Hiromi Rakugi

Enhancement of insulin sensitivity by troglitazone lowers blood pressure in diabetic hypertensives

The association of hypertension with insulin resistance has been reported. Troglitazone (CS-045) is a newly developed antidiabetic agent that enhances insulin sensitivity. Its antidiabetic effects have been confirmed in diabetic animals and patients. The present study was performed to evaluate whether the amelioration of hyperinsulinemia by troglitazone lowers blood pressure in essential hypertensives. Troglitazone was administered orally to 18 outpatients with essential hypertension complicated by mild diabetes at a dose of 200 mg twice a day for 8 weeks. Blood pressure was decreased from 164 +/- 3/94 +/- 2 mm Hg to 146 +/- 3 (P < .001)/82 +/- 3 (P < .05) mm Hg at 8 weeks of the treatment period. Pulse rate did not change. Fasting plasma glucose changed from 159 +/- 10 mg/dL to 144 +/- 14 mg/dL at 8 weeks (P < .05). Plasma insulin (IRI) levels changes from 9.1 +/- 1.2 microU/mL to 6.3 +/- 0.8 microU/mL at the endpoint of treatment (P < .1). Decrease in mean blood pressure from the control period to the endpoint of the treatment correlated significantly with decrease in IRI (r = 0.59, P < .05). In summary, troglitazone treatment induces improvement in both glucose metabolism and blood pressure control in essential hypertensive patients with diabetes mellitus. These results suggest that insulin resistance or plasma insulin level plays a role in the pathogenesis of essential hypertension.

Induction of angiotensin converting enzyme in the neointima after vascular injury. Possible role in restenosis.

Angiotensin II (Ang II) promotes growth of vascular smooth muscle cells in vitro. Consistent with this, Ang II enhances neointimal proliferation in vivo after vascular injury, while angiotensin converting enzyme (ACE) inhibitors attenuate this process. Since tissue ACE plays a key role in the control of local Ang II production, we examined whether vascular injury resulted in an increase in vascular ACE expression that may result in increased Ang II production. Abdominal aorta of Sprague-Dawley rats were injured with a 2 French balloon catheter. Morphometrical changes, ACE enzymatic activity, and localization of ACE by immunohistochemistry in injured and uninjured aorta were analyzed. Vascular ACE activity in the injured aorta was significantly higher than in the uninjured aorta, while serum and lung ACE levels were not different between the two groups. The cellular distribution of the ACE protein in the neointima was similar to that of alpha smooth muscle actin but differed from those of endothelial (von Willebrand factor) or monocytes/macrophages (ED-1) markers, demonstrating that ACE was expressed in neointimal smooth muscle cells. These data demonstrate that vascular injury results in the induction of vascular ACE and suggest that the inhibition of vascular ACE may be important in the prevention of restenosis after balloon injury.

Potential importance of tissue angiotensin-converting enzyme inhibition in preventing neointima formation.

Angiotensin II (Ang II) induces vascular smooth muscle cell migration and growth in vitro and induces DNA synthesis in vascular smooth muscle in vivo. Angiotensinconverting enzyme (ACE) inhibitors and angiotensin II receptor antagonists inhibit neointimal hyperplasia in many experimental models of restenosis. However, recent clinical trials (MERCATOR and MARCATOR) reported that treatment with low (antihypertensive) doses of an ACE inhibitor (cilazapril) failed to prevent restenosis. Because ACE activity is induced in the neointima after injury, we hypothesize that the inhibition of neointimal development may be dependent on the suppression of tissue ACE activity, which in turn is dependent on the dose of the ACE inhibitor. Methods and ResultsTo test this hypothesis, we treated rats with increasing doses of an ACE inhibitor, quinapril, before injury of the carotid artery. Blood pressure, serum and tissue ACE activity, and neointimal area were measured. The results demonstrated a dose-dependent inhibition by quinapril of serum and tissue ACE activities and neointima formation. However, the IC50s for blood pressure reduction and serum ACE inhibition were significantly lower than that observed for the suppression of neointima formation. The degree of neointimal formation showed a better correlation with residual tissue ACE than with serum ACE or blood pressure. ConclusionsThese results demonstrate a dissociation of the ability of an ACE inhibitor to decrease blood pressure and inhibit circulating ACE activity from its ability to inhibit tissue ACE activity. These results suggest that the need for a higher dose of an ACE inhibitor for the inhibition of neointima formation may be due to the relative difficulty in inhibiting tissue ACE activity.

Vascular injury induces angiotensinogen gene expression in the media and neointima.

BackgroundAngiotensin II promotes growth of vascular smooth muscle cells in vitro via the autocrine production of growth factors such as platelet-derived growth factor, basic fibroblast growth factor, and transforming growth factor-β. Furthermore, experimental studies have demonstrated that angiotensin infusion can enhance smooth muscle proliferation after balloon injury in vivo. Consistent with this, angiotensin converting enzyme inhibitors have been shown to prevent myointimal proliferation. The origin of vascular angiotensin that participate in this process is of interest. We have demonstrated the presence of angiotensinogen messenger RNA (mRNA) in the adventitial and medial layers of the rat aorta and have speculated that local angiotensinogen production may play an important role during myointimal proliferation. To provide further evidence toward this hypothesis, we compared the localization and expression of angiotensinogen mRNA in control and balloon injured vessels using in situ hybridization. Methods and ResultsAbdominal aorta of Sprague-Dawley rats were studied before or after injury with a balloon catheter. Neointimal hyperplasia developed as documented morphologically by a progressive increase in the ratio of neointimal to medial thickness from 0.17 at 1 week to 1.17 at 6 weeks after injury. Angiotensinogen mRNA was detected clearly in the adventitia and media of control and injured aorta. However, at 1 week after injury, the medial-to-adventitial angiotensinogen mRNA ratio was higher in the injured aorta, suggesting increased gene expression in the media compared with control. Of potential importance, angiotensinogen mRNA was also detected in the neointima of the injured aorta, and this was also highest at 1 week after injury. ConclusionsThese data are consistent with the hypothesis that balloon injury leads to activation of the vascular renin-angiotensin system, which may participate in the myointimal proliferation.

Enhanced Predictability of Myocardial Infarction in Japanese by Combined Genotype Analysis

To explore the genes responsible for myocardial infarction and restenosis after percutaneous transluminal coronary angioplasty, we performed association studies of the polymorphisms of the angiotensinogen and angiotensin-converting enzyme (ACE) genes. In the first study, normotensive myocardial infarction patients (n = 103) and control subjects (n = 103), who were matched for established risk factors with the myocardial infarction patients, were randomly selected. The angiotensinogen-TT genotype (T indicates threonine instead of methionine at position 235) was more frequent in the myocardial infarction group than in the control group (P < .05). The ACE-DD genotype (D indicates a deletion polymorphism in intron 16) was also more frequent in the myocardial infarction group (P < .0001). The odds ratio estimated by the combined analysis of the angiotensinogen-TT and ACE-DD genotypes (11.2) was markedly increased compared with that estimated separately from the angiotensinogen-TT (1.75) or ACE-DD (4.43) genotype. In the second study, we investigated 91 consecutive patients with acute myocardial infarction who underwent successful direct angioplasty. Combined analysis showed that the angiotensinogen-TT genotype did not enhance the predictability of myocardial infarction from the ACE-DD genotype. In conclusion, the angiotensinogen-TT genotype is a predictor for myocardial infarction, as well as the ACE-DD genotype, and the combined analysis of the angiotensinogen-TT and ACE-DD genotypes further enhanced the predictability of myocardial infarction in Japanese, suggesting its future clinical usefulness.

Angiotensin I-Converting Enzyme Gene Polymorphism Is Associated With Myocardial Infarction, but Not With Retinopathy or Nephropathy, in NIDDM

OBJECTIVE To clarify the relationship between the angiotensin I-converting enzyme (ACE) gene polymorphism and diabetic micro- and macroangiopathy in patients with non-insulin-dependent diabetes mellitus (NIDDM). RESEARCH DESIGN AND METHODS We examined 267 NIDDM patients with various stages of diabetic retinopathy, 61 patients with myocardial infarction (MI), and 136 patients without MI. An insertion/deletion polymorphism of the ACE gene was typed by polymerase chain reaction. RESULTS Although no association was found between ACE gene polymorphism and diabetic retinopathy or nephropathy, this polymorphism was associated with MI in the patients with NIDDM. Homozygotes for the deletion polymorphism (DD genotype) were found more frequently in diabetic patients with MI (31.1%) than in diabetic patients without ischemic heart disease (16.9%), with a relative risk of 2.22 (95% confidence interval 1.11–4.46, P = 0.024). CONCLUSION These data indicate that ACE gene polymorphism is associated with MI, but not with retinopathy or nephropathy, in patients with NIDDM and suggest that the ACE gene confers susceptibility to diabetic macroangiopathy but not to microangiopathy.

Effects of an angiotensin II receptor antagonist, CV-11974, on angiotensin II-induced increases in cytosolic free calcium concentration, hyperplasia, and hypertrophy of cultured vascular smooth muscle cells.

The effects of CV-11974, a potent nonpeptide antagonist of the angiotensin II (AII) type-1 receptor (AT1), on cytosolic free calcium concentration ([Ca2 + ]i), hyperplasia, and hypertrophy of cultured vascular smooth muscle cells (VSMC) from rat aorta were studied. [Ca2 + ]i was measured by fura 2, and hyperplasia and hypertrophy were determined by incorporation of [3H]thymidine and [3H]leucine, respectively. CV-11974 had no effect on [Ca2 + ]i itself, but suppressed 10-7 M AII-induced increase in [Ca2 + ]i dose dependently at concentrations from 10-10 M and completely at 10-7 M. CV-11974 suppressed both Ca2+ release from intracellular Ca2+ stores and Ca2+ influx from the extracellular space. However, CV-11974 had no effect on the increases in [Ca2 α ]; induced by prostaglandin F2α (PGF2α), a potent vasoconstrictor, or ionomycin, a Ca2+ ionophore. These results indicate that the suppressive effects of CV-11974 act on the binding of AH and its specific receptors. AH 10-7 M increased the synthesis of DNA and protein to 1.5 and 1.7 times the control values, respectively. CV-11974 had no effect on synthesis of DNA or protein, but suppressed the AII-stimulated synthesis of DNA and protein dose dependently at concentrations >10-8 and 10-10 M, respectively and completely at 10 -6 M. These results indicate that All increases [Ca2 + ]i and synthesis of DNA and protein in VSMC through activation of AT,. CV-11974 showed no partial agonistic effects on AH. Thus, CV-11974 may act not only as an antihypertensive agent, but also as an inhibitor of vascular injury stimulated by AII.

EFFECT OF AN ANTIHYPERTENSIVE DRUG ON BRAIN ANGIOTENSIN II LEVELS IN RENAL AND SPONTANEOUSLY HYPERTENSIVE RATS

1. Although numerous studies suggest that brain angiotensin (AII) may play an important role in the regulation of blood pressure, it is still unclear what factors may influence brain All. In this study, we hypothesized that brain AII is influenced by circulating factors. To investigate the role of blood pressure and plasma All in brain AII level, we studied the effect of an antihypertensive drug on brain AII in two‐kidney, one‐clip (2K1C) and spontaneously hypertensive (SHR) rats.

Differential Regulation of Brain Angiotensin II in Genetically Hypertensive and Normotensive Rats after Nephrectomy

To investigate the role of tissue angiotensin II (Ang II) in the maintenance of hypertension after nephrectomy in spontaneously hypertensive rats (SHR), Ang II levels were measured in various tissues of both 12-week-old SHR and normotensive control, Wistar-Kyoto rats (WKY), 48 h after nephrectomy or sham operation. Ang II was determined by radioimmunoassay coupled with high performance liquid chromatography. Nephrectomy caused a decrease of plasma renin activity and plasma Ang II concentration in both SHR and WKY. Aortic Ang II levels were significantly lowered by nephrectomy only in WKY, and not in SHR. Ang II levels in hypothalamic block, brainstem and cerebellum of SHR increased after nephrectomy, whereas those of WKY were unchanged. Intracerebroventricular administration of ceronapril, an angiotensin converting enzyme inhibitor, significantly decreased sustained high blood pressure in SHR 48 h after nephrectomy compared with vehicle administration, whereas intravenous administration had no effect. These results suggest that in spite of the important role of the renal renin-angiotensin system in maintenance of high blood pressure in SHR, control mechanisms may switch to other systems after nephrectomy, and that the increased brain Ang II levels after nephrectomy may be related to these mechanisms.

AUGMENTATION OF ANGIOTENSIN II RELEASE FROM ISOLATED MESENTERIC ARTERIES OF WISTAR‐KYOTO AND SPONTANEOUSLY HYPERTENSIVE RATS FOLLOWING NEPHRECTOMY

1. We previously reported that angiotensin II release from the mesenteric arteries of Wistar‐Kyoto (WKY) and spontaneously hypertensive rats (SHR) increased in a time‐dependent manner as a result of the isolation of the arteries and perfusion. This phenomenon appeared to be due to the withdrawal of circulating angiotensin II (AII).