Upregulation of AT2 receptor and iNOS impairs angiotensin II-induced contraction without endothelium influence in young normotensive diabetic rats

Exercise training and vascular heterogeneity in db/db mice: evidence for regional- and duration-dependent effects

Exercise training (ET) has several health benefits; however, our understanding of regional adaptations to ET is limited. We examined the functional and molecular adaptations to short- and long-term ET in elastic and muscular conduit arteries of db/db mice in relation to changes in cardiovascular risk factors. Diabetic mice and their controls were exercised at moderate intensity for 4 or 8 weeks. The vasodilatory and contractile responses of thoracic aortae and femoral arteries isolated from the same animals were examined. Blood and aortic samples were used to measure hyperglycemia, oxidative stress, inflammation, dyslipidemia, protein expression of SOD isoforms, COX, eNOS, and Akt. Short-term ET improved nitric oxide (NO) mediated vasorelaxation in the aortae and femoral arteries of db/db mice in parallel with increased SOD2 and SOD3 expression, reduced oxidative stress and triglycerides, and independent of weight loss, glycemia, or inflammation. Long-term ET reduced body weight in parallel with reduced systemic inflammation and improved insulin sensitivity along with increased SOD1, Akt, and eNOS expression and improved NO vasorelaxation. Exercise did not restore NOS- and COX-independent vasodilatation in femoral arteries, nor did it mitigate the hypercontractility in the aortae of db/db mice; rather ET transiently increased contractility in association with upregulated COX-2. Long-term ET differentially affected the aortae and femoral arteries contractile responses. ET improved NO-mediated vasodilation in both arteries likely due to collective systemic effects. ET did not mitigate all diabetes-induced vasculopathies. Optimization of the ET regimen can help develop comprehensive management of type 2 diabetes.

Nicotine Exposure during Rodent Pregnancy Alters the Composition of Maternal Gut Microbiota and Abundance of Maternal and Amniotic Short Chain Fatty Acids

Tobacco smoking is the leading cause of preventable death. Numerous reports link smoking in pregnancy with serious adverse outcomes, such as miscarriage, stillbirth, prematurity, low birth weight, perinatal morbidity, and infant mortality. Corollaries of consuming nicotine in pregnancy, separate from smoking, are less explored, and the mechanisms of nicotine action on maternal–fetal communication are poorly understood. This study examined alterations in the maternal gut microbiome in response to nicotine exposure during pregnancy. We report that changes in the maternal gut microbiota milieu are an important intermediary that may mediate the prenatal nicotine exposure effects, affect gene expression, and alter fetal exposure to circulating short-chain fatty acids (SCFAs) and leptin during in utero development.

Vitamin D, Thyroid Hormones and Cardiovascular Risk: Exploring the Components of This Novel Disease Triangle

The role of thyroid hormones (THs) in the cardiovascular (CV) system, through several direct and indirect effects is recognized. Even very small modification in TH levels (as those observed in subclinical hypothyroidism or hyperthyroidism, and low triiodothyronine syndrome) may adversely affect the CV system, whereas thyroid hormones benefit the CV system and improve the prognosis. There is also evidence of vitamin D effects on cardiometabolic disease (e.g., through modulation of endothelial and smooth muscle cell activity, renin-angiotensin-aldosterone system, nitric oxide, oxidative stress, and inflammatory response), as well as an association between vitamin D [25(OH)D] deficiency and autoimmune thyroid diseases or cancer, and a relationship between vitamin D concentration and titers of antibodies and thyroid autoimmunity replacement. Interestingly, experimental data indicate a direct effect of vitamin D on Type 2 deiodinase expression causing subsequential peripheral conversion of T4 into T3. However, the functional links among THs, vitamin D and the cardiovascular system, and clinical effects of coexisting abnormalities in this new troublesome triad, have not yet been reviewed. The main aim of this review is to discuss pathophysiology of this relationship, proposing new mechanistic insights involving vitamin D in the modulation of cardiometabolic disease and thyroid profile.

Divergent impact of gestational diabetes mellitus between the thoracic and abdominal rat aorta: Influence of endothelium and angiotensin II receptors

Gestational diabetes mellitus (GDM) affects 5-10% of pregnancies and increases the risk of fetal and maternal adverse outcomes. Interestingly, the vascular response to AngII is decreased by pregnancy while the response is increased by diabetes. It remains unclear how GDM affects vascular tone and how angiotensin II receptors contribute to these changes. In this work, we sought to establish the vascular impact of a hypercaloric diet-induced GDM through changes in AT1 and AT2 receptor's expression. Female rats fed for 7 weeks with standard (SD) or hypercaloric (HD) diet were divided at week 4. Half of the rats of each group were mated to become pregnant and those fed with a HD developed GDM. AngII-induced vasoconstriction was measured in thoracic or abdominal aorta rings using a conventional isolated organ bath and AT1 and AT2 receptors were searched by immunohistochemistry. Experiments where conducted on the pregnant standard diet group (PSD) and the pregnant hypercaloric-gestational diabetes mellitus group (PHD-GDM). Vasoconstriction was reduced in the thoracic aorta (P < 0.05 vs PSD) but increased in the abdominal aorta of PHD-GDM rats (P < 0.05 vs PSD). Blockade of AT2 receptors using PD123319 decreased vasoconstriction, particularly in the abdominal aorta of PHD-GDM animals (P < 0.05 vs PSD). PHD-GDM increased AT1 receptors expression (P < 0.05 vs PSD). Also, PHD-GDM reverted physiologic hypoglycemia and hypotension of healthy pregnancy. Findings provide new insight into the hypercaloric diet induced damage on the vasculature during pregnancy.

Role of the central renin‑angiotensin system in hypertension (Review)

Present in more than one billion adults, hypertension is the most significant modifiable risk factor for mortality resulting from cardiovascular disease. Although its pathogenesis is not yet fully understood, the disruption of the renin-angiotensin system (RAS), consisting of the systemic and brain RAS, has been recognized as one of the primary reasons for several types of hypertension. Therefore, acquiring sound knowledge of the basic science of RAS and the under- lying mechanisms of the signaling pathways associated with RAS may facilitate the discovery of novel therapeutic targets with which to promote the management of patients with cardiovascular and kidney disease. In total, 4 types of angiotensin II receptors have been identified (AT1R-AT4R), of which AT1R plays the most important role in vasoconstriction and has been most extensively studied. It has been found in several regions of the brain, and its distribution is highly associated with that of angiotensin-like immunoreactivity in nerve terminals. The effect of AT1R involves the activation of multiple media and signaling pathways, among which the most important signaling pathways are considered to be AT1R/JAK/STAT and Ras/Raf/MAPK pathways. In addition, the regulation of the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) and cyclic AMP response element-binding (CREB) pathways is also closely related to the effect of ATR1. Their mechanisms of action are related to pro-inflammatory and sympathetic excitatory effects. Central AT1R is involved in almost all types of hypertension, including spontaneous hypertension, salt-sensitive hypertension, obesity-induced hypertension, renovascular hypertension, diabetic hypertension, L-NAME-induced hypertension, stress-induced hypertension, angiotensin II-induced hyper- tension and aldosterone-induced hypertension. There are 2 types of central AT1R blockade, acute blockade and chronic blockade. The latter can be achieved by chemical blockade or genetic engineering. The present review article aimed to high- light the prevalence, functions, interactions and modulation means of central AT-1R in an effort to assist in the treatment of several pathological conditions. The identification of angiotensin-derived peptides and the development of AT-2R agonists may provide a wider perspective on RAS, as well as novel therapeutic strategies.

Angiotensin II Type 2 Receptor: A Target for Protection Against Hypertension, Metabolic Dysfunction, and Organ Remodeling

The renin-angiotensin system is of vital significance not only in the maintenance of blood pressure but also because of its role in the pathophysiology of different organ systems in the body. Of the 2 Ang II (angiotensin II) receptors, the AT₁R (Ang II type 1 receptor) has been extensively studied for its role in mediating the classical functions of Ang II, including vasoconstriction, stimulation of renal tubular sodium reabsorption, hormonal secretion, cell proliferation, inflammation, and oxidative stress. The other receptor, AT₂R (Ang II type 2 receptor), is abundantly expressed in both immune and nonimmune cells in fetal tissue. However, its expression is increased under pathological conditions in adult tissues. The role of AT₂R in counteracting AT₁R function has been discussed in the past 2 decades. However, with the discovery of the nonpeptide agonist C21, the significance of AT₂R in various pathologies such as obesity, hypertension, and kidney diseases have been examined. This review focuses on the most recent findings on the beneficial effects of AT₂R by summarizing both gene knockout studies as well as pharmacological studies, specifically highlighting its importance in blood pressure regulation, obesity/metabolism, organ protection, and relevance in the treatment of coronavirus disease 2019 (COVID-19).

Chronic administration of the angiotensin type 2 receptor agonist C21 improves insulin sensitivity in C57BL/6 mice

The renin-angiotensin system modulates insulin action. Angiotensin type 1 receptor exerts a deleterious effect, whereas the angiotensin type 2 receptor (AT2R) appears to have beneficial effects providing protection against insulin resistance and type 2 diabetes. To further explore the role of the AT2R on insulin action and glucose homeostasis, in this study we administered C57Bl/6 mice with the synthetic agonist of the AT2R C21 for 12 weeks (1 mg/kg per day; ip). Vehicle-treated animals were used as control. Metabolic parameters, glucose, and insulin tolerance, in vivo insulin signaling in main insulin-target tissues as well as adipose tissue levels of adiponectin, and TNF-α were assessed. C21-treated animals displayed decreased glycemia together with unaltered insulinemia, increased insulin sensitivity, and increased glucose tolerance compared to nontreated controls. This was accompanied by a significant decrease in adipocytes size in epididymal adipose tissue and significant increases in both adiponectin and UCP-1 expression in this tissue. C21-treated mice showed an increase in both basal Akt and ERK1/2 phosphorylation levels in the liver, and increased insulin-stimulated Akt activation in adipose tissue. This positive modulation of insulin action induced by C21 appeared not to involve the insulin receptor. In C21-treated mice, adipose tissue and skeletal muscle became unresponsive to insulin in terms of ERK1/2 phosphorylation levels. Present data show that chronic pharmacological activation of AT2R with C21 increases insulin sensitivity in mice and indicate that the AT2R has a physiological role in the conservation of insulin action.

The effects of Ins2(Akita) diabetes and chronic angiotensin II infusion on cystometric properties in mice

AIMS

Diabetes is associated with both dysfunction of the lower urinary tract (LUT) and overactivity of the renin-angiotensin system (RAS). Although it is well known that the RAS affects normal LUT function, very little is known about RAS effects on the diabetic LUT. Accordingly, we investigated the effects of chronic angiotensin II (AngII) treatment on the LUT in a model of type 1 diabetes.

METHODS

Ins2(Akita) diabetic mice (20 weeks old) and their age-matched background controls underwent conscious cystometric evaluation after 4 weeks of chronic AngII treatment (700 ng/kg/min by osmotic pump) or vehicle (saline).

RESULTS

Diabetic mice had compensated LUT function with bladder hypertrophy. Specifically, micturition volume, residual volume, and bladder capacity were all increased, while voiding efficiency and pressure generation were unchanged as bladder mass, contraction duration, and phasic urethral function were increased. AngII significantly increased voiding efficiency and peak voiding pressure and decreased phasic frequency irrespective of diabetic state and, in diabetic but not normoglycemic control mice, significantly decreased residual volume and increased contraction duration and nonphasic contraction duration.

CONCLUSIONS

The Ins2(Akita) diabetic mice had compensated LUT function at 20 weeks of age. Even under these conditions, AngII had beneficial effects on LUT function, resulting in increased voiding efficiency. Future studies should therefore be conducted to determine whether AngII can rescue the decompensated LUT function occurring in end-stage diabetic uropathy.

Upregulation of ERK1/2-eNOS via AT2 receptors decreases the contractile response to angiotensin II in resistance mesenteric arteries from obese rats

It has been clearly established that mitogen-activated protein kinases (MAPKS) are important mediators of angiotensin II (Ang II) signaling via AT1 receptors in the vasculature. However, evidence for a role of these kinases in changes of Ang II-induced vasoconstriction in obesity is still lacking. Here we sought to determine whether vascular MAPKs are differentially activated by Ang II in obese animals. The role of AT2 receptors was also evaluated. Male monosodium glutamate-induced obese (obese) and non-obese Wistar rats (control) were used. The circulating concentrations of Ang I and Ang II, determined by HPLC, were increased in obese rats. Ang II-induced isometric contraction was decreased in endothelium-intact resistance mesenteric arteries from obese compared with control rats and exhibited a retarded AT1 receptor antagonist response. Blocking of AT2 receptors and inhibition of either endothelial nitric oxide synthase (eNOS) or extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) restored Ang II-induced contraction in obese rats. Western blot analysis revealed increased protein expression of AT2 receptors in arteries from obese rats. Basal and Ang II-induced ERK1/2 phosphorylation was also increased in obese rats. Blockade of either AT1 or AT2 receptors corrected the increased ERK1/2 phosphorylation in arteries from obese rats to levels observed in control preparations. Phosphorylation of eNOS was increased in obese rats. Incubation with the ERK1/2 inhibitor before Ang II stimulation did not affect eNOS phosphorylation in control rats; however, it corrected the increased phosphorylation of eNOS in obese rats. These results clearly demonstrate that enhanced AT2 receptor and ERK1/2-induced, NO-mediated vasodilation reduces Ang II-induced contraction in an endothelium-dependent manner in obese rats.

Transition from oxidative stress to nitrosative stress in rostral ventrolateral medulla underlies fatal intoxication induced by organophosphate mevinphos

As the most widely used pesticides in the world, fatal incidence of suicidal poisoning by organophosphate compounds is high and is often associated with cardiovascular toxicity. Using the pesticide mevinphos as our tool, we investigated the roles of oxidative stress and nitrosative stress at the rostral ventrolateral medulla (RVLM), the brain stem site that maintains arterial pressure (AP) and sympathetic vasomotor tone, in the cardiovascular depressive effects of organophosphate poisons. Microinjection of mevinphos (10 nmol) into the RVLM of anesthetized Sprague-Dawley rats induced progressive hypotension that was accompanied by an increase (phase I), followed by a decrease (phase II) of an experimental index of baroreflex-mediated sympathetic vasomotor tone, with a fatality rate of 35%. During phase I, there was a preferential upregulation of angiotensin type I receptor (AT1R) messenger RNA (mRNA) and protein that leads to activation of NADPH oxidase (Nox) and increase in superoxide at the RVLM. Pharmacological antagonism of these signals exacerbated fatality and shorted survival time by eliminating baroreflex-mediated sympathetic vasomotor tone, AP, and heart rate. During phase II, there was a progressive upregulation of angiotensin type II receptor (AT2R) mRNA and protein that leads to increase in peroxynitrite in the RVLM, blockade of both sustained brain stem cardiovascular regulation and improved survival. We further found that AT1R and AT2R cross-interacted at transcriptional and signaling levels in the RVLM. We conclude that a transition from AT1R-mediated oxidative stress to AT2R-mediated nitrosative stress in the RVLM underlies the shift from sustained to impaired brain stem cardiovascular regulation that underpins cardiovascular fatality during mevinphos intoxication.

Emerging role of angiotensin type 2 receptor (AT2R)/Akt/NO pathway in vascular smooth muscle cell in the hyperthyroidism

Hyperthyroidism is characterized by increased vascular relaxation and decreased vascular contraction and is associated with augmented levels of triiodothyronine (T3) that contribute to the diminished systemic vascular resistance found in this condition. T3 leads to augmented NO production via PI3K/Akt signaling pathway, which in turn causes vascular smooth muscle cell (VSMC) relaxation; however, the underlying mechanisms involved remain largely unknown. Evidence from human and animal studies demonstrates that the renin-angiotensin system (RAS) plays a crucial role in vascular function and also mediates some of cardiovascular effects found during hyperthyroidism. Thus, in this study, we hypothesized that type 2 angiotensin II receptor (AT2R), a key component of RAS vasodilatory actions, mediates T3 induced-decreased vascular contraction. Marked induction of AT2R expression was observed in aortas from T3-induced hyperthyroid rats (Hyper). These vessels showed decreased protein levels of the contractile apparatus: α-actin, calponin and phosphorylated myosin light chain (p-MLC). Vascular reactivity studies showed that denuded aortic rings from Hyper rats exhibited decreased maximal contractile response to angiotensin II (AngII), which was attenuated in aortic rings pre-incubated with an AT2R blocker. Further study showed that cultured VSMC stimulated with T3 (0.1 µmol/L) for 24 hours had increased AT2R gene and protein expression. Augmented NO levels and decreased p-MLC levels were found in VSMC stimulated with T3, both of which were reversed by a PI3K/Akt inhibitor and AT2R blocker. These findings indicate for the first time that the AT2R/Akt/NO pathway contributes to decreased contractile responses in rat aorta, promoted by T3, and this mechanism is independent from the endothelium.

Oxidative stress and heart failure in altered thyroid States

Increased or reduced action of thyroid hormone on certain molecular pathways in the heart and vasculature causes relevant cardiovascular derangements. It is well established that hyperthyroidism induces a hyperdynamic cardiovascular state, which is associated with a faster heart rate, enhanced left ventricular systolic and diastolic function whereas hypothyroidism is characterized by the opposite changes. Hyperthyroidism and hypothyroidism represent opposite clinical conditions, albeit not mirror images. Recent experimental and clinical studies have suggested the involvement of ROS tissue damage under altered thyroid status. Altered-thyroid state-linked changes in heart modify their susceptibility to oxidants and the extent of the oxidative damage they suffer following oxidative challenge. Chronic increase in the cellular levels of ROS can lead to a catastrophic cycle of DNA damage, mitochondrial dysfunction, further ROS generation and cellular injury. Thus, these cellular events might play an important role in the development and progression of myocardial remodeling and heart failure in altered thyroid states (hypo- and hyper-thyroidism). The present review aims at elucidating the various signaling pathways mediated via ROS and their modulation under altered thyroid state and the possibility of antioxidant therapy.

Impaired insulin-stimulated myosin phosphatase Rho-interacting protein signaling in diabetic Goto-Kakizaki vascular smooth muscle cells

Insulin resistance associated with Type 2 diabetes contributes to impaired vasorelaxation and therefore contributes to the enhanced incidence of hypertension observed in diabetes. In this study, we examined the role of insulin on the association of the myosin-binding subunit of myosin phosphatase (MYPT1) to myosin phosphatase Rho-interacting protein (MRIP), a relatively novel member of the myosin phosphatase complex that directly binds RhoA in vascular smooth muscle cells (VSMCs). Through a series of molecular and cellular studies, we investigated whether insulin stimulates the binding of MRIP to MYPT1 and compared the results generated from VSMCs isolated from both Wistar-Kyoto (WKY) control and Goto-Kakizaki (GK) diabetic rats. We demonstrate for the first time that insulin stimulates the binding of MRIP to MYPT1 in a dose- and time-dependent manner, as determined by immunoprecipitation, implying a regulatory role for MRIP in insulin-induced vasodilation signaling via MYPT1 interaction. VSMCs from GK model of Type 2 diabetes had impaired insulin-induced MRIP/MYPT1 binding as well as reduced MRIP expression. Adenovirus-mediated overexpression of MRIP in GK VSMCs led to significantly improved insulin-stimulated MRIP/MYPT1 binding. Finally, insulin-stimulated MRIP translocation out of stress fibers, which was observed in control VSMCs, was impaired in GK VSMCs. We believe the impaired expression of MRIP, and therefore decreased insulin-stimulated MRIP/MYPT1 association, in the GK diabetic model may contribute to the impaired insulin-mediated vasodilation observed in the diabetic vasculature and provides a novel therapeutic strategy for the treatment of Type 2 diabetes.

LOX-1 and angiotensin receptors, and their interplay

The renin-angiotensin system (RAS) plays an important role in regulating blood pressure, water-salt balance and the pathogenesis of cardiovascular diseases. Angiotensin II (Ang II) is the physiologically active mediator and mediates the main pathophysiological actions in RAS. Ang II exerts the effects by activating its receptors, primarily type 1 (AT1R) and type 2 (AT2R). Most of the known pathophysiological effects of Ang II are mediated by AT1R activation. The precise physiological function of AT2R is still not clear. Generally, AT2R is considered to oppose the effects of AT1R. Lectin-like oxidized low-density lipoprotein scavenger receptor-1 (LOX-1) is one of the major receptors responsible for binding, internalizing and degrading ox-LDL. The activation of LOX-1 has been known to be related to many pathophysiological events, including endothelial dysfunction and injury, fibroblast growth, and vascular smooth muscle cell hypertrophy. Many of these alterations are present in atherosclerosis, hypertension, and myocardial ischemia and remodeling. A growing body of evidence suggests the existence of a cross-talk between LOX-1 and Ang II receptors. Their interplays are embodied in the reciprocal regulation of their expression and activity. Their interplays are involved in a series of signals. Recent studies suggests that reactive oxygen species (ROS), nitric oxide (NO), protein kinase C (PKC) and mitogen activated protein kinases (MAPKs) are important signals responsible for their cross-talk. This paper reviews these aspects of dyslipidemia and RAS activation.

AT2 receptor signaling and sympathetic regulation

There is a growing consensus that the balance between Angiotensin Type 1 (AT1R) and Angiotensin Type 2 (AT2R) signaling in many tissues may determine the magnitude and, in some cases the direction, of the biological response. Sympatho-excitation in cardiovascular diseases is mediated by a variety of factors and is, in part, dependent on Angiotensin II signaling in the central nervous system. Recent data have provided evidence that the AT2R can modulate sympatho-excitation in animals with hypertension and heart failure. The evidence for this concept is reviewed and a model is put forward to support the rationale that therapeutic targeting of the central AT2R may be beneficial in the setting of chronic heart failure.

High glucose up-regulates angiotensin II subtype 2 receptors via interferon regulatory factor-1 in proximal tubule epithelial cells

Earlier studies have reported an increase in the proximal tubule AT(2) receptor (AT(2)R) expression in diabetes, with a beneficial role in kidney function and blood pressure regulation. Here, we demonstrate that the increase in AT(2)R protein expression is associated with an increased expression of transcription factor IRF-1 in hyperglycemic rat and in high glucose-treated HK2 cells. Knock-down of IRF-1 by siRNA in HK2 cells prevented high glucose-induced AT(2)R up-regulation. The data suggest that IRF-1 is a transcriptional regulator of AT(2)R expression in hyperglycemia, and warrant further studies to understand the physiological role of IRF-1 along with AT(2)R in diabetic kidney.

Targeting the angiotensin II type 2 receptor (AT2R) in colorectal liver metastases

BACKGROUND

Blockade of the angiotensin (ANG) II type 1 receptor (AT1R) inhibits tumour growth in several cancers, including colorectal cancer (CRC) liver metastases. While AT1R blockade has been extensively studied, the potential of targeting the antagonistically acting AT2R in cancer has not been investigated. This study examined the effect of AT2R activation with the agonist CGP42112A in a mouse model of CRC liver metastases.

RESULTS

In vitro, mouse CRC cell (MoCR) proliferation was inhibited by treatment with CGP42112A in a dose dependent manner while apoptosis was increased. Immunofluorescent staining for key signalling and secondary messengers, PLA2 and iNOS, were also increased by CGP42112A treatment in vitro. Immunohistochemical staining for proliferation (PCNA) and the apoptosis (active caspase 3) markers confirmed a CGP42112A-associated inhibition of proliferation and induction of apoptosis of mouse CRC cells (MoCR) in vivo. However, angiogenesis and vascular endothelial growth factor (VEGF) appeared to be increased by CGP42112A treatment in vivo. This increase in VEGF secretion by MoCRs was confirmed in vitro. Despite this apparent pro-angiogenic effect, a syngenic orthotopic mouse model of CRC liver metastases showed a reduction in liver to body weight ratio, an indication of tumour burden, following CGP42112A treatment compared to untreated controls.

CONCLUSIONS

These results suggest that AT2R activation might provide a novel target to inhibit tumour growth. Its potential to stimulate angiogenesis could be compensated by combination with anti-angiogenic agents.

Thyroid hormone stimulates NO production via activation of the PI3K/Akt pathway in vascular myocytes

AIMS

Thyroid hormone (TH) rapidly relaxes vascular smooth muscle cells (VSMCs). However, the mechanisms involved in this effect remain unclear. We hypothesize that TH-induced rapid vascular relaxation is mediated by VSMC-derived nitric oxide (NO) production and is associated with the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signalling pathway.

METHODS AND RESULTS

NO levels were determined using a NO-specific fluorescent dye (DAF-2) and nitrite (NO2-) levels. Expression of NO synthase (NOS) isoforms and proteins of the PI3K/Akt pathway was determined by both western blotting and immunocytochemistry. Myosin light chain (MLC) phosphorylation levels were also investigated by western blotting. Exposure of cultured VSMCs from rat thoracic aortas to triiodothyronine (T3) resulted in a significant decrease of MLC phosphorylation levels. T3 also induced a rapid increase in Akt phosphorylation and increased NO production in a dose-dependent manner (0.001-1 microM). VSMCs stimulated with T3 for 30 min showed an increase in the expression of all three NOS isoforms and augmented NO production, effects that were prevented by inhibitors of PI3K. Vascular reactivity studies showed that vessels treated with T3 displayed a decreased response to phenylephrine, which was reversed by NOS inhibition. These data suggest that T3 treatment induces greater generation of NO both in aorta and VSMCs and that this phenomenon is endothelium independent. In addition, these findings show for the first time that the PI3K/Akt signalling pathway is involved in T3-induced NO production by VSMCs, which occurs with expressive participation of inducible and neuronal NOS.

CONCLUSION

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.

Ang-II-induced Ca(2+) influx is mediated by the 1/4/5 subgroup of the transient receptor potential proteins in cultured aortic smooth muscle cells from diabetic Goto-Kakizaki rats

Angiotensin-II (Ang-II) exerts many of its vascular effects, including the pathophysiological changes associated with type 2 diabetes, through changes in intracellular calcium concentration [Ca(2+)](i). We sought to clarify the mechanism responsible for Ang-II-induced Ca(2+) influx in cultured aortic VSMC using the Goto-Kakizaki (GK) rat model of type 2 diabetes. Ang-II-induced Ca(2+) influx was blocked by neither VDCC nor c-src inhibition but was sensitive to inositol 1,4,5-trisphosphate receptor inhibition, lanthanide and the diacylglycerol analogue, oleoyl-2-acetyl-sn-glycerol. Since transient receptor potential canonical (TRPC)-3 gene expression was undetectable in both WKY and GK VSMCs and TRPC6 gene and protein expression were significantly down-regulated in GK, we believe the 1/4/5 subgroup of TRPC proteins plays a significant role. Furthermore, in GK VSMC the elevated calcium influx observed was not attributable to increased TRPC expression, but rather an alteration of TRPC activity.

Protective role of angiotensin II subtype 2 receptor in blood pressure increase in obese Zucker rats

Earlier, we reported that there was an increase in angiotensin II type 2 (AT(2)) receptor expression in the renal proximal tubule, and selective activation of the AT(2) receptor by AT(2) agonist inhibits Na,K-ATPase activity in the proximal tubules and increases urinary Na excretion in obese Zucker rats. We hypothesized that the AT(2) receptor has a protective role against blood pressure increase in obese Zucker rats. To test this hypothesis, we treated obese Zucker rats with the AT(2) receptor antagonist PD123319 (PD; 30 microg/kg per minute) using osmotic pumps. Age-matched lean rats and vehicle-treated obese Zucker rats served as controls. On day 15 of the treatment with PD, arterial blood pressure was measured by cannulation of the left carotid artery under anesthesia. Control obese rats exhibited higher mean arterial pressure (122.0+/-3.4 mm Hg) compared with lean control rats (97.0+/-4.8 mm Hg). The PD treatment of obese rats raised mean arterial pressure further by 13 mm Hg. The plasma renin activity was significantly increased in the PD-treated obese compared with control-obese or lean rats. Western blot analysis revealed that the PD treatment in obese rats caused an approximately 3-fold increase in the renin expression in the kidney cortex but had no effect on the expression of the cortical angiotensin II type 1 and AT(2) receptors. The present study suggests that the renal AT(2) receptors provide a protective role against blood pressure increase in obese Zucker rats, and this protective effect, in part, could be because of the ability of the AT(2) receptors to keep the kidney renin expression low in obese rats.

Impaired insulin-mediated vasorelaxation in diabetic Goto-Kakizaki rats is caused by impaired Akt phosphorylation

Insulin resistance associated with Type 2 diabetes contributes to impaired vasorelaxation. Previously, we showed the phosphorylation of myosin-bound phosphatase substrate MYPT1, a marker of the vascular smooth muscle cell (VSMC) contraction, was negatively regulated by Akt (protein kinase B) phosphorylation in response to insulin stimulation. In this study we examined the role of Akt phosphorylation on impaired insulin-induced vasodilation in the Goto-Kakizaki (GK) rat model of Type 2 diabetes. GK VSMCs had impaired basal and insulin-induced Akt phosphorylation as well as increases in basal MYPT1 phosphorylation, inducible nitric oxide synthase (iNOS) expression, and nitrite/nitrate production compared with Wistar-Kyoto controls. Both iNOS expression and the inhibition of angiotensin (ANG) II-induced MYPT1 phosphorylation were resistant to the effects of insulin in diabetic GK VSMC. We also measured the isometric tension of intact and denuded GK aorta using a myograph and observed significantly impaired insulin-induced vasodilation. Adenovirus-mediated overexpression of constitutively active Akt in GK VSMC led to significantly improved insulin sensitivity in terms of counteracting ANG II-induced contractile signaling via MYPT1, myosin light chain dephosphorylation, and reduced iNOS expression, S-nitrosylation and survivin expression. We demonstrated for the first time the presence of Akt-independent iNOS expression in the GK diabetic model and that the defective insulin-induced vasodilation observed in the diabetic vasculature can be restored by the overexpression of active Akt, which advocates a novel therapeutic strategy for treating diabetes.