Constrictor responses of resistance arterioles during diabetes mellitus

Phosphatidylinositol 3-kinase-δ up-regulates L-type Ca2+ currents and increases vascular contractility in a mouse model of type 1 diabetes

BACKGROUND AND PURPOSE

Vasculopathies represent the main cause of morbidity and mortality in diabetes. Vascular malfunctioning in diabetes is associated with abnormal vasoconstriction and Ca(2+) handling by smooth muscle cells (SMC). Phosphatidylinositol 3-kinases (PI3K) are key mediators of insulin action and have been shown to modulate the function of voltage-dependent L-type Ca(2+) channels (Ca(V) 1.2). In the present work, we investigated the involvement of PI3K signalling in regulating Ca(2+) current through Ca(V) 1.2 (I(Ca,L) ) and vascular dysfunction in a mouse model of type I diabetes.

EXPERIMENTAL APPROACH

Changes in isometric tension were recorded on myograph. Ca(2+) currents in freshly dissociated mice aortic SMCs were measured using the whole-cell patch-clamp technique. Antisense techniques were used to knock-down the PI3Kδ isoform. KEY RESULTS Contractile responses to phenylephrine and KCl were strongly enhanced in diabetic aorta independent of a functional endothelium. The magnitude of phenylephrine-induced I(Ca,L) was also greatly augmented. PI3Kδ expression, but not PI3Kα, PI3Kβ, PI3Kγ, was increased in diabetic aortas and treatment of vessels with a selective PI3Kδ inhibitor normalized I(Ca,L) and contractile response of diabetic vessels. Moreover, knock-down of PI3Kδin vivo decreased PI3Kδ expression and normalized I(Ca,L) and contractile response of diabetic vessels ex vivo.

CONCLUSIONS AND IMPLICATIONS

Phosphatidylinositol 3-kinase δ was essential to the increased vascular contractile response in our model of type I diabetes. PI3Kδ signalling was up-regulated and most likely accounted for the increased I(Ca,L,) leading to increased vascular contractility. Blockade of PI3Kδ may represent a novel therapeutic approach to treat vascular dysfunction in diabetic patients.

Early inhibition of EGFR signaling prevents diabetes-induced up-regulation of multiple gene pathways in the mesenteric vasculature

Diabetes mellitus is associated with vascular complications including an impairment of vascular function and alterations in the reactivity of blood vessels to vasoactive hormones. However, the signaling mechanisms leading to vascular dysfunction in diabetes are not fully understood. This microarray-based study was designed to identify differential gene expression between the normal and diabetic mesenteric vasculature and to investigate the effect of inhibiting epidermal growth factor receptor (EGFR) signaling on global gene expression in the mesenteric bed of streptozotocin (STZ)-induced diabetic rats. Transcriptome analysis was performed in triplicate using oligonucleotide microarrays housing 10,000 rat genes on the mesenteric bed of normal, diabetic, and diabetic rats treated with AG1478, a selective inhibitor of EGFR. Four weeks of diabetes led to a profound alteration in gene expression within the mesenteric bed with 1167 of the 3074 annotated genes being up-regulated and 141 genes down-regulated by at least 2-fold. The up-regulated gene ontologies included receptor tyrosine kinases, G-protein coupled receptors and ion channel activity. In particular, significant overexpressions of colipase, phospholipase A2, carboxypeptidases, and receptor tyrosine kinases such as EGFR, erbB2 and fibroblast growth factor receptor were observed in diabetes mesenteric vasculature. A 4-week intraperitoneal treatment of diabetic animals with AG1478 (1.2 mg/kg/alt diem) beginning on the same day as STZ injection prevented up-regulation of the majority (approximately 95%) of the genes associated with STZ diabetes including those apparently "unrelated" to the known EGFR pathway without correction of hyperglycemia. These results suggest that activation of EGFR signaling is a key initiating step that leads to induction of multiple signaling pathways in the development of diabetes-induced vascular dysfunction. Thus, therapeutic targeting of EGFR may represent a novel strategy for the prevention and/or treatment of vascular dysfunction in diabetes.

Phosphoinositide 3-kinase contributes to diabetes-induced abnormal vascular reactivity in rat perfused mesenteric bed

Phosphatidylinositol 3-kinase (PI3K) is a signaling enzyme that plays key roles in vascular growth, proliferation, and cellular apoptosis and is implicated in modulating vascular smooth muscle contractility. The aim of this study was to determine whether PI3K contributes to development of diabetes-induced abnormal vascular reactivity to selected vasoactive agonists. The effect of 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), a selective PI3K inhibitor, on isolated perfused mesenteric vascular bed from streptozotocin (STZ)-diabetic rats was investigated. Changes in perfusion pressure, which reflected peripheral resistance, were measured using isolated perfused mesenteric vascular beds. Our results showed that STZ treatment produced an increase in the vasoconstrictor response to norepinephrine (NE), angiotensin II (Ang II) and endothelin-1 (ET-1), and an attenuated vasodilator response to carbachol and histamine in the isolated perfused mesenteric vascular bed from STZ-diabetic animals. Chronic inhibition of PI3K with LY294002 resulted in prevention of diabetes-induced abnormal vascular reactivity to the vasoactive agonists. However, the high blood glucose levels were not normalized. Results of this study indicate that selective inhibition of PI3K can attenuate the development of diabetes-induced abnormal vascular responsiveness in the isolated perfused mesenteric vascular bed.

Angiotensin-(1-7) prevents diabetes-induced cardiovascular dysfunction

The aim of this study was to test the hypothesis that treatment with angiotensin-(1-7) [ANG-(1-7)] or ANG-(1-7) nonpeptide analog AVE-0991 can produce protection against diabetes-induced cardiovascular dysfunction. We examined the influence of chronic treatment (4 wk) with ANG-(1-7) (576 microg.kg(-1).day(-1) ip) or AVE-0991 (576 microg.kg(-1).day(-1) ip) on proteinuria, vascular responsiveness of isolated carotid and renal artery ring segments and mesenteric bed to vasoactive agonists, and cardiac recovery from ischemia-reperfusion in streptozotocin-treated rats (diabetes). Animals were killed 4 wk after induction of diabetes and/or treatment with ANG-(1-7) or AVE-0991. There was a significant increase in urine protein (231 +/- 2 mg/24 h) in diabetic animals compared with controls (88 +/- 6 mg/24 h). Treatment of diabetic animals with ANG-(1-7) or AVE-0991 resulted in a significant reduction in urine protein compared with vehicle-treated diabetic animals (183 +/- 16 and 149 +/- 15 mg/24 h, respectively). Treatment with ANG-(1-7) or AVE-0991 also prevented the diabetes-induced abnormal vascular responsiveness to norepinephrine, endothelin-1, angiotensin II, carbachol, and histamine in the perfused mesenteric bed and isolated carotid and renal arteries. In isolated perfused hearts, recovery of left ventricular function from 40 min of global ischemia was significantly better in ANG-(1-7)- or AVE-0991-treated animals. These results suggest that activation of ANG-(1-7)-mediated signal transduction could be an important therapeutic strategy to reduce cardiovascular events in diabetic patients.

Cerebral vascular dysfunction in TallyHo mice: a new model of Type II diabetes

The purpose of this study was to characterize vascular responses and to examine mechanisms of vascular dysfunction in TallyHo mice, a new polygenic model of Type II diabetes. Responses of cerebral arterioles and carotid arteries were examined in vivo by using a cranial window and in vitro by using tissue baths, respectively. Dilatation of cerebral arterioles (baseline diameter = 33 +/- 1 micro m) in response to acetylcholine, but not to nitroprusside, was markedly reduced (P < 0.05) in TallyHo mice. Responses of cerebral arterioles to acetylcholine in TallyHo mice were restored to normal with polyethylene glycol-superoxide dismutase (100 U/ml; a superoxide scavenger). Responses to acetylcholine were also greatly impaired (P < 0.05) in the carotid arteries from TallyHo mice. Phenylephrine- and serotonin-, but not to KCl- or U46619-, induced contraction was increased two- to fourfold (P < 0.05) in carotid arteries of TallyHo mice. Responses to phenylephrine and serotonin were reduced to similar levels in the presence of Y-27632 (an inhibitor of Rho kinase; 3 micro mol/l). These findings provide the first evidence that vascular dysfunction is present in TallyHo mice and that oxidative stress and enhanced activity of Rho kinase may contribute to altered vascular function in this genetic model of Type II diabetes.

Signal transduction through Ras-GTPase and Ca2+/ calmodulin-dependent protein kinase II contributes to development of diabetes-induced renal vascular dysfunction

This study examined the role of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and Ras-GTPase in the development of abnormal reactivity to vasoactive agents in the renal artery of diabetic rats. The vasoconstrictor response induced by norepinephrine (NE), endothelin-1 (ET-1) or angiotensin II (Ang II) was significantly increased whereas vasodilator response to carbachol, histamine or sodium nitroprusside (SNP) was not altered in the renal artery segments of the streptozotocin (STZ)-diabetic rats. Chronic intraperitoneal administration of KN-93 (5 mg/kg/ alt diem), an inhibitor of CaMKII or FPTIII (1.5 mg/kg/ alt diem), an inhibitor of Ras-GTPase, produced significant normalization of the altered agonist-induced vasoconstrictor responses without affecting blood glucose levels. All the inhibitors were administered for four weeks starting from day one of diabetes induction. Inhibition of Ras-GTPase or CaMKII did not affect the agonist-induced vasoconstrictor and vasodilator responses in the non-diabetic control animals. These data suggest that inhibition of signal transduction involving CaMKII and Ras-GTPase can prevent development of diabetes-induced abnormal vascular reactivity in the renal artery.

Phosphoinositide 3-kinase mediated signalling contributes to development of diabetes-induced abnormal vascular reactivity of rat carotid artery

Diabetes mellitus is associated with vascular complications, including an impairment of vascular function and alterations in the reactivity of blood vessels to vasoactive agents. Phosphatidylinositol 3-kinase (PI3K) is a signalling enzyme that plays key roles in vascular growth, proliferation and cellular apoptosis and is implicated in modulating vascular smooth muscle contractility. The aim of this study was to determine whether PI3K plays a role in development of diabetes-induced altered vascular reactivity to selected vasoconstrictors and vasodilators. The effect of 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), a selective PI3K inhibitor, on isolated segments of carotid arteries from streptozotocin (STZ)-diabetic rats was investigated. Ring segments of the isolated carotid arteries were mounted in organ baths to measure changes in isometric tension. Our results showed that STZ treatment produced an increase in the vasoconstrictor response to norepinephrine (NE), angiotensin II (Ang II) and endothelin-1 (ET-1) and an attenuated vasodilator response to carbachol and histamine in the isolated carotid arteries from STZ-diabetic animals. Diabetes-induced impaired vascular responsiveness to the vasoactive agonists was prevented by chronic inhibition of PI3K by LY294002 even though blood glucose levels remained high. This is the first study to show that selective inhibition of PI3K can attenuate the development of diabetes-induced abnormal vascular reactivity in the isolated carotid arteries of diabetic rats.

Insulin resistance does not impair contractile responses of cerebral arteries

Insulin resistance (IR) impairs endothelium-mediated vasodilation in cerebral arteries as well as K+ channel function in vascular smooth muscle. Peripheral arteries also show an impaired endothelium-dependent vasodilation in IR and concomitantly show an enhanced contractile response to endothelin-1 (ET-1). However, the contractile responses of the cerebral arteries in IR have not been examined systematically. This study examined the contractile responses of pressurized isolated middle cerebral arteries (MCAs) in fructose-fed IR and control rats. IR MCAs showed no difference in pressure-mediated (80 mmHg) vasoconstriction compared to controls, either in time to develop spontaneous tone (control: 61+/-3 min, n=30; IR: 63+/-2 min, n=26) or in the degree of that tone (control: 60 min: 33+/-2%, n=22 vs. IR 60 min: 34+/-3%, n=17). MCAs treated with ET-1 (10(-8.5) M) constrict similarly in control (53+/-3%, n=14) and IR (53+/-3%, n=14) arteries. Constrictor responses to U46619 (10(-6) M) are also similar in control (48+/-9%, n=8) and IR (42+/-5%, n=6) MCAs as are responses to extraluminal uridine 5'-triphosphate (UTP; 10(-4.5) M) (control: 35+/-7%, n=11 vs. IR: 38+/-3%, n=10). These findings demonstrate that constrictor responses remain intact in IR despite a selective impairment of dilator responses and endothelial and vascular smooth muscle K+ channel function in cerebral arteries. Thus, it appears that the increased susceptibility to cerebrovascular abnormalities associated with IR and diabetes (including cerebral ischemia, stroke, vertebrobasilar transient ischemic attacks) is not due to an enhanced vasoreactivity to constrictor agents.

Effect of chronic endothelin blockade on PKC isoform distribution in mesenteric arteries from diabetic rats

Hemodynamic changes, including increased vasoconstriction and reduced blood flow have been detected in both human diabetic patients and in animal models of diabetes. We previously demonstrated that the endothelin (ET) system was upregulated and involved in mediating the exaggerated vasoconstrictor responses in superior mesenteric artery (SMA) from diabetic rats. Chronic treatment of diabetic rats with the dual endothelin receptor antagonist, bosentan abolished the enhanced contractile responses in diabetic SMA. The biological actions of ET-1 have been shown to be coupled to the hydrolysis of phosphotidylinositol 4,5-biphosphate and phosphotidylcholine and the subsequent production of diacylglycerol (DAG). DAG is an activator of the classical and novel isoforms of PKC. Increases in PKC activity, associated with translocation of specific PKC isoforms from the cytosol to the membrane, have been implicated in the vasoconstrictor effect of ET-1. The goal of the present study was to determine whether chronic treatment of diabetic rats with bosentan influences the activation of specific PKC isoforms in SMA from diabetic rats. Elevated levels of PKCbeta2 in both the cytosol and membrane fractions and PKCepsilon in the membrane fraction were detected in SMA from diabetic rats. However, neither the levels nor the distribution between the cytosol and membrane fractions of any of these PKC isoforms were affected by the treatment of the diabetic rats with bosentan. These observations indicate that bosentan improves vascular reactivity in STZ-diabetic rats by mechanisms other than correction of increased activities of PKC isoforms.

Epidermal growth factor receptor tyrosine kinase-mediated signalling contributes to diabetes-induced vascular dysfunction in the mesenteric bed

In order to characterize the roles of tyrosine kinases (TKs) and epidermal growth factor receptor (EGFR) in diabetes-induced vascular dysfunction, we investigated the ability of a chronic administration of genistein, a broad-spectrum inhibitor of TKs and AG1478, a specific inhibitor of EGFR TK activity to modulate the altered vasoreactivity of the perfused mesenteric bed to common vasoconstrictors and vasodilators in streptozotocin (STZ)-induced diabetes in rats. The vasoconstrictor responses induced by norepinephrine (NE), endothelin-1 (ET-1) and angiotensin II (Ang II), were significantly increased, whereas vasodilator responses to carbachol and histamine were significantly reduced in the perfused mesenteric bed of STZ-induced diabetic rats in comparison with healthy rats. Treatment of diabetic animals with genistein or AG1478 produced a significant normalization of the altered agonist-induced vasoconstrictor and vasodilator responses without affecting blood glucose levels. In contrast, neither inhibitor had any effect on the vascular responsiveness of control (nondiabetic) animals. Treatment of diabetic animals with diadzein, an inactive analogue of genistein, did not affect the vasoconstrictor and vasodilator responses in control or diabetic animals. Phosphorylated EGFR levels were markedly raised in the mesenteric bed from diabetic animals and were normalized upon treatment with AG1478 or genistein. These data suggest that activation of TK-mediated pathways, including EGFR TK signalling are involved in the development of diabetic vascular dysfunction.

Diabetes-Induced Renal Vascular Dysfunction Is Normalized by Inhibition of Epidermal Growth Factor Receptor Tyrosine Kinase

Contribution of receptor tyrosine kinase activation to development of diabetes-induced renal artery dysfunction is not known. We investigated the ability of a chronic administration of genistein, a broad-spectrum inhibitor of tyrosine kinases (TKs), and AG1478, a specific inhibitor of epidermal growth factor receptor (EGFR) TK activity, to modulate the altered vasoreactivity of isolated renal artery ring segments to common vasoconstrictors in streptozotocin-induced diabetes. In diabetic renal artery, the vasoconstrictor responses induced by norepinephrine, endothelin-1 and angiotensin II were significantly increased. Inhibition of TKs or the EGFR pathway did not affect the agonist-induced vasoconstrictor responses in the non-diabetic control animals. However, inhibition of TKs by genistein or EGFR TK by AG1478 treatment produced a significant normalization of the altered agonist-induced vasoconstrictor responses without affecting blood glucose levels. Treatment with diadzein, an inactive analogue of genistein, did not affect the vasoconstrictor responses in the diabetic animals. Western blotting showed that phosphorylated EGFR protein levels were increased in vehicle-treated diabetic animals. In renal arteries from AG1478-treated diabetic animals, EGFR protein levels were similar to non-diabetic control animals. These data suggest that activation of TK-mediated pathways, including the EGFR TK signalling pathway, are involved in the development of diabetic vascular dysfunction in the renal artery.

The role of tyrosine kinase-mediated pathways in diabetes-induced alterations in responsiveness of rat carotid artery

1 G-protein-coupled receptor signalling, including transactivation of receptor tyrosine kinases (RTKs), has been implicated in vascular pathology. However, the role of specific RTKs in the development of diabetes-induced cardiovascular complications is not known. 2 We investigated the ability of a chronic administration of genistein, a broad-spectrum inhibitor of tyrosine kinases (TKs), AG1478, a specific inhibitor of epidermal growth factor receptor (EGFR) TK activity, and AG825, a specific inhibitor of Erb2, to modulate the altered vasoreactivity of isolated carotid artery ring segments to common vasoconstrictors and vasodilators in streptozotocin (STZ)-induced diabetes. 3 In diabetic carotid artery, the vasoconstrictor responses induced by noradrenaline (NE), endothelin-1 (ET-1), and angiotensin II (Ang II), were significantly increased whereas vasodilator responses to carbachol and histamine were significantly reduced. Inhibition of TKs, EGFR or Erb2 pathway did not affect the body weight or agonist-induced vasoconstrictor and vasodilator responses in the non-diabetic control animals. However, inhibition of TKs by genistein, EGFR TK by AG1478 or Erb2 by AG825 treatment produced a significant normalization of the altered agonist-induced vasoconstrictor responses without affecting blood glucose levels. Treatment with diadzein, an inactive analogue of genistein, did not affect the vasoconstrictor and vasodilator responses in the diabetic animals. 4 Treatment with genistein, AG1478 or AG825 resulted in a significant improvement in diabetes-induced impairment in endothelium-dependent relaxation to carbachol and histamine. 5 These data suggest that activation of TK-mediated pathways, including EGFR TK signalling and Erb2 pathway, are involved in the development of diabetic vascular dysfunction in the carotid artery.

Histamine-induced vasodilation in the perfused kidney of STZ-diabetic rats: role of EDNO and EDHF

In this study, we have examined the contribution of endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) to histamine-induced endothelium-dependent relaxation in the perfused kidney of rats treated with streptozotocin (STZ) to induce diabetes. Histamine-induced vasodilatation in the perfused kidney preparations of both control and diabetic animals, which was not significantly different. Sodium nitroprusside (SNP)-induced relaxation was also not affected in diabetic and control rats. In order to isolate the EDHF component of histamine-induced vasodilator response, L-NAME (10(-4)M) and indomethacin (10(-6)M) were added to the Krebs' solution throughout the experiment. TBA (0.5 mM) produced a significant reduction in histamine-induced maximal vasodilator response in both preparations from control and diabetic animals, indicating the involvement of K+ channels in mediating this response. Charybdotoxin (0.05 microM) but not glibenclamide (0.1 microM) produced significant reduction in histamine-induced vasodilator responses. To test the contribution of EDNO in mediating histamine-induced vasodilatation, the vascular preparations were perfused with 20 mM K+ -Krebs' solution to inhibit the EDHF component of the response. Under this condition, histamine-induced vasodilator response was not significantly different in both preparations from control and diabetic rats. Pre-treatment with L-NAME (10(-4)M) attenuated histamine-induced vasodilatation. There was a more significant attenuation in histamine-induced vasodilatation in the vascular preparations from diabetic rats. The vasodilator effect of calcium ionophore A23187 was investigated in preparations from control and diabetic rats to examine receptor dysfunction associated with diabetes. A23187 produced dose-dependent vasodilator response in the preparations from both control and diabetic rats. In conclusion, our results indicate that histamine-induced vasodilatation in the perfused kidney of the STZ-induced diabetic rats is mediated by the two vasodilator components, namely EDHF and EDNO. The EDHF component was not significantly affected by diabetes. However, histamine-induced vasodilatation mediated by the EDNO component was more significantly reduced in diabetic rats. Results have also indicated that the EDHF component of histamine-induced vasodilatation was mediated through Ca2+ -activated K+ channels in perfused kidney preparations from both control and diabetic rats.

New in vitro model to study high glucose-dependent endothelial dysfunctions

Several thrombogenic abnormalities are associated with diabetes. Since endothelial dysfunction occurs at early stages of disease, it may reflect pathophysiological changes that are responsible for alterations in vascular structure, growth and modifications of adhesivity to platelets and leukocytes, leading to atherosclerosis and thrombosis. Predisposing factors of vascular diseases, such as diabetes, are also associated with endothelial dysfunction. Restoration or replacement of endothelium-related factors like nitric oxide impede the progression of vascular thrombogenic diseases, and prevent the action of vasoconstrictor factors such as endothelin or other prothrombotic factors such as plasminogen-activator inhibitor-1. Since high glucose concentration in blood is the hallmark of diabetes and because the vascular lesions of atherosclerosis are localized in large artheries, we have cultured endothelial cells from the human aorta. Two endothelial cell strains from the same aortic tract that show different characteristics and behavior in high glucose were isolated. Such findings reflect the importance to have well characterized and standardized cell culture systems to carry out experiments to study the glucose-dependent atherosclerotic process in vitro. Our cell strains may represent a useful in vitro model to study the complex pathophysiology of diabetes-related atherosclerosis.

Neural regulation of submandibular gland blood flow in the streptozotocin-diabetic rat: evidence for impaired endothelium-dependent vasodilatation

Functional changes in vascular tone and reactivity arise early in diabetes, and endothelial dysfunction plays a central role in the development of these microvascular abnormalities. Blood flow in the rat submandibular gland is mainly under neural regulation, which is mediated in part via endothelium-dependent mechanisms. Given the role of the endothelium in regulating blood flow and the deleterious effects of diabetes on endothelial cell function, we hypothesised that diabetes would significantly impair neural regulation of submandibular gland vascular perfusion. Three weeks after the induction of streptozotocin diabetes continuous 2 Hz sympathetic stimulation resulted in a similar degree of vasoconstriction (as measured by a decrease in perfusion) in both diabetic (-31+/-17%) and control rats (-22+/-7%). However, the magnitude and the duration of the after-dilatation were significantly less in diabetic animals. The same number of impulses delivered at 20 Hz in bursts (1s in every 10s) also resulted in vasoconstriction with each burst, but unlike the effects of burst stimulation in control rats the initial vasoconstriction was not converted to a net vasodilatation between bursts. Parasympathetic stimulation (2, 5 and 10 Hz) caused a marked vasodilatation in both control and diabetic rats, but the initial responses were delayed in diabetic animals, the maintained phases were smaller in magnitude (P<0.02) and it took longer to return to resting levels. In conclusion, submandibular gland vascular responses are altered in streptozotocin-induced diabetic rats. Vasoconstrictor responses evoked by sympathetic impulses were unaffected, but vasodilatory responses, particularly those associated with endothelium-dependent mechanisms, were significantly reduced.

Inhibition of Ras-GTPase improves diabetes-induced abnormal vascular reactivity in the rat perfused mesenteric vascular bed

OBJECTIVE

The signalling mechanisms involved in regulating altered vascular reactivity in diabetes are not fully understood. The aim of this study was to investigate the role of Ras-GTPase in the development of abnormal vascular reactivity in diabetes.

MATERIALS AND METHODS

We investigated the ability of chronic administration of FPTIII (1.5 mg/kg), an inhibitor of Ras-GTPase, to modulate the altered vasoreactivity of the rat perfused mesenteric bed to common vasoconstrictors and vasodilators in streptozotocin (STZ)-induced diabetes.

RESULTS

The vasoconstrictor responses induced by norepinephrine (NE) and endothelin-1 (ET-1) were significantly increased whereas vasodilator responses to carbachol, histamine and isoprenaline were significantly reduced in the perfused mesenteric bed of the STZ-diabetic rats. Inhibition of Ras-GTPase by chronic administration of FPTIII produced a significant normalization of the altered agonist-induced vasoconstrictor and vasodilator responses without affecting blood glucose levels. Inhibition of Ras-GTPase did not affect the agonist-induced vasoconstrictor and vasodilator responses in the control animals.

CONCLUSION

These data suggest that signal transduction pathways activated by Ras-GTPase are involved in the development of diabetic vascular dysfunction. Potential strategies aimed at modifying actions of signal transduction pathways involving Ras-GTPase may therefore prove to be beneficial in treatment of vascular complications in diabetes.

Augmented Contractile Response of Vascular Smooth Muscle in a Diabetic Mouse Model

The vasomotor properties of isolated aortae and mesenteric arteries of insulin-resistant ob/ob and 57CBL/6J mice were compared in organ bath studies. Vessels from ob/ob mice were more sensitive to phenylephrine. Pretreatment with L-NAME caused similar leftward shifts of the phenylephrine concentration response curves in diabetic and non-diabetic vessels. The ob/ob aortae contracted in response to phenylephrine with roughly twice the force while they were not stiffer than control aortae. L-NAME caused a greater percentage increase in maximal force in the control than in the ob/ob tissue. Denudation potentiated force in the control aortae, but not in the ob/ob aortae. Endothelium-dependent relaxation in the ob/ob aortae and mesenteric arteries was impaired as manifested by a decreased sensitivity and maximal relaxation to acetylcholine, while the aortic basal eNOS mRNA levels did not differ between the two strains. In addition, ob/ob aortae were less sensitive to the nitric oxide donor sodium nitroprusside. Inhibition of endogenous prostaglandin synthesis with indomethacin (10 microM) partly normalized the contractile response of the ob/ob aortae and enhanced their endothelium-dependent relaxation. Neither blockade of endothelin-1 receptors (bosentan, 10 microM) nor PKC inhibition (calphostin, 1 microM) affected the contractile response to phenylephrine in the mouse aortae of either strain. In conclusion, vascular dysfunction in the aorta and mesenteric artery of ob/ob mice are due to increased smooth muscle contractility and impaired dilation but not to changes in elasticity of the vascular wall. Endothelium-produced prostaglandins contribute to the increased vasoconstriction.

Inhibition of calcium/calmodulin-dependent protein kinase II normalizes diabetes-induced abnormal vascular reactivity in the rat perfused mesenteric vascular bed

1. Calcium/calmodulin-dependent protein kinase II (CaMKII) has an important function in mediating insulin release but its role in the development of diabetes-induced cardiovascular complications is not known. 2. We investigated the ability of a chronic administration of KN-93 (5 mg kg(-1) alt diem for 4 weeks), an inhibitor of CaMKII, to modulate the altered vasoreactivity of the perfused mesenteric bed to common vasoconstrictors and vasodilators in streptozotocin (STZ)-induced diabetes. 3. The vasoconstrictor responses induced by noradrenaline (NE), endothelin-1 (ET-1), and angiotensin II (Ang II), were significantly increased whereas, vasodilator responses to carbachol and histamine were significantly reduced in the perfused mesenteric bed of the STZ-diabetic rats as compared with non-diabetic controls. 4. Inhibition of CaMKII by KN-93 treatment did not affect blood glucose levels but produced a significant normalization of the altered agonist-induced vasoconstrictor and vasodilator responses. KN-93 did not affect agonist-induced responses in control animals. In addition, KN-93 significantly reduced weight loss in diabetic rats. 5. The present data suggest that CaMKII is an essential mediator in the development of diabetic vascular dysfunction and may also play an important role in signalling pathways leading to weight loss during diabetes.

Exaggerated coronary reactivity to endothelin-1 in diabetes: reversal with bosentan

We previously demonstrated that chronic endothelin receptor blockade (with bosentan) improved functional cardiac performance in streptozotocin-diabetic rats, suggesting a novel role of endothelin-1 (ET-1) in modulating diabetic heart dysfunction. To gain insight into the mechanism(s) underlying this effect, we examined the coronary vascular responses to ET-1 in hearts from diabetic and control rats treated with or without bosentan. Rats were divided into control, control-treated, diabetic, and diabetic-treated groups. The control-treated and diabetic-treated groups received bosentan (100 mg x kg(-1) x d(-1)) for 8 weeks. Following treatment, hearts were isolated and perfused, and coronary reactivity to ET-1 was assessed by measuring the changes in coronary perfusion pressure in response to ET-1 (50 and 100 pM). Additionally, maximal coronary blood flow (assessed with 10(-5) M adenosine) was measured in isolated perfused hearts. The key observation is that coronary reactivity to ET-1 was significantly higher in the diabetic than the control rats. This effect was normalized in diabetic rats chronically receiving bosentan. Maximal coronary vasodilation did not differ between the four groups. In conclusion, the reactivity of ET-1 is altered in the isolated perfused coronary vascular bed from diabetic rats, and chronic ET receptor blockade restores this reactivity to control values. These observations provide a possible mechanism for the improvement in diabetic heart function observed after chronic bosentan treatment.

Chronic bosentan treatment improves renal artery vascular function in diabetes

OBJECTIVE

Endothelin-1 (ET-1) has been suggested to play an important role in the pathogenesis of diabetes-induced vascular complications. The primary purpose of the present study was to examine the potential beneficial effects of chronic ET receptor blockade (with bosentan) on vascular function in renal arteries from streptozotocin (STZ)-induced diabetic rats.

DESIGN

Wistar rats were divided into four groups: control (C), control bosentan-treated (CB), diabetic (D) and diabetic bosentan-treated (DB). Following 10 weeks of bosentan treatment, vascular responses to norepinephrine (NE), ET-1, acetylcholine (ACh) were determined in vascular segments of renal arteries, both with and without the endothelium denuded, according to the following protocol: (1) a cumulative dose-response curve (DRC) to NE in the absence and presence of the nitric oxide synthase (NOS) inhibitor L-NAME (2) cumulative DRC to ET-1 and (3) cumulative DRC to ACh in precontracted arteries. In addition, plasma ET-1 was assayed and ET-1-like immunoreactivity was determined in vascular tissues by immunohistochemistry.

RESULTS

The maximum contractile responses to NE and ET-1 were markedly exaggerated in endothelium-intact renal arteries from untreated D rats while ACh responses were preserved. Arteries denuded of endothelium did not exhibit exaggerated responses to NE or ET-1. L-NAME treatment did not affect responses to NE in arteries with or without endothelium. Strikingly, responses to NE and ET-1 (in arteries with endothelium) were completely normalized following long-term bosentan treatment. In addition, plasma ET-1 levels did not differ between C and D groups. However, renal arteries isolated from the D group exhibited increased ET-1-like immunoreactivity (local ET-1 content).

CONCLUSION

These data uncover, for the first time, beneficial effects of mixed ETA/ETB receptor blockade on renal artery vascular function in diabetes. Alterations in the production and/or action of ET-1 may have important implications in the development of vascular dysfunction in experimental diabetes.