Several studies have implicated the renin angiotensin system in the cardiac hypertrophy induced by thyroid hormone. However, whether Angiotensin type 1 receptor (AT1R) is critically required to the development of T3-induced cardiomyocyte hypertrophy as well as whether the intracellular mechanisms that are triggered by AT1R are able to contribute to this hypertrophy model is unknown. To address these questions, we employed a selective small interfering RNA (siRNA, 50 nM) or an AT1R blocker (Losartan, 1 microM) to evaluate the specific role of this receptor in primary cultures of neonatal cardiomyocytes submitted to T3 (10 nM) treatment. The cardiomyocytes transfected with the AT1R siRNA presented reduced mRNA (90%, P < 0.001) and protein (70%, P < 0.001) expression of AT1R. The AT1R silencing and the AT1R blockade totally prevented the T3-induced cardiomyocyte hypertrophy, as evidenced by lower mRNA expression of atrial natriuretic factor (66%, P < 0.01) and skeletal alpha-actin (170%, P < 0.01) as well as by reduction in protein synthesis (85%, P < 0.001). The cardiomyocytes treated with T3 demonstrated a rapid activation of Akt/GSK-3beta/mTOR signaling pathway, which was completely inhibited by the use of PI3K inhibitors (LY294002, 10 microM and Wortmannin, 200 nM). In addition, we demonstrated that the AT1R mediated the T3-induced activation of Akt/GSK-3beta/mTOR signaling pathway, since the AT1R silencing and the AT1R blockade attenuated or totally prevented the activation of this signaling pathway. We also reported that local Angiotensin I/II (Ang I/II) levels (120%, P < 0.05) and the AT1R expression (180%, P < 0.05) were rapidly increased by T3 treatment. These data demonstrate for the first time that the AT1R is a critical mediator to the T3-induced cardiomyocyte hypertrophy as well as to the activation of Akt/GSK-3beta/mTOR signaling pathway. These results represent a new insight into the mechanism of T3-induced cardiomyocyte hypertrophy, indicating that the Ang I/II-AT1R-Akt/GSK-3beta/mTOR pathway corresponds to a potential mediator of the trophic effect exerted by T3 in cardiomyocytes.

Our data strongly indicate that T3 causes NO-dependent rapid relaxation of VSMC and that this effect is mediated by the PI3K/Akt signalling pathway.

-The present study assessed the possible involvement of the renin-angiotensin system (RAS) and the sympathetic nervous system (SNS) in thyroxine (T 4)-induced cardiac hypertrophy. Hemodynamic parameters, heart weight (HW), ratio of HW to body weight (HW/BW), and myocyte width were evaluated in absence of thyroid hormone (hypothyroidism) and after T 4 administration. Male Wistar rats were used. Some were subjected to thyroidectomies, whereas hyperthyroidism was induced in others via daily intraperitoneal injection of T 4 (25 or 100 g ⅐ 100 g BW Ϫ1 ⅐ day Ϫ1 ) for 7 days. In some cases, T4 administration was combined with the angiotensin I-converting enzyme inhibitor enalapril (Ena), with the angiotensin type 1 (AT1) receptor blocker losartan (Los) or with the ␤-adrenergic blocker propanolol (Prop). Hemodynamics and morphology were then evaluated. Systolic blood pressure (SBP) was not altered by administration of either T4 alone or T4 in combination with the specific inhibitors. However, SBP decreased significantly in hypothyroid rats. An increased heart rate was seen after administration of either T4 alone or T4 in combination with either Los or Ena. Although the higher dose of T 4 significantly increased HW, HW/BW increased in both T 4-treated groups. Ena and Prop inhibited the increase in HW or HW/BW in hyperthyroid rats. Morphologically, both T 4 dose levels significantly increased myocyte width, an occurrence prevented by RAS or SNS blockers. There was a good correlation between changes in HW/BW and myocyte width. These results indicate that T4-induced cardiac hypertrophy is associated with both the SNS and the RAS. cardiac myocytes; thyroid hormone; angiotensin-converting enzyme; angiotensin II receptors CHANGES IN HEMODYNAMIC LOADING appear to be an important stimulus for cardiac growth. However, dissociation between elevated arterial pressure and increased myocardial mass has been demonstrated in hypertensive cardiac hypertrophy in animals and humans (25). This dissociation suggests that, in addition to blood pressure, various stimuli are involved in the development and regression of cardiac hypertrophy (25). Over the past several decades, many neural and hormonal stimuli have been implicated in cardiac muscle growth, including, but not limited to, ␣-and ␤-adrenergic agonists, ANG II, glucocorticoids, insulin, growth hormone, glucagon, and thyroxine (T 4 ) (25).Mechanisms of cardiac hypertrophy produced by elevated T 4 include a direct effect of the hormone on the heart and indirect effects related to stimulation of the adrenergic nervous system or altered left ventricular loading conditions. Decreased systemic vascular resistance and the subsequent increase in cardiac work contribute to this T 4 -induced hypertrophy (15, 25). However, in support of a direct effect of thyroid hormone on heart growth, some authors have observed that T 4 -induced cardiac hypertrophy in isolated heart preparations is accompanied by increased (31) quantity and rate of protein and ribosome synthesis (33).It is well established t...

There have been only a few reports on the sympathoadrenal and renin-angiotensin systems in children of small gestational age. The purpose of the present study was to investigate plasma levels of ACE (angiotensin-converting enzyme) activity, angiotensin and catecholamines in 8- to 13-year-old children and to determine whether there are correlations between the components of these systems with both birthweight and BP (blood pressure) levels. This clinical study included 66 children (35 boys and 31 girls) in two groups: those born at term with an appropriate birthweight [AGA (appropriate-for-gestational age) group, n=31] and those born at term but with a small birthweight for gestational age [SGA (small-for-gestational age) group, n=35]. Concentrations of angiotensin, catecholamines and ACE activity were determined in plasma. Circulating noradrenaline levels were significantly elevated in SGA girls compared with AGA girls (P=0.036). In addition, angiotensin II and ACE activity were higher in SGA boys (P=0.024 and P=0.050 respectively). There was a significant association of the circulating levels of both angiotensin II and ACE activity with BP levels in our study population. Although the underlying mechanisms that link restricted fetal growth with later cardiovascular events are not fully understood, the findings in the present study support the link between low birthweight and overactivity of both sympathoadrenal and renin-angiotensin systems into later childhood.

Although most of effects of Angiotensin II (Ang II) related to cardiac remodelling can be attributed to type 1 Ang II receptor (AT(1)R), the type 2 receptor (AT(2)R) has been shown to be involved in the development of some cardiac hypertrophy models. In the present study, we investigated whether the thyroid hormone (TH) action leading to cardiac hypertrophy is also mediated by increased Ang II levels or by change on AT(1)R and AT(2)R expression, which could contribute to this effect. In addition, we also evaluated the possible contribution of AT(2)R in the activation of Akt and in the development of TH-induced cardiac hypertrophy. To address these questions, Wistar rats were treated with thyroxine (T(4), 0.1 mg/kg BW/day, i.p.), with or without AT(2)R blocker (PD123319), for 14 days. Cardiac hypertrophy was identified based on heart/body weight ratio and confirmed by analysis of atrial natriuretic factor mRNA expression. Cardiomyocyte cultures were used to exclude the influence of TH-related hemodynamic effects. Our results demonstrate that the cardiac Ang II levels were significantly increased (80%, P < 0.001) as well as the AT(2)R expression (50%, P < 0.05) in TH-induced cardiac hypertrophy. The critical involvement of AT(2)R to the development of this cardiac hypertrophy in vivo was evidenced after administration of AT(2) blocker, which was able to prevent in 40% (P < 0.01) the cardiac mass gain and the Akt activation induced by TH. The role of AT(2)R to the TH-induced cardiomyocyte hypertrophy was also confirmed after using PD123319 in the in vitro studies. These findings improve understanding of the cardiac hypertrophy observed in hyperthyroidism and provide new insights into the generation of future therapeutic strategies.

No abstract

Bicarbonate reabsorption was evaluated by stationary microperfusion "in vivo" early distal (ED) and late distal (LD) segments of at kidney. Intratubular pH was recorded by double-barreled of H+ exchange resin/reference (1 M KCl) microelectrodes for the determination of HCO3- reabsorption. In the presence of angiotensin II (ANG II) (10(-12) M), a significant increase in HCO3- reabsorption was observed both in ED (from 0.930 +/- 0.060 to 2.64 +/- 0.210 nmol.cm-2.s-1 in luminally perfused tubules and from 0.850 +/- 0.040 to 2.03 +/- 0.210 nmol.cm-2.s-1 during capillary perfusion) and LD segments from 0.310 +/- 0.130 to 2.16 +/- 0.151 nmol.cm-2.s-1 during luminal perfusion and from 0.530 +/- 0.031 to 2.16 +/- 0.211 nmol.cm-2.s-1 with capillary perfusion). The addition of the AT1-receptor antagonist losartan (10(-6) M) to luminal perfusion blocked luminal ANG II-mediated stimulation in ED and LD segments. 5-(N,N-hexamethylene)amiloride (10(-4) M) added to luminal perfusion inhibited luminal ANG II-mediated stimulation in ED (by 81%) and LD (by 54%) segments. The addition of bafilomycin A1 (2 x 10(-7) M) to luminal perfusion does not affect luminal ANG II-mediated stimulation in ED segments but reduces it in LD segments (by 33%). During the addition of atrial natriuretic peptide (ANP) (10(-6) M) or ANG II plus ANP in both segments, no significant differences in HCO3- reabsorption were observed. Our results indicate that luminal ANG II acts to stimulate Na+/H+ exchange in ED and LD segments via activation of AT1 receptors, as well as the vacuolar H(+)-adenosinetriphosphatase in LD segments. ANP does not affect HCO3- reabsorption in either ED or LD segments and does not impair the stimulation caused by ANG II.

Studies were conducted in rats to determine the effect of maternal diabetes and the consequent hyperglycemia on cardiovascular function in the offspring. Diabetes was induced in pregnant Wistar rats through streptozotocin injection (50 mg/kg). Cardiovascular parameters were measured in 2-mo-old offspring animals of diabetic (OD, n ϭ 12) and control rats (OC, n ϭ 8). Arterial pressure (AP), heart rate (HR), baroreflex sensitivity, and vascular responsiveness to phenylephrine (PH) and sodium nitroprusside (SN) were measured. Angiotensinconverting enzyme (ACE) activity in heart, kidney, and lung was determined. OD rats exhibited increases in systolic AP (138 Ϯ 8 vs. 119 Ϯ 6 mmHg, OD vs. OC), with no change in HR (342 Ϯ 21 vs. 364 Ϯ 39 beats per minute (bpm), OD vs. OC). The reflex tachycardia elicited by SN was reduced in OD rats, as indicated by the slope of the linear regression (Ϫ2.2 Ϯ 0.4 vs. Ϫ3.6 Ϯ 0.8 bpm/mmHg, OD vs. OC). Vascular responsiveness to PH was increased 63% in OD rats compared with OC. OD rats showed increases in ACE activity in heart, kidney, and lung (1.13 Ϯ 0.24, 3.04 Ϯ 0.86, 40.8 Ϯ 8.9 vs. 0.73 Ϯ 0.19, 1.7 Ϯ 0.45, 28.1 Ϯ 6 nmol His-Leu ⅐ min Ϫ1 mg protein Ϫ1 , OD vs. OC). Results suggest that diabetes during pregnancy affects cardiovascular function in offspring, seen as hypertension, baroreflex dysfunction, and activation of tissue renin-angiotensin system. cardiovascular; heart rate; development; angiotensin-converting enzyme; renin-angiotensin system; hyperglycemia EVIDENCE SUGGESTS THAT THE mother's lifestyle may have longlasting effects on offspring. For example, smoking, alcohol consumption, and presence of disease states such as diabetes and hypertension during pregnancy all affect fetal development (8,27). Alterations in fetal development could contribute to pathologies in the adult. With regard to diabetes, even when treated, the maternal disease has profound consequences on the fetus, seen as changes in brain, pancreas, lung, kidney, and heart (2, 14, 21, 44).To study diabetes in the experimental setting, chemical toxins have been widely used. Streptozotocin (STZ) is a pancreatic toxin that induces hyperglycemia, hypoinsulinemia, polyuria, and weight loss in rats (9,28,38,45). When STZinduced hyperglycemia is present during pregnancy, there are changes in fetal development and metabolism, including growth restriction and abnormal pancreatic function (5, 22, 36). Epidemiological and animal studies have shown that low birth weight increases the incidence of cardiovascular disease and diabetes mellitus in adulthood (3). Intrauterine growth restriction produced by placental insufficiency in pregnant rats was associated with marked elevation in blood pressure of the offspring (1). Adult offspring of STZ-diabetic rats also showed signs of cardiovascular dysfunction, seen as a reduced response to endothelium-dependent vasodilators and enhanced norepinephrine-induced vasoconstriction (23).There is evidence for an association between the development of diabetes and the activation of the reni...