Angiotensin receptor subtypes in the uterine artery during ovine pregnancy

This study was undertaken to determine if changes in receptor density or affinity could account for the reduced vascular sensitivity to angiotensin II seen during pregnancy. Angiotensin receptor subtypes in the uterine arteries of non-pregnant, pregnant and postpartum ewes were investigated using saturation and competition receptor binding techniques with the specific receptor antagonists, losartan (DuP-753) and PD-123319 (S)1-[[4-(dimethylamino)-3-methylphenyl]-methyl]-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid, ditrifluoroacetate, monohydrate). Receptor density and affinity of total angiotensin receptors, as well as the angiotensin AT₁ and AT₂ receptor subtypes in uterine arteries were compared with those in the mesenteric artery and aorta. The uterine artery contains both AT₁ and AT₂ receptor subtypes, whereas the mesenteric artery and aorta contain primarily the AT₁ receptor subtype. In uterine arteries from pregnant sheep, angiotensin receptor density was increased because AT₂ receptors were increased. AT₁ receptor density was not altered. This change was not seen in the aorta. In the uterine artery, receptor affinity for [Sar¹,Ile⁸]angiotensin II decreased in mid-gestation (IC₅₀ 7.7±1.2×10⁻⁹ M) compared with non-pregnant ewes (IC₅₀ 3.0±0.6×10⁻⁹ M, P=0.006), and there was decreased affinity of angiotensin AT₁ receptors for losartan during pregnancy (IC₅₀ 2.8±1.0×10⁻⁴ M) compared with non-pregnant ewes (IC₅₀ 2.2±1.3×10⁻⁶ M, P=0.025). Our results show changes in the density and affinity of the angiotensin receptor subtypes in the uterine artery which could explain its reduced responsiveness to circulating angiotensin II during pregnancy.     

Putative roles of kinin receptors in the therapeutic effects of angiotensin 1-converting enzyme inhibitors in diabetes mellitus

The role of endogenous kinins and their receptors in diabetes mellitus is being confirmed with the recent developments of molecular and genetic animal models. Compelling evidence suggests that the kinin B₂ receptor is organ-protective and partakes to the therapeutic effects of angiotensin 1-converting enzyme inhibitors (ACEI) and angiotensin AT₁ receptor antagonists. Benefits derive primarily from vasodilatory, antihypertensive, antiproliferative, antihypertrophic, antifibrotic, antithrombotic and antioxidant properties of kinin B₂ receptor activation. Mechanisms include the formation of nitric oxide and prostacyclin and the inhibition of NAD(P)H oxidase activity involving classical and novel signalling pathways. Kinin B₂ receptor also ameliorates insulin resistance by increasing glucose uptake and supply, and by inducing glucose transporter-4 translocation either directly or through phosphorylation of insulin receptor. The kinin B₁ receptor, which is induced by the cytokine network, growth factors and hyperglycaemia, mediates hyperalgesia, vascular hyperpermeability and leukocytes infiltration in diabetic animals. However, emerging data highlight reno- and cardio-protective effects mediated by kinin B₁ receptor under chronic ACEI therapy in diabetes mellitus. Thus, the Janus-faced of kinin receptors needs to be taken into account in future drug development. For instance, locally acting kinin B₁/B₂ receptor agonists if used in a safe therapeutic window may represent a more rationale strategy in the prevention and management of diabetic complications. Because kinin B₂ receptor antagonists may further increase insulin resistance, the persisting dogma that restricts the development of kinin receptor analogues to antagonists (that is still relevant to abrogate pain and inflammation) needs to be revisited.     

Enhancement of losartan (DuP 753)-induced angiotensin II receptor antagonism by PD123177 in rats

Losartan (DuP 753) and PD123177 are angiotensin II type 1 (AT₁) and type 2 (AT₂) receptor selective ligands, respectively. In rats, PD123177 did not exhibit angiotensin II antagonism or hypotensive activity but enhanced these activities of a submaximal dose of losartan. As PD123177 displaced losartan from its rat plasma protein binding sites and thus increased the free concentration of losartan, this may account for its enhancement of the in vivo activities of losartan in rats.     

EXP597, a nonpeptide angiotensin II receptor antagonist with high affinities for the angiotensin AT1 and AT2 receptor subtypes

AT₁ and AT₂ are the two major receptor subtypes for angiotensin II that have been pharmacologically defined by using the selective ligands losartan and PD123177, respectively. EXP597 (4-[(5-(2-benzoyl)benzyloxycarbonyl-4-ethyl-2-n-propylimidazole- 1-yl)methyl]-3-fluoro-2′-isoamyloxycarbonylaminosulfonyl-[1,1′]-biphenyl, potassium salt) is a nonpeptide angiotensin II receptor ligand which in the rat adrenal exhibits binding affinities (IC₅₀) of 0.5 and 0.7 nM for angiotensin AT₁ and AT₂ receptor subtypes, respectively. Further, EXP597 is an insurmountable angiotensin II receptor antagonist in the isolated rabbit aorta and lowers blood pressure in renal hypertensive rats with i.v. and p.o. ED₃₀ values of 0.05 and 0.9 mg/kg, respectively.     

Angiotensin II-induced responses in vascular smooth muscle cells: inhibition by non-peptide receptor antagonists

The present study investigates the effect of angiotensin II and LR-B/081 (-methyl 2-[[4-butyl-2-methyl-6-oxo-5-[[2′-(1H-tetra-zol-5-yl) [1,1′-biphenyl]-4-yl] methyl]-1(6H)-pyrimidinyl] methyl]-3-thiophenecarboxylate), a novel non-peptide angiotensin II receptor antagonist, on both early and late responses in rat vascular smooth muscle cells. Angiotensin II induced a rapid and transient elevation of inositol trisphosphate intracellular levels, triggered the release of both prostaglandin E₂ and prostaglandin I₂ (EC₅₀ = 21 ± 3 and 16 ± 2 nM, respectively), and, in long-term studies, increased leucine and thymidine incorporation. All angiotensin II effects were antagonized by LR-B/081 and losartan, the reference non-peptide angiotensin AT₁-selective receptor antagonist, whereas they were unaffected by PD123177 (1-(4-amino-3-methylphenyl)methyl-5-diphenylacetyl-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine carboxylic acid), a non-peptide angiotensin AT₂-selective receptor antagonist. LR-B/081 displayed a much higher potency than losartan in inhibiting angiotensin II-induced prostaglandin E₂ (IC₅₀ = 0.15 ± 0.02 and 39 ± 9 nM, respectively) and prostaglandin I₂ release (IC₅₀ = 0.18 ± 0.04 and 134 ± 40 nM, respectively) and was also more potent in blocking the increase in protein synthesis (IC₅₀ = 242 ± 119 nM and 1221 ± 687 nM, respectively). Moreover, LR-B/081 and losartan blocked the response to angiotensin III but failed to inhibit the prostaglandin release stimulated by vasopressin or the mitogenic effect of serum. LR-B/081 and losartan were devoid of intrinsinc agonistic properties in the experimental conditions employed. The present results describe LR-B/081 as a novel, highly specific and potent, non-peptide angiotensin AT₁-selective receptor antagonist, that is capable of blocking angiotensin II-proliferative responses, which may be of relevance for cardiovascular diseases.     

Identification and characterisation of angiotensin II receptor subtypes in human brain

Autoradiographic and homogenate binding studies using the radioligand, [¹²⁵I]angiotensin II, identified a heterogeneous distribution of specific binding sites (defined by angiotensin II, 1.0 μM) throughout the human forebrain. Highest AT receptor densities were detected in the paraventricular nucleus, median eminence, substantia nigra, putamen and caudate nucleus (2.4, 1.2, 1.0, 0.30 and 0.24 fmol/mg tissue equivalent, respectively). The AT₁ receptor antagonist, losartan (1.0 μM) competed for the majority of the specific binding. [¹²⁵I]Angiotensin II-specific binding (although not consistently above non-specific binding levels) was also detected in various other brain regions (e.g. amygdala, entorhinal cortex, hippocampus, inferior colliculus, nucleus accumbens, parietal cortex, periaquaductal grey, superior colliculus, striate cortex, temporal cortex, thalamus). In the presence of losartan (1.0 μM), angiotensin II, saralasin, losartan and PD123177 competed for [¹²⁵I]angiotensin II binding to membranes prepared from the cerebellum or substantia nigra with a rank order of affinity; angiotensin II = saralasin > PD123177 > losartan. In the presence of PD123177 (1.0 μM), the rank order of affinity of losartan and PD123177 was reversed. These studies indicate the presence of both AT₁ and AT₂ receptor subtypes within various regions of the human forebrain.     

Neuroprotective effect of catalpol against MPP(+)-induced oxidative stress in mesencephalic neurons

Cerebral ischemia results in enhanced expression of smooth muscle cell endothelin and angiotensin receptors in cerebral arteries. We hypothesise that this phenomenon may be detrimental and that acute treatment with a combined non-hypotensive dose of the angiotensin AT₁ receptor inhibitor candesartan and the endothelin ET_A receptor antagonist ZD1611 reduces the infarct in experimental ischemic stroke. Transient middle cerebral artery occlusion was induced in male Wistar rats by the intraluminal filament technique for 2 h followed by recirculation. The animals received systemic candesartan (0.05 mg/kg/day), ZD1611 (0.15 mg/kg/day), both combined or vehicle with start immediately after the occlusion. After 48 h the rats were sacrificed, the brains sliced and stained with 1% 2, 3, 5-triphenyltetrazolium chloride (TTC) and the volume of ischemic damage determined. The middle cerebral arteries were harvested for immunocytochemical studies of angiotensin AT₁ and endothelin ET_A receptor expression. Candesartan or ZD1611 did alone not significantly decrease the brain damage or improve neurological scores as compared to vehicle controls. The combined inhibition of angiotensin AT₁ and endothelin ET_A receptors however decreased the brain damage and improved the neurological scores (both P < 0.05). The treatment did not change resting mean arterial blood pressure. In addition, there was an upregulation of angiotensin AT₁ receptors in the ischemic middle cerebral artery smooth muscle cells, which was normalised by the combined treatment. In conclusion, the present study shows that combined inhibition of angiotensin AT₁ and endothelin ET_A receptors reduces the brain damage and improves the neurological outcome after ischemic stroke in rat.     

Angiotensin II potentiates inflammatory edema in rats: Role of mast cell degranulation

The aim of this study was to evaluate the effect of angiotensin II on models of acute inflammation. This study shows that angiotensin II potentiates the carrageenan- and dextran-induced paw edema. The administration of angiotensin II does not change the myeloperoxidase activity, neither the tissue content of interleukin-1 beta and tumor necrosis alpha nor the neutrophil migration to the peritoneal cavity, but induces significant enhancement of mast cell degranulation. The anti-histamine, mepyramine, and the anti-serotonin, metisergyde, reduce the angiotensin II-facilitated dextran-induced edema. Our results suggest that angiotensin II increases the vascular permeability through induction of mast cell degranulation and that this effect is mediated by the angiotensin AT₂ receptor, since the angiotensin AT₁ receptor antagonist and the angiotensin AT₂ receptor agonist potentiated the paw edema.     

Structure elucidation and conformational study of V8: a novel synthetic non peptide AT(1) antagonist

AT₁ antagonists constitute the most recent class of antihypertensive drugs which act through the Renin Angiotensin System (RAS). In an effort to comprehend their stereoelectronic features, a study was initiated to compare the conformational properties of drugs already marketed for the treatment of hypertension with synthetic ones, possessing common structural characteristics. In this study, the synthetic AT₁ antagonist V8 is structurally elucidated and its conformational properties are studied through a combination of NMR spectroscopy and computational analysis. Its conformational properties are compared with those of the structurally similar prototype AT₁ antagonist losartan.     

Olmesartan ameliorates a dietary rat model of non-alcoholic steatohepatitis through its pleiotropic effects

Insulin resistance is a major pathological condition associated with obesity and metabolic syndrome. Insulin resistance and the renin-angiotensin system are intimately linked. We evaluated the role of the renin-angiotensin system in the pathogenesis of insulin resistance-associated, non-alcoholic steatohepatitis by using the angiotensin II type 1 receptor blocker olmesartan medoxomil in a diabetic rat model. The effects of olmesartan on methionine- and choline-deficient (MCD) diet-induced steatohepatitis were investigated in obese, diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats and control Long-Evans Tokushima Otsuka (LETO) rats. Components of the renin-angiotensin system were up-regulated in the livers of OLETF rats, compared with LETO rats. In OLETF, but not LETO, rats, oral administration of olmesartan for 8 weeks ameliorated insulin resistance. Moreover, olmesartan suppressed MCD diet-induced hepatic steatosis and the hepatic expression of lipogenic genes (sterol regulatory element-binding protein-1c and fatty acid synthase) in OLETF, but not LETO, rats. In both OLETF and LETO rats, olmesartan inhibited hepatic oxidative stress (4-hydroxy-2-nonenal-modified protein) and expression of NADPH oxidase. Olmesartan also inhibited hepatic fibrosis, stellate cell activation, and expression of fibrogenic genes (transforming growth factor-beta, alpha 1 [I] procollagen, plasminogen activator inhibitor-1) in both OLETF and LETO rats. In conclusion, pharmacological blockade of the angiotensin II type 1 receptor slows the development of steatohepatitis in the OLETF rat model. This angiotensin II type 1 receptor blocker may exert insulin resistance-associated effects against hepatic steatosis and inflammation as well as direct effects against the generation of reactive oxygen species and fibrogenesis.     

Role of the median preoptic nucleus in the chronic hypotensive effect of losartan in sodium-replete normal rats

1. We have shown previously that the chronic hypotensive effect of the angiotensin II AT₁ receptor antagonist losartan is mediated, in part, by the subfornical organ (SFO). However, the neural pathway(s) mediating this central effect of losartan downstream from the SFO has not been completely elucidated.
2. The present study was designed to test the hypothesis that the median preoptic nucleus (MnPO) is a crucial part of the neural pathway necessary for the chronic hypotensive effect of losartan. To test this hypothesis, male Sprague-Dawley rats were subjected to either Sham or electrolytic lesion of the MnPO (MnPOx). Rats were instrumented with radiotelemetric transducers and aortic flow probes for the continuous measurement of mean arterial pressure (MAP) and heart rate and cardiac output (CO), respectively. Total peripheral resistance (TPR) was calculated as MAP/CO. After 3 days of baseline measurements, rats were infused intraperitoneally with losartan (10 mg/kg per day) via an osmotic minipump at a rate of 5 μL/min.
3. The data revealed that, by Day 9 of losartan treatment, MAP had decreased 34 ± 2 mmHg in MnPOx rats ( n  = 9), whereas the MAP of Sham-lesioned rats ( n  = 8) had only decreased 24 ± 3 mmHg. These findings were accompanied by a greater decrease in TPR in MnPOx compared with Sham rats (−0.464 vs −0.237 mmHg/mL per min, respectively), whereas CO remained unchanged throughout the study protocol.
4. These results do not support the hypothesis that an intact MnPO is necessary to mediate the full chronic hypotensive effect of losartan in normal rats. Instead, they appear to suggest that the MnPO may play an important role in buffering the profound hypotension induced by losartan.     

Development of insulin resistance and reversal by thiazolidinediones in C2C12 skeletal muscle cells

AIM/HYPOTHESIS: The aim of this study was to develop an insulin-resistant cell culture model in skeletal muscle cell line by chronic presence of insulin in serum-free medium and to determine the effect of thiazolidinediones on insulin signaling. METHODS: We differentiated C2C12 in a combination of serum-free medium in presence or absence of insulin and determined differentiation by creatine kinase activity, myogenin and MyoD expression. The development of insulin resistance was determined by tyrosine phosphorylation of insulin receptor and insulin receptor substrate-1, phosphatidylinositol 3-kinase activity associated with insulin receptor substrate-1 and glucose uptake. We treated the cells with 50 microM of thiazolidinediones to determine the effect on these parameters. RESULTS: C2C12 cells were differentiated normally in the serum-free medium in the absence or presence of insulin. Chronic treatment of insulin resulted in reduced tyrosine phosphorylation of insulin receptor and insulin receptor substrate-1; activation of phosphatidylinositol 3-kinase was impaired and insulin-stimulated glucose uptake was reduced. The treatment of insulin-resistant cells with thiazolidinediones resulted in the enhancement of insulin signaling pathway by increasing tyrosine phosphorylation of insulin receptor, insulin receptor substrate-1, phosphatidylinositol 3-kinase activity and glucose uptake. CONCLUSION/INTERPRETATION: These results indicate that insulin resistance can be developed in C2C12 skeletal muscle cell line. These findings implicate a direct mechanism of action of thiazolidinediones on skeletal muscle.     

替米沙坦对OLETF大鼠脂肪细胞因子网膜素、视黄醇结合蛋白4及内脂素的影响

目的：研究血管紧张素Ⅱl型(AT1)受体阻滞剂替米沙坦对改善OLETF大鼠胰岛素抵抗(IR)的作用及其机制。方法：肥胖自发2型糖尿病雄性OLETF大鼠47只,高脂喂养22周诱导建立胰岛素抵抗大鼠模型。随机分为5组,胰岛素抵抗对照组（OLETF）大鼠给予高脂饮食,替米沙坦组(L)高脂饮食加替米沙坦,二甲双胍组（MET）高脂饮食加二甲双胍,吡格列酮组（P）高脂饮食加吡格列酮,低剂量替米沙坦组(VL) 高脂饮食加低剂量替米沙坦,干预26周后测定空腹血糖、空腹胰岛素、游离脂肪酸、血脂、网膜素、视黄醇结合蛋白4、内脂素水平。结果：替米沙坦具有改善OLETF自发胰岛素抵抗大鼠的胰岛素抵抗和糖、脂代谢的作用,药物干预组与胰岛素抵抗对照组比较,血清网膜素表达水平明显升高(F=6.888,P<0.001), 血清视黄醇结合蛋白4表达水平明显降低(F=7.236,P<0.001),血清内脂素表达水平明显降低(F=4.165,P=0.003),血脂水平和胰岛素抵抗得到明显改善。结论：替米沙坦可能通过提高血清网膜素表达、降低血清视黄醇结合蛋白4及内脂素表达,调节血脂水平,改善胰岛素抵抗。     

CEP-11004, an inhibitor of the SAPK/JNK pathway, reduces TNF-alpha release from lipopolysaccharide-treated cells and mice

Oxidative stress and low-grade inflammation are hallmarks of diabetes mellitus. We explored protective, blood pressure-independent effects of the angiotensin II type 1 (AT₁) receptor antagonist candesartan and the selective β₁-adrenoceptor antagonist metoprolol. Diabetes mellitus was induced in 8-week-old Sprague–Dawley rats after injection of streptozotocin. Diabetic rats were randomized to treatment with candesartan or metoprolol in sub-antihypertensive doses or to placebo treatment. In the quadriceps, musculature markers of oxidative stress and inflammation were determined. Function of the inherent vascular bed was measured in vivo in the autoperfused hindlimb. Increases in NAD(P)H activity, expression of its cytosolic subunit p22^phox and of endothelial NO synthase e(NOS) displayed enhanced oxidative stress. Upregulated intercellular (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 and of inducible NOS (iNOS) revealed inflammatory processes. Diabetes was associated with severe impairment of endothelium-dependent and -independent vasodilatation. Candesartan, but not metoprolol, reduced NAD(P)H activity, attenuated diabetes-induced over-expression of p22^phox and eNOS mRNA as well as ICAM-1, VCAM-1, iNOS and eNOS immunoreactivity and led to a substantial improvement of endothelium-dependent vasodilatation (+ 46.3% vs. placebo treatment; P < 0.05). Angiotensin AT₁ receptor antagonism, but not β₁-adrenoceptor antagonism, ameliorates diabetes-generated oxidative stress, indicating a pivotal role of the renin–angiotensin system in the development of diabetic complications.     

Comparison of vasculoprotective effects of benidipine and losartan in a rat model of metabolic syndrome

Although antihypertensive drugs confer improvement in endothelial dysfunction and protection from atherogenesis in hypertension, different classes of antihypertensive drugs may elicit different degrees of vasculoprotective effects. We have investigated the effects of a long-acting calcium antagonist, benidipine, and an angiotensin AT(1) receptor antagonist, losartan, on the vascular damage observed in OLETF rats, an animal model of metabolic syndrome. At 34 weeks of age, OLETF rats were treated with either benidipine (3 mg/kg/day, per os) or losartan (25 mg/kg/day, per os) for 8 weeks. The extent of blood pressure reduction, restoration endothelium-dependent aortic relaxation, and elevation of serum nitrite/nitrate concentration did not differ significantly between benidipine- and losartan-treated OLETF rats. Benidipine and losartan also reduced the aortic expression of transforming growth factor-beta1 mRNA and thickening of the vascular wall to a similar extent. Increased cardiac fibrosis was also inhibited by both benidipine and losartan. These data suggest that, when used in an antihypertensive dose, benidipine is as effective as losartan in restoring vascular endothelial function and in suppressing of cardiovascular remodeling in an animal model of metabolic syndrome.     

Functional coupling of angiotensin II type 1 receptor with insulin resistance of energy substrate uptakes in immortalized cardiomyocytes (HL-1 cells)

BACKGROUND AND PURPOSE: Increased angiotensin II levels and insulin resistance coexist at the early stages of cardiomyopathies. To determine whether angiotensin II increases insulin resistance in cardiomyocytes, we studied the effect of angiotensin II on basal and insulin-stimulated transport rate of energy substrates in immortalized cardiomyocytes (HL-1 cells). EXPERIMENTAL APPROACH: Glucose and palmitic acid uptakes were measured using [(3)H]2-deoxy-D-glucose and [(14)C]palmitic acid, respectively, in cells exposed or not exposed to angiotensin II (100 nM), angiotensin II plus irbesartan or PD123319, type 1 and 2 receptor antagonists, or PD98059, an inhibitor of ERK1/2 activation. Cell viability, DNA, protein synthesis and surface area were evaluated by the MTT test, [(3)H]thymydine, [(3)H]leucine and morphometric analysis, respectively. Type 1 receptor levels were measured by western blot analysis. KEY RESULTS: Basal uptakes of glucose and palmitic acid by HL-1 cells (0.37+/-0.07 and 7.31+/-0.22 pmol per 10(4)cells per min, respectively) were both stimulated by 100 nM insulin (+91 and +64%, respectively). Cells exposed to angiotensin II remained viable and did not show signs of hypertrophy. In these conditions, the basal palmitic acid uptake of the cells increased (11.41+/-0.46 pmol per 10(4) cells per min) and insulin failed to stimulate the uptake of glucose and fatty acids. Changes in the rate of uptake of energy substrates were prevented or significantly reduced by irbesartan or PD98059. CONCLUSIONS AND IMPLICATIONS: Angiotensin II is a candidate for increasing insulin resistance in cardiomyocytes. Our results suggest a further mechanism for the cardiovascular protection offered by the angiotensin II type 1 receptor blockers.     

Effects of quinapril and losartan on insulin sensitivity in genetic hypertensive rats with different metabolic abnormalities.

This study was designed to investigate the effects of the angiotensin-converting enzyme (ACE) inhibitor quinapril and the angiotensin II-receptor antagonist losartan on insulin sensitivity in two types of genetic hypertensive rats with insulin resistance. Quinapril (3 mg/kg) and losartan (10 mg/kg) decreased the systolic blood pressure to almost the same extent in both spontaneously hypertensive rats (SHRs) and Dahl salt-sensitive (Dahl S) rats. Quinapril increased the glucose requirement for the euglycemic clamp test in both SHRs and Dahl S rats, whereas losartan increased it in SHRs but not in Dahl S rats. The severity of the metabolic abnormalities may be responsible for the failure of losartan to improve the insulin sensitivity in Dahl S rats because serum insulin, total cholesterol, triglyceride, and free fatty acids (FFAs) were higher in the Dahl S rats than in SHRs. A kinin antagonist, Hoe 140, inhibited the increase in the glucose requirement by quinapril without affecting the depressor effect of quinapril in SHRs. In conclusion, quinapril improved the insulin sensitivity more effectively than did losartan in the genetic hypertensive rats with insulin resistance and relatively severe metabolic abnormalities. Based on our findings, one of the mechanisms underlying the difference between quinapril and losartan may thus be endogenous kinins.     

The mechanisms of insulin sensitivity improving effects of angiotensin converting enzyme inhibitor

It is well-known that angiotensin converting enzyme (ACE) inhibitor not only decreases blood pressure (BP) but also improves insulin sensitivity. To elucidate the mechanisms of these actions of ACE inhibitor, we evaluated its effect on both BP and insulin sensitivity (M-value) as estimated by the glucose clamp technique in essential hypertensives in comparison with the effect of angiotensin receptor (AT) antagonist. We also evaluated the effect of ACE inhibitor on BP, M-value and muscle fiber composition in fructose-fed rats (FFR) as an insulin-resistant hypertensive model with or without treatment with Hoe 140 (kinin receptor antagonist). In essential hypertensives, both ACE inhibitor and AT antagonist decreased BP and improved insulin sensitivity to the same extent. In FFR, ACE inhibitor also decreased BP and improved insulin sensitivity. Moreover, Hoe 140 showed no effect on these actions of ACE inhibitor. The composite ratio of type I fiber of soleus muscle was decreased significantly in FFR compared to control and ACE inhibitor produced a recovery of the composite ratio of type I fiber to the same as control. These results suggested that muscle fiber composition of skeletal muscle is linked to insulin resistance, and that ACE inhibitor may modulate muscle fiber composition through its vasodilative effect in hypertension. These results also suggest that for vasodilation, it is more important to inhibit angiotensin II than to block degradation of kinins or to improve insulin sensitivity by ACE inhibitor.     

Improvement of insulin sensitivity in obese Zucker rats by myricetin extracted from Abelmoschus moschatus

In an attempt to develop new substances for treating insulin resistance, obese Zucker rats were employed to screen the effect of myricetin, an active principle of Abelmoschus moschatus (Malvaceae), on insulin resistance. Myricetin purified from the aerial portion of the plant was administered intravenously ( I. V.) into animals. A dose-dependent decrease in the plasma glucose concentration of obese Zucker rats was observed 30 min following an I. V. injection. Moreover, repeated I. V. injection of myricetin (1 mg/kg) into obese Zucker rats 3 times daily for 1 week reduced the value of the glucose-insulin index, an index of insulin resistance calculated from the areas under the curve of glucose and insulin during the intraperitoneal glucose tolerance test. Additionally, repeated myricetin treatments overturned the inability of insulin to increase the expression of glucose transporter subtype 4 (GLUT 4) and to increase the protein levels and phosphorylation of insulin receptor substrate-1 (IRS-1) in soleus muscle of these obese rats. The inability of insulin to increase expression of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3-kinase) and to promote Akt serine phosphorylation in soleus muscle of these rats were also overturned by repeated myricetin treatments. These findings indicate that myricetin improves insulin sensitivity through increased post-receptor insulin signaling mediated by enhancements in IRS-1-associated PI3-kinase and GLUT 4 activity in muscles of obese Zucker rats. Myricetin might be used as a model substance for the development of antidiabetic compounds.     

Different activation of vascular mitogen-activated protein kinases in spontaneously and DOCA-salt hypertensive rats

Regulation mechanisms of the activity of vascular mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, may be altered in hypertension. To examine whether vascular MAP kinase activation mechanisms are altered in hypertension, we measured the activity of MAP kinases in rat aorta strips from spontaneously hypertensive rats (SHR) and from deoxycorticosterone acetate (DOCA)-salt hypertensive rats, and examined whether vascular angiotensin and endothelin systems are responsible for the alteration of MAP kinase activation in these hypertensive models. Endothelium-denuded aorta strips were incubated at 37 degrees C in medium. MAP kinase activity after incubation was increased in rat aorta strips. The MAP kinase activation was greater in 9- and 15-week-old SHR aorta strips than in age-matched Wistar Kyoto rats (WKY) aorta strips. Similarly, MAP kinase activation was enhanced in aorta strips from DOCA-salt hypertensive rats. In aorta strips from these kinds of rats, the angiotensin receptor antagonist, losartan, and the endothelin receptor antagonist, cyclo (D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl) (BQ123), inhibited the MAP kinase activation. The losartan-induced, but not BQ123-induced, inhibition of MAP kinase activation was enhanced in 15-week-old SHR aorta strips, whereas the BQ123-induced, but not losartan-induced, inhibition of MAP kinase activation was enhanced in DOCA-salt hypertensive rat aorta strips. Angiotensin II-induced MAP kinase activation was enhanced in 15-week-old SHR aorta strips, whereas it was depressed in DOCA-salt hypertensive rat aorta strips. These results indicate that MAP kinase activation function is enhanced in aorta strips from both kinds of hypertensive rats. It appears that the enhancement of MAP kinase activation results partly from enhanced vascular angiotensin system in SHR and from enhanced vascular endothelin system in DOCA-salt hypertensive rats.