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Background: The MicroArray Quality Control (MAQC) project evaluated the inter-and intra-

Abstract-Hyperinsulinemia and insulin resistance are closely associated with hypertension in humans and in animal models. Gender differences have been found in the development of hypertension in fructose-fed rats. The objectives of the present study were, first, to clarify whether androgens are required in the development of hyperinsulinemia, insulin resistance, and hypertension in fructose-fed rats, and second, to determine if cyclooxygenase-1 and cyclooxygenase-2 are also increased in the arteries of these rats. Male rats were gonadectomized or sham-operated and fed a 60% fructose diet beginning at age 7 weeks. Blood pressure was measured by a tail-cuff method, and an oral glucose tolerance test was performed to assess insulin sensitivity after 8 weeks of fructose feeding. Cyclooxygenase-1 and cyclooxygenase-2 mRNA expression was also assessed in the thoracic aortae and mesenteric arteries. Gonadectomy prevented hypertension from developing in the fructose-fed rats, but hyperinsulinemia and insulin resistance developed. There was an increase in cyclooxygenase-2 expression in the thoracic aortae and mesenteric arteries of the fructose-fed sham-operated rats while the expression of cyclooxygenase-1 remained unchanged. Gonadectomy prevented the mRNA overexpression of vascular cyclooxygenase-2 in the fructose-fed rats. These results suggest that the presence of androgens is necessary for the development of fructose-induced hypertension. Androgens apparently act as a link between hyperinsulinemia/insulin resistance and hypertension in fructose-hypertensive rats. Furthermore, an increase in the expression of cyclooxygenase-2 is implicated in the development of hypertension. The mechanisms involved require further study. Key Words: fructose Ⅲ insulin resistance Ⅲ hyperinsulinemia Ⅲ hypertension H yperinsulinemia and insulin resistance are closely linked to the development of hypertension in humans and in animal models. [1][2][3] Several mechanisms have been proposed, including the sympathetic nervous system, 4 renal abnormalities in handling sodium, 5,6 and changes in endothelial function and vasoactive mediators such as endothelin-1, nitric oxide, and thromboxane A 2 (TXA 2 ) 3,7,8 However, the exact mechanisms remain to be clarified. Recently, we reported that chronic insulin treatment impaired insulin sensitivity in male and female rats; however, the impairment occurred to a greater degree in male rats. 9 Interestingly, increased blood pressure (BP) was seen only in male rats. These results suggest that the association between hyperinsulinemia/insulin resistance and hypertension is gender-dependent and exists only in male rats. Based on these findings, we speculated that androgens might play an essential role in the relationship between hyperinsulinemia/insulin resistance and hypertension.Gender-associated differences in BP have been widely observed and confirmed in humans. Women during their reproductive years are less prone to hypertension and hypertensionrelated diseases than men or postmenopausal women. 10 Stu...

Protein kinase C (PKC) and angiotensin II (AngII) can regulate cardiac function in pathological conditions such as in diabetes or ischemic heart disease. We have reported that expression of connective tissue growth factor (CTGF) is increased in the myocardium of diabetic mice. Now we showed that the increase in CTGF expression in cardiac tissues of streptozotocin-induced diabetic rats was reversed by captopril and islet cell transplantation. Infusion of AngII in rats increased CTGF mRNA expression by 15-fold, which was completely inhibited by co-infusion with AT1 receptor antagonist, candesartan. Similarly, incubation of cultured cardiomyocytes with AngII increased CTGF mRNA expression by 2-fold, which was blocked by candesartan and a general PKC inhibitor, GF109203X. The role of PKC isoform-dependent action was further studied using adenoviral vector-mediated gene transfer of dominant negative (dn) PKC or wild type PKC isoforms. Expression of dnPKC␣, -⑀, and -isoforms suppressed AngII-induced CTGF expression in cardiomyocytes. In contrast, expression of dominant negative PKC␦ significantly increased AngII-induced CTGF expression, whereas expression of wild type PKC␦ inhibited this induction. This inhibitory effect was further confirmed in the myocardium of transgenic mice with cardiomyocyte-specific overexpression of PKC␦ (␦Tg mice). Thus, AngII can regulate CTGF expression in cardiomyocytes through a PKC activation-mediated pathway in an isoform-selective manner both in physiological and diabetic states and may contribute to the development of cardiac fibrosis in diabetic cardiomyopathy.

To investigate the role of thromboxane A 2 in the development of hypertension in the fructose-fed rat, we treated male fructose-fed rats with dazmegrel (a thromboxane synthase inhibitor) and monitored blood pressure, fasting plasma parameters, and insulin sensitivity for 7 weeks. Systolic blood pressure was measured each week using tail plethysmography, and an oral glucose tolerance test was performed at the end of the study to assess insulin sensitivity. Treatment with a 60% fructose diet and dazmegrel (100 mg · kg −1 · d −1 via oral gavage) was initiated on the same day. Plasma triglyceride levels increased 2-fold in both fructose- and fructose/dazmegrel-treated groups, and plasma insulin levels tended to be higher in these groups, although not significantly. Systolic blood pressure increased significantly throughout the study in the fructose-fed group only (132±3 versus 112±4 mm Hg in control rats, 118±2 mm Hg in control-treated rats, 116±2 mm Hg in fructose-treated rats). Both fructose groups demonstrated a higher peak insulin response to oral glucose challenge and had 40% to 60% lower insulin sensitivity index values. The results of this study show that treatment with a thromboxane synthase inhibitor, dazmegrel, can prevent the development of hypertension but does not improve insulin sensitivity or other fructose-induced metabolic impairments. Based on these data, we conclude that the potent vasoconstrictor thromboxane is involved in the link between hyperinsulinemia/insulin resistance and hypertension.

High-density oligonucleotide arrays were used to compare gene expression of rat hearts from control, untreated diabetic, and diabetic groups treated with islet cell transplantation (ICT), protein kinase C (PKC)␤ inhibitor ruboxistaurin, or ACE inhibitor captopril. Among the 376 genes that were differentially expressed between untreated diabetic and control hearts included key metabolic enzymes that account for the decreased glucose and increased free fatty acid utilization in the diabetic heart. ICT or insulin replacements reversed these gene changes with normalization of hyperglycemia, dyslipidemia, and cardiac PKC activation in diabetic rats. Surprisingly, both ruboxistaurin and ACE inhibitors improved the metabolic gene profile (confirmed by real-time RT-PCR and protein analysis) and ameliorated PKC activity in diabetic hearts without altering circulating metabolites. Functional assessments using Langendorff preparations and 13 C nuclear magnetic resonance spectroscopy showed a 36% decrease in glucose utilization and an impairment in diastolic function in diabetic rat hearts, which were normalized by all three treatments. In cardiomyocytes, PKC inhibition attenuated fatty acid-induced increases in the metabolic genes PDK4 and UCP3 and also prevented fatty acid-mediated inhibition of basal and insulin-stimulated glucose oxidation. Thus, PKC␤ or ACE inhibitors may ameliorate cardiac metabolism and function in diabetes partly by normalization of fuel metabolic gene expression directly in the myocardium. Diabetes 56:1410-1420, 2007 C ardiac failure in diabetic patients can be induced by vascular insufficiency and contractile dysfunction resulting from abnormal levels of metabolites (1,2). For the latter, elevations of plasma glucose and free fatty acids (FFAs) in diabetes may decrease the efficiency of energy production by suppressing glucose utilization and enhancing FFA metabolism (3,4). Because enhancements of angiotensin and protein kinase C (PKC) actions may cause myocardial dysfunction (5,6), we have studied the effects of ACE and PKC inhibitors on the gene expression profile, glucose metabolism, and functions of the myocardium in diabetes.Cardiovascular protective actions of ACE inhibitors in diabetic patients (5) have been ascribed secondarily to hemodynamic effects or to their additional anti-ischemic and metabolic effects (7,8). High glucose levels can induce functional abnormalities in isolated ventricular myocytes, which are prevented by angiotensin II type 1 receptor blockade (9), suggesting that local angiotensin II may be involved in mediating high glucose-induced effects.Multiple isoforms of the PKC family, a family of 12 serine-threonine kinases, can affect cardiac functions and partially mediate angiotensin II actions. We have previously reported (6) that the ␤-isoform is preferentially activated in the diabetic rat heart. Transgenic mice overexpressing the ␤2 isoform of PKC specifically in the myocardium develop cardiac hypertrophy, fibrosis, impairment of left ventricular performance, and prog...

To evaluate the potential contribution of endothelin-1 (ET-1) toward the cardiovascular complications of diabetes, the present study examined the effects of chronic ET receptor blockade with bosentan on heart function and vascular reactivity in streptozotocin (STZ)-induced diabetic rats. Wistar rats were divided into four groups: control, control bosentan-treated, diabetic, and diabetic bosentan-treated. After chronic bosentan treatment, cardiac function and vascular reactivity were assessed. Exvivo working heart function was determined in terms of rate of contraction (+dP/dt), rate of relaxation (-dP/dt), and left ventricular developed pressure (LVDP). Contractile responses to ET-1 were determined in isolated superior mesenteric arteries. In addition, ET-1-like immunoreactivity was determined in ventricular and vascular tissues by immunohistochemistry. Cardiac function was depressed in the untreated-diabetic group. Bosentan treatment improved working heart function; hearts from the diabetic bosentan-treated group exhibited improved LVDP and -dP/dt. The contractile responses of mesenteric arteries to ET-1 were exaggerated in the untreated-diabetic group. Long-term bosentan treatment normalized these responses. Immunohistochemical analyses revealed increased ET-1-like immunoreactivity in ventricular and vascular tissues from untreated diabetic rats. These data show the beneficial effects of ET(A/B) receptor blockade on cardiovascular function in STZ-diabetic rats. An altered ET-1 system may contribute toward the pathogenesis of cardiovascular dysfunction in diabetes.

Effects of pioglitazone on plasma insulin levels, systolic blood pressure and arterial reactivity were studied in spontaneously hypertensive (SH) rats. Chronic treatment of SH rats with pioglitazone decreased plasma insulin levels and blood pressure. Direct effects of pioglitazone on vascular reactivity were also studied in aortae and superior mesenteric arteries from SH rats. Pioglitazone markedly inhibited arginine vasopressin (AVP) and norepinephrine (NE) responses without affecting responses to potassium chloride (KCl). These data suggest that (a) antihypertensive effects of pioglitazone in SH rats may be mediated via a direct vasodepressor effect, and (b) vasodilation may be coupled to insulin sensitivity in SH rats.