulting in identical renal perfusion pressure in SHR and wKY under these conditions. These results indicate that attenuated ACh-induced vasorelaxation in the SHR kidney may be attributed to a decrease in EDHF rather than that in EDNO.     

Reduced connexin-43 expression in the aorta of prehypertensive rats

Genetic component represents an important factor in the development of hypertension, which is known to be associated with changes in expression of vascular gap junction protein connexin 43 (Cx43). The aim of the study was to examine the distribution and expression of Cx43 in the aortic endothelium of adult normotensive Wistar rats (W), borderline hypertensive rats (BHR) and spontaneously hypertensive rats (SHR). Rings of the thoracic aorta were processed for immunofluorescence and Western blot analysis of endothelial Cx43 and for electron microscopy. Both, BHR and SHR exhibited significantly increased blood pressure vs. W (132+/-2 mm Hg and 185+/-3 mm Hg vs. 110+/-2 mm Hg). Reduced Cx43 immunofluorescence was observed in the endothelium of BHR and these alterations were more pronounced in SHR. Western blot analysis showed significant suppression of Cx43 expression in the aorta of both BHR (p<0.05) and SHR (p<0.001) vs. W. Electron microscopy revealed local subcellular alterations of interendothelial connections in BHR including extended tight junctions. These alterations were more frequent and marked in SHR. The results indicate that connexin 43 expression is reduced in the aortic endothelium already in prehypertensive period, which may affect cell-to-cell communication and thus participate in acceleration of hypertensive disease.     

Insulin resistance in spontaneously hypertensive rats is associated with endothelial dysfunction characterized by imbalance between NO and ET-1 production

Insulin stimulates production of NO in vascular endothelium via activation of phosphatidylinositol (PI) 3-kinase, Akt, and endothelial NO synthase. We hypothesized that insulin resistance may cause imbalance between endothelial vasodilators and vasoconstrictors (e.g., NO and ET-1), leading to hypertension. Twelve-week-old male spontaneously hypertensive rats (SHR) were hypertensive and insulin resistant compared with control Wistar-Kyoto (WKY) rats (systolic blood pressure 202 +/- 11 vs. 132 +/- 10 mmHg; fasting plasma insulin 5 +/- 1 vs. 0.9 +/- 0.1 ng/ml; P < 0.001). In WKY rats, insulin stimulated dose-dependent relaxation of mesenteric arteries precontracted with norepinephrine (NE) ex vivo. This depended on intact endothelium and was blocked by genistein, wortmannin, or N(omega)-nitro-l-arginine methyl ester (inhibitors of tyrosine kinase, PI3-kinase, and NO synthases, respectively). Vasodilation in response to insulin (but not ACh) was impaired by 20% in SHR (vs. WKY, P < 0.005). Preincubation of arteries with insulin significantly reduced the contractile effect of NE by 20% in WKY but not SHR rats. In SHR, the effect of insulin to reduce NE-mediated vasoconstriction became evident when insulin pretreatment was accompanied by ET-1 receptor blockade (BQ-123, BQ-788). Similar results were observed during treatment with the MEK inhibitor PD-98059. In addition, insulin-stimulated secretion of ET-1 from primary endothelial cells was significantly reduced by pretreatment of cells with PD-98059 (but not wortmannin). We conclude that insulin resistance in SHR is accompanied by endothelial dysfunction in mesenteric vessels with impaired PI3-kinase-dependent NO production and enhanced MAPK-dependent ET-1 secretion. These results may reflect pathophysiology in other vascular beds that directly contribute to elevated peripheral vascular resistance and hypertension.     

Decrease in urinary excretion of active kallikrein in conscious young and adult spontaneously hypertensive rats

Urinary excretion of active kallikrein was determined every day (amidolytic assay) in 6 male Okamoto-Aoki spontaneously hypertensive rats (SHR) and 6 male normotensive Wistar-Kyoto rats (WKY) from ages 4 to 7 weeks and from 12 to 15 weeks. The rats were housed in individual metabolic cages and were allowed free access to food having normal sodium content and to tap water. Urinary kallikrein excretion was lower in 4-week-old SHR than in age-matched WKY (7.8 +/- 1.4 vs. 15.5 +/- 2.3 nkat/24 h respectively, P less than 0.01) at a moment when systolic blood pressure (BP) in SHR was already higher than in WKY. The slope of the increase in active kallikrein excretion from week 4 to 7 was not different for SHR and WKY (6.34 +/- 1.05 vs. 7.50 +/- 1.02 nkat/24 h-1 . wk-1 respectively). In contrast, from week 12 to 15, this slope was not significant for SHR (1.67 +/- 2.55 nkat/24 h-1 . wk-1) while it remained positive in WKY (7.36 +/- 3,44 nkat/24 h-1 . wk-1). In both SHR and WKY, urinary kallikrein excretion was directly related to BP from week 4 to 7 but the slope of the regression line was less for SHR than for WKY (0.19 +/- 0.05 vs. 0.48 +/- 0.12 nkat/24 h-1 . mm Hg respectively). From ages 12 to 15 weeks, kallikrein excretion was still related to pressure in WKY (y = 1.92 x - 180.8; r = 0.93) but not in SHR (y = 0.71 x - 81.48; r = 0.52).(ABSTRACT TRUNCATED AT 250 WORDS)     

L-carnitine and propionyl-L-carnitine improve endothelial dysfunction in spontaneously hypertensive rats: different participation of NO and COX-products

L-carnitine and propionyl-L-carnitine are supplements to therapy in cardiovascular pathologies. Their effect on endothelial dysfunction in hypertension was studied after treatment with either 200 mg/kg of L-carnitine or propionyl-L-carnitine during 8 weeks of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). Endothelial function was assessed in aortic rings by carbachol-induced relaxation (CCh 10(-8) to 10(-4) M) and factors involved were characterized in the presence of the inhibitors: L-NAME, indomethacin, the TXA2/PGH2 Tp receptor antagonist ICI-192,605 and the thromboxane synthetase inhibitor-Tp receptor antagonist, Ro-68,070. The effect on phenylephrine-induced contractions was also observed. To identify the nature of vasoactive COX-derived products, enzyme-immunoassay of incubation media was assessed. Involvement of reactive oxygen species was evaluated by incubating with superoxide dismutase and catalase. Nitric oxide production was evaluated by serum concentration of NO2+NO3.Treatment with both compounds improved endothelial function of rings from SHR without blood pressure change. Propionyl-L-carnitine increased NO participation in WKY and SHR. L-carnitine reduced endothelium-dependent responses to CCh in WKY due to an increase of TXA2 production. In both SHR and WKY, L-carnitine enhanced concentration of PGI2 and increased participation of NO. Results in the presence of SOD plus catalase show that it might be related to antioxidant properties of L-carnitine and propionyl-L-carnitine. Comparison between the effect of both compounds shows that both may reduce reactive oxygen species and increase NO participation in endothelium-dependent relaxations in SHR. However, only L-carnitine was able to increase the release of the vasodilator PGI2 and even enhanced TXA2 production in normotensive rats.     

NAD(P)H oxidase-derived peroxide mediates elevated basal and impaired flow-induced NO production in SHR mesenteric arteries in vivo

Nitric oxide (NO) and reactive oxygen species (ROS) have fundamentally important roles in the regulation of vascular tone and remodeling. Although arterial disease and endothelial dysfunction alter NO and ROS levels to impact vasodilation and vascular structure, direct measurements of these reactive species under in vivo conditions with flow alterations are unavailable. In this study, in vivo measurements of NO and H2O2 were made on mesenteric arteries to determine whether antioxidant therapies could restore normal NO production in spontaneously hypertensive rats (SHR). Flow was altered from approximately 50-200% of control in anesthetized Wistar-Kyoto rats (WKY) and SHR by selective placement of microvascular clamps on adjacent arteries while NO and H2O2 were directly measured with microelectrodes. Relative to WKY, SHR had significantly increased baseline NO and H2O2 concentrations (2,572 +/- 241 vs. 1,059 +/- 160 nM, P < 0.01; and 26 +/- 7 vs. 7 +/- 1 microM, P < 0.05, respectively). With flow elevation, H2O2 but not NO increased in SHR; NO but not H2O2 was elevated in WKY. Apocynin and polyethylene-glycolated catalase decreased baseline SHR NO and H2O2 to WKY levels and restored flow-mediated NO production. Suppression of NAD(P)H oxidase with gp91ds-tat decreased SHR H2O2 to WKY levels. Addition of topical H2O2 to increase peroxide to the basal concentration measured in SHR elevated WKY NO to levels observed in SHR. The results support the hypothesis that increased vascular peroxide in SHR is primarily derived from NAD(P)H oxidase and increases NO concentration to levels that cannot be further elevated with increased flow. Short-term and even acute administration of antioxidants are able to restore normal flow-mediated NO signaling in young SHR.     

High flaxseed (linseed) diet restores endothelial function in the mesenteric arterial bed of spontaneously hypertensive rats.

The effect of high flaxseed diet (HFD) on blood pressure (BP) and mesenteric arterial bed (MAB) reactivity was studied in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. HFD did not affect BP in either SHR (control, 157 +/- 3; HFD, 153 +/- 3 mmHg) or WKY (control, 114 +/- 2; HFD, 117 +/- 2 mmHg) rats. Increases in perfusion pressure of the endothelium-intact MAB to phenylephrine and norepinephrine were higher (p < 0.05) in SHR than in WKY rats and the HFD failed to alter these responses. Vasorelaxant responses to acetylcholine (ACh) and bradykinin (BK) were greater (p < 0.05) in SHR maintained on HFD compared to SHR on control diet. While HFD also enhanced ACh responses in WKY, the effect was less than in SHR. Responses to sodium nitroprusside (SNP), were similar in all groups. Since ACh and BK-induced responses of the MAB were augmented in SHR on HFD, with no changes in BP, it is suggested that HFD improves endothelial vasorelaxant function through a pressure-independent mechanism.     

Enhancement of vasorelaxation in hypertension following high-intensity exercise

Exercise can ameliorate vascular dysfunction in hypertension, but its underlying mechanism has not been explored thoroughly. We aimed to investigate whether the high-intensity exercise could enhance vasorelaxation mediated by insulin and insulin-like growth factor-1 (IGF-1) in hypertension. Sixteen-week-old spontaneously hypertensive rats were randomly divided into non-exercise sedentary (SHR) and high-intensity exercise (SHR+Ex) groups conducted by treadmill running at a speed of 30 m/ min until exhaustion. Age-matched Wistar-Kyoto rats (WKY) were used as the normotensive control group. Immediately after exercise, the agonist-induced vasorelaxation of aortas was evaluated in organ baths with or without endothelial denudation. Selective inhibitors were used to examine the roles of nitric oxide synthase (NOS) and phosphatidylinositol-3 kinase (PI3K) in the vasorelaxation. By adding superoxide dismutase (SOD), a superoxide scavenger, the role of superoxide production in the vasorelaxation was also clarified. We found that, the high-intensity exercise significantly (P < 0.05) induced higher vasorelaxant responses to insulin and IGF-1 in the SHR+Ex group than that in the SHR group; after endothelial denudation and pre-treatment of the PI3K inhibitor, NOS inhibitor, or SOD, vasorelaxant responses to insulin and IGF-1 became similar among three groups; the protein expression of insulin receptor, IGF-1 receptor, and endothelial NOS (eNOS) was significantly (P < 0.05) increased in the SHR+Ex group compared with the SHR group;] the relaxation to sodium nitroprusside, a NO donor, was not different among three groups. Our findings suggested that the high-intensity exercise ameliorated the insulin- and IGF-1-mediated vasorelaxation through the endothelium-dependent pathway, which was associated with the reduced level of superoxide production.     

Body fluids and plasma atrial peptide after its chronic infusion in hypertensive rats

To determine the role of body fluid volume in the chronic hypotensive effect of atrial natriuretic factor (ANF), spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats were infused with the peptide (Arg 101-Tyr 126) at a rate of 100 ng/h/rat for 5 days. Blood pressure (BP) was decreased from 176 +/- 4 to 133 +/- 3 mmHg in the SHR group 4 days after ANF infusion was initiated, whereas no changes were observed in ANF-infused WKY animals. Starting 5 days after the infusion began, body fluid measurements revealed no differences in plasma, blood and extracellular fluid volumes or in interstitial spaces. BP and plasma ANF concentrations were determined in another set of experiments before, during and after chronic ANF infusion. BP declined from 169 +/- 3 to 133 +/- 5 mmHg in SHR 5 days after the infusion commenced, but returned to basal values by day 10 or 11. Plasma ANF was significantly higher in SHR than in WKY rats throughout the observation period. However, there were no discernible changes in this parameter in ANF-infused SHR compared to non-infused SHR. A 3-fold rise in plasma ANF was noted in infused WKY rats at day 3 only. It is concluded that the chronic hypotensive effect of ANF in hypertensive animals is not related to changes in either body fluid volume or distribution. Moreover, the finding that chronic ANF infusion reduces BP in SHR without altering its plasma levels suggests a rapid ANF turnover.     

Elevated production of 20-HETE in the cerebral vasculature contributes to severity of ischemic stroke and oxidative stress in spontaneously hypertensive rats

Hypertension is a major risk factor for stroke, but the factors that contribute to the increased incidence and severity of ischemic stroke in hypertension remain to be determined. 20-hydroxyeicosatetraenoic acid (20-HETE) has been reported to be a potent constrictor of cerebral arteries, and inhibitors of 20-HETE formation reduce infarct size following cerebral ischemia. The present study examined whether elevated production of 20-HETE in the cerebral vasculature could contribute to the larger infarct size previously reported after transient middle cerebral artery occlusion (MCAO) in hypertensive strains of rat [spontaneously hypertensive rat (SHR) and spontaneously hypertensive stroke-prone rat (SHRSP)]. The synthesis of 20-HETE in the cerebral vasculature of SHRSP measured by liquid chromatography-tandem mass spectrometry was about twice that seen in Wistar-Kyoto (WKY) rats. This was associated with the elevated expression of cytochrome P-450 (CYP)4A protein and CYP4A1 and CYP4A8 mRNA. Infarct volume after transient MCAO was greater in SHRSP (36+/-4% of hemisphere volume) than in SHR (19+/-5%) or WKY rats (5+/-2%). This was associated with a significantly greater reduction in regional cerebral blood flow (rCBF) in SHR and SHRSP than in WKY rats during the ischemic period (78% vs. 62%). In WKY rats, rCBF returned to 75% of control following reperfusion. In contrast, SHR and SHRSP exhibited a large (166+/-18% of baseline) and sustained (1 h) postischemic hyperperfusion. Acute blockade of the synthesis of 20-HETE with N-hydroxy-N'-(4-butyl-2-methylphenyl)-formamidine (HET0016; 1 mg/kg) reduced infarct size by 59% in SHR and 87% in SHRSP. HET0016 had no effect on the fall in rCBF during MCAO but eliminated the hyperemic response. HET0016 also attenuated vascular O2*- formation and restored endothelium-dependent dilation in cerebral arteries of SHRSP. These results indicate the production of 20-HETE is elevated in the cerebral vasculature of SHRSP and contributes to oxidative stress, endothelial dysfunction, and the enhanced sensitivity to ischemic stroke in this hypertensive model.     

Effect of tetrahydrobiopterin and exercise training on endothelium-dependent vasorelaxation in SHR

We examined whether the improvement of impaired NO-dependent vasorelaxation by exercise training could be mediated through a BH₄-dependent mechanism. Male spontaneously hypertensive rats (SHR, n?=?20) and Wistar-Kyoto rats (WKY, n?=?20) were trained (Tr) for 9 weeks on a treadmill and compared to age-matched sedentary animals (Sed). Endothelium-dependent vasorelaxation (EDV) was assessed with acetylcholine by measuring isometric tension in rings of femoral artery precontracted with 10^?5?M phenylephrine. EDV was impaired in SHR-Sed as compared to WKY-Sed (p?=?0.02). Training alone improved EDV in both WKY (p?=?0.01) and SHR (p?=?0.0001). Moreover, EDV was not different in trained SHR than in trained WKY (p?=?0.934). Pretreatment of rings with L-NAME (50 μM) cancelled the difference in ACh-induced relaxation between all groups, suggesting that NO pathway is involved in these differences. The presence of 10^?5?M BH₄ in the organ bath significantly improved EDV for sedentary SHR (p?=?0.030) but not WKY group (p?=?0.815). Exercise training turned the beneficial effect of BH₄ on SHR to impairment of ACh-induced vasorelaxation in both SHR-Tr (p?=?0.01) and WKY-Tr groups (p?=?0.04). These results suggest that beneficial effect of exercise training on endothelial function is due partly to a BH₄-dependent mechanism in established hypertension.     

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.     

The Role of Preventing Nitric Oxide Deficiency in the Antihypertensive Effect of Adaptation to Hypoxia

Shortage of endothelial nitric oxide (NO) manifested as decreased daily urinary excretion of nitrate and nitrite as well as attenuated endothelium-dependent relaxation of conduit and resistance vessels progresses with age-related increase of blood pressure (BP) in stroke-prone spontaneously hypertensive rats (SHRSP). Simultaneous NO-dependent suppression of vascular contractions is, apparently, due to the inducible NO synthase activity in vascular smooth muscle specific for spontaneously hypertensive rat. The adaptation of rats to hypobaric hypoxia initiated at early hypertensive stage (at the age of 5–6 weeks) decelerates hypertension progress. The antihypertensive effect of the adaptation was accompanied by stimulation of endothelial NO synthesis and prevention of impaired NO-dependent response in isolated blood vessels. Nitric oxide stores were formed in the vascular wall of SHRSP and WKY rats at the same time. The obtained data indicate that the correction of endothelial NO deficiency plays a significant role in the antihypertensive effect of adaptation to hypoxia.     

Alpha-lactorphin lowers blood pressure measured by radiotelemetry in normotensive and spontaneously hypertensive rats

Cardiovascular effects of subcutaneous administration of synthetic alpha-lactorphin, a tetrapeptide (Tyr-Gly-Leu-Phe) originally derived from milk alpha-lactalbumin, were studied in conscious spontaneously hypertensive rats (SHR) and in normotensive Wistar Kyoto rats (WKY) with continuous radiotelemetric monitoring. Alpha-lactorphin dose-dependently lowered blood pressure (BP) without affecting heart rate in SHR and WKY. The lowest dose which reduced BP was 10 microg/kg, and the maximal reductions in systolic and diastolic BP (by 23+/-4 and 17+/-4 mm Hg, respectively) were observed at 100 microg/kg dose in SHR. No further reductions were obtained at a higher dose of 1 mg/kg. There were no significant differences in the BP responses to alpha-lactorphin between SHR and WKY. Naloxone (1 and 3 mg/kg s.c.), a specific opioid receptor antagonist, abolished the alpha-lactorphin-induced reduction in BP and reversed it into a pressor response, which provides evidence for an involvement of opioid receptors in the depressor action of the tetrapeptide.     

Erythropoietin increases cytosolic free calcium concentration and thrombin induced changes in cytosolic free calcium in platelets from spontaneously hypertensive rats

Using fura-2 cytosolic free calcium concentrations were measured in intact washed platelets from 9 spontaneously hypertensive rats (SHR) and from 9 age-matched normotensive Wistar-Kyoto rats (WKY). In resting platelets cytosolic free calcium concentration was significantly higher in SHR than in WKY (171.8 +/- 64.4 nM vs 93.1 +/- 59.0 nM, p less than 0.05). After preincubation with erythropoietin cytosolic free calcium concentration was significantly higher in SHR than in WKY (197.5 +/- 83.2 vs 93.0 +/- 60.1, p less than 0.01). Using platelets from SHR erythropoietin increased mean resting cytosolic free calcium concentration by 14.9% (p less than 0.05) and mean thrombin induced changes of cytosolic free calcium by 58.3% (p less than 0.01). In contrast, erythropoietin caused no significant increase in the resting calcium concentration or in thrombin induced changes of cytosolic free calcium in platelets from WKY. It is concluded that erythropoietin is involved in the pathogenesis of hypertension by elevating cytosolic free calcium concentration.     

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.     

Intestinal brush border calcium uptake in spontaneously hypertensive rats and their genetically matched WKY rats

The current studies were designed to characterize calcium transport by intestinal brush border membrane in the spontaneously hypertensive rat (SHR) and normotensive control, the Wistar-Kyoto (WKY) rat. The biochemical and functional purity of the intestinal brush border membranes in SHR and WKY rats was validated by marker enzymes and the ability to transiently transport D-glucose in the presence of Na+ gradient. Calcium transport into duodenal and jejunal vesicles represented a minor binding component and transmembrane movement as evident by initial rate studies, A23187 studies, and lanthanum displacement experiments. Initial rate and time course of calcium uptake was lower in SHR compared with WKY rats. Kinetic analysis of calcium uptake by the jejunum (total uptake minus binding component) showed a Vmax of 6.98 +/- 0.2 and 1.8 +/- 0.2 nmol/mg protein/7 sec in WKY rats and SHR, respectively (P less than 0.001), whereas Km values were 0.76 +/- 0.04 and 0.87 +/- 0.1 mM for WKY rats and SHR, respectively. Similar kinetic analysis of calcium uptake by the duodenal segments showed a Vmax of 10.3 +/- 0.8 and 2.8 +/- 0.2 nmol/mg protein/7 sec in WKY rats and SHR, respectively (P less than 0.01). Km values were 0.7 +/- 0.2 and 0.3 +/- 0.06 mM (P greater than 0.05). Vmax of calcium uptake in the 2-week-old rats (prehypertensive period) was 6.0 +/- 0.3 and 3.53 +/- 0.3 nmol/mg protein/7 sec in WKY rats and SHR, respectively (P less than 0.001), whereas Km values were 0.60 +/- 0.07 and 0.5 +/- 0.01 mM, respectively. These results suggest that calcium binding and uptake by duodenal and jejunal intestinal brush border membranes of SHR is significantly decreased compared with WKY rats. The decrease in transmembrane calcium uptake is secondary to decrease in Vmax and is present before the appearance of hypertension, implying a genetically determined defect in calcium uptake in intestinal brush border membranes of the SHR.