Impaired endothelium-dependent relaxation in isolated resistance arteries of spontaneously diabetic rats

Rutin ameliorates nitrergic and endothelial dysfunction on vessels and corpora cavernosa of diabetic animals

Endothelial dysfunction is an early complication of diabetes and it is related to both micro- and macroangiopathies. In addition, >70% of diabetic patients develop autonomic neuropathies. Increased oxidative stress has a major role in the development of both nitrergic and endothelial dysfunction. The aim of this work is to evaluate whether rutin, a potent antioxidant, could ameliorate nitrergic and/or endothelial dysfunction in diabetic animals. Primary and secondary treatment protocols with rutin were investigated on rat aortic rings and the mesenteric arteriolar bed, and on rabbit aortic rings and corpora cavernosa (RbCC) from both euglycemic and alloxan-diabetic animals. Acetylcholine endothelium-dependent and sodium nitroprusside endothelium-independent relaxations were compared in tissues from euglycemic or diabetic animals. Electrical field stimulation (EFS)-induced relaxation was performed only in the RbCC. Endothelial-dependent relaxations were blunted by 40% in vessels and neuronal relaxation was blunted by 50% in RbCC taken from diabetic animals when compared to euglycemic animals. Pre-treatment with rutin restored both neuronal and endothelial dependent relaxations in diabetic animals towards the values achieved in control euglycemic tissues. Rutin was able to ameliorate both endothelial dysfunction and nitrergic neuropathy in animal experimental models. Rutin could be a lead compound in the primary or secondary preventive ancillary treatment of endothelial and nitrergic dysfunction in the course of diabetes.

Capsaicin Alleviates Vascular Endothelial Dysfunction and Cardiomyopathy via TRPV1/eNOS Pathway in Diabetic Rats

Background

Endothelial dysfunction and cardiomyopathy are considered to be important vascular complications associated with diabetes. This study was designed to investigate whether capsaicin (CAP), a selective TRPV1 agonist, could prevent diabetes-induced endothelial dysfunction and cardiomyopathy.

Methods

Male Sprague Dawley rats aged 8 weeks were injected intraperitoneally with streptozotocin (STZ, 50 mg/kg) to establish the diabetes model. The diabetic rats were randomly divided into the untreated diabetes group (DM, 10/group) and diabetes plus CAP treatment group (DM+CAP, 10/group); meanwhile, the nondiabetic healthy rats were used as normal controls (10/group). DM+CAP group were treated with CAP by gavage for 8 weeks. The cultured mouse vascular endothelial cells were exposed to different concentrations of glucose in the presence or absence of CAP treatment. The TRPV1 inhibitor capsazepine (CPZ) and eNOS inhibitor L-NAME were used in vivo and in vitro experiment.

Results

CAP treatment significantly decreased the serum total cholesterol (TC) and total triglyceride (TG) and ameliorated the pathogenesis and fibrosis in the heart, while did not significantly improve plasma glucose level and the body weights of diabetic rats. In addition, CAP enhanced the expression of TRPV1 and eNOS in the heart and normalized the vascular permeability under diabetic state. Similarly, CAP treatment also increased nitric oxide and reduced reactive oxygen species. The same results were observed in cultured mouse vascular endothelial cells by CAP treatment. These beneficial effects of CAP were abolished by either CPZ or L-NAME.

Conclusions

CAP might protect against hyperglycemia-induced endothelial dysfunction and diabetic cardiomyopathy through TRPV1/eNOS pathway.

Heart failure in diabetes

Heart failure and cardiovascular disorders represent the leading cause of death in diabetic patients. Here we present a systematic review of the main mechanisms underlying the development of diabetic cardiomyopathy. We also provide an excursus on the relative contribution of cardiomyocytes, fibroblasts, endothelial and smooth muscle cells to the pathophysiology of heart failure in diabetes. After having described the preclinical tools currently available to dissect the mechanisms of this complex disease, we conclude with a section on the most recent updates of the literature on clinical management.

Nitric Oxide Resistance, Induced in the Myocardium by Diabetes, Is Circumvented by the Nitric Oxide Redox Sibling, Nitroxyl

Aim: Impairment of tissue responsiveness to exogenous and endogenous nitric oxide (NO^•), known as NO^• resistance, occurs in many cardiovascular disease states, prominently in diabetes and especially in the presence of marked hyperglycemia. In this study, we sought to determine in moderate and severe diabetes (i) whether NO^• resistance also occurs in the myocardium, and (ii) whether the NO^• redox sibling nitroxyl (HNO) circumvents this. Results: The spectrum of acute NO^• effects (induced by diethylamine-NONOate), including vasodilation, and enhanced myocardial contraction and relaxation were impaired by moderately diabetic rats ([blood glucose] ∼20 mM). In contrast, acute HNO effects (induced by isopropylamine-NONOate) were preserved even in more severe diabetes ([blood glucose] >28 mM). Intriguingly, the positive inotropic effects of HNO were significantly enhanced in diabetic rat hearts. Further, progressive attenuation of soluble guanylyl cyclase (sGC) contribution to myocardial NO^• responses occurred with increasing severity of diabetes. Nevertheless, activation of sGC by HNO remained intact in the myocardium. Innovation: Diabetes is associated with marked attenuation of vascular and myocardial effects of NO and NO donors, and this NO^• resistance is circumvented by HNO, suggesting potential therapeutic utility for HNO donors in cardiovascular emergencies in diabetics. Conclusion: These results provide the first evidence that NO^• resistance occurs in diabetic hearts, and that HNO largely circumvents this problem. Further, the positive inotropic and lusitropic effects of HNO are enhanced in a severely diabetic myocardium, a finding that warrants further mechanistic interrogation. The results support a potential role for therapeutic HNO administration in acute treatment of ischemia and/or heart failure in diabetics.

Exploring the role of orexin B-sirtuin 1-HIF-1α in diabetes-mellitus induced vascular endothelial dysfunction and associated myocardial injury in rats

AIM

The present study explored the role and possible interrelationship between orexin B-sirtuin 1-HIF-1α signaling pathways in diabetes-mellitus induced vascular dysfunction and enhancement in myocardial injury.

MATERIAL AND METHODS

Streptozotocin (60 mg/kg) was employed to induce diabetes mellitus in male Wistar albino rats, which were kept for eight weeks. The vascular function was noted by assessing acetylcholine-induced relaxation in norepinephrine precontracted mesenteric arteries. The hearts were subjected to ischemia-reperfusion injury on the Langendorff apparatus. Myocardial injury was assessed by noting the release of CK-MB, cardiac troponin and measuring myocardial infarction. The levels of orexin B, sirtuin 1 and HIF-1α were measured. YNT-185 (orexin B type 2 receptor agonist), STR2104 (sirtuin 1 agonist) and EX527 (sirtuin 1 antagonist) were employed as pharmacological tools.

RESULTS

Diabetes led to significant development of vascular dysfunction and enhanced ischemia-reperfusion injury in isolated hearts. There was a significant decrease in the levels of orexin B, sirtuin 1 and HIF-1α in diabetic animals. Treatment with YNT-185 and/or STR2104 significantly attenuated the diabetes-induced increase in myocardial injury and vascular dysfunction. Co-administration of EX527 abolished the effects of YNT-185 suggesting orexin B-mediated effects may be through activation of sirtuin 1. Moreover, YNT-185-induced increase in the expression of sirtuin 1 and HIF-1α was also abolished in the presence of EX527.

CONCLUSION

Diabetes-induced significant decline in orexin B levels in the plasma along with a decrease in the expression of sirtuin 1 and HIF-1α in the heart following ischemia-reperfusion injury may possibly contribute in exacerbating the myocardial injury and vascular dysfunction.

Vascular endothelial dysfunction, a major mediator in diabetic cardiomyopathy

Diabetes mellitus is currently a major public health problem. A common complication of diabetes is cardiac dysfunction, which is recognized as a microvascular disease that leads to morbidity and mortality in diabetic patients. While ischemic events are commonly observed in diabetic patients, the risk for developing heart failure is also increased, independent of the severity of coronary artery disease and hypertension. This diabetes-associated clinical entity is considered a distinct disease process referred to as "diabetic cardiomyopathy". However, it is not clear how diabetes promotes cardiac dysfunction. Vascular endothelial dysfunction is thought to be one of the key risk factors. The impact of diabetes on the endothelium involves several alterations, including hyperglycemia, fatty acid oxidation, reduced nitric oxide (NO), oxidative stress, inflammatory activation, and altered barrier function. The current review provides an update on mechanisms that specifically target endothelial dysfunction, which may lead to diabetic cardiomyopathy.

O-Linked β-N-acetylglucosamine (O-GlcNAc) modification: a new pathway to decode pathogenesis of diabetic retinopathy

The incidence of diabetes continues to rise among all ages and ethnic groups worldwide. Diabetic retinopathy (DR) is a complication of diabetes that affects the retinal neurovasculature causing serious vision problems, including blindness. Its pathogenesis and severity is directly linked to the chronic exposure to high glucose conditions. No treatments are currently available to stop the development and progression of DR. To develop new and effective therapeutic approaches, it is critical to better understand how hyperglycemia contributes to the pathogenesis of DR at the cellular and molecular levels. We propose alterations in O-GlcNAc modification of target proteins during diabetes contribute to the development and progression of DR. The O-GlcNAc modification is regulated through hexosamine biosynthetic pathway. We showed this pathway is differentially activated in various retinal vascular cells under high glucose conditions perhaps due to their selective metabolic activity. O-GlcNAc modification can alter protein stability, activity, interactions, and localization. By targeting the same amino acid residues (serine and threonine) as phosphorylation, O-GlcNAc modification can either compete or cooperate with phosphorylation. Here we will summarize the effects of hyperglycemia-induced O-GlcNAc modification on the retinal neurovasculature in a cell-specific manner, providing new insight into the role of O-GlcNAc modification in early loss of retinal pericytes and the pathogenesis of DR.

ENDOTHELIUM-DEPENDENT VASCULAR REACTIVITY IN DIABETES MELLITUS TYPE 2

The review presents modern information on the development of disorders of endothelium-dependent vascular reactivity in diabetes mellitus (DM) type 2. In type 2 DM, disorders of endothelium-dependent vascular reactivity associated with hyperglycemia and oxidative stress, manifesting by a reduced vascular response to vasodilators and pressor (paradoxical) vascular reactions to them, directly associated with cardiovascular events are observed.

Mild type 2 diabetes mellitus improves remote endothelial dysfunction after acute myocardial infarction

AIMS

Myocardial infarction (MI) is a common cause of mortality in patients with diabetes mellitus (DM) and vascular dysfunction is a major component of diabetic cardiomyopathy. We investigated the systemic influence of acute MI on the diabetes-induced pathogenic changes in the rat aorta.

METHODS

Nondiabetic Wistar (W) and type-2 diabetic Goto-Kakizaki (GK) rats underwent 45min of left anterior descending coronary artery occlusion followed by 24h of reperfusion. Isometric force was measured using organ bath.

RESULTS

Plasma glucose-levels were significantly higher in diabetic rats (GK+sham: 13±2mM; GK+MI: 19±2mM) compared to nondiabetic rats (W+sham: 8±0mM; W+MI: 8±1mM). Acetylcholine-induced relaxation was significantly weaker in rings from W+MI and GK+MI rats compared to corresponding sham-operated animals. Myocardial reperfusion injury was smaller in GK+MI than W+MI rats, and the concentration-response curves to acetylcholine were significantly enhanced in rings from GK+MI than W+MI rats. Nevertheless, the relaxation response to acetylcholine was similar in W+sham and GK+sham. Densitometric analysis of bands for endothelial nitric oxide synthase showed a significant decrease in W+MI rats compared to W+sham and GK+sham animals. Aortas from both GK+sham and GK+MI rats showed impaired contractile responses to phenylephrine in comparison with the nondiabetics.

CONCLUSIONS

For the first time we showed that short-term and mild type-2 DM improved remote endothelial dysfunction after reperfused acute MI.

Activation of peroxisome proliferator-activated receptor-β/-δ (PPARβ/δ) prevents endothelial dysfunction in type 1 diabetic rats

Endothelial dysfunction plays a key role in the pathogenesis of diabetic vascular disease. Herein, we have analyzed if the peroxisome proliferator-activated receptor-β/-δ (PPARβ/δ) agonist GW0742 exerts protective effects on endothelial function in type 1 diabetic rats. The rats were divided into 4 groups: control, control-treated (GW0742, 5 mg kg(-1)day(-1) for 5 weeks), diabetic (streptozotocin injection), and diabetic-treated. GW0742 administration in diabetic rats did not alter plasma glucose, systolic blood pressure, or heart rate, but reduced plasma triglyceride levels. The vasodilatation induced by acetylcholine was decreased in aortas from diabetic rats. GW0742 restored endothelial function, increasing eNOS phosphorylation. Superoxide production, NADPH oxidase activity, and mRNA expression of prepro endothelin-1, p22(phox), p47(phox), and NOX-1 were significantly higher in diabetic aortas, and GW0742 treatment prevented these changes. In addition, GW0742 prevented the endothelial dysfunction and the upregulation of prepro endothelin-1 and p47(phox) after the in vitro incubation of aortic rings with high glucose and these effects were prevented by the PPARβ/δ antagonist GSK0660. PPARβ/δ activation restores endothelial function in type 1 diabetic rats. This effect seems to be related to an increase in nitric oxide bioavailability as a result of reduced NADPH oxidase-driven superoxide production and downregulation of prepro endothelin-1.

Alpha lipoic acid treatment improved endothelium-dependent relaxation in diabetic rat aorta

The aim of this study was to ascertain the effects of α-lipoic acid (ALA) treatment on relaxant responses of acetylcholine (ACh) and isoprenaline (ISO) in aortic rings precontracted with serotonin (5-HT, 10(-6) M) obtained from streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in the rats by 50 mg/kg streptozotocin (STZ) via an intraperitoneal injection. Rat body and aorta weights were measured. The isometric tension to ACh (10(-9)-3×10(-6) M) and ISO (10(-9)-10(-4) M) of 5-HT-precontracted diabetic and non-diabetic rat (control), diabetic-ALA-treated, and ALA-treated aortas, in organ baths were recorded. Six weeks after STZ treatment blood glucose was elevated compared to control rats. In aortic rings from diabetic rats ACh and ISO-induced relaxations were impaired whereas endothelium-independent relaxation to sodium nitroprusside (SNP) was unaffected. ALA (100 mg/kg/day) treatment for 5 weeks enhanced ACh and ISO-induced relaxation in diabetic aortas. This recovering effect was via NO because prevented by incubating the vessels with N(G)-nitro-L-arginine methyl ester (L-NAME, a NOS inhibitor). It may be assumed that ALA treatment in vivo, can protect against impaired vascular responsiveness in STZ-induced diabetic rats.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

Oxygen-derived free radicals mediate endothelium-dependent contractions in femoral arteries of rats with streptozotocin-induced diabetes

BACKGROUND AND PURPOSE

The present experiments were designed to study the contribution of oxygen-derived free radicals to endothelium-dependent contractions in femoral arteries of rats with streptozotocin-induced diabetes.

EXPERIMENTAL APPROACH

Rings with and without endothelium were suspended in organ chambers for isometric tension recording. The production of oxygen-derived free radicals in the endothelium was measured with 2',7'-dichlorodihydrofluorescein diacetate using confocal microscopy. The presence of protein was measured by western blotting.

KEY RESULTS

In the presence of L-NAME, the calcium ionophore A23187 induced larger endothelium-dependent contractions in femoral arteries from diabetic rats. Tiron, catalase, deferoxamine and MnTMPyP, but not superoxide dismutase reduced the response, suggesting that oxygen-derived free radicals are involved in the endothelium-dependent contraction. In the presence of L-NAME, A23187 increased the fluorescence signal in femoral arteries from streptozotocin-treated, but not in those from control rats, confirming that the production of oxygen-derived free radicals contributes to the enhanced endothelium-dependent contractions in diabetes. Exogenous H2O2 caused contractions in femoral arterial rings without endothelium which were reduced by deferoxamine, indicating that hydroxyl radicals contract vascular smooth muscle and thus could be an endothelium-derived contracting factor in diabetes. The reduced presence of Mn-SOD and the decreased activity of catalase in femoral arteries from streptozotocin-treated rats demonstrated the presence of a redox abnormality in arteries from rats with diabetes.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that the redox abnormality resulting from diabetes increases oxidative stress which facilitates and/or causes endothelium-dependent contractions.

Mechanisms of endothelial dysfunction with development of type 1 diabetes mellitus: role of insulin and C-peptide

Complications associated with insulin-dependent diabetes mellitus (type-1diabetes) primarily represent vascular dysfunction that has its origin in the endothelium. While many of the vascular changes are more accountable in the late stages of type-1diabetes, changes that occur in the early or initial functional stages of this disease may precipitate these later complications. The early stages of type-1diabetes are characterized by a diminished production of both insulin and C-peptide with a significant hyperglycemia. During the last decade numerous speculations and theories have been developed to try to explain the mechanisms responsible for the selective changes in vascular reactivity and/or tone and the vascular permeability changes that characterize the development of type-1diabetes. Much of this research has suggested that hyperglycemia and/or the lack of insulin may mediate the observed functional changes in both endothelial cells and vascular smooth muscle. Recent studies suggest several possible mechanisms that might be involved in the observed decreases in vascular nitric oxide (NO) availability with the development of type-1 diabetes. In addition more recent studies have indicated a direct role for both endogenous insulin and C-peptide in the amelioration of the observed endothelial dysfunction. These results suggest a synergistic action between insulin and C-peptide that facilitates increase NO availability and may suggest new clinical treatment modalities for type-1 diabetes mellitus.

Augmented endothelium-derived hyperpolarizing factor-mediated relaxations attenuate endothelial dysfunction in femoral and mesenteric, but not in carotid arteries from type I diabetic rats

Individual vascular beds exhibit differences in vascular reactivity. The present study investigates the effects of streptozotocin-induced type I diabetes on endothelium-dependent responses of rat carotid, femoral, and mesenteric arteries. Rings with and without endothelium, suspended in organ chambers for isometric tension recording, were contracted with phenylephrine and exposed to increasing concentrations of acetylcholine. In carotid and femoral arteries, acetylcholine produced concentration- and endothelium-dependent relaxations that were abolished by Nomega-nitro-L-arginine methyl ester (L-NAME; specific nitric-oxide synthase inhibitor) and were impaired slightly in preparations from streptozotocin-treated rats (STZ-rats). This impairment could be prevented by L-arginine. In femoral arteries incubated with L-NAME, acetylcholine caused endothelium-dependent contractions that were abolished by 3-[(6-amino-(4-chlorobenzensulfonyl)-2-methyl-5,6,7,8-tetrahydronapht]-1-yl) propionic acid (S18886) (antagonist of thromboxane A2/prostaglandins H2-receptors) and reversed to relaxation by indomethacin (inhibitor of cyclooxygenase). The latter relaxation was inhibited by charybdotoxin plus apamin, suggesting a role of endothelium-dependent hyperpolarizing factor (EDHF). This EDHF-mediated component was augmented slightly in arteries from STZ-rats. In mesenteric arteries, relaxations to acetylcholine were only partially inhibited by L-NAME, and the L-NAME-resistant component was abolished by charybdotoxin plus apamin. In the mesenteric arteries from STZ-rats, L-NAME-sensitive relaxations to acetylcholine were reduced and the EDHF-component was augmented. These findings demonstrate a marked heterogeneity in endothelium-dependent responses in rat arteries and their differential adaptation in the course of type I diabetes. In particular, the EDHF-mediated component not only compensates for the reduced bioavailability of nitric oxide in the femoral and mesenteric artery but also counteracts the augmented endothelium-dependent contractions in the former.

The nitric oxide synthesis/pathway mediates the inhibitory serotoninergic responses of the pressor effect elicited by sympathetic stimulation in diabetic pithed rats

We investigated the involvement of the nitric oxide pathway in the inhibitory mechanisms of 5-hydroxytryptamine (5-HT) in the pressor responses induced by stimulation of sympathetic vasopressor outflow in diabetic pithed rats. Diabetes was induced in male Wistar rats by a single s.c. injection of alloxan. Four weeks later, the animals were anaesthetized, pretreated with atropine, and pithed. Electrical stimulation of the sympathetic outflow from the spinal cord (0.1, 0.5, 1 and 5 Hz) resulted in frequency-dependent increases in blood pressure. The inhibition of electrically induced pressor responses by 5-HT (10 microg/kg/min) in diabetic pithed rats could not be elicited after i.v. treatment with 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 microg/kg), a guanylyl cyclase inhibitor, or N-omega-L-Arginine methyl ester hydrochloride (L-NAME) (10 mg/kg), a nitric oxide synthase (NOS) inhibitor. The inhibitory effect produced by infusion of the selective 5-HT(1A) receptor agonist 8-hydroxydipropylaminotretalin hydrobromide (8-OH-DPAT) (20 microg/kg/min) was abolished in the presence of ODQ (10 microg/kg), or L-NAME (10 mg/kg) in diabetic pithed rats. The administration of L-Arginine (100 mg/kg) 30 min after L-NAME reproduced the inhibitory effect caused by 5-HT (10 microg/kg/min) and 8-OH-DPAT (20 microg/kg/min) on the electrically induced pressor responses, whereas in the presence of D-Arginine (100 mg/kg)+L-NAME the 5-HT or 8-OH-DPAT inhibitory effect on the pressor responses was abolished. In conclusion, in diabetic pithed rats, the inhibition produced by prejunctional 5-HT(1A) activation on electrically induced sympathetic pressor responses is mediated by the NO synthesis/pathway.

Effects of angiotensin II receptor antagonist on impaired endothelium-dependent and endothelium-independent relaxations in type II diabetic rats

BACKGROUND

Diabetes mellitus is an important risk factor for cardiovascular diseases, and vasodilator dysfunction may contribute to vascular complications in diabetes. We previously demonstrated that the angiotensin II receptor blocker (ARB) corrected the impaired endothelium-derived hyperpolarizing factor (EDHF)-mediated arterial hyperpolarization and relaxation associated with hypertension or aging, partially independently of blood pressure.

OBJECTIVE

To test whether EDHF-mediated, as well as endothelium-independent, relaxations would be altered in arteries from type II diabetic Goto-Kakizaki rats, and whether ARB would correct these alterations.

METHODS

Goto-Kakizaki rats were treated with either the ARB candesartan or a combination of hydralazine and hydrochlorothiazide for 8 weeks, beginning at 10 weeks of age. Membrane potentials and contractile responses were recorded from the isolated mesenteric arteries.

RESULTS

The two treatments lowered blood pressure comparably. Acetylcholine-induced, EDHF-mediated hyperpolarization and relaxation in mesenteric arteries were markedly impaired in untreated Goto-Kakizaki rats compared with age-matched Wistar rats, and neither ARB nor the combination therapy improved these responses. On the other hand, relaxations to endothelium-derived nitric oxide, assessed in rings precontracted with high potassium solution, were similar among the four groups. Relaxation to the nitric oxide donor sodium nitroprusside and that to levcromakalim, an ATP-sensitive K-channel opener, were also impaired in untreated Goto-Kakizaki rats, and the response to sodium nitroprusside was partially improved in treated Goto-Kakizaki rats.

CONCLUSIONS

These findings suggest that EDHF-mediated hyperpolarization and relaxation and endothelium-independent relaxations are both impaired in arteries of type II diabetic rats, and antihypertensive treatment with or without ARB partially corrects endothelium-independent relaxations to the nitric oxide donor but not EDHF-mediated responses.

Time-Dependent Changes in Antioxidant Enzymes and Vascular Reactivity of Aorta in Streptozotocin-Induced Diabetic Rats Treated With Curcumin

In the present study changes in oxidative stress and vascular reactivity in aortic rings of chronic streptozotocin-diabetic (STZ-CON) and nondiabetic (ND-CON) rats is studied at 4 weekly intervals up to 24 weeks. The effect of chronic curcumin (200 mg/kg) treatment was also studied. Blood glucose and blood pressure levels were significantly higher in the STZ-CON group and curcumin administration had no significant effect on it. Superoxide dismutase and catalase activity were either unchanged or significantly increased during the early stage of diabetes whereas during the medium and late stage were significantly reduced. Reduced glutathione and lipid peroxidation levels significantly decreased as time after STZ administration increased. Phenylephrine (PE)-induced contraction was significantly (P < 0.05) increased during the early stage of diabetes, whereas it was significantly (P < 0.05) reduced at the medium and late stage of diabetes. Acetylcholine (Ach)-induced relaxation significantly decreased with respect to time after STZ administration. Sodium nitroprusside (SNP)-induced relaxation was unaltered up to initial stage but after medium stage there was a rightward shift and the pD2 value significantly decreased. Though curcumin treatment had no significant effect on superoxide dismutase, catalase, and reduced glutathione levels, it significantly reduced lipid peroxidation compared with diabetic control. Curcumin treatment attenuated the phenylephrine-induced increase in contraction during the early stage. However, curcumin treatment had no significant effect at the medium and late stage. Though curcumin administration improved Ach-induced relaxation it did not restore it to normal. Inability of curcumin to prevent oxidative stress during the late stage may be due to the fact that chronic diabetes (hyperglycemia) leads to excessive production of free radicals. Hence the present study shows that variations reported in antioxidant enzymes and vascular reactivity are due to the duration of diabetes or time after diabetes induction in STZ model and this can not be completely reversed by chronic treatment with curcumin.

Effects of prostanoids on phenylephrine-induced contractions in the mesenteric vascular bed of rats with streptozotocin-induced diabetes mellitus

The main aim of this study was to compare the vascular reactivity of the perfused (Krebs, 4 ml/min) mesenteric vascular bed (MVB) isolated from rats with streptozotocin (STZ)-induced diabetes of 8 weeks duration to that of the MVB from non-diabetic (ND) Wistar rats. There were no differences in basal perfusion pressure between the MVB isolated from STZ and ND rats. The addition of indomethacin to the perfusate increased the basal perfusion pressure in both ND (18.8 +/- 0.7 vs 29.4 +/- 3.7 mmHg, p < 0.05) and STZ rats (18.3 +/- 0.9 vs 27.2 +/- 2.6 mmHg, p < 0.05), suggesting the release of a vasodilator prostaglandin. Remotion of the endothelium did not affect this response, indicating that prostaglandin was released from vascular smooth muscle. The response to phenylephrine was reduced in STZ rats compared to ND rats (2.3 [1.6-3.8] vs 8.3 [3.5-19.4], ED50. [IC 95%]) and was not modified by removal of the endothelium or by perfusion of L-nitro-arginine (50 microM). In contrast, indomethacin was able to reduce the response to phenylephrine in ND but not in STZ rats (2.3 [1.6-3.8] vs 4.7 [3.2-6.0], ED50. [IC 95%], p=0.02), suggesting that the blunted response to phenylephrine observed in STZ was due to the abolition of the release of prostaglandin by vascular smooth muscle. In conclusion, experimental diabetes induction in the rat is followed by a reduction of the contractile effect of phenylephrine due to the lack of release of a vasoconstrictor prostaglandin from vascular smooth muscle.

Effects of chronic insulin on endothelial dysfunction of basilar arteries from established streptozotocin-diabetic rats

Our goals were to determine both the effects of chronic insulin treatment on the impaired endothelium-dependent relaxation present in basilar arteries from established diabetic rats and the molecular basis of these effects. Acetylcholine-induced relaxation in basilar artery rings was impaired in the streptozotocin-induced diabetic group, and this impaired response was recovered by insulin treatment. The contraction induced by a nitric oxide synthase inhibitor was decreased in the insulin-untreated diabetic group, but was increased by insulin or NAD(P)H oxidase inhibitor treatment. The manganese-superoxide dismutase (Mn-SOD) mRNA level was significantly lower in basilar arteries from insulin-untreated diabetic rats than in those from the controls, whereas the mRNA for gp91phox, an NAD(P)H oxidase subunit, was increased. In the insulin-treated group, the basilar artery p22phox mRNA level was reduced (vs. insulin-untreated diabetic). These results suggest that the presence of endothelial dysfunction in the diabetic basilar artery is related to increased oxidative stress, and that insulin preserves endothelial function by alleviating oxidative stress. Furthermore, we directly demonstrated that the expression profile for SOD and NAD(P)H oxidase was altered in the streptozotocin-induced diabetic basilar artery.

Melatonin treatment protects against diabetes-induced functional and biochemical changes in rat aorta and corpus cavernosum

Enhanced oxidative stress due to diabetes is accepted to lead to endothelial dysfunction, and this is known to play a key role in the pathogenesis of diabetic vascular diseases and complications. This study was designed to determine the possible protective effect of melatonin and/or insulin treatment on the functional and biochemical changes caused by hyperglycemia in aorta and corpus cavernosum of diabetic rats. Wistar albino male rats were rendered diabetic by injecting streptozotocin (60 mg/kg, intraperitoneally (i.p.)). Melatonin (10 mg/kg, i.p.) and/or insulin (6 U/kg, subcutaneously (s.c.)) were administered for 8 weeks. In the diabetic group, the contractile responses of aortic strips to phenylephrine were significantly impaired (EC(50) 5.5 x 10(-7) M in diabetic and EC(50) 1.47 x 10(-7) M in the control group, P<0.001). Treatment with melatonin (EC(50) 4.6 x 10(-7) M) or insulin+melatonin (EC(50) 1.68 x 10(-7) M, P<0.001) improved the contractile responses. Acetylcholine caused a dose-dependent relaxation response (EC(50) 1.58 x 10(-7) M) which was impaired in the diabetic group (EC(50) 26 x 10(-7) M, P<0.001). There was less impairment in melatonin-, insulin- and insulin+melatonin-treated groups (EC(50) 11.61 x 10(-7), 7.3 x 10(-7) and 1.41 x 10(-7) M, respectively, P<0.01). Contractile responses to phenylephrine were also impaired in the corpus cavernosum strips (EC(50) 2.06 x 10(-5) M in diabetic and 0.94 x 10(-5) M in the control group, P<0.001). In the melatonin- (EC(50) 1.59 x 10(-5) M) and insulin+melatonin-treated (EC(50) 1.53 x 10(-5) M, P<0.5) groups contractile responses were improved. In the diabetic group, the relaxation responses of corpus cavernosum strips to acetylcholine were impaired (EC(50) 24.12 x 10(-5) M, P<0.001), and treatment with melatonin (EC(50) 0.68 x 10(-5) M), insulin (EC(50) 0.53 x 10(-5) M) or insulin+melatonin (0.98 x 10(-5) M, P<0.001) restored the responses to acetylcholine. In diabetic tissues, malondialdehyde levels were increased while glutathione levels were decreased, demonstrating oxidative damage. This was also prevented by treatment with melatonin or the melatonin and insulin combination. The diabetic state enhances the generation of free radicals, and both melatonin and insulin treatments reduced this oxidative stress; however, treatment with the combination was the most efficient in preventing diabetes-induced damage. Thus, our results suggested that giving diabetic patients adjuvant therapy with melatonin may have some benefit in controlling diabetic complications.

Microvascular dysfunction after transient high glucose is caused by superoxide-dependent reduction in the bioavailability of NO and BH(4)

We hypothesized that transient high-glucose concentration interferes with mediation by nitric oxide (NO) of flow-induced dilation (FID) of arterioles due to enhanced production of superoxide. In isolated, pressurized (80 mmHg) rat gracilis muscle arterioles ( approximately 130 microm) after transient high-glucose treatment (tHG; incubation with 30 mM glucose for 1 h), FID was reduced (maximum: control, 38 +/- 4%; after tHG, 17 +/- 3%), which was not further diminished by the NO synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME; 18 +/- 2%). Correspondingly, an enhanced polyethylene-glycol-SOD (PEG-SOD)-sensitive superoxide production was detected after tHG in carotid arteries by dihydroethydine (DHE) staining. Presence of PEG-SOD during tHG prevented the reduction of FID (41 +/- 3%), which could be inhibited by l-NAME (20 +/- 4%). Administration of PEG-SOD after tHG did not prevent the reduction of FID (22 +/- 3%). Sepiapterin, a precursor of the NO synthase cofactor tetrahydrobiopterin (BH(4)), administered during tHG did not prevent the reduction of FID (maximum, 15 +/- 5%); however, it restored FID when administered after tHG (32 +/- 4%). Furthermore, inhibition of either glycolysis by 2-deoxyglucose or mitochondrial complex II by 2-thenoyltrifluoroacetone reduced the tHG-induced DHE-detectable enhanced superoxide production in carotid arteries and prevented FID reduction in arterioles (39 +/- 5 and 35 +/- 2%). Collectively, these findings suggest that in skeletal muscle arterioles, a transient elevation of glucose via its increased metabolism, elicits enhanced production of superoxide, which decreases the bioavailability of NO and the level of the NOS cofactor BH(4), resulting in a reduction of FID mediated by NO.

Synergistic effects of C-peptide and insulin on coronary flow in early diabetic rats

The aims of the present study are (1) to examine whether coronary flow is increased and (2) to examine the role of C-peptide in relation to nitric oxide (NO) production and coronary flow in a rat heart (Wistar) during the early stages of type 1 diabetes. Coronary flow increased by 36.4% +/-10.6% (P <.05) during the early stages of streptozotocin-induced diabetes of isolated perfused rat hearts, but NO production increased without significance. C-peptide alone did not change coronary flow, but increased NO production in diabetes. In the presence of insulin, C-peptide reversed both flow and NO production to the control level of normal rats (P <.05). In conclusion, during the early stages of type 1 diabetes, coronary flow was increased, and C-peptide in the presence of insulin synergistically normalized the excessive flow and NO production induced by C-peptide to the control level of normal rats.

Endothelial dysfunction and reduced nitric oxide in resistance arteries in autosomal-dominant polycystic kidney disease

BACKGROUND

Patients with autosomal-dominant polycystic kidney disease (ADPKD) have defective endothelium-dependent relaxation (EDR). We investigated the relationship between endothelial dysfunction and nitric oxide generation in hypertension and chronic renal insufficiency (CRI) in ADPKD.

METHODS

We contrasted acetylcholine (ACh)-induced EDR, 3-morphollinosydnonimine (SIN-1)-induced endothelium-independent relaxation (EIDR) and constitutive nitric oxide synthase (cNOS) activity in subcutaneous resistance vessels and plasma levels and excretion of NO2-/NO3- (NOX) in normal, control (N = 10) patients with ADPKD or essential hypertension.

RESULTS

EDR was decreased significantly in normotensive ADPKD (N = 9), but more severely in hypertensive ADPKD (N = 6), or those with CRI (N = 5) and in essential hypertension (N = 9). The increases in EDR with l-arginine and decreases with LG-nitro-l-arginine methyl ester (L-NAME) were lost in all groups of patients with ADPKD and in essential hypertension except for a modest effect of L-NAME in normotensive ADPKD. EIDR was unimpaired throughout. Vascular cNOS activity and renal NOX excretion were reduced profoundly in patients with all categories of ADPKD and especially in those with hypertension.

CONCLUSION

EDR in resistance vessels from patients with ADPKD is impaired even in the absence of hypertension or CRI, but becomes more marked as hypertension develops. Patients with ADPKD have defective nitric oxide generation from diminished cNOS activity. Endothelial dysfunction and impaired cNOS activity in ADPKD may predispose to hypertension whose occurrence is accompanied by a further sharp deterioration in EDR.

Relationship between peroxisome proliferator-activated receptors (PPAR alpha and PPAR gamma) and endothelium-dependent relaxation in streptozotocin-induced diabetic rats

(1) The aim of the present study was to investigate the causal relationship between peroxisome proliferator-activated receptor (PPAR) and endothelium-dependent relaxation in streptozotocin (STZ)-induced diabetic rats. (2) Acetylcholine (ACh)-induced endothelium-dependent relaxation was significantly weaker in diabetic rats than in age-matched controls. The decreased relaxation in diabetes was improved by the chronic administration of bezafibrate (30 mg kg-1, p.o., 4 weeks). (3) The expressions of the mRNAs for PPARalpha and PPARgamma were significantly decreased in STZ-induced diabetic rats (compared with the controls) and this decrease was restored partially, but not completely, by the chronic administration of bezafibrate. (4) Superoxide dismutase activity in the aorta was not significantly different between diabetic rats and bezafibrate-treated diabetic rats. (5) The expression of the mRNA for the p22phox subunit of NAD(P)H oxidase was significantly higher in diabetics than in controls, but it was lower in bezafibrate-treated diabetic rats than in nontreated diabetic rats. Although the expression of the mRNA for prepro ET-1 (ppET-1) was markedly increased in diabetic rats (compared with controls), this increase was prevented to a significant extent by the chronic administration of bezafibrate. (6) These results suggest that downregulations of PPARalpha and PPARgamma may lead to an increased expression of ppET-1 mRNA in diabetic states and this increment may trigger endothelial dysfunction.

Acquired microvascular dysfunction in inflammatory bowel disease: Loss of nitric oxide-mediated vasodilation

BACKGROUND & AIMS

Inflammatory bowel disease (IBD; i.e., Crohn's disease, ulcerative colitis) is characterized by refractory inflammatory ulceration and damage to the intestine. Mechanisms underlying impaired healing are not defined. Because microvascular dysfunction resulting in diminished vasodilatory capacity and tissue hypoperfusion is associated with impaired wound healing, we hypothesized that microvascular dysfunction may also occur in chronic IBD.

METHODS

Intact submucosal arterioles from control, involved, and uninvolved IBD specimens were assessed using in vitro videomicroscopy to assess endothelium-dependent vasodilation in response to acetylcholine (Ach) and fluorescence microscopy to detect oxyradicals.

RESULTS

Normal microvessels dilated in a dose-dependent and endothelium-dependent manner to Ach (maximum, 82% +/- 2%; n = 34). Inhibition of nitric oxide synthase with N(G)-nitro-L-arginine methyl ester (L-NAME) reduced maximal dilation to 54% +/- 6% (P < 0.05, n = 7), and further reduction was observed after inhibiting cyclooxygenase (indomethacin; 23% +/- 10%, n = 6). Chronically inflamed IBD microvessels showed significantly reduced Ach-induced vasodilation (maximum, 15% +/- 2%; n = 33), with no effect of L-NAME. Indomethacin eliminated the remaining Ach-induced vasodilation, resulting in frank vasoconstriction (-54% +/- 9%, n = 6). Uninvolved IBD gut vessels and non-IBD inflammatory controls responded in a fashion similar to normal vessels. IBD-involved microvessels generated significantly higher levels of reactive oxygen species compared with control and uninvolved IBD vessels (P < 0.01).

CONCLUSIONS

Human intestinal microvessels from chronically inflamed IBD show microvascular endothelial dysfunction, characterized by loss of NO-dependent dilation that may contribute to reduced perfusion, poor wound healing, and maintenance of chronic inflammation.

Time-dependent hyperreactivity to phenylephrine in aorta from untreated diabetic rats: role of prostanoids and calcium mobilization

Diabetes alters vascular smooth muscle contractility. Changes in reactivity to phenylephrine (Phe) in aortas from controls and untreated 1- and 4-week streptozotocin (STZ)-induced diabetic rats were investigated. In 1-week diabetic (DB1) aortas, the maximum response (E(max)) and sensitivity (pD(2)) to Phe were similar to controls (CT1), but in 4-week diabetic (DB4) aortas, the E(max) for Phe was increased compared to CT4 aortas (E(max), DB4: 125+/-8.4% vs. CT4: 89.8+/-4.5%, P<.001). Endothelial denudation increased the response to Phe, and E(max) was increased in the DB4 aortas compared to CT4 (E(max), DB4: 156+/-4.2% vs. CT4: 125+/-3.8%, P<.001). Pretreatment of CT4 and DB4 aortas with indomethacin reduced E(max) and pD(2) for Phe. After indomethacin treatment, no differences in E(max) and pD(2) to Phe were observed in either group. SQ 29548 did not alter the Phe actions in CT4 aortas. However, in DB4 aortas, E(max) was reduced to control level. CT4 and DB4 aortas incubated in free-Ca(2+) solution plus Phe, contracted upon addition of CaCl(2), this response was increased in DB4 aortas. No changes were observed for acetylcholine (ACh) or sodium nitroprusside (SNP) responses. Nitric oxide (NO) release in response to Phe determined by acute L-NAME administration showed no differences in the percentage increase of the contraction in CT1 and DB1 aortas, but was enhanced in DB4 aortas. Results suggested that diabetes induces time-dependent changes in the vascular reactivity to Phe. This response is not related to a reduction of endothelium-derived NO but might be due to an increase in prostaglandin H(2) (PGH(2))/thromboxane A(2) (TxA(2)) and/or an enhanced extracellular Ca(2+) influx.

Effect of 5-aminoimidazole-4-carboxamide riboside (AICA-r) on isolated thoracic aorta responses in streptozotocin-diabetic rats

Diabetes mellitus alters the vascular responsiveness to several vasoconstrictors and vasodilators. 5-amino-4-imidazole-carboxamide riboside (AICA-r), a nucleoside corresponding to AICA-ribotide and an intermediate of the de novo pathway of purine biosynthesis, was recently proposed as a new insulinotropic tool in non-insulin-dependent diabetes mellitus. The aim of the present study was to define whether AICA-r affects altered vascular responsiveness to vasoconstrictors and vasodilators in the thoracic aorta of neonatal streptozotocin (STZ)-diabetic rats. The results of this study indicate that a 1-month treatment with AICA-r significantly increases the body weight in diabetic rats; significantly decreases the blood glucose level of diabetic rats (from 302+/-47 to 135+/-11 mg/dL, p<0.001); does not significantly affect the fast, slow, and total components of responses to noradrenaline in all the experimental groups; reverses the increased Emax values of noradrenaline in diabetic rats to near-control values; reverses the completely abolished responses of acetylcholine (pD2 and percent relaxation) in diabetic rats to control values; and reverses the decreased pD2 values of sodium nitroprussiate in diabetic rats to control values. In conclusion, AICA-r treatment in neonatal STZ-diabetic rats improved increased blood glucose levels, accelerated weight gain, reversed endothelial dysfunction, and normalized vascular responses.

Effects of chronic administration of the novel endothelin antagonist J-104132 on endothelial dysfunction in streptozotocin-induced diabetic rat

1. The biosynthesis of endothelin-1 is increased in the diabetic state. So this peptide may cause diabetic vascular complications. We tested this possibility by chronically administering J-104132, a potent orally active mixed antagonist of endothelin A and B (ET(A)/ET(B)) receptors to streptozotocin (STZ)-induced diabetic rats and focusing on changes in endothelial function. 2. The acetylcholine (ACh)-induced endothelium-dependent relaxation was impaired in diabetic rats and this impairment was significantly attenuated following chronic administration of J-104132 (10 mg kg(-1), p.o., daily for 4 weeks). 3. In an in vitro experiment using aortae from diabetic rats, the ACh-induced relaxation was not changed by the presence of J-104132 (3 x 10(-9) M). 4. The expression levels of the mRNA for endothelial nitric oxide synthase was comparable among aortae from the three groups (control, diabetic and chronically J-104132-treated diabetic). 5. The amount of superoxide anion was significantly greater in aortae from diabetic rats than in controls. Chronic J-104132 treatment significantly decreased the level of superoxide anion in diabetic rats. 6. The expression of the p22phox mRNA for the NADH/NADPH oxidase subunit was significantly increased in STZ-induced diabetic rats and this increase was completely prevented by chronic administration of J-104132. 7. These results suggest that in STZ-induced diabetic rats, ET-1 may be directly involved in impairing endothelium-dependent relaxation via increased superoxide-anion production.

The coronary circulation in diabetes: influence of reactive oxygen species on K+ channel-mediated vasodilation

Enhanced oxidative stress, particularly an excess production of superoxide, has been implicated in the altered vasomotor responsiveness observed in diabetes mellitus (DM). Recent evidence suggests that an altered regulation of K+ channel activity by enhanced oxidative stress may participate in the abnormal vascular responses. This review examines the mechanism of hyperglycemia-induced superoxide production and describes the consequences on hyperpolarization-mediated vasodilation. Several pathways have been proposed as mechanisms for hyperglycemia-induced superoxide overproduction, including increased flux through the polyol pathway, depletion of nicotinamide adenine dinucleotide phosphate (NADPH), altered endogenous antioxidant enzymes, and reduced availability of tetrahydrobiopterin, an essential cofactor for nitric oxide synthase (NOS). The resulting excess production of superoxide has been implicated in the impaired dilator responses to ATP-sensitive K+ (KATP) channel openers in aorta and in mesenteric and cerebral arteries of streptozotocin-induced diabetic rats. This may have important implications for ischemia-mediated vasodilation. Potential alterations in voltage-sensitive K+ (KV) channel regulation also have been implicated in the vascular pathogenesis of DM. For example, incubation of small rat coronary arteries in high glucose for 24 h greatly reduces KV channel activity and functional responses, both of which can be partially restored by antioxidant treatment. However, not all K+ channels are adversely affected by reactive oxygen species (ROS). For example, high-conductance Ca(2+)-activated K+ (BKCa) channels may compensate for the loss of other vasodilator mechanisms in disease states such as atherosclerosis where ROS generation is increased. Therefore, BKCa channels may be refractory to superoxide, providing a compensatory mechanism for partially reversing the reduced dilator responses attributed to the dysfunction of other K+ channel types. In summary, determining the effect of ROS on K+ channel-mediated dilation will be important for understanding the pathophysiology of diabetic vascular dysfunction and for developing therapies to improve tissue perfusion in this disease.

The interaction of nitric oxide and prostaglandins in the control of corporal smooth muscle tone: evidence for production of a cyclooxygenase-derived endothelium-contracting factor

OBJECTIVE

To investigate the interaction of endothelium-derived nitric oxide (NO) and prostaglandins (PGs) in regulating corporal smooth muscle tone in vitro. Materials and methods Strips of rabbit corpus cavernosum were mounted in organ chambers for the measurement of isometric tension. Strips were submaximally contracted with noradrenaline and concentration-response curves (CRCs) to acetylcholine (ACh) were constructed before and after treatment with 5 micromol/L atropine, 20 micromol of the cyclooxygenase inhibitor indomethacin and 10 micromol of the PGH2/thromboxane A2 receptor antagonist SQ29548. The NO synthase (NOS) inhibitors L-NG-monomethyl arginine (L-NMMA) and L-NG-nitroarginine (L-NOARG) were added to strips at tonic tension in the presence and absence of indomethacin, and after this CRCs to ACh were constructed.

RESULTS

The addition of ACh to strips produced a concentration-dependent relaxation which was inhibited by atropine. Indomethacin, but not SQ29548, significantly increased relaxation to ACh. Relaxation to ACh was impaired by L-NMMA, but adding ACh to strips treated with L-NOARG resulted in contractile responses, whilst both effects were reversed by indomethacin. L-NMMA and L-NOARG led to increases in tonic tone which were unaffected by indomethacin.

CONCLUSIONS

In rabbit corpus cavernosum there is a tonic release of NO which does not appear to be inhibited by a vasoconstrictor prostanoid. Endothelium-dependent relaxation to ACh results in the dual production of NO and a cyclooxygenase-derived endothelium contracting factor which acts in opposition to NO; this factor is unlikely to act on PGH2/TXA2 receptors.

Depressed modulation of oxygen consumption by endogenous nitric oxide in cardiac muscle from diabetic dogs

Our previous study indicated that nitric oxide (NO)-dependent coronary vasodilation was impaired in conscious dogs with diabetes. Our goal was to determine whether modulation of O(2) consumption by NO is depressed in canine cardiac muscle after diabetes. Diabetes was induced by injection of alloxan (40-60 mg/kg iv), dogs were killed after diabetes was induced (4-5 wk), and the cardiac muscle from the left ventricle was cut into 15- to 30-mg slices. O(2) uptake by the muscle slices was measured polarographically with a Clark-type O(2) electrode. S-nitroso-N-acetylpenicillamine decreased O(2) consumption in normal and diabetic tissues (10(-4) M, 61 +/- 7 vs. 61 +/- 8%, P > 0.05). Bradykinin (10(-4) M)- or carbachol (CCh, 10(-4) M)-induced inhibition of O(2) consumption was impaired in diabetic tissues (51 +/- 6 vs. 17 +/- 4% or 48 +/- 4 vs. 19 +/- 3%, respectively, both P < 0.05 compared with normal). The inhibition of O(2) consumption by kininogen or kallikrein was depressed in diabetic tissues as well. In coronary microvessels from diabetic dogs, bradykinin or ACh (10(-5) M) caused smaller increases in NO production than those from normal dogs. Our results indicate that the modulation of O(2) consumption by endogenous, but not exogenous, NO is depressed in cardiac muscle from diabetic dogs, most likely because of decreased release of NO from the vascular endothelium.

Endothelium-dependent relaxation of small resistance vessels is impaired in patients with autosomal dominant polycystic kidney disease

Impaired endothelium-dependent relaxation has been demonstrated previously in resistance vessels of Han:SPRD polycystic kidney disease rats. The aim of the present study was to investigate whether endothelium-dependent relaxation is reduced also in patients with autosomal dominant polycystic kidney disease (ADPKD) and whether this is influenced by the nitric oxide (NO) system. Small subcutaneous resistance vessels from normotensive ADPKD patients with normal or near-normal renal function (n = 9) and from healthy control subjects (n = 10) were mounted in a Mulvany-Halpern myograph. The morphology of the vessels and acetylcholine (ACh)-induced endothelium-dependent relaxation, as well as 3-morpholino-sydnonimine (SIN-1, NO donor)-induced endothelium-independent relaxation were investigated. The results showed that: (1) there were no significant differences in morphologic parameters of resistance vessels between the two groups; (2) the maximal ACh-induced relaxation rate was decreased in ADPKD patients compared with control subjects (71.5 +/- 12.1 versus 85.2 +/- 8.7%, P < 0.01); (3) in the presence of L-arginine (a substrate of NO synthase), a left shift of the ACh dose-response curves was found in control subjects, but not in ADPKD patients; (4) in the presence of the N(G)-nitro-L-arginine methyl ester (an inhibitor of NO synthase), a right shift of the ACh dose-response curve was found in control subjects, but not in ADPKD patients; and (5) endothelium-independent relaxation rate induced with SIN-1 was similar in patients and control subjects. In conclusion, endothelium-dependent relaxation was impaired in resistance vessels from patients with ADPKD. The reduced response of the vessels to both the substrate and inhibitor of NO synthase in ADPKD suggests that an impairment of NO synthase may be involved in the mechanism of endothelial dysfunction in ADPKD.

Endothelial dysfunction in diabetes

Endothelial dysfunction plays a key role in the pathogenesis of diabetic vascular disease. The endothelium controls the tone of the underlying vascular smooth muscle through the production of vasodilator mediators. The endothelium-derived relaxing factors (EDRF) comprise nitric oxide (NO), prostacyclin, and a still elusive endothelium-derived hyperpolarizing factor (EDHF). Impaired endothelium-dependent vasodilation has been demonstrated in various vascular beds of different animal models of diabetes and in humans with type 1 and 2 diabetes. Several mechanisms of endothelial dysfunction have been reported, including impaired signal transduction or substrate availibility, impaired release of EDRF, increased destruction of EDRF, enhanced release of endothelium-derived constricting factors and decreased sensitivity of the vascular smooth muscle to EDRF. The principal mediators of hyperglycaemia-induced endothelial dysfunction may be activation of protein kinase C, increased activity of the polyol pathway, non-enzymatic glycation and oxidative stress. Correction of these pathways, as well as administration of ACE inhibitors and folate, has been shown to improve endothelium-dependent vasodilation in diabetes. Since the mechanisms of endothelial dysfunction appear to differ according to the diabetic model and the vascular bed under study, it is important to select clinically relevant models for future research of endothelial dysfunction.

Bradykinin-induced vasodilation of human forearm resistance vessels is primarily mediated by endothelium-dependent hyperpolarization

Bradykinin (BK) stimulates endothelial cells to release a number of relaxing factors, such as NO, prostanoids (PGs), and an endothelium-derived hyperpolarizing factor (EDHF). However, the contributions of NO, PG, and EDHF in the vascular relaxation to BK vary with species and anatomic origin of blood vessels used. Therefore, the present study was designed to investigate the contributions of NO, PG, and EDHF in vasodilation caused by BK in human forearm resistance vessels. Forearm blood flow (FBF) was recorded with venous occlusion plethysmography in healthy nonsmoking subjects. At first, studies were performed to validate the NO clamp technique for its ability to inhibit endogenous NO generation. Brachial artery infusion of serotonin (0.6, 1.8, and 6 ng. 100 mL forearm volume [FAV](-1). min(-1)) caused significant forearm vasodilation (2.6 to 4.6 mL. 100 mL FAV(-1). min(-1)), which is known to be NO mediated. Indeed, during the NO clamp, cumulative doses of serotonin caused no vasodilation (2.4 to 2.6 mL. 100 mL FAV(-1). min(-1)), indicating that the generation of endogenous NO was completely blocked. Thereafter, the vasodilative actions of BK were investigated. Brachial artery infusion of BK (50, 100, and 200 ng. 100 mL FAV(-1). min(-1)) caused significant forearm vasodilation in all studies (from 3.1 to 20.4 mL. 100 mL FAV(-1). min(-1)). After the inhibition of cyclooxygenase and NO synthase activity through the use of aspirin and the NO-clamp technique, BK increased FBF in a similar manner (3.9 to 18.9 mL. 100 mL FAV(-1). min(-1)), indicating that the vasodilative actions of BK are independent of NO and PG generation. However, vasodilation caused by the 2 lower doses of BK were significantly attenuated after K(Ca) channel activity was blocked with tetraethylammonium chloride (0.1 mg. 100 mL FAV(-1). min(-1)), suggesting that in the lower dose range, BK mediates vasodilation through the opening of vascular potassium channels. In conclusion, BK is a potent vasodilator peptide in human forearm resistance vessels, causing vasodilation through hyperpolarization of the vascular wall independent of NO and PG production. In addition, the NO-clamp technique is a valid instrument to investigate the contribution of NO in the vasodilative response to different agents.

Influence of experimental diabetes on regulatory mechanisms of vascular response of rabbit carotid artery to acetylcholine

The purpose of this study was to analyse the influence of experimental diabetes on vascular response of rabbit carotid artery to acetylcholine (Ach). We compared the Ach-induced relaxant response of isolated arterial segments obtained from both control and diabetic animals. To assess the influence of the endothelium, this cell layer was mechanically removed in some of the arterial segments ("rubbed arteries") from each experimental group. Ach induced a concentration-related endothelium-mediated relaxation of carotid artery from control rabbits that was significantly higher with respect to that obtained in diabetic animals. Pre-treatment with N(G)-nitro-L-arginine (L-NA) induced a concentration-dependent inhibition of relaxant response to Ach, which was significantly higher in carotid arteries isolated from diabetic rabbits. Incubation of rubbed arteries with L-NA almost abolished the relaxant response to Ach in arterial segments from both control and diabetic animals. Indomethacin potentiated Ach-induced response of carotid arteries from control rabbits, without modifying that obtained in those from diabetic animals. Aminoguanidine did not significantly inhibit the relaxant action of Ach in arterial segments from either control or diabetic rabbits. These results suggest that diabetes impairs endothelial modulatory mechanisms of vascular response of rabbit carotid artery to Ach. This endothelial dysfunction is neither related with a lower release of nitric oxide (NO) or prostacyclin. Diabetes impairs the production of some arachidonic acid vasoconstrictor derivative. There has been observed an increased modulatory activity of NO, but this is not related with the expression of an inducible isoform of NO synthase.

Gene transfer of endothelial nitric oxide synthase improves relaxation of carotid arteries from diabetic rabbits

BACKGROUND

Diabetes mellitus is associated with impairment of NO-mediated vascular relaxation. The purpose of this study was to determine whether adenovirus-mediated gene transfer of endothelial NO synthase (eNOS) or Cu/Zn superoxide dismutase (SOD1) improves responsiveness to acetylcholine in alloxan-induced diabetic rabbits.

METHODS AND RESULTS

After 8 weeks, plasma glucose was greater in diabetic rabbits (418+/-35 mg/dL) (mean+/-SEM) than in normal rabbits (105+/-4 mg/dL). Carotid arteries were removed and cut into ring segments. Arteries were incubated for 2 hours with adenoviral vectors driven by a CMV promoter expressing beta-galactosidase (beta-gal), eNOS, SOD1, or vehicle. After incubation with virus, arteries were incubated for an additional 24 hours to allow transgene expression. Vascular reactivity was examined by recording isometric tension. After precontraction with phenylephrine, responses to the endothelium-independent vasodilator sodium nitroprusside were similar in diabetic and normal arteries. Endothelium-dependent relaxation to acetylcholine (3x10(-6) mol/L) was significantly less in arteries from diabetic animals (68+/-5%) than in normal vessels (90+/-3%). Adenoviral transfection of arteries with eNOS improved relaxation in response to acetylcholine in diabetic (EC(50) eNOS=0.64+/-0.12x10(-7) mol/L versus vehicle =1. 70+/-0.43x10(-7) mol/L) but not normal arteries. Vasorelaxation in response to acetylcholine was inhibited by N(omega)-nitro-L-arginine (100 micromol/L) in all groups. Responses to acetylcholine were unchanged after gene transfection of SOD1 or beta-gal in arteries from diabetic or normal rabbits.

CONCLUSIONS

Adenovirus-mediated gene transfer of eNOS, but not SOD, improves impaired NO-mediated relaxation in vessels from diabetic rabbits.

Diabetes alters neuronal nitric oxide release from rat mesenteric arteries. Role of protein kinase C

The objective of the present study was to assess the influence of diabetes in the neuronal nitric oxide (NO) release elicited by electrical field stimulation (EFS, 200 mA, 0.3 ms, 1-16 Hz, for 30 s, at 1 min interval) in endothelium-denuded mesenteric artery segments from control and streptozotocin-induced diabetic rats, assessing the influence of protein kinase C (PKC) in this release. N(G)-nitro-L-arginine-methyl ester (L-NAME, 10 microM, a NO synthase inhibitor) enhanced EFS-elicited contractions in control, and specially in diabetic rats, whereas they were unaltered by AMT (5 nM, an inducible NO synthase inhibitor) and capsaicin (0.5 microM, a sensory neurone toxin). Calphostin C (0.1 microM, a PKC inhibitor) increased the contraction elicited by EFS in both types of arteries. This increase was further enhanced by calphostin C + L-NAME in diabetic rats. Phorbol 12,13-dibutyrate (PDBu, 1 microM) reduced and unaltered EFS-induced contractions in control and diabetic rats, respectively. The further addition of L-NAME reversed the reduction obtained in control rats, and enhanced the response observed in diabetic rats. These results suggest that the EFS-induced NO release from perivascular nitrergic nerves, that negatively modulates the contraction, which is synthesized by neuronal constitutive NO synthase. The NO synthesis is positively stimulated by PKC. This NO release is increased in diabetes, likely due to an increase in the activity of this enzyme. The sensory nerves of these arteries do not seem to be involved in the contractile response.

The role of prostaglandins in penile erection

The balance of penile smooth muscle tone is finely controlled, with contractile factors acting in opposition to relaxant factors. The principal agents in this process are undoubtedly noradrenaline and nitric oxide. Prostaglandins probably have a crucial role in the 'fine tuning' of corporal smooth muscle tone. Their effects on control mechanisms in the healthy penis are more likely to be modulatory rather than direct.

Altered endothelium-dependent responsiveness in the aortas and renal arteries of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus

We examined endothelium-dependent relaxation in the aortas and renal arteries of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus, in comparison with non-diabetic Long-Evans Tokushima Otsuka rats as controls. Acetylcholine-induced relaxation in both arteries was attenuated, and the attenuation was restored to the control level by indomethacin. The relaxation was inhibited completely in the aortas, but only partially in renal arteries by N(G)-nitro-L-arginine methyl ester, and the degree of the latter inhibition was greater in OLETF rats than in the controls. The relaxation was inhibited by aminoguanidine in both arteries of OLETF rats but not in the controls. Serum NO(2) plus NO(3) levels significantly increased in OLETF rats. These results suggest that impairment of relaxation in OLETF rat arteries is due to increased release of contractile factors but not decreased release of nitric oxide.