Vascular reactivity to noradrenaline and neuropeptide Y in the streptozotocin-induced diabetic rat

H2 S donor improves heart function and vascular relaxation in diabetes

BACKGROUND AND AIMS

Diabetes dramatically increases the risk of cardiovascular complications and mortality. Hydrogen sulphide plays an important role in reducing oxidative stress. Several studies demonstrated that hydrogen sulphide protects islet beta cells from oxidant stress damage and decreases apoptosis. The aim of the work is to investigate the effect of hydrogen sulphide donor on heart functions and endothelium-dependent relaxation of aortic smooth muscle in diabetes.

MATERIALS AND METHODS

Rats were divided into control and diabetic groups. Diabetes mellitus was induced with a single intraperitoneally injection of streptozotocin (60 mg kg^-1 ). The functional cardiohemodynamic indicators were registered via microcatheter and Pressure-Volume System. The sodium hydrosulphide NaHS (15.8 mg kg^-1 ) was administered intraperitoneally. The contractile activity of the muscle preparations of the thoracic aorta was recorded using a strain gauge.

RESULTS

We demonstrate that the NaHS improves pumping function and restores diastolic heart function in streptozotocin-induced (STZ) diabetes rats. We show that pretreatment with NaHS increased the stroke volume by 43.1%, and the ejection fraction increased by 48.64%. NaHS improves the ventriculo-arterial coupling and increases by 3.4 times acetylcholine-induced relaxation of the aorta in diabetic rats. The inhibition of NOS activity by blocker L-NAME abolished NaHS-mediated vasodilatation in the intact endothelium of the aorta in diabetes. It indicates that the NaHS caused vasodilatation by a NOS-dependent mechanism.

CONCLUSION

The exogenous hydrogen sulphide can improve pumping function and restore diastolic heart function in diabetes. The pretreatment with NaHS can prevent endothelial dysfunction in diabetes due to the NOS-dependent mechanism.

The Role of Epoxyeicosatrienoic Acids in Diabetes Mellitus-Induced Impaired Vascular Relaxation of Aortic Rings in Ovariectomized Sprague-Dawley Rats

AIM

The present study was aimed at determining if type 1 diabetes mellitus (DM) affects vascular function and at elucidating the mechanisms mediating vasorelaxation in both nonovariectomized and ovariectomized Sprague-Dawley (SD) rats.

MATERIALS AND METHODS

Eighty female SD rats were divided into four groups: nonovariectomized healthy (non-OVX-CTR) and diabetic (non-OVX-DM) rats and ovariectomized healthy (OVX-CTR) and diabetic (OVX-DM) rats. Bilateral ovariectomy was performed at the age of 5 weeks, and type 1 DM was induced by streptozotocin at the age of 6 weeks. At the age of 12 weeks, acetylcholine-induced relaxation (AChIR) was assessed in aortic rings in the absence/presence of L-NAME, Indomethacin, and MS-PPOH. Aortic tissue mRNA expression of eNOS, iNOS, COX-1, COX-2, thromboxane synthase 1 (TBXAS1), CYP4A1, CYP4A3, and CYP2J3, as well as plasma oxidative stress, was measured.

RESULTS

AChIR did not differ in non-OVX-DM rats compared to non-OVX-CTR ones. AChIR was significantly reduced in the OVX-DM group compared to the OVX-CTR group. MS-PPOH did not reduce AChIR in OVX-DM rats as it did in OVX-CTR ones. CYP4a3 mRNA expression in OVX-DM rats was significantly lower compared to that in the OVX-CTR group.

CONCLUSIONS

Female sex hormones may protect vasorelaxation in type 1 diabetic rats. Type 1 diabetes impairs vasorelaxation in response to ACh in ovariectomized rats (but not in nonovariectomized rats) by affecting vasorelaxation pathways mediated by EETs.

Could angiotensin-(1-7) be connected with improvement of microvascular function in diabetic patients? Angiotensin-(1-7) iontophoresis may provide the answer

Diabetes mellitus, a metabolic disorder with significant global health care burden, causes chronic microvascular and macrovascular complications that still comprise a therapeutic challenge. Angiotensin-(1-7), a heptapeptide with vasodilatory properties, has been found to restore vascular reactivity and endothelial cell function, mostly in experiments on larger isolated animal vessels and in cell cultures. The presented hypothesis suggests that angiotensin-(1-7) might have beneficial effects on microvascular function that is damaged in diabetic patients, alleviating endothelial dysfunction and increasing microvascular reactivity to various vasoactive agents in diabetes. It is further proposed that iontophoresis with angiotensin-(1-7) might be used to explore this potential beneficial effect, as well as provide a possible future therapeutic delivery method for angiotensin-(1-7). Since other peptides and proteins have been previously tested and used in iontophoretic transdermal delivery, it is plausible that angiotensin-(1-7) would be a suitable candidate for transdermal iontophoretic application for research (and potentially therapeutic) purposes. If confirmed, the delineated hypothesis would have immense implications for more effective care of diabetic patients, as well as for better understanding of microcirculatory pathophysiological mechanisms in diabetes.

Hyperbaric oxygenation modulates vascular reactivity to angiotensin-(1-7) in diabetic rats: potential role of epoxyeicosatrienoic acids

Previously, a facilitating effect of hyperbaric oxygenation (HBO₂) on aortic ring responses to angiotensin-(1-7) in healthy rats was reported, with epoxyeicosatrienoic acids (EETs) possibly playing an important role. The aim of this study was to assess whether HBO₂ exerts similar effects in diabetic rats and to further explore the role of specific cytochrome P450 (CYP) enzymes in changes induced by HBO₂. Aortic relaxation to angiotensin-(1-7) was significantly higher in HBO₂ diabetic rats compared to control diabetic rats, while HBO₂ had no effect on angiotensin II contraction. N-methylsulphonyl-6-(2-propargyloxyphenyl/hexanamide inhibited the facilitation of angiotensin-(1-7) responses in HBO₂ rats, suggesting an important role of EETs in this modulation. mRNA expression of CYP2J3 and protein expression of CYP2C11 were significantly upregulated in HBO₂ diabetic rats, whereas CYP4A1, CYP4A2 and CYP4A3 mRNA and CYP2J3 protein expression was similar between groups. Mean arterial pressure, ferric reducing ability of plasma and Thiobarbituric Acid Reactive Substances levels and serum angiotensin-(1-7) concentrations were not significantly changed.

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.

Enhanced neuropeptide Y immunoreactivity and vasoconstriction in mesenteric small arteries from the early non-obese diabetic mouse

The present study investigated whether sympathetic neurotransmission is altered at an early stage of diabetes in mesenteric small arteries isolated from female non-obese diabetic (NOD) and control animals without diabetes from the same mouse strain. The NOD diabetic mice had increased plasma glucose and hypertension. Confocal microscopy showed distribution of nerve terminals was similar, but immunoreaction intensity for neuropeptide Y (NPY) and tyrosine hydroxylase was higher in small arteries from NOD diabetic compared with NOD control mice. In the presence of prazosin and activated with vasopressin, electrical field stimulation evoked contractions which were more pronounced in mesenteric arteries from NOD diabetic versus NOD control mice and inhibited by the NPY Y(1) receptor antagonist, BIBP 3226. NPY concentration-response curves were leftward shifted in arteries from NOD diabetic versus NOD control both in arteries with and without endothelium, but not in the presence of the BIBP 3226. The present findings suggest that enhanced NPY content and vasoconstriction to NPY by activation of NPY Y(1) receptors in arteries from diabetic mice may contribute to the enhanced sympathetic nerve activity and vascular resistance in female non-obese early diabetic animals.

The effect of long-term streptozotocin-induced diabetes on contractile and relaxation responses of coronary arteries: selective attenuation of CGRP-induced relaxations

1. This study investigates the effect of partially metabolic controlled long-term (34 weeks) streptozotocin (STZ)-induced diabetes on relaxation and contractile responses of isolated coronary arteries to seven different vasoactive agents. 2. The average fasting and non-fasting blood glucose concentrations (mM) were significantly elevated in STZ-induced diabetic rats (P<0.0001; 10.4+/-0.4 and 16. 6+/-1.1, n=15) compared to those (4.3+/-0.03 and 4.7+/-0.18, n=11) in age-matched controls. The level of glycated haemoglobin (HbA(1)) was also significantly (P<0.0001) increased in STZ-induced diabetic rats. In STZ-induced diabetic rats, the HbA(1) levels were significantly correlated with the non-fasting blood glucose concentrations (r=0.76; P=0.003; n=13). In both groups, there was no significant correlation between the HbA(1) levels and maximal responses or sensitivities to the vasoactive agents. 3. The maximal relaxation induced by rat-alphacalcitonin gene-related peptide (rat-alphaCGRP) was significantly attenuated in the coronary arteries of STZ-induced diabetic rats (P<0.05; 40+/-7%, n=15) compared to that in age-matched controls (63+/-3%, n=11). However, there was no significant difference in the sensitivity to rat-alphaCGRP between the two groups. 4. There was no significant difference in either maximal response or sensitivity to any of the six other vasoactive agents between STZ- induced diabetic rats (n=15) and age-matched controls (n=11). 5. Our results show that partially metabolic controlled long-term (34 weeks) STZ-induced diabetes causes a selective depression of rat-alphaCGRP-induced relaxation in the intramural coronary arteries of Wistar rats.

Studies on the influence of insulin on cyclic adenosine monophosphate in human vascular smooth muscle cells: dependence on cyclic guanosine monophosphate and modulation of catecholamine effects

Insulin increases both cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) in human vascular smooth muscle cells (hVSMC) and attenuates noradrenaline-induced vasoconstriction. In the present study, we aimed at investigation in hVSMC: 1) the interrelationships between insulin-induced increases of cGMP and cAMP; 2) the insulin effect on the catecholamine modulation of cAMP. Catecholamines cause both vasoconstriction and vasodilation. Vasoconstriction is attributable to the reduced synthesis of cAMP in hVSMC through alpha 2-adrenoceptors and to direct effects on calcium fluxes through alpha 1-adrenoceptors; vasodilation is attributable to the increased synthesis of cAMP through beta-adrenoceptors. In the present study, we determined the influence of insulin on cAMP in hVSMC incubated with or without: a) the inhibitor of guanylate cyclase methylene blue or the inhibitor of nitric oxide synthase NG-monomethyl-L-arginine (L-NMMA); b) the beta-adrenergic agonists isoproterenol and salbutamol; c) the physiological catecholamines noradrenaline and adrenaline; d) noradrenaline+the beta-adrenergic antagonist propranolol or the alpha 2-adrenergic antagonist yohimbine; e) noradrenaline+methylene blue of L-NMMA. We demonstrated that: 1) the inhibition of the insulin-induced cGMP synthesis blunts the insulin-induced increase of cAMP; 2) insulin induces a significant increase of cAMP also in the presence of isoproterenol, salbutamol, noradrenaline and adrenaline: the combined effects of insulin and catecholamines were additive in some, but not in all the experiments; 3) insulin enhances the cAMP concentrations induced by noradrenaline also in the presence of alpha 2- or beta-adrenergic antagonists; 4) in the presence of methylene blue or L-NMMA insulin does not modify the noradrenaline effects on cAMP.