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

Female prediabetic rats are protected from vascular dysfunction: the role of nitroso and sulfide signaling

BACKGROUND

The activity of perivascular adipose tissue (PVAT), a specific deposit of adipose tissue surrounding blood vessels, could contribute to sex differences in vascular tone control, particularly in dyslipidemic disorders; however, the mutual associations remain unclear. This study aimed to evaluate the relationships among sex, PVAT and vascular function in Wistar and hereditary hypertriglyceridemic (HTG) rats. Vasoactive responses of the isolated thoracic aorta with preserved or removed PVAT were compared in adult male and female Wistar and HTG rats, and the roles of nitric oxide (NO), hydrogen sulfide (H2S), cyclooxygenase (COX) and inflammatory signaling in vascular function were monitored in females.

RESULTS

HTG rats were hypertensive, but females less than males. Increased 2-h glycemia was observed in HTG rats regardless of sex; however, HTG females exhibited better glucose utilization than males did. Females, independent of strain, had better preserved endothelial function than males did. PVAT inhibited endothelium-dependent relaxation in all the rats except HTG females. In HTG males, pathologically increased aortic contractility was noted; however, in HTG females, the contractile responses were lower, thus approaching physiological levels despite the pro-contractile action of COX products. In HTG females, NO contributed to endothelial function to a lesser extent than it did in controls, but the presence of PVAT eliminated this difference, which corresponded with increased NO synthase activity. Although increased protein expression of several proinflammatory factors (TNFα, IL-6, iNOS, and NfκB) was confirmed in the aortic and PVAT tissue of HTG females, the protein expression of factors regulating the adhesion and infiltration of monocytes (ICAM-1 and MCP-1) was decreased in PVAT. Moreover, in HTG females, unlike in controls, H2S produced by PVAT did not inhibit endothelial relaxation, and regardless of PVAT, endogenous H2S had beneficial anticontractile effects, which were associated with increased protein expression of H2S-producing enzymes in both aortic and PVAT tissues.

CONCLUSIONS

Despite increased inflammation and the pathological impact of cyclooxygenase signaling in female HTG rats, protective vasoactive mechanisms associated with milder hypertension and improved endothelial function and contractility linked to PVAT activity were triggered. Sulfide and nitroso signaling represent important compensatory vasoactive mechanisms against hypertriglyceridemia-associated metabolic disorders and may be promising therapeutic targets in prediabetic females.

Dimethyl fumarate ameliorates diabetes-associated vascular complications through ROS-TXNIP-NLRP3 inflammasome pathway

Vascular complications are a leading cause of morbidity and mortality among diabetic patients. This work aimed to investigate possible influences of dimethyl fumarate (DMF) on streptozotocin (STZ) diabetes-associated vascular complications in rats, exploring its potential to modulate ROS-TXNIP-NLRP3 inflammasome pathway. Two weeks after induction of diabetes (via a single injection of 50 mg/kg STZ, i.p.), diabetic rats were administered either DMF (25 mg/kg/day) or its vehicle for further eight weeks. Age-matched normal and DMF-administered non-diabetic rats served as controls. DMF treatment elicited a mild ameliorative effect on diabetic glycemia. DMF reduced serum TG and AGE levels and enhanced serum HDL-C concentrations in diabetic rats. Moreover, DMF significantly diminished aortic levels of ROS and MDA and restored aortic GSH, SOD and Nrf2 to near-normal levels in STZ rats. Aortic mRNA levels of TXNIP, NLRP3 and NF-κB p65 in diabetic rats were significantly reduced by DMF treatment. Serum and aortic protein levels of TXNIP and aortic contents of IL-1β, iNOS, NLRP3 and TGF-β1 were significantly lower in DMF-diabetic animals than non-treated diabetic rats. Furthermore, protein expression of TNF-α and caspase-3 in diabetic aortas was greatly attenuated by DMF administration. DMF enhanced eNOS mRNA and protein levels and increased bioavailable NO in diabetic aortas. Functionally, DMF attenuated contractile responses of diabetic aortic rings to KCl and phenylephrine and enhanced their relaxant responses to acetylcholine. DMF also mitigated diabetes-induced fibrous tissue proliferation in aortic tunica media. Collectively, these findings demonstrate that DMF offered vasculoprotective influences on diabetic aortas via attenuation of ROS-TXNIP-NLRP3 inflammasome pathway.

Endothelial overexpression of endothelin-1 modulates aortic, carotid, iliac and renal arterial responses in obese mice

Endothelin-1 (ET-1) is essential for mammalian development and life, but it has also been implicated in increased cardiovascular risk under pathophysiological conditions. The aim of this study was to determine the impact of endothelial overexpression of the prepro-endothelin-1 gene on endothelium-dependent and endothelium-independent responses in the conduit and renal arteries of lean and obese mice. Obesity was induced by high-fat-diet (HFD) consumption in mice with Tie-1 promoter-driven, endothelium-specific overexpression of the prepro-endothelin-1 gene (TET^het) and in wild-type (WT) littermates on a C57BL/6N background. Isometric tension was measured in rings (with endothelium) of the aorta (A), carotid (CA) and iliac (IA) arteries as well as the main (MRA) and segmental renal (SRA) arteries; all experiments were conducted in the absence or presence of L-NAME and/or the COX inhibitor meclofenamate. The release of prostacyclin and thromboxane A2 was measured by ELISA. In the MRA, TET^het per se increased contractions to endothelin-1, but the response was decreased in SRA in response to serotonin; there were also improved relaxations to acetylcholine but not insulin in the SRA in the presence of L-NAME. HFD per se augmented the contractions to endothelin-1 (MRA) and to the thromboxane prostanoid (TP) receptor agonist U46619 (CA, MRA) as well as facilitated relaxations to isoproterenol (A). The combination of HFD and TET^het overexpression increased the contractions of MRA and SRA to vasoconstrictors but not in the presence of meclofenamate; this combination also augmented further relaxations to isoproterenol in the A. Contractions to endothelin-1 in the IA were prevented by endothelin-A receptor antagonist BQ-123 but only attenuated in obese mice by BQ-788. The COX-1 inhibitor FR122047 abolished the contractions of CA to acetylcholine. The release of prostacyclin during the latter condition was augmented in samples from obese TET^het mice and abolished by FR122047. These findings suggest that endothelial TET^het overexpression in lean animals has minimal effects on vascular responsiveness. However, if comorbid with obesity, endothelin-1-modulated, prostanoid-mediated renal arterial dysfunction becomes apparent.

Treatment with high dose of atorvastatin reduces vascular injury in diabetic rats

BACKGROUND

Previous reports showed conflicting results regarding the treatment effects of statin on Diabetes mellitus (DM). We investigated how treatment with high dose of atorvastatin affects the impaired vascular function in diabetic rats.

METHODS

Atorvastatin (80mg/kg/day, oral gavage, 4 weeks) or its vehicle was administered to male control or streptozotocin (STZ)-induced diabetic rats. Aortic segments were used to investigate the vascular reactivity, protein expression of cyclooxygenase-2 (COX-2) and nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) 1 (NOX1) and superoxide anions levels.

RESULTS

Atorvastatin treatment did not affect glycemia levels. In diabetic rats, the vascular reactivity to phenylephrine increased compared with controls and the atorvastatin treatment reduced this response. Removal of the endothelium increased the response to phenylephrine in control rats, but not in the diabetic group. Atorvastatin increased the endothelial modulation in diabetic rats. L-NAME (100μM) increased the reactivity in all groups, but this effect was greater in atorvastatin-treated diabetic rats. Indomethacin (10μM) and NS398 (1μM) decreased the contractile response in diabetic rats and atorvastatin reversed these effects, without changing COX-2 expression. Apocynin (30μM) decreased the phenylephrine response in diabetic rats, which also showed increased NOX1 and superoxide anions; these effects were prevented by atorvastatin treatment.

CONCLUSIONS

The results suggest that treatment with high dose of atorvastatin, independent of glycemia, improves endothelial function in aortas from diabetic rats by reducing the constrictor prostanoids derived from COX-2 and by reducing the oxidative stress by NADPH oxidase, as well as a possible increasing of nitric oxide participation.

Biphasic Effect of Diabetes on Neuronal Nitric Oxide Release in Rat Mesenteric Arteries

INTRODUCTION

We analysed possible time-dependent changes in nitrergic perivascular innervation function from diabetic rats and mechanisms implicated.

MATERIALS AND METHODS

In endothelium-denuded mesenteric arteries from control and four- (4W) and eight-week (8W) streptozotocin-induced diabetic rats the vasoconstriction to EFS (electrical field stimulation) was analysed before and after preincubation with L-NAME. Neuronal NO release was analysed in the absence and presence of L-arginine, tetrahydrobiopterine (BH4) and L-arginine plus BH4. Superoxide anion (O2-), peroxynitrite (ONOO-) and superoxide dismutase (SOD) activity were measured. Expressions of Cu-Zn SOD, nNOS, p-nNOS Ser1417, p-nNOS Ser847, and Arginase (Arg) I and II were analysed.

RESULTS

EFS response was enhanced at 4W, and to a lesser extent at 8W. L-NAME increased EFS response in control rats and at 8W, but not at 4W. NO release was decreased at 4W and restored at 8W. L-arginine or BH4 increased NO release at 4W, but not 8W. SOD activity and O2- generation were increased at both 4W and 8W. ONOO- decreased at 4W while increased at 8W. Cu-Zn SOD, nNOS and p-NOS Ser1417 expressions remained unmodified at 4W and 8W, whereas p-nNOS Ser847 was increased at 4W. ArgI was overexpressed at 4W, remaining unmodified at 8W. ArgII expression was similar in all groups.

CONCLUSIONS

Our results show a time-dependent effect of diabetes on neuronal NO release. At 4W, diabetes induced increased O2- generation, nNOS uncoupling and overexpression of ArgI and p-nNOS Ser847, resulting in decreased NO release. At 8W, NO release was restored, involving normalisation of ArgI and p-nNOS Ser847 expressions.

Comparison of the effects of levocetirizine and losartan on diabetic nephropathy and vascular dysfunction in streptozotocin-induced diabetic rats

This work was designed to investigate the effects of levocetirizine, a histamine H1 receptor antagonist, on diabetes-induced nephropathy and vascular disorder, in comparison to an angiotensin II receptor antagonist, losartan. Diabetes was induced in male Sprague Dawley rats by a single intraperitoneal injection of streptozotocin (50mg/kg). Diabetic rats were divided into three groups; diabetic, diabetic-levocetirizine (0.5mg/kg/day) and diabetic-losartan (25mg/kg/day). Treatments were started two weeks following diabetes induction and continued for additional eight weeks. At the end of the experiment, urine was collected and serum was separated for biochemical measurements. Tissue homogenates of kidney and aorta were prepared for measuring oxidative stress, nitric oxide (NO), transforming growth factor-β1 (TGF-β1) and tumor necrosis factor-α (TNF-α). Moreover, histological analyses were conducted and aortic vascular reactivity was investigated. Levocetirizine improved renal function in diabetic rats (evidenced by mitigation of diabetes-induced changes in kidney to body weight ratio, serum albumin, urinary proteins and creatinine clearance). Moreover, levocetirizine attenuated the elevated renal levels of TNF-α and TGF-β1, ameliorated renal oxidative stress and restored NO bioavailability in diabetic kidney. These effects were comparable to or surpassed those produced by losartan. Moreover, levocetirizine, similar to losartan, reduced the enhanced responsiveness of diabetic aorta to phenylephrine. Histological evaluation of renal and aortic tissues further confirmed the beneficial effects of levocetirizine on diabetic nephropathy and revealed a greater attenuation of diabetes-induced vascular hypertrophy by levocetirizine than by losartan. In conclusion, levocetirizine may offer comparable renoprotective effect to, and possibly superior vasculoprotective effects than, losartan in streptozotocin-diabetic rats.

Chronic iron overload in rats increases vascular reactivity by increasing oxidative stress and reducing nitric oxide bioavailability

AIMS

Iron overload in animal models and humans increases oxidative stress and induces cardiomyopathy. It has been suggested that the vasculature is also damaged, but the impacts on vascular reactivity and the underlying mechanisms remain poorly understood. In this study, we aimed to identify possible changes in the vascular reactivity of aortas from iron overloaded rats and investigate the underlying mechanisms.

MAIN METHODS

Rats were treated with 100mg/kg/day iron-dextran, ip, five days a week for four weeks and compared to a saline-injected group.

KEY FINDINGS

Chronic iron administration increased serum iron and transferrin saturation with significant deposition in the liver. Additionally, iron overload significantly increased the vasoconstrictor response in aortic rings as assessed in vitro, with reduced influence of endothelial denudation or l-NAME incubation on the vascular reactivity. In vitro assay with DAF-2 indicated reduced NO production in the iron overload group. Iron overload-induced vascular hyperactivity was reversed by incubation with tiron, catalase, apocynin, allopurinol and losartan. Moreover, malondialdehyde was elevated in the plasma, and O2(•-) generation and NADPH oxidase subunit (p22phox) expression were increased in the aortas of iron-loaded rats.

SIGNIFICANCE

Our results demonstrated that chronic iron overload is associated with altered vascular reactivity and the loss of endothelial modulation of the vascular tone. This iron loading-induced endothelial dysfunction and reduced nitric oxide bioavailability may be a result of increased production of reactive oxygen species and local renin-angiotensin system activation.

Onset of diabetes modulates the airway smooth muscle reactivity of guinea pigs: role of epithelial mediators

BACKGROUND

Diabetes induces lung dysfunction, leading to alteration in the pulmonary functions. Our aim was to investigate whether the early stage of diabetes alters the epithelium-dependent bronchial responses and whether nitric oxide (NO), KATP channels and cyclooxygenase (COX) pathways contribute in this effect.

METHODS

Guinea pigs were treated with a single injection of streptozotocin (180 mg/kg, i.p.) for induction of diabetes. Airway conductivity was assessed by inhaled histamine, using a non-invasive body plethysmography. The contractile responses of tracheal rings induced by acetylcholine (ACh) and relaxant responses of precontracted rings, induced by isoproterenol (IP) were compared in the presence and absence of the epithelium. Effects of N(ω)-Nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor), glybenclamide (a KATP channel inhibitor) and indomethacin (a COX inhibitor) were also assessed in diabetic guinea pigs.

RESULTS

Early stage diabetes did not alter the airway conductivity. ACh-induced bronchoconstriction in epithelium intact tracheal rings was not affected by the onset of diabetes, however a reduction in the increased ACh responses due to epithelium removal, to L-NAME or to indomethacin was observed. The relaxation response to IP was impaired in trachea from guinea pigs in which diabetes had just developed. Early diabetes significantly reduced the IP response to glybenclamide and to indomethacin.

CONCLUSION

Our results demonstrate that the early stage of diabetes, modulate the bronchial reactivity to both ACh and IP by disrupting the NO, KATP channels and COX pathways, without affecting the airway conductivity in guinea pigs.

Chrysin and luteolin alleviate vascular complications associated with insulin resistance mainly through PPAR-γ activation

Chrysin and luteolin are two flavonoids with Peroxisome proliferators-activated receptor γ (PPAR-γ) stimulating activity. Here, we investigated the protective effect of chrysin and luteolin from vascular complications associated with insulin resistance (IR). IR was induced in rats by drinking fructose for 12 weeks while chrysin and luteolin were given for 6 weeks with or without PPAR-γ antagonist, bisphenol A diglycidyl ether (BADGE). Then, blood pressure (BP) was recorded and serum levels of glucose, insulin, advanced glycation end products (AGEs) and lipids were measured. Concentration response curves for phenylephrine (PE), KCl, and acetylcholine (ACh) were obtained in thoracic aorta rings. Aortic reactive oxygen species (ROS) and nitric oxide (NO) generation were also studied. Chrysin and luteolin significantly alleviated systolic BP elevations caused by IR, while the co-administration of BADGE prevented chrysin alleviation. Although, neither chrysin nor luteolin affected ACh impaired vasodilatation, they both alleviated exaggerated vasoconstrictions to PE and KCl in IR animals. In addition, incubation of the aorta from IR animals with chrysin or luteolin prevented exaggerated vasoconstrictions to PE and KCl. On the other hand, co-administration of BADGE or co-incubation with GW9662, the selective PPAR-γ antagonist, prevented chrysin alleviation. Both chrysin and luteolin inhibited the developed hyperinsulinemia and increases in serum AGEs, lipids while, BADGE reduced the effect of chrysin on hyperinsulinemia and dyslipidemia. Chrysin and luteolin markedly inhibited elevated NO and ROS in IR aortae while BADGE did not change their effect on NO and ROS. In conclusion, chrysin and luteolin alleviate vascular complications associated with IR mainly through PPAR-γ dependent pathways.

Toll-like receptor 4 upregulation by angiotensin II contributes to hypertension and vascular dysfunction through reactive oxygen species production

Hypertension is considered as a low-grade inflammatory disease, with adaptive immunity being an important mediator of this pathology. TLR4 may have a role in the development of several cardiovascular diseases; however, little is known about its participation in hypertension. We aimed to investigate whether TLR4 activation due to increased activity of the renin-angiotensin system (RAS) contributes to hypertension and its associated endothelial dysfunction. For this, we used aortic segments from Wistar rats treated with a non-specific IgG (1 µg/day) and SHRs treated with losartan (15 mg/kg·day), the non-specific IgG or the neutralizing antibody anti-TLR4 (1 µg/day), as well as cultured vascular smooth muscle cells (VSMC) from Wistar and SHRs. TLR4 mRNA levels were greater in the VSMC and aortas from SHRs compared with Wistar rats; losartan treatment reduced those levels in the SHRs. Treatment of the SHRs with the anti-TLR4 antibody: 1) reduced the increased blood pressure, heart rate and phenylephrine-induced contraction while it improved the impaired acetylcholine-induced relaxation; 2) increased the potentiation of phenylephrine contraction after endothelium removal; and 3) abolished the inhibitory effects of tiron, apocynin and catalase on the phenylephrine-induced response as well as its enhancing effect of acetylcholine-induced relaxation. In SHR VSMCs, angiotensin II increased TLR4 mRNA levels, and losartan reduced that increase. CLI-095, a TLR4 inhibitor, mitigated the increases in NAD(P)H oxidase activity, superoxide anion production, migration and proliferation that were induced by angiotensin II. In conclusion, TLR4 pathway activation due to increased RAS activity is involved in hypertension, and by inducing oxidative stress, this pathway contributes to the endothelial dysfunction associated with this pathology. These results suggest that TLR4 and innate immunity may play a role in hypertension and its associated end-organ damage.

Chronic treatment with qiliqiangxin ameliorates aortic endothelial cell dysfunction in diabetic rats

Qiliqiangxin (QL), a traditional Chinese medicine, has been shown to be beneficial for chronic heart failure. However, whether QL can also improve endothelial cell function in diabetic rats remains unknown. Here, we investigated the effect of QL treatment on endothelial dysfunction by comparing the effect of QL to that of benazepril (Ben) in diabetic Sprague-Dawley rats for 8 weeks. Cardiac function was evaluated by echocardiography and catheterization. Assays for acetylcholine-induced, endothelium-dependent relaxation (EDR), sodium nitroprusside-induced endothelium-independent relaxation, serum nitric oxide (NO), and nitric oxide synthase (NOS) as well as histological analyses were performed to assess endothelial function. Diabetic rats showed significantly inhibited cardiac function and EDR, decreased expression of serum NO and phosphorylation at Ser(1177) on endothelial NOS (eNOS), and impaired endothelial integrity after 8 weeks. Chronic treatment for 8 weeks with either QL or Ben prevented the inhibition of cardiac function and EDR and the decrease in serum NO and eNOS phosphorylation caused by diabetes. Moreover, either QL or Ben suppressed inducible NOS (iNOS) protein levels as well as endothelial necrosis compared with the diabetic rats. Additionally, QL prevented the increase in angiotensin-converting enzyme 1 and angiotensin II receptor type 1 in diabetes. Thus, chronic administration of QL improved serum NO production, EDR, and endothelial integrity in diabetic rat aortas, possibly through balancing eNOS and iNOS activity and decreasing renin-angiotensin system expression.

Role of nitric oxide and endothelin in endothelial maintenance of vasoconstrictor responses in aortas of diabetic female rats

BACKGROUND

Diabetes differentially affects the vascular system in males and females. Although various results have been reported, very few studies have focused on responses in females. In the present study, we investigated contractile responses to norepinephrine in aortas of alloxan-diabetic female rats and evaluated endothelial modulation of these responses.

METHODS

Concentration-response curves were constructed to norepinephrine in the absence or presence of N(G) -nitro-l-arginine methyl ester (l-NAME), indomethacin, losartan, tezosentan, and calphostin C; pre-pro-endothelin mRNA expression was evaluated; and norepinephrine-stimulated expression of phosphorylated (p-) Akt Ser(473) , p-endothelial nitric oxide synthase (eNOS) Ser(1177) , and p-eNOS Ser(633) was determined in endothelial cells incubated in the presence of low (5 mmol/L) or high (25 mmol/L) glucose concentrations.

RESULTS

Similar maximal responses (Rmax ) to norepinephrine were seen in control and diabetic endothelium-intact aortas; however, Rmax was reduced in diabetic endothelium-denuded aortas. Incubation of endothelium-intact aortas with 100 μmol/L l-NAME increased Rmax in the control group only. Inhibition of cyclo-oxygenase (10 μmol/L indomethacin) and blockade of angiotensin II receptors (10 μmol/L losartan) reduced Rmax in endothelium-intact aortas in both the control and diabetic groups. Blockade of endothelin receptors (0.1 μmol/L tezosentan) and inhibition of protein kinase C (PKC; 0.1 μmol/L calphostin C) reduced Rmax only in endothelium-intact aortas from diabetic rats. Pre-pro-endothelin mRNA expression was increased in aortas from diabetic female rats. Finally, p-Akt Ser(473) , p-eNOS Ser(1177) , and p-eNOS Ser(633) levels were enhanced after norepinephrine stimulation only in low glucose-treated endothelial cells.

CONCLUSIONS

In aortas of diabetic female rats, reductions in smooth muscle contractile responses to norepinephrine are counterbalanced by the endothelium via reduced eNOS activation and increased endothelin release and PKC activation.

Aldose reductase inhibitors zopolrestat and ferulic acid alleviate hypertension associated with diabetes: effect on vascular reactivity

This study investigated the effect of aldose reductase (AR) inhibitors on hypertension in diabetes. Diabetes was induced with streptozotocin, while AR inhibitors zopolrestat and ferulic acid were administered at 2 weeks after streptozotocin treatment and for 6 weeks afterwards. Then, blood pressure (BP) and serum level of glucose were determined. Concentration–response curves for phenylephrine (PE), KCl, and acetylcholine (ACh) were obtained in isolated aorta. In addition, ACh-induced NO and reactive oxygen species (ROS) generation in aorta and histopathology were examined. Compared with the control animals, diabetes increased diastolic and systolic BP. AR inhibitors reduced diastolic BP elevation without affecting the developed hyperglycaemia. Diabetes increased the contractile response of aorta to KCl, and decreased the relaxation response to Ach, while administering AR inhibitors prevented an impaired response to ACh. Incubation of aorta isolated from diabetic animals with AR inhibitors did not affect the impaired relaxation response to ACh. In addition, AR inhibitors negated the impaired Ach-stimulated NO generation seen in aorta isolated from diabetic animals. Furthermore, diabetes was accompanied with marked infiltration of leukocytes in aortic adventitia, endothelial cell pyknosis, and increased ROS formation. AR inhibitors reduced leukocyte infiltration and inhibited endothelial pyknosis and ROS formation. In conclusion, AR inhibitors negate diabetes-evoked hypertension via ameliorating impaired endothelial relaxation and NO production.

Increased cyclooxygenase-2-derived prostanoids contributes to the hyperreactivity to noradrenaline in mesenteric resistance arteries from offspring of diabetic rats

This study analyzed the effect of in utero exposure to maternal diabetes on contraction to noradrenaline in mesenteric resistance arteries (MRA) from adult offspring, focusing on the role of cyclooxygenase (COX)-derived prostanoids. Diabetes in the maternal rat was induced by a single injection of streptozotocin (50 mg/kg body weight) on day 7 of pregnancy. Contraction to noradrenaline was analyzed in isolated MRA from offspring of diabetic (O-DR) and non-diabetic (O-CR) rats at 3, 6 and 12 months of age. Release of thromboxane A₂ (TxA₂) and prostaglandins E₂ (PGE₂) and F_2α (PGF_2α), was measured by specific enzyme immunoassay kits. O-DR developed hypertension from 6 months of age compared with O-CR. Arteries from O-DR were hyperactive to noradrenaline only at 6 and 12 months of age. Endothelial removal abolished this hyperreactivity to noradrenaline between O-CR and O-DR. Preincubation with either the COX-1/2 (indomethacin) or COX-2 inhibitor (NS-398) decreased noradrenaline contraction only in 6- and 12-month-old O-DR, while it remained unmodified by COX-1 inhibitor SC-560. In vessels from 6-month-old O-DR, a similar reduction in the contraction to noradrenaline produced by NS-398 was observed when TP and EP receptors were blocked (SQ29548+AH6809). In 12-month-old O-DR, this effect was only achieved when TP, EP and FP were blocked (SQ29548+AH6809+AL8810). Noradrenaline-stimulated TxB₂ and PGE₂ release was higher in 6- and 12-month-old O-DR, whereas PGF_2α was increased only in 12-month-old O-DR. Our results demonstrated that in utero exposure to maternal hyperglycaemia in rats increases the participation of COX-2-derived prostanoids on contraction to noradrenaline, which might help to explain the greater response to this agonist in MRA from 6- and 12-month-old offspring. As increased contractile response in resistance vessels may contribute to hypertension, our results suggest a role for these COX-2-derived prostanoids in elevating vascular resistance and blood pressure in offspring of diabetic rats.

Endothelial dysfunction in cardiovascular and endocrine-metabolic diseases: an update

The endothelium plays a vital role in maintaining circulatory homeostasis by the release of relaxing and contracting factors. Any change in this balance may result in a process known as endothelial dysfunction that leads to impaired control of vascular tone and contributes to the pathogenesis of some cardiovascular and endocrine/metabolic diseases. Reduced endothelium-derived nitric oxide (NO) bioavailability and increased production of thromboxane A2, prostaglandin H2 and superoxide anion in conductance and resistance arteries are commonly associated with endothelial dysfunction in hypertensive, diabetic and obese animals, resulting in reduced endothelium-dependent vasodilatation and in increased vasoconstrictor responses. In addition, recent studies have demonstrated the role of enhanced overactivation of β-adrenergic receptors inducing vascular cytokine production and endothelial NO synthase (eNOS) uncoupling that seem to be the mechanisms underlying endothelial dysfunction in hypertension, heart failure and in endocrine-metabolic disorders. However, some adaptive mechanisms can occur in the initial stages of hypertension, such as increased NO production by eNOS. The present review focuses on the role of NO bioavailability, eNOS uncoupling, cyclooxygenase-derived products and pro-inflammatory factors on the endothelial dysfunction that occurs in hypertension, sympathetic hyperactivity, diabetes mellitus, and obesity. These are cardiovascular and endocrine-metabolic diseases of high incidence and mortality around the world, especially in developing countries and endothelial dysfunction contributes to triggering, maintenance and worsening of these pathological situations.

Cinnamaldehyde protects from the hypertension associated with diabetes

Here we investigated cinnamaldehyde (CA) effect on diabetes-induced hypertension. Insulin deficiency was induced by streptozotocin while, insulin resistance by fructose. Rats were left 8 weeks or 12 weeks after STZ or fructose administration respectively. CA (20 mg kg(-1)day(-1)) was daily administered in the last 6 weeks. Then, blood pressure (BP) was recorded. Isolated Aorta reactivity to phenylephrine (PE), KCl, acetylcholine (ACh) was studied as well as nitric oxide (NO) generation plus Ca(2+) influx. Insulin deficiency was associated with elevated BP, increased response to PE and KCl, decreased response to ACh and impaired NO generation. CA treatment prevented hyperglycemia and its associated impaired vascular reactivity. Insulin resistance was associated with elevated BP while, CA prevented this elevation. Insulin resistance increased response to PE and KCl, decreased response to ACh, while CA treatment normalized response to KCl and PE but not to ACh. Insulin resistance was accompanied with reduced NO generation but exaggerated Ca(2+) influx while CA restored normal Ca(2+) influx but did not affect NO generation. In conclusion, CA prevents development of hypertension in insulin deficiency and insulin resistance through normalization of vascular contractility in addition to its insulinotropic effect in insulin deficiency.

Aldosterone alters the participation of endothelial factors in noradrenaline vasoconstriction differently in resistance arteries from normotensive and hypertensive rats

This study analyzed the effect of aldosterone (0.05mg/kg per day, 3 weeks) on vasoconstriction induced by noradrenaline in mesenteric resistance arteries from WKY rats and SHR. Contraction to noradrenaline was measured in mesenteric resistance arteries from untreated and aldosterone-treatedrats from both strains. Participation of nitric oxide (NO), superoxide anions, thromboxane A(2) (TxA(2)) and prostacyclin in this response was determined. 6-keto-prostaglandin (PG)F1alpha and thromboxane B(2) (TxB(2)) releases were determined by enzyme immunoassay. NO and superoxide anion release were also determined by fluorescence and chemiluminiscence, respectively. Aldosterone did not modify noradrenaline-induced contraction in either strain. In mesenteric resistance arteries from both aldosterone-treated groups, endothelium removal or preincubation with NO synthesis inhibitor L-NAME increased the noradrenaline-induced contraction, while incubation with the superoxide anion scavenger tempol decreased it. Preincubation with either the COX-1/2 or COX-2 inhibitor (indomethacin and NS-398, respectively) decreased the noradrenaline contraction in aldosterone-treated animals, while this response was not modified by COX-1 inhibitor SC-560. TxA(2) synthesis inhibitor (furegrelate), or TxA2 receptor antagonist (SQ 29 548) also decreased the noradrenaline contraction in aldosterone-treated animals. In untreated SHR, but not WKY rats, this response was increased by L-NAME, and reduced by tempol, indomethacin, NS-398 or SQ 29 548. Aldosterone treatment did not modify NO or TxB(2) release, but it did increase superoxide anion and 6-keto-PGF(1alpha) release in mesenteric resistance arteries from both strains. In conclusion, chronic aldosterone treatment reduces smooth muscle contraction to alpha-adrenergic stimuli, producing a new balance in the release of endothelium-derived prostanoids and NO.

Rho kinase and protein kinase C involvement in vascular smooth muscle myofilament calcium sensitization in arteries from diabetic rats

BACKGROUND AND PURPOSE

Diabetes mellitus (DM) causes multiple dysfunctions including circulatory disorders such as cardiomyopathy, angiopathy, atherosclerosis and arterial hypertension. Rho kinase (ROCK) and protein kinase C (PKC) regulate vascular smooth muscle (VSM) Ca(2+) sensitivity, thus enhancing VSM contraction, and up-regulation of both enzymes in DM is well known. We postulated that in DM, Ca(2+) sensitization occurs in diabetic arteries due to increased ROCK and/or PKC activity.

EXPERIMENTAL APPROACH

Rats were rendered hyperglycaemic by i.p. injection of streptozotocin. Age-matched control tissues were used for comparison. Contractile responses to phenylephrine (Phe) and different Ca(2+) concentrations were recorded, respectively, from intact and chemically permeabilized vascular rings from aorta, tail and mesenteric arteries.

KEY RESULTS

Diabetic tail and mesenteric arteries demonstrated markedly enhanced sensitivity to Phe while these changes were not observed in aorta. The ROCK inhibitor HA1077, but not the PKC inhibitor chelerythrine, caused significant reduction in sensitivity to agonist in diabetic vessels. Similar changes were observed for myofilament Ca(2+) sensitivity, which was again enhanced in DM in tail and mesenteric arteries, but not in aorta, and could be reduced by both the ROCK and PKC blockers.

CONCLUSIONS AND IMPLICATIONS

We conclude that in DM enhanced myofilament Ca(2+) sensitivity is mainly manifested in muscular-type blood vessels and thus likely to contribute to the development of hypertension. Both PKC and, in particular, ROCK are involved in this phenomenon. This highlights their potential usefulness as drug targets in the pharmacological management of DM-associated vascular dysfunction.

Alteration of vascular reactivity in diabetic human mammary artery and the effects of thiazolidinediones

Vascular reactivity was investigated in endothelium-denuded human internal mammary artery (IMA) rings from type 2 diabetic patients. It was also investigated whether insulin sensitizer thiazolidinedione drugs, pioglitazone and rosiglitazone, can directly affect the reactivity of IMA. Using organ bath techniques, cumulative concentration-response curves to phenylephrine (PE), KCl, cromakalim (CRO) and sodium nitroprusside (SNP) were constructed in diabetic and non-diabetic IMA rings. Means of maximal responses (% Emax) and pEC50 values (sensitivity) were compared. Emax values and the sensitivity to PE and KCl were increased while KATP-channel-mediated relaxations were reduced significantly in diabetic rings compared with non-diabetic rings (n = 5–12, P < 0.05). No changes were observed for SNP responses (n = 5, P > 0.05). Incubations with pioglitazone (1 and 10 μM) and rosiglitazone (1 and 20 μM), for 30 min, did not affect KATP-channel-mediated relaxations (n = 5 each, P > 0.05). Pioglitazone partly inhibited pre-contractions of PE and KCl at 10 μM, rosiglitazone did not. Vascular dysfunction observed in diabetic IMA may be of specific importance since they are widely used as coronary bypass material. Thiazolidinedione drugs may not worsen arterial dilatation through KATP channels in ischaemic or hypoxic insults in diabetic patients who are prone to such conditions. Pioglitazone has vasorelaxant property in the grafts.

Impairment of α1-adrenoceptor-mediated contractile activity in caudal arterial smooth muscle from type 2 diabetic Goto-Kakizaki rats

1. In the present study, we compared the responsiveness of de-endothelialized caudal artery smooth muscle strips, isolated from Type 2 diabetic Goto-Kakizaki (GK) and normal Wistar rats, to alpha(1)-adrenoceptor stimulation (cirazoline) and membrane depolarization (K(+)). 2. The contractile and myosin 20 kDa light chain (LC(20)) phosphorylation responses to 0.3 micromol/L cirazoline of caudal artery strips isolated from 12-week-old GK rats were significantly reduced compared with those of age-matched Wistar rats, whereas the contractile and LC(20) phosphorylation responses to 60 mmol/L K(+) were unaltered. 3. Stimulation of fura 2-AM-loaded strips from GK rats with 0.3 micromol/L cirazoline induced a significantly smaller rise in [Ca(2+)](i) (by approximately 20%) compared with that in strips from Wistar rats, whereas comparable Ca(2+) transients were evoked by K(+) in both. 4. Using quantitative polymerase chain reaction, no significant differences were detected in the mRNA expression of alpha(1A)-, alpha(1B)- and alpha(1D)-adrenoceptor subtypes between GK and Wistar rats. 5. Cirazoline (1 micromol/L)- and caffeine (20 mmol/L)-induced contractions in the absence of extracellular Ca(2+) were unaltered in GK rats, suggesting that the release of Ca(2+) from the sarcoplasmic reticulum in response to cirazoline does not differ between GK and Wistar rats. 6. The results of the present study suggest that Ca(2+) entry from the extracellular space via alpha(1)-adrenoceptor-activated, Ca(2+)-permeable channels, but not via membrane depolarization and voltage-gated L-type Ca(2+) channels, is impaired in caudal artery smooth muscle of GK rats.

Effect of salvianolic acid A on vascular reactivity of streptozotocin-induced diabetic rats

AIMS

The present study aims to evaluate the beneficial effect of salvianolic acid A (SAA) on the alterations in vascular reactivity of streptozotocin (STZ)-induced diabetic rats.

MAIN METHODS

Diabetes was induced by a single intraperitoneal injection of STZ (60 mg/kg). Following 16 weeks of SAA treatment (1 mg/kg/day), thoracic aortic rings of rats were mounted in organ baths. Contractile responses to noradrenaline (NA) and KCl and relaxant responses to acetylcholine (ACh) and sodium nitroprusside (SNP) were assessed.

KEY FINDINGS

Loss of weight, hyperglycemia, elevated content of malondialdehyde (MDA) and decline of total antioxidant capacity (TAC) were observed in diabetic rats. SAA could reverse these metabolic and biochemical abnormalities. Compared to the control, the maximum contraction (E(max)) to NA, but not sensitivity (pD(2)), increased significantly in diabetic aortas, which was prevented by SAA treatment. However, the response of rat aortas to KCl (E(max) and pD(2)) was not altered either in diabetic group or SAA treatment compared with that of normal control group. We also observed the significant decrease in relaxation to ACh rather than SNP in diabetic group compared with controls, and SAA treatment could revert the ACh response.

SIGNIFICANCE

It is concluded that oral administration of SAA can significantly improve glucose metabolism and inhibit oxidative injury as well as protect against impaired vascular responsiveness in STZ-induced diabetic rats.

Increased superoxide contributes to enhancement of vascular contraction in Ins2(Akita) diabetic mice, an autosomal dominant mutant model

Superoxide has been reported to be involved in vascular dysfunction in diabetes. The Ins2(Akita) mouse is an autosomal dominant mutant diabetic model that can serve as an excellent substitute for the Type 1 diabetic mouse model induced by chemical diabetogens. The purpose of the present study was to investigate the role of superoxide on vascular dysfunction using this new diabetic model. Compared with age-matched normal C57BL/6 mice, in Ins2(Akita) diabetic mice arterial superoxide, lipid peroxidation production (1.2 +/- 0.1 vs 17.4 +/- 1.9 mmol/mg tissue, respectively; P < 0.01) and plasma lipid peroxidation production (0.08 +/- 0.02 vs 0.40 +/- 0.03 mmol/L, respectively; P < 0.01) were increased. Meanwhile, expression of vascular adhesion molecule-1, E-selectin and monocyte chemoattractant protein-1 in the aorta and/or plasma was elevated. The contraction of carotid arteries to U46619 in Ins2(Akita) diabetic mice was significantly enhanced compared with control mice (P < 0.05). Tempol (a scavenger of superoxide), apocynin (an inhibitor of NADPH oxidase) and allopurinol (an inhibitor of xanthine oxidase) all not only decreased superoxide in carotid arteries, but also suppressed arterial contractions to U46619 in Ins2(Akita) diabetic mice. Indomethacin, an inhibitor of cyclo-oxygenase, and chelerythrine, an inhibitor of protein kinase C, also suppressed the enhanced vascular contraction. These results suggest that increased arterial superoxide generated from diverse sources may potentiate the contractions of carotid arteries in Ins2(Akita) diabetic mice.

Atrial natriuretic peptide prevents diabetes-induced endothelial dysfunction

Atrial natriuretic peptide (ANP) exerts beneficial effects on the cardiovascular system in part by exerting antioxidant activity. Given that oxidant stress is a key cause of endothelial dysfunction in diabetes, we investigated whether ANP improves endothelial function in rats with diabetes. Rats were injected with streptozotocin (55 mg/kg iv) to induce type 1 diabetes or the citrate vehicle as controls (n=12). After 4 weeks the diabetic rats were treated with ANP (10 pmol/kg/min sc, n=12) or the antioxidant tempol (1.5 mmol/kg/day sc, n=11), both by osmotic minipump, ramipril (1 mg/kg per day in the drinking water) or remained untreated (n=11). After a further 4 weeks, anaesthetised rats were killed by exsanguination and the thoracic aortae collected for examination of vascular activity and measurement of superoxide generation. Diabetic rats showed elevated plasma glucose concentration (45+/-3 mM) compared to controls (10+/-1 mM) and this was not affected by ANP (43+/-3 mM), ramipril (41+/-2 mM) or tempol (43+/-2 mM). Endothelium-dependent relaxation ex vivo in response to acetylcholine was impaired in diabetic rats (Rmax=66+/-4%) compared to control rats (Rmax=94+/-1%) but treatment with ANP (Rmax=80+/-4%), ramipril (Rmax=88+/-2%) or tempol (Rmax=81+/-5%) significantly improved those responses. Relaxant responses to the endothelium-independent vasodilator sodium nitroprusside were enhanced by treatment of diabetic rats with ANP or ramipril and their combination; but not by tempol. Superoxide generation was significantly elevated in aorta from untreated diabetic rats (649+/-146% of control). In diabetic rats, superoxide generation was significantly attenuated by ANP (to 229+/-78%) or tempol (to 186+/-64%). This study demonstrates that ANP improves vascular oxidant stress in concert with endothelial function, independent of any effect on plasma glucose levels. These studies may lead to new therapies, based on natriuretic peptide and/or antioxidant approaches, for ameliorating the vascular complications of diabetes.

Functional and molecular evidence for impairment of calcium-activated potassium channels in type-1 diabetic cerebral artery smooth muscle cells

Cerebral vascular dysfunction and associated diseases often occur in type-1 diabetes, but the underlying mechanisms are largely unknown. In this study, we sought to determine whether big-conductance, Ca(2+)-activated K(+) (BK) channels were impaired in vascular (cerebral artery) smooth muscle cells (CASMCs) from streptozotocin-induced type-1 diabetic mice using patch clamp, molecular biologic, and genetic approaches. Our data indicate that the frequency and amplitude of spontaneous transient outward currents (STOCs) are significantly decreased, whereas the activity of spontaneous Ca(2+) sparks is increased, in diabetic CASMCs. The sensitivity of BK channels to voltage, Ca(2+), and the specific inhibitor iberiotoxin are all reduced in diabetic myocytes. Diabetic mice show increased myogenic tone and decreased contraction in response to iberiotoxin in cerebral arteries and elevated blood pressure. The expression of the BK channel beta1, but not alpha-subunit protein, is markedly decreased in diabetic cerebral arteries. Diabetic impairment of BK channel activity is lost in CASMCs from BK channel beta1-subunit gene deletion mice. In conclusion, the BK channel beta1-subunit is impaired in type-1 diabetic vascular SMCs, resulting in increased vasoconstriction and elevated blood pressure, thereby contributing to vascular diseases in type-1 diabetes.

Dexamethasone decreases contraction to electrical field stimulation in mesenteric arteries from spontaneously hypertensive rats through decreases in thromboxane A2 release

Glucocorticoids play a role in the control of vascular smooth muscle tone through the alteration of vasoconstrictor and vasodilator factor production. We studied the effect of dexamethasone on vasoconstriction induced by electrical field stimulation (EFS) in rat mesenteric arteries (MAs) and the role of hypertension in this effect. Endothelium-denuded MAs were obtained from Wistar-Kyoto rats and spontaneously hypertensive rats (SHRs). EFS response was analyzed by isometric tension recordings and cyclooxygenase (COX-1 and COX-2) expression by Western blot. Noradrenaline (NA) release was evaluated in segments incubated with [(3)H]NA. Dexamethasone (0.1 and 1 microM; 2-8 h) reduced vasoconstriction to EFS (200 mA, 0.3 ms, 1-16 Hz), in a dose- and time-dependent manner only in SHRs. However, the EFS-induced release of [(3)H]NA was increased in SHR arteries preincubated with dexamethasone (1 microM; 6 h). The thromboxane A(2) (TxA(2)) synthase inhibitor furegrelate (10 microM), the selective COX-2 inhibitor NS-398 (N-[2-cyclohexyloxy-4-nitrophenyl] methanesulfonamide; 10 microM), or the TxA(2) receptor antagonist SQ 29548 (1 microM), reduced EFS and NA induced vasoconstrictor responses. However, the effect of these drugs was abolished in arteries preincubated with dexamethasone. Both dexamethasone and phentolamine (1 microM) inhibited the increased thromboxane B(2) levels observed after EFS. COX-2 protein expression was reduced by dexamethasone in SHR arteries. Results suggest that dexamethasone reduces vasoconstriction to EFS in MAs from SHRs by decreasing COX-2 expression, thereby decreasing the smooth muscle TXA(2) release induced by alpha-adrenoceptor activation. The undetectable COX-2 expression in MAs from normotensive animals explains the noneffect of dexamethasone in their arteries.

Postnatal maturation modulates relationships among cytosolic Ca2+, myosin light chain phosphorylation, and contractile tone in ovine cerebral arteries

The present study tests the hypothesis that age-related changes in patterns of agonist-induced myofilament Ca(2+) sensitization involve corresponding differences in the relative contributions of thick- and thin-filament regulation to overall myofilament Ca(2+) sensitivity. Posterior communicating cerebral arteries from term fetal and nonpregnant adult sheep were used in measurements of cytosolic Ca(2+), myosin light chain (MLC) phosphorylation, and contractile tensions induced by varying concentrations of K(+) or serotonin [5-hydroxytryptamine (5-HT)]. The results were used to assess the relative contributions of the relationships between cytosolic Ca(2+) and MLC phosphorylation (thick-filament reactivity), along with the relationships between MLC phosphorylation and contractile tension (thin-filament reactivity), to overall myofilament Ca(2+) sensitivity. For K(+)-induced contractions, both fetal and adult arteries exhibited similar basal myofilament Ca(2+) sensitivity. Despite this similarity, thick-filament reactivity was greater in fetal arteries, whereas thin-filament reactivity was greater in adult arteries. In contrast, 5-HT-induced contractions exhibited increased myofilament Ca(2+) sensitivity compared with K(+)-induced contractions for both fetal and adult cerebral arteries, and the magnitude of this effect was greater in fetal compared with adult arteries. When interpreted together with our previous studies of 5-HT-induced myofilament Ca(2+) sensitization, we attributed the present effects to agonist enhancement of thick-filament reactivity in fetal arteries mediated by G protein receptor activation of a PKC-independent but RhoA-dependent pathway. In adult arteries, agonist stimulation enhanced thin-filament reactivity was also probably mediated through G protein-coupled activation of RhoA-dependent and PKC-independent mechanisms. Overall, the present data demonstrate that agonist-enhanced myofilament Ca(2+) sensitivity can be partitioned into separate thick- and thin-filament effects, the magnitudes of which are different between fetal and adult cerebral arteries.

Carvedilol ameliorates endothelial dysfunction in streptozotocin-induced diabetic rats

The beta-blocker, carvedilol has an additional endothelium-dependent vasodilating properties in patients with hypertension or heart failure. Whether carvedilol can improve endothelium-dependent relaxation in a diabetic animal model and its mechanism of action are unknown. The aim of this study was to investigate the effect of carvedilol on the endothelial-response of aortas from diabetic rats and the underlying mechanism. Acetylcholine-induced endothelium-dependent relaxation, sodium nitroprusside (SNP)-induced endothelium-independent relaxation, and expression of nitric oxide synthase 3 (NOS3) mRNA were measured in aortas isolated from both non-diabetic and streptozotocin-induced diabetic rats. The level of NO in serum was also measured 5 weeks after carvedilol administration (1 or 10 mg/kg/day). Endothelium-dependent relaxation declined along with the decrease of serum NO level in aortas from diabetic rats. Treatment with carvedilol for 5 weeks prevented the inhibition of endothelium-dependent relaxation and the decrease of serum NO levels caused by diabetes. The expression of NOS3 mRNA, protein expression and NOS3 phosphorylation at Ser1177 in diabetic rat aorta was very low in untreated diabetic aortas compared with the healthy group. Administration of carvedilol not only significantly increased the expression of NOS3 mRNA but also protein expression and NOS3 phosphorylation at Ser1177 in the healthy and diabetic groups. In conclusion, chronic carvedilol administration significantly ameliorated the endothelial dysfunction in diabetic rat aortas, in which increased NO level, up-regulated NOS3 mRNA and phosphorylation at Ser1177 may be involved.

Ethanolic extract of Spirulina maxima alters the vasomotor reactivity of aortic rings from obese rats

BACKGROUND

Aortic rings with endothelium excised from fructose-fed obese rats develop more tension in response to phenylephrine and relax less in response to carbachol than corresponding rings from lean rats. This altered vascular reactivity is prevented when Spirulina maxima is added to the fructose-rich diet. In the present study the effects of a raw ethanolic extract of Spirulina maxima on the vasomotor responses of aorta rings from sucrose-fed obese hypertensive rats were analyzed.

METHODS

The experiments were performed on aorta rings from sucrose-fed obese male rats. For each experiment, a pair of rings from the same aorta (one with intact endothelium, the other without a functional endothelium) was used. In this study we analyzed, in vitro, the effects of the ethanolic extract of Spirulina maxima on the reactivity of the aortic rings to phenylephrine and to carbachol.

RESULTS

On rings with endothelium, the extract produced the following effects: a) a concentration-dependent (0.06-1.0 mg/mL) decrease of the contractile response to phenylephrine; b) a rightward shift and a decrease in maximal developed tension, of the concentration-response curve to phenylephrine; c) a concentration-dependent relaxation of phenylephrine-precontracted rings. These effects persisted in the presence of indomethacin but were prevented by L-NAME. The extract had no effect on the concentration-response curve of phenylephrine-precontracted rings to carbachol. On endothelium-denuded rings the extract caused a significant rightward shift of the concentration response curve to phenylephrine without any effect on maximal tension development.

CONCLUSIONS

These results suggest that, in rings from obese rats, the extract, in addition to increasing the synthesis/release of NO, also inhibits the synthesis/release of a cyclooxygenase-dependent vasoconstrictor metabolite of arachidonic acid, which is increased in obesity.

General administration of cyclohexenonic long-chain fatty alcohol ameliorates hyperreactivity of STZ-induced diabetic rat aorta

Diabetic neuropathy, a major complication of diabetes mellitus, is associated with the development of vascular dysfunction and autonomic neuropathy. We studied the effects of cyclohexenonic long-chain fatty alcohol (FA) on streptozotocin-diabetic hyperreactivity in the rat aorta smooth muscle. The rats were divided randomly into four groups and were maintained for 4 weeks: age-matched control rats, diabetic rats without treatment with FA, and diabetic rats treated with FA (2 and 8 mg/kg, i.p. everyday). The serum glucose and insulin levels were determined, and the contractile responses of the aorta induced by a thromboxane A2 agonist, U46619 and KCl were investigated. Treatment with FA did not alter rats' diabetic status, i.e., body weight, thickness of the aorta, serum glucose levels, and serum insulin levels, but significantly improved the diabetic-induced hyperreactivity of the rat aorta in a dose-dependent manner. Removal of endothelium did not change contractile force between groups. In histological examinations, thinning of smooth muscle bundle in the wall of aorta was observed in the diabetic rat, which was not significantly improved by treatment with FA. Our data indicate that FA can prevent hyperreactivity in the diabetic aorta.

Chronic ethanol consumption enhances phenylephrine-induced contraction in the isolated rat aorta

Changes in reactivity to phenylephrine in aortas isolated from 2-, 6-, and 10-week ethanol-treated rats and their age-matched control and isocaloric rats were investigated. Chronic ethanol consumption enhances the contractile response of endothelium-intact and -denuded rat aortic rings to phenylephrine, a response that is time-independent. Pretreatment with indomethacin reduced E(max) for phenylephrine in denuded aortas from ethanol-treated rats but not control or isocaloric rats. After indomethacin treatment, no differences in E(max) from phenylephrine were observed among the groups. SQ29548 ([1S-[1alpha-2alpha(Z)3alpha,4alpha]]-7-[3-[[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid), an antagonist of prostaglandin H(2)/thromboxane A(2) (TXA(2)) receptors, did not alter phenylephrine-induced contraction in control or isocaloric aortas. However, in ethanol-treated aortas, E(max) was reduced to control level. Moreover, phenylephrine-stimulated release of thromboxane B(2), a stable metabolite of TXA(2), was higher in tissues from ethanol-treated rats. Simultaneous measurement of the changes in [Ca(2+)](i) and contraction induced by phenylephrine showed that both parameters are higher in the rat aorta from ethanol-treated rats. CaCl(2)-induced contraction in free Ca(2+) solution containing phenylephrine was increased in ethanol-treated aortas. Additionally, the enhancement in CaCl(2)-induced contraction was prevented by SQ29548. The major contribution of the present study is that it demonstrates a detailed description of the mechanisms involved in the enhancement of phenylephrine-induced contraction in rat aorta from ethanol-treated rats. We provided evidence that this response was not different among the three periods of treatment employed in this study and that it is maintained by two mechanisms: an increased release of vascular smooth muscle-derived vasoconstrictor prostanoids (probably TXA(2)) and an enhanced extracellular Ca(2+) influx.

Chronic hypoxia modulates relations among calcium, myosin light chain phosphorylation, and force differently in fetal and adult ovine basilar arteries

The present study tests the hypothesis that age-related differences in contractility of cerebral arteries from hypoxic animals involve changes in myofilament Ca2+ sensitivity. Basilar arteries from term fetal and nonpregnant adult sheep maintained 110 days at 3,820 m were used in measurements of cytosolic calcium concentration ([Ca2+]i), myosin light chain phosphorylation, and contractile tensions induced by graded concentrations of K+ or serotonin (5-HT). Slopes relating [Ca2+]i to tension were similar in fetal (0.83 +/- 0.07) and adult (1.02 +/- 0.08) arteries for K+ contractions but were significantly greater for fetal (3.77 +/- 0.64) than adult (2.00 +/- 0.13) arteries for 5-HT contractions. For both K+ and 5-HT contractions, these relations were left shifted in fetal compared with adult arteries, indicating greater Ca2+ sensitivity in fetal arteries. In contrast, slopes relating [Ca2+]i and %myosin phosphorylation for K+ contractions were less in fetal (0.37 +/- 0.08) than adult (0.81 +/- 0.07) arteries, and the fetal curves were right shifted. For 5-HT contractions, the slope of the Ca2+-phosphorylation relation was similar in fetal (0.33 +/- 0.09) and adult (0.33 +/- 0.23) arteries, indicating that 5-HT depressed Ca2+-induced myosin phosphorylation in adult arteries. For slopes relating %myosin phosphorylation and tension, fetal values (K+: 1.52 +/- 0.22, 5-HT: 7.66 +/- 1.70) were less than adult values (K+: 2.13 +/- 0.30, 5-HT: 8.29 +/- 2.40) for both K+- and 5-HT-induced contractions, although again fetal curves were left shifted relative to the adult. Thus, in hypoxia-acclimatized basilar arteries, a downregulated ability of Ca2+ to promote myosin phosphorylation is offset by an upregulated ability of phosphorylated myosin to produce force yielding an increased fetal myofilament Ca2+ sensitivity. Postnatal maturation reprioritizes the mechanisms regulating hypoxic contractility through changes in the source of activator Ca2+, the pathways governing myosin light chain phosphorylation, and its interaction with actin.

Implications for repetitive application of acetylcholine in the determination of the mechanisms of endothelium-dependent relaxation

The influence of repetitive vasodilator concentration response curve determination was investigated in rat mesenteric and femoral small arteries. Arteries were precontracted with noradrenaline and relaxed with acetylcholine (ACh) or K+. Mesenteric arteries exhibited attenuation of ACh-stimulated relaxations during repetitive precontraction/relaxation cycles that was not prevented by SQ29548. Apamin, but not charybdotoxin, prevented the attenuation of this relaxation response. Borderline (p=0.064) statistical differences in the relaxations of mesenteric arteries in response to ACh remained in the presence of the nitric oxide synthase inhibitor L-NNA. In contrast, femoral arterial relaxations increased with repeated acetylcholine challenges. The enhanced responsiveness was prevented with L-NNA or Ba2+. In one experimental series, Ba2+ appeared to be without influence upon K+-stimulated relaxation of femoral arteries but a significant inhibitory effect was revealed when appropriate time control experiments were considered. These experiments reveal that impairment of SK(Ca) function and, to a lesser extent, an impaired NO signalling account for the attenuation of the relaxation responses of rat mesenteric arteries. In contrast, alterations of nitric oxide signalling and inward rectifier K channel activity contribute to enhanced relaxation responses in rat femoral arteries. These experiments highlight the importance of appropriate time control experiments for the proper interpretation of results derived from pharmacological experiments directed toward the elucidation of mechanisms of arterial vasorelaxation.