2-Methoxyestradiol mediates the protective effects of estradiol in monocrotaline-induced pulmonary hypertension

When exposed to chronic hypoxia or toxin monocrotaline (MCT), female animals develop less severe pulmonary arterial hypertension (PH) compared to males; ovariectomy (OVX) exacerbates PH, and OVX animals treated with estradiol (E2) develop less severe disease. There is a line of evidence suggesting that cardiovascular protective effects of E2 are mediated by its major metabolite, 2-methoxyestradiol (2ME). Recently, we have shown that 2ME attenuates the development and retards the progression of MCT-induced pulmonary hypertension in male rats. We hypothesized that the protective effects of E2 in experimental PH are mediated by 2ME. Subsets of intact and OVX female rats were injected saline (Cont and OXV groups) or MCT (60 mg/kg; MCT and OVX-MCT groups) and some of OVX-MCT animals were treated with 2ME (10 microg/kg/h via osmotic minipumps; OVX-MCT+2ME). After 28 days, MCT caused PH, i.e., increased right ventricular peak systolic pressure (RVPSP) and right ventricle/left ventricle+septum (RV/LV+S) ratio, induced inflammatory response in the lungs and caused media hypertrophy (media thickness and % media index) and adventitia widening of small size pulmonary arteries. Ovariectomy exacerbated the disease, i.e., further increased RVPSP, and RV/LV+S ratio, and augmented vascular remodeling and inflammatory response. In diseased OVX rats, treatment with 2ME prevented the worsening of PH and attenuated the inflammatory response and vascular remodeling. No mortality was recorded in the OVX-MCT+2ME group vs. 10% and 36% mortality in the MCT and OVX-MCT group, respectively. This study suggests that 2-methoxyestradiol (a major non-estrogenic metabolite of E2) may mediate the protective effects of estradiol in MCT-induced PH, and warrants further evaluation of 2ME for treatment of PH.     

2-Methoxyestradiol and 2-ethoxyestradiol retard the progression of renal disease in aged, obese, diabetic ZSF1 rats

The metabolic syndrome is a main cause for cardiovascular disease and for the accelerating epidemic of chronic renal failure. Previous studies show that 2-hydroxyestradiol (2-HE), an estradiol metabolite with little estrogenic activity, decreases obesity and arterial blood pressure and attenuates the development of renal disease in young, obese, diabetic ZSF1 rats. In humans, however, diabetic renal disease is more frequent and severe in older patients. In vivo, 2-HE is readily converted to 2-methoxyestradiol (2-ME), an estradiol metabolite with no estrogenic activity. Accordingly, one purpose of this study was to determine whether 2-ME would provide benefit in aged rats with a very severe form of diabetic renal disease. Another objective was to determine whether synthetic analogs of estradiol metabolites might be beneficial in diabetic renal disease. To achieve these objectives we examined the effects of 2-ME and its analog 2-ethoxyestradiol (2-EE) in aged (35-week-old), obese ZSF1 rats. Animals were treated for 9 weeks with vehicle (PEG-400, 0.5 microL per hour), 2-ME or 2-EE (18 microg/kg per hour). Metabolic and renal function were measured at weeks 0, 3, 6, and 9, and renal hemodynamics and excretory function were assessed at week 9. Aged ZSF1 rats had elevated levels of glycosylated hemoglobin; increased renal cortical expression of proliferating cell nuclear antigen (PCNA), nuclear factor kappa B (NF-kappaB), and vascular endothelial growth factor (VEGF); glycosuria, hypertension; and proteinuria. 2-ME and 2-EE did not affect obesity or hypertension and had variable effects on glucose homeostasis, yet they attenuated proteinuria; increased renal blood flow and glomerular filtration; and reduced renal cortical expression of PCNA, NFkappaB, and VEGF. We conclude that 2ME and 2EE are strikingly renoprotective even in aged animals with severe diabetic renal disease. The present study warrants further investigation of 2-ME and analogs of estradiol metabolites for treatment of kidney disease associated with the metabolic syndrome.     

Estrogens and development of pulmonary hypertension: interaction of estradiol metabolism and pulmonary vascular disease

Severe pulmonary arterial hypertension (PAH) is characterized by clustered proliferation of endothelial cells (ECs) in the lumina of small size pulmonary arteries resulting in concentric obliteration of the lumina and formation of complex vascular structures known as plexiform lesions. This debilitating disease occurs more frequently in women, yet both animal studies in classical models of PAH and limited clinical data suggest protective effects of estrogens: the estrogen paradox in pulmonary hypertension. Little is known about the role of estrogens in PAH, but one line of evidence strongly suggests that the vascular protective effects of 17β-estradiol (estradiol; E2) are mediated largely by its downstream metabolites. Estradiol is metabolized to 2-hydroxyestradiol (2HE) by CYP1A1/CYP1B1, and 2HE is converted to 2-methoxyestradiol (2ME) by catechol-O-methyl transferase. 2ME is extensively metabolized to 2-methoxyestrone, a metabolite that lacks biologic activity, but which may be converted back to 2ME. 2ME has no estrogenic activity, and its effects are mediated by estrogen receptors–independent mechanism(s). Notably, in systemic and pulmonary vascular ECs, smooth muscle cells, and fibroblasts, 2ME exerts stronger antimitotic effects than E2 itself. E2 and 2ME, despite having similar effects on other cardiovascular cells, have opposing effects on ECs; that is, in ECs, E2 is promitogenic, proangiogenic, and antiapoptotic, whereas 2ME is antimitogenic, antiangiogenic, and proapoptotic. This may have significant ramifications in severe PAH that involves uncontrolled proliferation of monoclonal apoptosis-resistant ECs. Based on its cellular effects, 2ME should be expected to attenuate the progression of disease and provide protection in severe PAH. In contrast, E2, due to its mitogenic, angiogenic, and antiapoptotic effects (otherwise desirable in normal quiescent ECs), may even adversely affect endothelial remodeling in PAH, and this may be even more significant if the E2's effects on injured endothelium are not opposed by 2ME (eg, in the event of reduced E2 conversion to 2ME due to hypoxia, inflammation, drugs, environmental factors, or genetic polymorphism of metabolizing enzymes). This review focuses on the effects of estrogens and their metabolites on pulmonary vascular pathobiology and the development of experimental PAH and offers potential explanation for the estrogen paradox in PAH. Furthermore, we propose that unbalanced estradiol metabolism may lead to the development of PAH. Recent animal data and studies in patients with PAH support this concept.     

Estradiol metabolites attenuate monocrotaline-induced pulmonary hypertension in rats

Pulmonary arterial hypertension (PH) is a deadly disease characterized by pulmonary arterial vasoconstriction and hypertension, pulmonary vasculature remodeling, and right ventricular hypertrophy. Our previous in vivo studies, performed in several models of cardiac, vascular, and/or renal injury, suggest that the metabolites of 17beta-estradiol may inhibit vascular and cardiac remodeling. The goal of this study was to determine whether 2-methoxyestradiol (2ME), major non-estrogenic estradiol metabolite, prevents the development and/or retards the progression of monocrotaline (MCT)-induced PH. First, a total of 27 male Sprague Dawley rats were injected with distillated water (Cont, n=6) or monocrotaline (MCT; 60 mg/kg, i.p.; n=21). Subsets of MCT animals (n=7 per group) received 2ME or its metabolic precursor 2-hydroxyestradiol (2HE; 10 microg/kg/h via osmotic minipumps) for 21 days. Next, an additional set (n=24) of control and MCT rats was monitored for 28 days, before right ventricular peak systolic pressure (RVPSP) was measured. Some pulmonary hypertensive animals (n=8) were treated with 2ME (10 microg/kg/h) beginning from day 14 after MCT administration. MCT caused pulmonary hypertension (ie, increased right ventricle/left ventricle+septum [RV/LV+S] ratio and wall thickness of small-sized pulmonary arteries, and elevated RVPSP) and produced high and late (days 22 to 27) mortality. Pulmonary hypertension was associated with strong proliferative response (PCNA staining) and marked inflammation (ED1+cells) in lungs. Both metabolites significantly attenuated the RV/LV+S ratio and pulmonary arteries media hypertrophy and reduced proliferative and inflammatory responses in the lungs. Furthermore, in diseased animals, 2ME (given from day 14 to 28) significantly decreased RVPSP, RV/LV+S ratio and wall thickness, and reduced mortality by 80% (mortality rate: 62.5% vs. 12.5%, MCT vs. MCT+2ME day 14 to 28). This study provides the first evidence that 2ME, a major non-estrogenic, non-carcinogenic metabolite of estradiol, prevents the development and retards the progression of monocrotaline-induced pulmonary hypertension. Further evaluation of 2ME for management of pulmonary arterial hypertension is warranted.     

Predisposition of spontaneously hypertensive rats to develop renal injury during nitric oxide synthase inhibition

Chronic nitric oxide (NO) synthase (NOS) inhibition results in renal injury. Hypertension is an important risk factor for renal injury. We studied the influence of preexistent hypertension on the sensitivity for renal injury induced by chronic NOS inhibition in rats. Spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats were treated with 3, 10, 30 and 100 mg/l Nomega-nitro-L-arginine (L-NNA) until death. Systolic blood pressure and proteinuria were measured regularly and compared with time-control measurements in untreated SHR and WKY. In WKY, 3 and 10 mg/l L-NNA did not affect systolic blood pressure, while 30 and 100 mg/l L-NNA resulted in an increase in systolic blood pressure after 12 and 4 weeks, respectively. In contrast in SHR, every dose of L-NNA resulted in an increase in systolic blood pressure after 2 weeks. In WKY, 3 and 10 mg/l L-NNA did not affect proteinuria or survival, while 30 and 100 mg/l L-NNA resulted in an increase in proteinuria after 30 and 9 weeks, and a median survival of 36 and 12 weeks, respectively. In SHR, 3, 10, 30 and 100 mg/l L-NNA resulted in an increase in proteinuria after 30, 12, 3 and 3 weeks, and a median survival of 41, 20, 5 and 3 weeks, respectively. Thus, at every dose of the inhibitor, chronic NOS inhibition resulted in far earlier increases in systolic blood pressure and proteinuria and a marked increase in mortality in SHR as compared to WKY. Indeed, a very low dosage of L-NNA that caused no harm in WKY was followed by marked increases in proteinuria and blood pressure and decreased survival in SHR. Hypertension strongly increases the vulnerability to cardiovascular risk factors that compromise the NO-system.     

复合离子盐对高血压大鼠肾脏皮质磷酸化ERK1/2表达的影响

目的：观察复合离子盐对自发性高血压大鼠（SHR）肾脏皮质磷酸化ERK1／2（p-ERK1／2）表达的影响．探讨复合离子盐对SHR肾脏保护作用的可能机制。方法：38只8周龄雄性SHR随机分为4组，8％食盐摄入组（US组）；1％复合离子盐摄入组（CIS组）；1％复合离子盐＋2．25％L-精氨酸摄入组（CIS＋L-Arg组）；1％食盐摄入组（NS组）．持续干预12周。干预期间定期观察大鼠体质量、血压、尿量的变化；干预结束后处死动物。进行肾脏组织HE及天狼猩红染色，观察病理变化并计算胶原容积分数；并通过western-blot法分析SHR肾脏皮质磷酸化ERK1／2蛋白表达的情况。结果：12周干预结束后，CIS组与CIS＋L-Arg组血压升高趋势明显低于NS组（P〈0．01）。与NS组相比，CIS组与CIS＋L-Arg组SHR肾小球及肾小管周胶原沉积量少，肾脏损害较轻，HS组SHR肾小球及肾小管周胶原沉积明显增多，肾脏损害较重，同时P-ERK1／2的表达在HS组明显增加，而p-ERK1的表达在CIS组与CIS＋L-Arg组明显降低（P〈0．05）。结论：复合离子盐与复合离子盐＋L-Arg的摄入可能通过影响p-ERK1／2的表达减轻SHR肾脏功能结构的损害。     

2-methoxyestradiol attenuates bleomycin-induced pulmonary hypertension and fibrosis in estrogen-deficient rats

Pulmonary hypertension (PH) is a common and life-threatening complication of pulmonary fibrosis. Estradiol (E2) is protective in experimental PH, and its non-estrogenic metabolite 2-methoxyestradiol (2ME) prevents the development and retards the progression of monocrotaline-induced PH in male and female rats. However, the effects of E2 and 2ME on pulmonary fibrosis and associated PH have not been examined. Therefore, we compared the growth inhibitory effects of E2 and 2ME in human lung fibroblasts (hLFs) and pulmonary vascular smooth muscle cells (hPASMCs), and we investigated the effects of estrogen deficiency and 2ME on bleomycin-induced pulmonary fibrosis and PH. Intact and ovariectomized (OVX) female Sprague–Dawley rats were administered intratracheally either saline or bleomycin (15 IU/kg), and a subset of OVX bleomycin-treated rats received 2ME (10 μg/kg/h) for 21 days. Estradiol had only limited inhibitory effects on growth in hPASMCs and no effect in hLFs, whereas 2ME exhibited strong and concentration-dependent (1–10 μM) antimitogenic effects in both cell types. Bleomycin caused lung injury/PH (significantly increased lung and right ventricle (RV) weights, RV peak systolic pressure (RVPSP), and RV/left ventricle + septum ratio (RV/LV + S); caused medial hypertrophy and adventitial widening of pulmonary arteries; induced marked focal/diffuse fibrosis with diffuse infiltration of inflammatory (ED1+) cells; and resulted in 30% mortality). OVX exacerbated the disease and increased mortality (to 75%); whereas 2ME tended to reduce mortality (55.5%) and in surviving animals reduced RVPSP and RV/LV + S ratio, and attenuated vascular remodeling, pulmonary inflammation and fibrosis. This study suggests that 2ME may have protective effects in bleomycin-induced PH and fibrosis. Further investigation of 2ME in pulmonary fibrosis and PH is warranted.     

PROTECTIVE EFFECTS OF ME3221 ON HYPERTENSIVE COMPLICATIONS AND LIFESPAN IN SALT-LOADED STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

1. A comparison was made on the protective effects of the following: ME3221, a competitive angiotensin AT₁ receptor antagonist; losartan, in which a major active metabolite is a non-competitive angiotensin AT₁ receptor antagonist; and enalapril, an angiotensin-converting enzyme inhibitor, using the salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP). 2. SHRSP received orally ME3221 (3 and 10mg/kg per day), losartan (10mg/kg per day) and enalapril (10mg/kg per day) from the 6th to the 20th week of age. All the control rats showed rapid elevation of systolic blood pressure (SBP), accompanied by hypertensive complications, and died by 15 weeks of age. 3. ME3221, losartan and enalapril suppressed the elevation of SBP in the salt-loaded SHRSP to a comparable degree. ME3221 and losartan increased the survival rate to >90%, and diminished hypertensive complications such as cerebral apoplexy (stroke), renal injury (increased proteinuria, and total N-acetyl-β-D-glucosaminidase activity) and heart failure (cardiac hypertrophy and pleural effusion). 4. Competitive (ME3221) and non-competitive (losartan) angiotensin AT₁ receptor antagonists showed comparable efficacy against the complications and mortality of the salt-loaded SHRSP; both were more potent than enalapril in the protective effect.     

Cardiovascular and renal actions of AHR-16303B, an antagonist of 5-HT2 receptors and calcium channels, in hypertensive and normotensive rats.

The cardiovascular and renal responses to AHR-16303B, a novel antagonist of 5-hydroxytryptamine (5-HT2) receptors and calcium channels, were examined in spontaneously hypertensive (SHR) and normotensive rats (NTR) and compared with verapamil and ritanserin. In SHR, AHR-16303B (10-300 mg/kg orally, p.o.) produced dose-related reductions in mean arterial blood pressure (MABP), accompanied by modest isokaliuretic diuresis and unchanged heart rate (HR). In NTR, 10-30 mg/kg p.o. AHR-16303B had no effect on MABP or renal excretory function; 100 and 300 mg/kg reduced MABP but had only transient effects on HR; 100 mg/kg produced antidiuresis in NTR. Both strains of rats tolerated doses of AHR-16303B as high as 300 mg/kg. In both SHR and NTR, verapamil (10-100 mg/kg p.o.) produced dose-related reductions in MABP, antinatriuresis at 60 and 100 mg/kg, and variable effects on HR. Oral ritanserin had no effect on MABP of SHR or NTR at 3 or 10 mg/kg. AHR-16303B is unique in that it simultaneously antagonizes 5-HT2 receptors and produces safe and effective reduction of elevated BP without altering HR or triggering renal compensatory antidiuresis. At effective 5-HT2/calcium antagonistic doses, AHR-16303B has no effect on cardiorenal homeostasis in normotensive animals.     

芝麻素对自发性高血压大鼠肾病的保护作用

目的:观察芝麻素对自发性高血压大鼠(SHR)肾病的保护作用。方法:SHR灌胃芝麻素(160、80、40mg/kg)16周,每日一次。测定动物给药前后血压及给药后血Cr和BUN含量;HE染色观察肾小球病理变化;MASSON染色观察肾小球和肾间质胶原纤维变化;透射电镜观察肾小球超微结构。结果:芝麻素(160mg/kg)给药16周,能明显降低大鼠的血压、血Cr和BUN含量;改善肾小球变形、萎缩、硬化甚至玻璃样变等病理改变;肾小球系膜区未见明显扩大,基底膜未增厚,足突细胞无明显融合;肾小管细胞损伤和间质纤维化明显减轻。结论:芝麻素具有改善肾功能、保护肾脏作用。     

Effects of early perturbation of the renin-angiotensin system on cardiovascular remodeling in spontaneously hypertensive rats

RATIONALE: The goal of this study was to analyze cardiovascular (CV) remodeling in early, short-term CAP treated SHR and their offspring. METHODS: We treated SHR with Captopril (CAP, 100 mg/kg) from in utero to 1 month of age (OCAP). Some of these rats were mated at 3-4 months of age and we used their offspring (2nd G). Controls were untreated SHR, normotensive Wistar Kyoto rats (WKY) and SHR maintained on CAP (SCAP). At 12-14 months of age, rats were cannulated for mean arterial blood pressure (MAP) measurements. An image analysis system was used to quantitate changes in cardiac and vascular (wall-to-lumen ratios, w/l) morphology and fibrosis. RESULTS: Early, short-term CAP treatment prevented the full expression of hypertension in treated rats and their offspring. MAPs were: SHR (180+/-2.2 mm Hg); WKY 125+/-3 mm Hg); SCAP 112+/-2.5mm Hg; OCAP 138+/-2.3 mm Hg; and 2nd G (145+/-2.0 mm Hg). There were significant decreases in heart weight/body weight ratios, large and small vessel morphology, and interstitial and perivascular fibrosis in CAP-treated animals and their offspring in comparison to untreated SHR. CONCLUSIONS: The CV protective properties of early, short-term CAP treatment were not solely due to a reduction in MAP. Although MAP was higher in OCAP and 2nd G, CV structure resembled that found in WKY and SCAP. The effects of our early treatment appear to be due to chronic blockade of the renin-angiotensin system and its effects on growth of CV tissues and the development of fibrosis.     

Renal Effects Of Efonidipine Hydrochloride, A New Calcium Antagonist, In Spontaneously Hypertensive Rats With Glomerular Injury

1. To obtain some insight into the renoprotective mechanism of the new calcium antagonist efonidipine hydrochloride, we evaluated the acute effects of efonidipine on proteinuria, glomerular haemodynamics and the tubuloglomerular feedback (TGF) mechanism in anaesthetized 24-25-week-old spontaneously hypertensive rats (SHR) with glomerular injury. 2. Efonidipine infusion at 10 micrograms/kg per h following a bolus dose of 10 micrograms/kg, i.v., reduced systemic blood pressure (BP) and renal vascular resistance, whereas renal plasma flow (RPF), glomerular filtration rate (GFR), filtration fraction, urine volume and urinary sodium excretion were unaltered. Urinary protein excretion was clearly diminished from 163 +/- 25 to 105 +/- 24 ng/min per g kidney weight. 3. Micropuncture experiments revealed that the maximal reduction of proximal stop-flow pressure (SFP), an index of glomerular capillary pressure (Pgc), induced by loop of Henle perfusion was significantly less with efonidipine treatment (6.7 +/- 1.0% of SFP with no loop flow) than in control (23.8 +/- 3.1%). In the presence of efonidipine, SFP at half-maximal reduction (SFP1/2max), which approximates Pgc at the in vivo steady state tubular flow rate, remained unchanged compared with control (36.9 +/- 0.8 vs 35.3 +/- 0.7 mmHg, respectively) and the slope of dependency on mean BP was not different between control and efonidipine. 4. These results indicate that efonidipine attenuates the TGF response in SHR by dilating the afferent arteriole, thus maintaining the level of RPF and GFR despite reduced renal perfusion pressure. Constant GFR and SFP1/2max under efonidipine suggest that single nephron GFR and Pgc remain unaltered and that a marked reduction in proteinuria is achieved without changes in single nephron GFR or Pgc of superficial nephrons.     

Comparison of the severity of the chronic cardiotoxicity produced by doxorubicin in normotensive and hypertensive rats

A comparison was made of the severity of chronic doxorubicin cardiotoxicity in adult male spontaneously hypertensive rats (SHR) and in genetically related normotensive Wistar-Kyoto rats (WKY). Groups of SHR and WKY were given 12 weekly iv injections of doxorubicin at 0.25, 0.5, or 1.0 mg/kg. When the study was concluded, mean arterial pressure was 127 to 161 nm Hg in doxorubicin-treated SHR compared with 74 to 87 mm Hg in similarly treated WKY. Lesions, consisting mainly of cytoplasmic vacuolization and myofibrillar loss, were noted in the hearts from both types of rats given the 1.0-mg/kg dose and were considerably more severe in SHR than in WKY (average scores 3.8 and 2.0). Renal lesions (glomerular vacuolization and dilatation of tubules with accumulations of proteinaceous material) were of comparable severity in both types of rats at the 9- and 12-mg/kg cumulative doses; however, they were more severe in SHR at the 6-mg/kg cumulative dose. Moderate cardiac alterations were present in all SHR (average score 1.6) given 0.5 mg doxorubicin/kg; at the same dose, lesions were minimal in two and absent in three WKY. In a second study, groups of rats were killed 1 week after 3,6,9, or 12 weekly iv injections of doxorubicin (1.0 mg/kg). Myocardial lesions were noted initially in SHR after six doses and in WKY after nine doses. Three of five SHR were dead by the 12th dose. These results indicate that spontaneously hypertensive rats are much more sensitive than normotensive rats to the cardiotoxic effects of doxorubicin.     

DIRECT RENAL EFFECTS OF ENDOTHELIN IN CHRONIC HYPOXIC SPONTANEOUSLY HYPERTENSIVE RATS

1. The direct renal effects of endothelin (ET) were studied in eight chronic hypoxic rats (HA) and eight sea level (SL) spontaneously hypertensive rats (SHR). 2. After 4 weeks of exposure to simulated 5486 m (18,000 ft) hypoxia, all HA rats were in apparently good health, and baseline renal function, except effective renal blood flow, was not significantly different from SL rats. 3. Intrarenal arterial administration of ET (600 ng/kg per h) reduced ipsilateral renal excretion of water, sodium and potassium, glomerular filtration rate and effective renal plasma flow in both SL and HA rats to almost the same extent. 4. Administration of ET antiserum, however, increased the renal excretion of water in HA rats. 5. It is concluded that ET may play a role in the renal regulation of chronic hypoxic SHR.     

Effects of the flavonoid quercetin and its methylated metabolite isorhamnetin in isolated arteries from spontaneously hypertensive rats

Chronic oral quercetin exerts antihypertensive effects in spontaneously hypertensive rats (SHR). In the present study, the vasodilator effects of the flavonoid quercetin and its main metabolite isorhamnetin were analysed in isolated thoracic aorta, iliac artery and on the isolated perfused mesenteric resistance vascular bed from SHR and normotensive Wistar Kyoto rats (WKY). In noradrenaline-precontracted vessels from SHR there was an inverse correlation between the relaxant potency (pIC50) of quercetin (4.76 +/- 0.02, 5.08 +/- 0.12, 5.30 +/- 0.18, in aorta, iliac arteries and mesentery, respectively) and isorhamnetin (4.90 +/- 0.11, 5.38 +/- 0.15 and 5.80 +/- 0.10, respectively) and the diameter of the vessel studied. Both flavonoids were more potent in endothelium-denuded aortae and iliac arteries from SHR than from normotensive WKY rats. In addition, in aortae from SHR both flavonoids restored the endothelial-dependent vasodilation. Isorhamnetin, but not quercetin, also reduced the endothelium-dependent contractile responses induced by acetylcholine. These direct vasodilator effects, together with the improvement of endothelial function, are good candidates to explain the blood pressure reduction and vascular protective effects of quercetin in animal models of hypertension and possibly in human cardiovascular diseases.     

Protective effect of cicletanine on hypertension-induced decreases in the renal kallikrein-kinin and prostaglandin systems in stroke-prone spontaneously hypertensive rats.

We investigated the effect of two oral (p.o.) doses of cicletanine (5 and 30 mg/kg/day) for 4 weeks on urinary excretion (UKE), renal concentration (RKC) of kallikrein, and prostaglandin E2 (PGE2) and 6-keto-PGF1 alpha urinary excretion of stroke-prone (SP) spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) rats submitted to a high sodium intake (1%). Both doses of cicletanine induced a significant antihypertensive effect in treated SHR as compared with hypertensive untreated controls (HC). After 4-week treatment, a significant difference in mortality was observed between normotensive controls (NC) (0%) and HC (84%). Both doses of cicletanine reduced the mortality of hypertensive animals (8% SHR with 5 mg and 24% SHR with 30 mg vs. 84% in HC). Whereas UKE and RKC were decreased in HC during the progression of untreated hypertension from week 1 to week 4, both doses of cicletanine administration significantly prevented this decrease. Consistently with maintenance of UKE during the course of hypertension, the level of tissue kallikrein was higher in hypertensive cicletanine-treated than in untreated SHR. This increased RKC was associated with a significantly higher rate of kallikrein biosynthesis. The increased level of the urinary excretion and tissue concentration of PGE2 and 6-keto-PGF1 alpha in cicletanine-treated SHR as compared with untreated animals was also of interest. This protective effect on PG excretion correlated with that on kallikrein excretion. The results confirm the efficiency of cicletatine as an antihypertensive treatment. The antihypertensive action includes protective effects on potential vasodepressor kallikrein-kinin and prostaglandin systems.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of single and repeated oral administration of MK-421 and captopril on blood pressures in normotensive and experimental hypertensive rats

In the single dose study, the aortic blood pressure in conscious normotensive rats, 2-kidney, 1-clip renal hypertensive rats (2K-RHR), 1-kidney, 1-clip renal hypertensive rats (1K-RHR) or DOCA hypertensive rats was measured for 24 hr after the oral administration of angiotensin converting enzyme (ACE) inhibitors such as MK-421 or captopril. MK-421 at 3 mg/kg and captopril at 10 mg/kg markedly lowered the blood pressure of 2K-RHR. MK-421 at 10 mg/kg and captopril at 30 mg/kg only modestly lowered the blood pressure of 1K-RHR. In contrast, both ACE inhibitors failed to reduce blood pressure in DOCA and normotensive rats. In the repeated dose study, the systolic blood pressures in normotensive rats, 2K-RHR or spontaneously hypertensive rats (SHR) were measured twice a week for 3 weeks treatment of either MK-421 at 3 mg/kg or captopril at 10 mg/kg. Both ACE inhibitors produced significant antihypertensive effects in these model rats, and the effects were sustained throughout the treatment period. The antihypertensive effects in 2K-RHR were greater than those in SHR and normotensive rats. These results indicate that MK-421 and captopril cause the most significant antihypertensive effect in 2K-RHR in which the renin-angiotensin system played a dominant role in blood pressure regulation. The antihypertensive effect of MK-421 was approximately 3 times as potent as that of captopril in these hypertensive models.     

Nicardipine decreases blood pressure and heart rate at nucleus tractus solitarii of spontaneously hypertensive rats

The effects of the dihydropyridine (DHP) calcium channel antagonist, nicardipine, on central cardiovascular regulation were investigated by injecting it into the cisterna magna or directly into the nucleus tractus solitarii (NTS), in anesthetized normotensive or spontaneously hypertensive (SHR) rats. Intracisternal injections of nicardipine (1-10 micrograms/kg) dose-dependently decreased blood pressure in SHR; there was no significant change in cardiovascular parameters in normotensive rats. In SHR, nicardipine (100 ng) microinjected bilaterally into the NTS produced hypotension and bradycardia. The same doses of nicardipine intravenously injected did not change either parameter. Previous administration of the beta-adrenoceptor blocking drug, tertatolol (50 micrograms/kg i.v.), prevented the nicardipine-induced bradycardia and hypotension after injection into the NTS. These data suggest that part of the central cardiovascular effects of nicardipine result from an interaction with DHP sites within the NTS leading to a withdrawal of the sympathetic tone.     

Synergistic therapeutic effects of 2-methoxyestradiol with either sildenafil or bosentan on amelioration of monocrotaline-induced pulmonary hypertension and vascular remodeling

2-Methoxyestradiol (2ME) is a major nonestrogenic metabolite of estradiol. Our previous studies suggest that 2ME, in several models of cardiac and/or vascular injury, strongly inhibits cardiac and vascular remodeling. Furthermore, our most recent study shows that in male rats, 2ME attenuates the development and retards the progression of monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH), and in female rats, 2ME eliminates the exacerbation of PAH and the increased mortality due to ovariectomy. The current standard of care of patients with PAH includes treatment with an endothelin receptor antagonist (eg, bosentan) or a phosphodiesterase5 inhibitor (eg, sildenafil). Moreover, combination therapy is often prescribed. Therefore, in the present study, we compared the efficacy of 2ME (10 μg · kg(-1) · h(-1), 2ME-10) to the effects of bosentan (200 mg/kg; BOS), sildenafil (50 mg/kg; SIL), and their respective combinations with 2ME-10 (2ME + BOS and 2ME + SIL groups, respectively). Treatments were initiated 12 days after administration of MCT (60 mg/kg). Twenty-eight days after MCT administration, right ventricular peak systolic pressure was measured and morphometric analysis was conducted. 2ME exhibited beneficial effects in pulmonary hypertensive animals and had efficacy comparable to that of BOS and SIL. Importantly, combination treatments had favorable effects on survival, vascular remodeling, and inflammatory response, and the 2ME + SIL combination was significantly more efficacious than any other treatment. These results indicate that 2ME is effective in experimental PAH and suggests that 2ME may provide additional therapeutic benefit over existing drugs used for the treatment of pulmonary hypertension.     

Hypotensive and hemodynamic effects of the new non-sulfhydryl angiotensin converting enzyme inhibitor N-[8-amino-1(S)-carboxyoctyl]-L-alanyl-L-proline

The hypotensive effects of N-[8-amino-1(S)-carboxyoctyl] -L-alanyl-L-proline (AB-47, CAS 120008-53-9) were examined in normotensive rats and various hypertensive rat models. The hemodynamic effect of AB-47 was also examined in anesthetized spontaneously hypertensive rats (SHR). In 2-kidney, 1-clip renal hypertensive rats (2K, 1C-RHR) and SHR, the single administration of AB-47 (10 mg/kg, p.o.) induced potent and long-lasting hypotensive effects. The repeated administration of AB-47 (1 to 10 mg/kg, p.o.) to SHR for 29 days produced a dose-dependently and sustained hypotensive effect of 20 to 70 mmHg. AB-47 (10 mg/kg, p.o.) had a weak hypotensive effect in DOCA-salt hypertensive rats but no effects in normotensive and 1-kidney, 1-clip renal hypertensive rats (1K, 1C-RHR). AB-47 (3 mg/kg, p.o.) reduced blood pressure in intact SHR but not in bilateral nephrectomized SHR. The single intravenous injection of AB-47 (10 to 100 micrograms/kg) dose-dependently lowered systemic blood pressure, left ventricular systolic pressure (LVSP) and dp/dtmax without affecting heart rate (HR) and these effects of AB-47 were more potent than those of captopril and enalaprilat. These results suggest that AB-47 is a potent and long-lasting hypotensive agent and may be useful for the therapy of both hypertension and congestive heart failure.