Voluntary running improves glucose tolerance and insulin resistance in female spontaneously hypertensive rats

We evaluated the effects of voluntary exercise training on glucose metabolism and measures of insulin sensitivity in female spontaneously hypertensive rats (SHR). Age-matched Wistar-Kyoto rats (WKY) were used as normotensive controls. Exercising SHR were housed in running wheels for 8 weeks (SHRx8) or 16 weeks (SHRx16). At 22 weeks of age, we measured systolic blood pressure, performed oral glucose tolerance tests, and determined hexokinase activity and glucose transporter (GLUT) 4 content in skeletal muscle to assess intracellular glucose metabolism. Blood pressure was lower in WKY (139 ± 12 mm Hg) than untrained SHR (216 ± 13 mm Hg). Exercise training caused a reduction in blood pressure (−18 mm Hg) for SHRx8. After a brief (5-h) fast, serum glucose was lower in SHR that exercised compared with sedentary SHR, whereas insulin concentrations were identical between all SHR and WKY. Corresponding free fatty acids (FFA) were twofold higher in SHR than in WKY. In response to glucose, SHR demonstrated higher glucose and FFA responses, with exercise decreasing the glucose values in a dose-dependent manner. Although the insulin response was comparable in all groups, the glucose-to-insulin ratio was higher in SHR, indicating a relative insulin resistance for both glucose disposal and suppression of free fatty acids. Hexokinase activity and GLUT4 content were elevated 1.4- and 2.8-fold, respectively, in plantaris muscle of SHRx16, suggesting an improvement in the capacity for glucose transport and phosphorylation with exercise. These results provide evidence that voluntary running in female SHR lowers blood pressure and selectively increases glucose uptake and insulin action, but not suppression of FFA.     

Decrease in endothelium dependent hypotension in spontaneously hypertensive rats

Endothelium-dependent and independent hypotension, vasodilation and relaxation were examined comparatively, in vivo and in vitro, in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY). In conscious and unrestrained animals, the dose-dependent hypotensive responses to both acetylcholine and adenosine triphosphate (ATP) were attenuated in SHR, compared to findings in the WKY, while sodium nitroprusside lowered mean arterial pressure (MAP), to a similar degree in SHR and WKY. Acetylcholine, ATP and nitroprusside increased the heart rate of SHR and WKY, in a dose-related manner. Mesenteric and femoral blood flow was altered by acetylcholine, ATP and nitroprusside, in a similar manner in the SHR and WKY anesthetized with urethane. However, an ATP-induced reduction in renal blood flow was greater in the SHR than in the WKY. Acetylcholine and nitroprusside led to a concentration-dependent relaxation in the isolated mesenteric artery, to a similar extent in both strains of rats. The relaxation response to acetylcholine was nearly abolished by mechanical removal of the endothelium, but the nitroprusside-induced relaxation was not altered by this denudation. ATP did not influence contraction of the mesentric artery but did produce endothelium-dependent relaxation of aorta, in a dose-dependent manner. All these events suggest that suppression of the endothelium dependent relaxation of resistant arterioles relates to the maintenance of hypertension, in the SHR.     

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.     

Attenuation of hypertension development by aminoguanidine in spontaneously hypertensive rats: role of methylglyoxal

BACKGROUND: Methylglyoxal (MG), a metabolite of glucose, and MG-induced advanced glycation endproducts (AGEs) are causatively associated with vascular complications of diabetes mellitus. We have previously reported elevated levels of MG and MG-induced AGEs in spontaneously hypertensive rats (SHR). The purpose of this study was to investigate the causative role of MG and MG-induced AGEs in the pathogenesis of hypertension in SHR. METHODS: Young SHR were treated with an AGE inhibitor, aminoguanidine, for 9 weeks. HPLC was used to determine plasma and aortic MG and reduced glutathione levels. The MG-induced AGEs, N epsilon-carboxyethyl-lysine (CEL) and argpyramidine, in the aorta were determined by immunohistochemistry. Vascular relaxation of small mesenteric arteries was measured using myograph. RESULTS: Chronic treatment with aminoguanidine attenuated age-dependent blood pressure (BP) increase in SHR. Plasma and aortic MG levels, and aortic levels of MG-induced AGEs, were significantly reduced after aminoguanidine treatment, which were comparable to those from age-matched Wistar Kyoto rats. Free radical level was significantly lowered, whereas reduced glutathione level was significantly increased by aminoguanidine treatment in the aortic tissues from SHR. Moreover, aminoguanidine therapy prevented the morphologic damage of vascular tissues in SHR and restored the endothelium-dependent relaxation to acetylcholine. Chronic aminoguanidine treatment also increased aortic endothelial nitric oxide synthase expression and reduced inducible nitric oxide synthase expression. CONCLUSIONS: The MG and MG-induced AGEs contribute to the pathogenesis of hypertension by altering the redox balance, causing vascular eutrophic inward remodeling, and inducing endothelial dysfunction in SHR.     

Antihypertensive and vasodilator actions of antioxidants in spontaneously hypertensive rats

This study was designed to determine whether the antioxidants ascorbic acid, aminotriazole, and glutathione acutely reduce blood pressure (BP) by endothelium-independent or -dependent vasorelaxation in spontaneously hypertensive rats. Blood pressure of male Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) was measured before and 4 h after administration of antioxidants. Thoracic aortic rings with and without endothelium were suspended in organ chambers for isometric tension recordings. Each of the antioxidants, administered in vivo, significantly decreased blood pressure in SHR but had no significant effect on BP in WKY rats. The endothelium-dependent impaired relaxation of SHR aortic rings to acetylcholine (ACh) was improved by prior in vivo administration of each antioxidant. ACh-induced relaxations of aortic rings from WKY was not affected by prior antioxidant treatment. Addition of each antioxidant directly to the organ chamber containing SHR or WKY aortas produced dose- and endothelium-dependent relaxations. Moreover, antioxidant pretreatment of SHR aortic rings significantly potentiated ACh-induced relaxations in these aortas, suggesting that this effect was endothelium dependent. Relaxations induced by the antioxidants alone or by ACh in the presence of antioxidants were inhibited by addition of either xanthine plus xanthine oxidase or nitro-l-arginine. These findings suggest that either excess production of oxidants or a deficiency of antioxidant systems may contribute to the high blood pressure and the endothelium-dependent impairment of vascular relaxation in SHR.     

Insulin Mediated Hemodynamic Responses in Spontaneous Hypertensive Rats (SHRs): Effect of Chromosome 4 Gene Transfer

The spontaneous hypertensive rat (SHR) is a widely studied model of essential hypertension and has been reported to exhibit alterations in carbohydrate and lipid metabolism. Genetic linkage studies implicated that SHR carries deletion variant of Cd36 gene of chromosome 4, the gene that encodes fatty acid transporter. Thus it could be possible that primary genetic defect in SHR is compromised tissue utilization of fatty acid that would form the basis for the pathogenesis of hyperinsulinemia, insulin resistance and insulin‐mediated responses. We measured both the hemodynamic and metabolic responses to insulin in SHR in comparison with the chromosome congenic spontaneous hypertensive rats (cSHRs) (rats in which piece of chromosome 4 containing wild type Cd36 was integrated into the SHR genome). A bolus infusion of insulin increased iliac conductance and decreased blood pressure in Wistar Kyoto (WKY) rats. However, in SHR insulin did not reduce blood pressure as in WKY but after about 15 min it significantly enhanced blood pressure and reduced iliac conductance. Whereas in cSHR insulin did not reduce blood pressure as in WKY rats. However, pressor responses to insulin were eliminated by chromosome 4 gene transfer. Glucose clearance was significantly slower in both SHR and cSHR. Glucose tolerance test revealed that SHR are hyperinsulinemic and insulin resistant. These findings indicate that transfer of segment of chromosome 4 from Brown Norway rats onto spontaneous hypertensive background eliminates hyperinsulinemia and pressor effects of insulin.     

Insulin mediated hemodynamic responses in spontaneous hypertensive rats (SHRs): effect of chromosome 4 gene transfer

The spontaneous hypertensive rat (SHR) is a widely studied model of essential hypertension and has been reported to exhibit alterations in carbohydrate and lipid metabolism. Genetic linkage studies implicated that SHR carries deletion variant of Cd36 gene of chromosome 4, the gene that encodes fatty acid transporter. Thus it could be possible that primary genetic defect in SHR is compromised tissue utilization of fatty acid that would form the basis for the pathogenesis of hyperinsulinemia, insulin resistance and insulin-mediated responses. We measured both the hemodynamic and metabolic responses to insulin in SHR in comparison with the chromosome congenic spontaneous hypertensive rats (cSHRs) (rats in which piece of chromosome 4 containing wild type Cd36 was integrated into the SHR genome). A bolus infusion of insulin increased iliac conductance and decreased blood pressure in Wistar Kyoto (WKY) rats. However, in SHR insulin did not reduce blood pressure as in WKY but after about 15 min it significantly enhanced blood pressure and reduced iliac conductance. Whereas in cSHR insulin did not reduce blood pressure as in WKY rats. However, pressor responses to insulin were eliminated by chromosome 4 gene transfer. Glucose clearance was significantly slower in both SHR and cSHR. Glucose tolerance test revealed that SHR are hyperinsulinemic and insulin resistant. These findings indicate that transfer of segment of chromosome 4 from Brown Norway rats onto spontaneous hypertensive background eliminates hyperinsulinemia and pressor effects of insulin.     

Functional and morphological pattern of vascular responses in two models of experimental hypertension

OBJECTIVES:

To determine the reactivity and accompanying structural changes in thoracic aorta and carotid artery from nitric oxide (NO)-deficient hypertensive and spontaneously hypertensive rats (SHR).

ANIMALS AND METHODS:

For the functional study, isolated rat arterial rings were precontracted with a submaximal concentration of phenylephrine (1 μM) and relaxant responses to cumulative concentrations of acetylcholine were obtained. For the morphological study, arteries were processed by a standard method for electron microscopy. The geometry of the arteries – the inner diameter and the wall thickness (tunica intima plus tunica media) – was evaluated by light microscopy.

RESULTS:

Increased systolic blood pressure was accompanied by increased heart weight to body weight ratio in both NO-deficient and SHR compared with normotensive controls, indicating cardiac hypertrophy. Morphometry of the thoracic aorta and carotid artery in both models of hypertension showed increased wall thickness, cross-sectional area and wall to diameter ratio. The inner diameter increased in aorta but not in carotid artery. In isolated arteries from normotensive rats, the addition of acetylcholine to precontracted vessels resulted in dose-dependent relaxation. The relaxing effect was more prominent in thoracic aorta than in carotid artery. Endothelium-dependent relaxation of arteries from NO-deficient hypertensive rats was markedly reduced. On the other hand, in aorta and carotid artery from SHR, the endothelium-dependent relaxation in response to acetylcholine was not significantly attenuated. The relaxation of arteries from SHRs, as well as the residual relaxation of arteries from NO-deficient hypertensive rats, was abolished by addition of N^G-nitro-l-arginine methyl ester, an inhibitor of NO synthase, to the incubation medium.

CONCLUSIONS:

These results suggest that increased systolic blood pressure and accompanying structural changes are not primarily responsible for impairment of endothelium-dependent relaxation in experimental hypertension.     

Aged spontaneously hypertensive rats exhibit a selective loss of EDHF-mediated relaxation in the renal artery

Endothelium-dependent relaxation is frequently attenuated in hypertension. We hypothesized that the contribution of the endothelium-derived hyperpolarizing factor (EDHF) to the acetylcholine (ACh)-induced, endothelium-dependent relaxation is attenuated with aging in the renal artery of spontaneously hypertensive rats (SHR) compared with age-matched Wistar-Kyoto (WKY) rats. ACh-induced, NO-mediated relaxation was identical in young (8-week-old) WKY and SHR, whereas EDHF-mediated relaxations (assessed in the presence of Nomega-nitro-l-arginine and diclofenac) were much more pronounced in SHR than WKY. KCl-induced relaxations were more pronounced in vessels from young WKY rats than from young SHR. The cytochrome P450 inhibitor sulfaphenazole significantly inhibited EDHF-mediated relaxation in vessels from young SHR but not WKY. Vessels from old (22 months) SHR exhibited a slightly reduced NO-mediated relaxation but a complete loss of EDHF-mediated responses. In contrast, aging did not affect EDHF-mediated responses in WKY. Moreover, ACh-induced hyperpolarization and resting membrane potential were decreased in old SHR but not in WKY. KCl-induced relaxation increased with age in WKY, whereas no response to KCl was recorded in arteries from aged SHR. In vessels from old WKY but not old SHR, mRNA expression of the Na-K-ATPase subunit alpha2 was increased by 2-fold compared with young animals. These data indicate that the increase in EDHF responses in renal arteries from aged WKY can be attributed to the release of K+ ions from the endothelium, whereas increased EDHF responses in renal arteries from young SHR can be attributed to a sulfaphenazole-sensitive cytochrome P450-dependent EDHF.     

Resveratrol lowers blood pressure in spontaneously hypertensive rats via calcium-dependent endothelial NO production

Objective: Resveratrol, a polyphenol of natural compounds, has beneficial cardiovascular effects, many of which are mediated by nitric oxide (NO). Resveratrol increases intracellular calcium and activates AMP-activated protein kinase (AMPK), all of which could increase NO production. We hypothesized that resveratrol via a calcium-dependent NO production lowers blood pressure (BP) in spontaneously hypertensive rats (SHR). Methods: Acetylcholine (Ach)-induced endothelium-dependent relaxations in rat aortas were examined by organ chamber. Blood pressures were determined by radiotelemetry methods. Results: Incubation of isolated aortas from SHR with resveratrol dramatically improved vasorelaxation induced by Ach. Preincubation of aortas with endothelial NO synthase (eNOS) inhibitor or calcium chelant blunted the effects of resveratrol on Ach-induced relaxation, as wells as NO production and eNOS phosphorylation. In animal studies, administration of resveratrol significantly lowered systemic BP in SHR. Conclusion: Resveratrol increases endothelial NO production to improve endothelial dysfunction and lowers BP in hypertensive rats, which depends on calcium-eNOS activation.     

DAILY EXERCISE ATTENUATES THE DEVELOPMENT OF ARTERIAL BLOOD PRESSURE RELATED CARDIOVASCULAR RISK FACTORS IN HYPERTENSIVE RATS

This study was designed to test the hypothesis that daily spontaneous running (DSR) attenuates the development of blood pressure-related cardiovascular disease risk factors (BP-related CVD risk factors) in spontaneously hypertensive rats (SHR). After 8 weeks of DSR or sedentary control, rats were chronically instrumented with arterial catheters. Daily exercise attenuated the development of all measures of BP-related CVD risk factors. Specifically DSR attenuated the increase in systolic blood pressure (Δ-22 mmHg), systolic blood pressure variability (Δ-2.5 mmHg), and systolic blood pressure load (Δ-27%). Similarly, DSR attenuated the increase in diastolic blood pressure (Δ-15 mmHg), diastolic blood pressure variability (Δ-1.19 mmHg), and diastolic blood pressure load (Δ-17%). Finally, DSR attenuated the development of tachycardia (Δ-63 bpm). These data demonstrate that daily exercise attenuates the development of hypertension and tachycardia in animals predisposed to hypertension.     

Antihypertensive effects of fasidotril, a dual inhibitor of neprilysin and angiotensin-converting enzyme, in rats and humans

The aim of this study was to assess the antihypertensive activity of fasidotril, a dual inhibitor of neprilysin (NEP) and angiotensin I-converting enzyme (ACE), in various models of hypertension in rats (spontaneously hypertensive rats [SHR]; renovascular Goldblatt 2-kidney, 1-clip rats; and deoxycorticosterone acetate [DOCA]-salt hypertensive rats) and in patients with mild-to-moderate essential hypertension. Fasidotril treatment (100 mg/kg PO twice daily for 3 weeks) resulted in a progressive and sustained decrease in systolic blood pressure (-20 to -30 mm Hg) in SHR and Goldblatt rats compared with vehicle-treated rats and prevented the progressive rise in blood pressure in DOCA-salt hypertensive rats. After a 4-week placebo run-in period, 57 patients with essential hypertension were included in a randomized double-blind, placebo-controlled, parallel-group study and received orally either fasidotril (100 mg twice daily) or placebo for 6 weeks. Blood pressure was measured during the 6 hours after the first intake and then at trough (12 hours after the last intake) on days 7, 28, and 42. The first dose of fasidotril had no significant effect on blood pressure. After 42 days, compared with placebo, fasidotril lowered supine systolic and diastolic blood pressures by 7.4/5.4 mm Hg and standing blood pressure by 7.6/6.8 mm Hg. Fasidotril, a dual NEP/ACE inhibitor, was an effective oral antihypertensive agent during chronic treatment in high-renin renovascular rats, normal-renin SHR, and low-renin DOCA-salt hypertensive rats and in patients with essential hypertension.     

Vascular and cardiac effects of grape powder in the spontaneously hypertensive rat

BackgroundWe previously reported that resveratrol, a polyphenol found in red grapes, attenuated changes in small artery geometry and stiffness, as well as cardiac hypertrophy and cardiac function in the spontaneously hypertensive rat (SHR). However, in addition to resveratrol, grapes contain a variety of bioactive polyphenols such as catechins, anthocyanins, and flavonoids. Therefore, we investigated the effects of grape consumption in SHR.MethodsWistar-Kyoto (WKY) rats and SHR were treated with freeze-dried grape powder for 10 weeks. Dilatory, geometry, and stiffness properties of mesenteric small arteries were assessed by pressurized myography. Left ventricular mass index and cardiac function were assessed by two-dimensional guided M-mode and pulse-wave Doppler echocardiography.ResultsElevated blood pressure in SHR was associated with remodeling and impaired endothelium-dependent relaxation of small arteries. Augmented left ventricular mass index (reflecting hypertrophy) and diminished cardiac function were also evident in SHR. Although grape treatment failed to affect cardiac dysfunction, it elicited a significant reduction in blood pressure, improved arterial relaxation, increased vascular compliance, and attenuated cardiac hypertrophy.ConclusionsTreatment with whole grape powder conferred mild vascular and cardiac benefits in SHR. Therefore, dietary grape consumption may be a feasible and salutary adjunct to pharmacological treatment of human hypertension.American Journal of Hypertension 2012; doi:10.1038/ajh.2012.98.     

Dexamethasone suppression of cushingoid degenerative changes in obese spontaneously hypertensive rats (SHR)

Male and female, young (2 months old) and mature (10 months old), obese and nonobese, spontaneously hypertensive rats (SHR) were treated with dexamethasone, 5 micrograms/rat and 10 micrograms/rat, respectively, subcutaneously (SC) 2 times daily for 5 months. Steroid treatment stilled the voracious appetite of the obese SHR, and the massively obese, mature animals were reduced to almost normal size. The young, steroid-treated, obese SHR did not develop their genetically programmed corpulency. The untreated, young and mature, obese SHR ate voraciously, became massively obese, and developed their characteristic Cushing's disease-like spectrum of degenerative changes, eg, hypertension, hyperlipidemia, hyperglycemia, muscle wasting, kidney stones, thin skin, and accelerated aging. The blood pressure of the steroid-treated animals was lowered concomitant with reduced levels of circulating ACTH, beta endorphin, insulin, triglycerides, and cholesterol. Dexamethasone caused hyperlipidemia, hyperglycemia, and increased BUN levels in young obese and nonobese SHR only. The mature obese SHR had giant-sized thymus glands that were further enlarged with steroid treatment; dexamethasone was thymolytic in young, obese and nonobese SHR. Dexamethasone caused severe reduction of pituitary and adrenal gland size, simulating the condition of hypophysectomy. These findings demonstrate that dexamethasone suppression of the pituitary-adrenal axis palliates and prevents the spontaneous development of Cushingoid degenerative changes in these genetically obese and hypertensive rats.     

Effects of different levels of exercise volume on endothelium-dependent vasodilation: roles of nitric oxide synthase and heme oxygenase

The objective of this study was to examine the effects of moderate and high levels of exercise volume on endothelium-dependent vasodilation and associated changes in vascular endothelial/inducible nitric oxide synthase (eNOS and iNOS) and heme oxygenase (HO). Male Sprague-Dawley rats were assigned to sedentary control, acute (2 weeks), or chronic (6 weeks) treadmill running at moderate intensity (50% maximal aerobic velocity) with different durations of exercise episodes: 2 h/d (endurance training, moderate volume) and 3 h/d (intense training, high volume). Endothelium-dependent vascular function was examined in isolated thoracic aorta. Co-localization and contents of aortic eNOS/iNOS and HO-1/HO-2 were determined with immunofluorescence and Western blotting. Compared with sedentary controls, rats subjected to acute and chronic endurance training showed enhanced endothelium-dependent relaxation (p<0.01). Whereas acetylcholine-induced dilation was inhibited completely by NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) in sedentary controls, the dilation in the training groups was only partly blocked by L-NAME (inhibition was 98+/-3%, 79+/-6%, and 77+/-5% in sedentary control, acute, and chronic training groups, respectively, p<0.01). The remnant dilation in the training groups was further inhibited by HO inhibitor protoporphyrin IX zinc, with concomitant elevation in aortic eNOS as well as HO-1 and HO-2. In contrast to endurance exercise, high-volume intense training resulted in mild hypertension with significant impairment in endothelium-dependent vasodilation and profuse increases in aortic iNOS and eNOS (p<0.01). In conclusion, endothelium-dependent vasodilation is improved by endurance exercise but impaired by chronic intense training. Elevations of vascular eNOS and HO-1/HO-2 may contribute to enhanced vasodilation, which can be offset by intense training and elevation in vascular iNOS.     

Daily exercise attenuates the development of arterial blood pressure related cardiovascular risk factors in hypertensive rats

This study was designed to test the hypothesis that daily spontaneous running (DSR) attenuates the development of blood pressure-related cardiovascular disease risk factors (BP-related CVD risk factors) in spontaneously hypertensive rats (SHR). After 8 weeks of DSR or sedentary control, rats were chronically instrumented with arterial catheters. Daily exercise attenuated the development of all measures of BP-related CVD risk factors. Specifically DSR attenuated the increase in systolic blood pressure (delta--22 mmHg), systolic blood pressure variability (delta--2.5 mmHg), and systolic blood pressure load (delta--27%). Similarly, DSR attenuated the increase in diastolic blood pressure (delta--15 mmHg), diastolic blood pressure variability (delta--1.19 mmHg), and diastolic blood pressure load (delta--17%). Finally, DSR attenuated the development of tachycardia (delta--63 bpm). These data demonstrate that daily exercise attenuates the development of hypertension and tachycardia in animals predisposed to hypertension.     

What should the clinician tell patients with mild hypertension about physical activity?

Recent guidelines recommend lifestyle measures, with physical activity as an integral component, for all patients with hypertension or prehypertension to lower blood pressure and control other risk factors. This review discusses both acute and long-term effects of dynamic aerobic endurance exercise and resistance exercise as nonpharmacologic tools to reduce blood pressure, respectively. The optimal exercise characteristics to lower blood pressure need to be more precisely defined, especially with regard to resistance exercise; so far, these effects have been shown to be immediate and elicited by low-intensity short-duration exercise. Based on the current evidence, hypertensive patients should be recommended to exercise on most, preferably all, days of the week, with moderate intensity (40% to 60% of VO₂ reserve) for at least 30 minutes of continuous or accumulated physical activity per day, consisting primarily of endurance training but supplemented by resistance training.     

罗格列酮改善高血压大鼠血管对胰岛素的反应性

目的研究罗格列酮（RSG）对自发性高血压大鼠（SHR）的高血压状态、血糖和胰岛素水平的影响及其离体血管对胰岛素的反应性。方法将实验动物分为3组：正常大鼠（WKY）对照组（幼年16只,成年15只）、未治疗的SHR组（幼年9只,成年9只）、RSG治疗的SHR组〔幼年6只,成年6只,3mg/（kg.d）,口服,治疗2周〕。2周后,测量未治疗组和治疗组成年SHR的收缩压、血糖和胰岛素水平;分离胸主动脉,采用离体血管灌流方法,对比观察不同处理组离体主动脉对胰岛素的舒血管反应。结果在成年SHR中,未治疗组和治疗组收缩压、血糖和胰岛素水平均无显著差异〔（187±4）vs（181±5）mmHg,P〉0.05;（6.2±0.2）vs（5.3±0.3）mmol/L,P〉0.05;（23.8±3.7）vs（20.4±0.8）mU/L,P〉0.05〕。治疗组对胰岛素的舒血管反应与未治疗组无显著差异〔最大收缩率：（72±8）%vs（73±4）%,P〉0.05〕;在幼年SHR中,未治疗组和治疗组血糖和胰岛素水平亦无显著差异,但治疗组对胰岛素的舒血管反应较未治疗组显著增加〔（40±6）%vs（61±5）%,P〈0.01〕。结论短期RSG治疗可改善幼年SHR血管对胰岛素的反应性。     

Characterization of endothelium-dependent vasodilation and vasoconstriction in coronary arteries from spontaneously hypertensive rats

Coronary artery disease often occurs in patients with hypertension. The present study was designed to evaluate coronary vascular function in isolated coronary arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats and to determine the effect of antihypertensive treatment on coronary vascular responsiveness. Male SHR and WKY rats (12 to 14 weeks old) were divided into control and hydralazine-treated (120 mg/L drinking water for 10 days) groups. After 10 days, arterial pressure and heart rate were recorded while rats were conscious and unrestrained. Left ventricular coronary arteries (200 to 300 μm diameter) were isolated and intraluminal diameter was continuously recorded while vessels were maintained at a constant intraluminal pressure of 40 mm Hg. Relaxation of coronary arteries to both acetylcholine and nitroprusside was slightly, but significantly, enhanced in vessels from SHR compared to WKY rats. The enhanced relaxation was a specific effect, since isoproterenol induced similar relaxation in coronary arteries from SHR and WKY rats. Contraction to phenylephrine, but not endothelin-1, was augmented in coronary arteries from SHR compared to WKY rats. Treatment with hydralazine significantly lowered arterial pressure in SHR and WKY rats, but did not alter the enhanced contraction to phenylephrine or the enhanced relaxation to acetylcholine and nitroprusside in coronary arteries from SHR. These results indicate that coronary arteries of 12 to 14 week-old SHR do not have impaired endothelium-dependent relaxation, but do exhibit enhanced α-adrenoreceptor-mediated contraction that is not reduced by lowering arterial pressure.     

The pancreatic islets in spontaneously hypertensive rats: islet blood flow and insulin production

The aim of the study was to investigate if hypertension affects pancreatic islet blood flow and endocrine function. For this purpose, spontaneously hypertensive rats (SHR) were compared with normotensive control Wistar-Kyoto rats (WKY). Both islet size and islet cell replication in 4-month-old SHR was increased compared with WKY. The (pro)insulin biosynthesis was reduced in islets isolated from SHR, whereas the insulin content was unchanged. A hyperinsulinemic response to glucose in vivo was observed in 4- and 12-month-old SHR. Pancreatic blood flow, measured using a microsphere technique, was lower in SHR than in WKY in rats aged 5 weeks, 4 months or 1 year. Islet blood flow was lower in 4-month-old and 1-year-old SHR. In 4-month-old animals, islet blood flow was unaffected by administration of enalaprilate and prazosin in both strains, but was markedly decreased by the administration of N(G)-methyl-L-arginine. It was concluded that the islets of SHR have a decreased insulin production in vitro and a decreased islet blood perfusion. The reasons for this are likely to be multifactorial. Because SHR maintained an essentially normal glucose tolerance, an adaptation of the beta-cells to the metabolic and hemodynamic changes imposed by hypertension occurred.