Increased vasodilator response to acetylcholine of renal blood vessels from diabetic rats

Role of Ang1-7 in renal haemodynamics and excretion in streptozotocin diabetic rats

The contribution of angiotensin (1-7) (Ang1-7) to control of extrarenal and renal function may be modified in diabetes. We investigated the effects of Ang1-7 supplementation on blood pressure, renal circulation and intrarenal reactivity (IVR) to vasoactive agents in normoglycaemic (NG) and streptozotocin diabetic rats (DM). In Sprague Dawley DM and NG rats, 3 weeks after streptozotocin (60 mg/kg i.p.) or solvent injection, Ang1-7 was administered (400 ng/min) over the next 2 weeks using subcutaneously implanted osmotic minipumps. For a period of 5 weeks, blood pressure (BP), 24 h water intake and diuresis were determined weekly. In anaesthetised rats, BP, renal total and cortical (CBF), outer (OMBF) and inner medullary (IMBF) perfusion and urine excretion were determined. To check IVR, a short-time infusion of acetylcholine or norepinephrine was randomly given to the renal artery. Unexpectedly, BP did not differ between NG and DM, and this was not modified by Ang-1-7 supplementation. Baseline IMBF was higher in NG vs. DM, and Ang1-7 treatment did not change it in NG but decreased it in DM. In the latter, Ang1-7 increased cortical IVR to vasoconstrictor and vasodilator stimuli. IMBF decrease after high acetylcholine dose seen in untreated NG was reverted to an increase in Ang1-7 treated rats. Irrespective of the glycaemia level, Ang1-7 did not modify BP. However, it impaired medullary circulation in DM, whereas in NG it rendered the medullary vasculature more sensitive to vasodilators. Possibly, the medullary hypoperfusion in DM was mediated by Ang1-7 activation of angiotensin AT-1 receptors which are upregulated by hyperglycaemia.

Gallic acid improves endothelium-dependent vasodilatory response to histamine in the mesenteric vascular bed of diabetic rats

BACKGROUND

Endothelial dysfunction is one of the many complications caused by diabetes mellitus. The aim of the present study was to evaluate the effects of gallic acid (GA) on the mesenteric vascular bed (MVB) response to histamine in diabetic rats.

METHODS

Forty male Wistar rats were randomly assigned to a control group, an untreated alloxan-induced diabetic group and three diabetic groups treated with different doses of GA. Six weeks after induction of diabetes and GA treatment, total antioxidant capacity (TAC), malondialdehyde (MDA) concentrations, and the vasodilatory response to histamine of the MVB (measured as changes in perfusion pressure) were determined.

RESULTS

The vasodilatory response to histamine and TAC decreased, whereas MDA increased in the plasma from diabetic rats (P < 0.01). However, in the presence of 3 × 10^-5  mol/L N ^G -nitro-l-arginine methyl ester (a nitric oxide synthase inhibitor) and 1 × 10^-5  mol/L indomethacin (an inhibitor of prostaglandin production), the vasodilatory response of the MVB to histamine was reduced in all groups (P < 0.001). Treatment of diabetic rats with 20 and 40 mg/kg per day GA, but not 10 mg/kg per day GA, increased TAC and decreased MDA concentrations (P < 0.01 and P < 0.001 vs untreated diabetic rats, respectively) and significantly improved the vasodilatory response to histamine (P < 0.05 and P < 0.001, respectively).

CONCLUSION

The results show that, in diabetic rats, the endothelium-dependent vasodilatory response of the MVB to histamine is significantly decreased and depends on both nitric oxide- and prostaglandin-producing pathways and may be mediated by oxidative stress. Treatment with the antioxidant GA restored the vasodilatory response of the MVB to histamine.

Sex-specific vascular responses of the rat aorta: effects of moderate term (intermediate stage) streptozotocin-induced diabetes

Hyperglycemia affects male and female vascular beds differently. We have previously shown that 1 week after the induction of diabetes with streptozotocin (STZ), male and female rats exhibit differences in aortic endothelial function. To examine this phenomenon further, aortic responses were studied in male and female rats 8 weeks after the induction of diabetes (intermediate stage). Endothelium-dependent vasodilation (EDV) to acetylcholine (ACh) was measured in phenylephrine (PE) pre-contracted rat aortic rings. Concentration response curves to PE were generated before and after L-NAME, a nitric oxide synthase (NOS) inhibitor. Furthermore, mRNA expression of endothelial nitric oxide synthase (eNOS) and NADPH oxidase subunit (Nox1) were determined. At 8 weeks, diabetes impaired EDV to a greater extent in female than male aortae. Furthermore, the responsiveness to PE was significantly enhanced only in female diabetic rats, and basal NO, as indicated by the potentiation of the response to PE after L-NAME, was reduced in female diabetic rat aortae to the same levels as in males. In addition, eNOS mRNA expression was decreased, while the Nox1 expression was significantly enhanced in diabetic female rats. These results suggest that aortic function in female diabetic rats after 8 weeks exhibits a more prominent impairment and that NO may be involved.

Sex differences in mesenteric endothelial function of streptozotocin-induced diabetic rats: a shift in the relative importance of EDRFs

Several studies suggest that diabetes affects male and female vascular beds differently. However, the mechanisms underlying the interaction of sex and diabetes remain to be investigated. This study investigates whether there are 1) sex differences in the development of abnormal vascular responses and 2) changes in the relative contributions of endothelium-derived relaxing factors in modulating vascular reactivity of mesenteric arteries taken from streptozotocin (STZ)-induced diabetic rats at early and intermediate stages of the disease (1 and 8 wk, respectively). We also investigated the mesenteric expression of the mRNAs for endothelial nitric oxide (NO) synthase (eNOS) and NADPH oxidase (Nox) in STZ-induced diabetes in both sexes. Vascular responses to acetylcholine (ACh) in mesenteric arterial rings precontracted with phenylephrine were measured before and after pretreatment with indomethacin (cyclooxygenase inhibitor), N(ω)-nitro-L-arginine methyl ester (NOS inhibitor), or barium chloride (K(ir) blocker) plus ouabain (Na(+)-K(+)-ATPase inhibitor). We demonstrated that ACh-induced relaxations were significantly impaired in mesenteric arteries from both male and female diabetic rats at 1 and 8 wk. However, at 8 wk the extent of impairment was significantly greater in diabetic females than diabetic males. Our data also showed that in females, the levels of eNOS, Nox2, and Nox4 mRNA expression and the relative importance of NO to the regulation of vascular reactivity were substantially enhanced, whereas the importance of endothelium-derived hyperpolarizing factor (EDHF) was significantly reduced at both 1 and 8 wk after the induction of diabetes. This study reveals the predisposition of female rat mesenteric arteries to vascular injury after the induction of diabetes may be due to a shift away from a putative EDHF, initially the major vasodilatory factor, toward a greater reliance on NO.

Oxidative stress is not associated with vascular dysfunction in a model of alloxan-induced diabetic rats

OBJECTIVES

To verify if an experimental model of alloxan-diabetic rats promotes oxidative stress, reduces nitric oxide bioavailability and causes vascular dysfunction, and to evaluate the effect of N-acetylcysteine (NAC) on these parameters.

METHODS

Alloxan-diabetic rats were treated or not with NAC for four weeks. Plasmatic levels of malondialdehyde (MDA) and nitrite/nitrate (NOx), the endothelial and inducible nitric oxide synthase (eNOS and iNOS) immunostaining and the vascular reactivity of aorta were compared among diabetic (D), treated diabetic (TD) and control (C) rats.

RESULTS

MDA levels increased in D and TD. NOx levels did not differ among groups. Endothelial eNOS immunostaining reduced and adventitial iNOS increased in D and TD. The responsiveness of rings to acetylcholine, sodium nitroprusside, and phenylephrine did not differ among groups.

CONCLUSIONS

NAC had no effect on the evaluated parameters and this experimental model did not promote vascular dysfunction despite the development of oxidative stress.

Temporal changes in vascular reactivity in early diabetes mellitus in rats: role of changes in endothelial factors and in phosphodiesterase activity

The aims of this study were to study the influence of the duration of diabetes, the role of endothelial-derived vasodilators, and the role of phosphodiesterase (PDE) isoform activity in the early changes in vascular reactivity of aortic rings from diabetic rats. Diabetes mellitus was induced in female rats by intravenous streptozotocin (85 mg/kg). Two or 4 wk later, thoracic aortic rings from control and diabetic rats were isolated, and vascular responses to acetylcholine (ACh), S-nitroso-N-acetylpenicillamine (SNAP) [nitric oxide (NO) donor], DMPPO (PDE5 inhibitor), and phenylephrine (PE) were obtained in the presence and absence of endothelium or other drugs. PDE isoform activity was also measured. At 2 wk, responses to ACh and DMPPO were enhanced, whereas those to PE were attenuated in diabetic rats relative to controls. Indomethacin and SQ-29548 (a thromboxane A(2) receptor antagonist), but not N(G)-nitro-L-arginine methyl ester, corrected these differences. The responses to SNAP, and cAMP and cGMP hydrolytic activities, were similar in the two groups. In contrast, at 4 wk, ACh, DMPPO, and PE produced similar responses in the two groups: N(G)-nitro-L-arginine methyl ester rendered the response to PE lower in the diabetic group, and this was corrected by indomethacin, but not SQ-29548, treatment. The response to SNAP was greater in the diabetic group, and this was corrected by DMPPO. Activity of all PDEs was decreased at 4 wk. We conclude that, at 2 wk, there is modulation of thromboxane A(2) production, but no change in the NO system or PDE isoform activities. At 4 wk, a reduction in NO activity is superimposed; at this stage, PDE activity is reduced, together with increased production of vasodilating prostaglandins, possibly as a compensatory mechanism to maintain normal vascular reactivity.

Effects of streptozotocin-induced diabetes on the pharmacology of rat conduit and resistance intrapulmonary arteries

Background

Poor control of blood glucose in diabetes is known to promote vascular dysfunction and hypertension. Diabetes was recently shown to be linked to an increased prevalence of pulmonary hypertension. The aim of this study was to determine how the pharmacological reactivity of intrapulmonary arteries is altered in a rat model of diabetes.

Methods

Diabetes was induced in rats by the β-cell toxin, streptozotocin (STZ, 60 mg/kg), and isolated conduit and resistance intrapulmonary arteries studied 3–4 months later. Isometric tension responses to the vasoconstrictors phenylephrine, serotonin and PGF_2α, and the vasodilators carbachol and glyceryl trinitrate, were compared in STZ-treated rats and age-matched controls.

Results

STZ-induced diabetes significantly blunted the maximum response of conduit, but not resistance pulmonary arteries to phenylephrine and serotonin, without a change in pEC₅₀. Agonist responses were differentially reduced, with serotonin (46% smaller) affected more than phenylephrine (32% smaller) and responses to PGF_2α unaltered. Vasoconstriction caused by K⁺-induced depolarisation remained normal in diabetic rats. Endothelium-dependent dilation to carbachol and endothelium-independent dilation to glyceryl trinitrate were also unaffected.

Conclusion

The small resistance pulmonary arteries are relatively resistant to STZ-induced diabetes. The impaired constrictor responsiveness of conduit vessels was agonist dependent, suggesting possible loss of receptor expression or function. The observed effects cannot account for pulmonary hypertension in diabetes, rather the impaired reactivity to vasoconstrictors would counteract the development of pulmonary hypertensive disease.

The effect of experimental diabetes on the twenty-four-hour pattern of the vasodilator responses to acetylcholine and isoprenaline in the rat aorta

The aim of this study was to investigate whether time-dependent variations in the relaxant effect of acetylcholine, an endothelium-dependent vasorelaxant via muscarinic receptors, and isoprenaline, a nonselective beta-adrenoceptor agonist in rat aorta, are influenced by streptozotocin (STZ)-induced experimental diabetes. Adult male rats were divided randomly into two groups: control and STZ-induced (STZ, 55 mg/kg, intraperitoneal) diabetes. The animals were synchronized to a 12:12 h light-dark cycle (lights on 08:00 h) and sacrificed at six different times of day (1, 5, 9, 13, 17, and 21 hours after lights on; HALO) eight weeks after STZ injection. The in vitro responsiveness of thoracic aorta rings obtained from control and diabetic rats to acetylcholine (10(-9)-10(-5) M) and isoprenaline (10(-10)-10(-3) M) was determined in six different times. EC(50) (the concentration inducing half of the maximum response) values and maximum responses were calculated from cumulative concentration-response curves of the agonists and were analyzed with respect to time and STZ treatment. Treatment, time, and interactions between treatment and time were tested by two-way analysis of variance (ANOVA). To analyze differences due to biological time, one-way ANOVA was used. STZ treatment did not significantly change EC(50) values or maximum responses for both agonists. There were statistically significant time-dependent variations in the EC(50) values for isoprenaline and maximum responses for both acetylcholine and isoprenaline in control groups by one-way ANOVA, but significant time-dependent variations disappeared in the aortas isolated from STZ-induced diabetic rats. The vasodilator responses to acetylcholine and isoprenaline failed to show any significant interaction (treatmentxtime of study) between STZ treatment and time of sacrifice in both EC(50) values and maximum responses by two-way ANOVA. These results indicate there is a basic temporal pattern in the responses to acetylcholine and isoprenaline in rat aorta which continues in diabetes. It is shown for the first time that experimental diabetes does not change the 24 h pattern of responses to acetylcholine and isoprenaline, and that time-dependent variations in the responses to these agonists disappear in diabetic animals. Although further studies are required to define the underlying mechanism(s) of these findings, results suggest that experimental diabetes can modify the time-dependent vasorelaxant responses of rat aorta. This may help to understand the circadian rhythms in cardiovascular physiology and pathology or in drug effects in diabetes.

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.

Acetylcholine-induced vasodilation in the perfused kidney of the streptozotocin-induced diabetic rat: role of prostacyclin

Using the perfused kidneys of age-matched controls and streptozotocin (STZ)-induced diabetic rats, we previously demonstrated that endothelial dysfunction is present in STZ-induced diabetic rats and that acetylcholine (ACh) increases the level of 6-keto-prostaglandin F(1 alpha) (a metabolite of prostacyclin) in the effluent from such perfused kidneys. Here, we investigated whether the ACh-induced relaxation in the perfused kidney is modulated by prostacyclin and/or thromboxane A(2) (TXA(2)) in the STZ-induced diabetic state. ACh-induced renal vasodilatation was significantly weaker in STZ-induced diabetic rats than in age-matched controls, and it was not affected by treatment with 10 microM furegrelate (TXA(2) -synthase inhibitor) or 1 microM SQ29548 (TXA(2) -receptor antagonist) in either group. However, it was attenuated by 10 microM tranylcypromine (prostacyclin-synthesis inhibitor), but only in the diabetic group. These results suggest that the endothelium-dependent relaxation induced by ACh in the renal vascular bed of STZ-induced diabetic rats is regulated by prostacyclin, not by TXA(2). Increased prostacyclin-signaling may occur to help compensate for the impaired endothelial function seen in the kidney in long-term diabetic states.

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

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

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

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

Increased expression of iNOS is associated with endothelial dysfunction and impaired pressor responsiveness in streptozotocin-induced diabetes

Studies in streptozotocin (STZ)-induced diabetic rats have demonstrated cardiovascular abnormalities such as depressed mean arterial blood pressure (MABP) and heart rate (HR), endothelial dysfunction, and attenuated pressor responses to vasoactive agents. We investigated whether these abnormalities are due to diabetes-associated activation of inducible nitric oxide synthase (iNOS). In addition, the effect of the duration of diabetes on these abnormalities was also evaluated. Diabetes was induced by administration of 60 mg/kg STZ via the tail vein. One, 3, 9, or 12 wk after STZ injection, MABP, HR, and endothelial function were measured in conscious unrestrained rats. Pressor response curves to bolus doses of methoxamine (MTX) and angiotensin II (ANG II) were constructed in the presence of N-[3(aminomethyl)benzyl]-acetamidine, dihydrochloride (1400W), a specific inhibitor of iNOS. Depressed MABP and HR and impairment of endothelial function were observed as early as 3 wk after induction of diabetes. Acute inhibition of iNOS with 1400W (3 mg/kg i.v.) restored the attenuated pressor responses to both MTX and ANG II without affecting the basal MABP and HR. Immunohistochemical and Western analysis blot studies in cardiovascular tissues revealed decreased expression of endothelial nitric oxide synthase (eNOS) concomitant with increased expression of iNOS and nitrotyrosine with the progression of diabetes. Our findings suggest that induction of iNOS in cardiovascular tissues is dependent on the duration of diabetes and contributes significantly to the depressed pressor responses to vasoactive agents and potentially to endothelial dysfunction.

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

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

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

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

Effect of melatonin on vascular reactivity in pancreatectomized rats

The present study was undertaken to assess whether the improvement of contractile performance of aortic rings by melatonin described in streptozotocin diabetic rats also occurs in another model of type I diabetes, the pancreatectomized rats. Adult male Wistar rats submitted to a subtotal pancreatectomy and exhibiting altered levels of fasting glucose and an abnormal tolerance glucose test, were used. Sham-operated laparotomized rats were employed as controls. Dose-response curves for acetylcholine-induced, endothelium-related relaxation of aortic rings (after previous exposure to phenylephrine) and for phenylephrine-induced vasoconstriction were conducted. This protocol was repeated with rings pre-incubated in a high glucose solution (44 mmol/l). Pancreatectomy decreased significantly acetylcholine-induced relaxation of aortic rings, but not phenylephrine-induced vasoconstriction, the effect being amplified by preincubation in high glucose solution. The deleterious effect of a high glucose medium was more pronounced in pancreatectomized rats. Melatonin (10(-5) M) did not modify acetylcholine-induced relaxation in normal glucose concentration but was effective to prevent the impairment of relaxation brought about by exposure to high glucose solution. The contractile response to phenylephrine of aortic rings obtained from pancreatectomized rats was not affected by melatonin. The results further support the improvement by melatonin of endothelial-mediated relaxation in blood vessels of diabetic rats.

Paradoxes of nitric oxide in the diabetic kidney

As an important modulator of renal function and morphology, the nitric oxide (NO) system has been extensively studied in the diabetic kidney. However, a number of studies in different experimental and clinical settings have produced often confusing data and contradictory findings. We have reviewed a wide spectrum of findings and issues that have amassed concerning the pathophysiology of the renal NO system in diabetes, pointed out the controversies, and attempted to find some explanation for these discrepancies. Severe diabetes with profound insulinopenia can be viewed as a state of generalized NO deficiency, including in the kidney. However, we have focused our hypotheses and conclusions on the events occurring during moderate glycemic control with some degree of treatment with exogenous insulin, representing more the clinically applicable state of diabetic nephropathy. Available evidence suggests that diabetes triggers mechanisms that in parallel enhance and suppress NO bioavailability in the kidney. We hypothesize that during the early phases of nephropathy, the balance between these two opposing forces is shifted toward NO. This plays a role in the development of characteristic hemodynamic changes and may contribute to consequent structural alterations in glomeruli. Both endothelial (eNOS) and neuronal NO synthase can contribute to altered NO production. These enzymes, particularly eNOS, can be activated by Ca(2+)-independent and alternative routes of activation that may be elusive in traditional methods of investigation. As the duration of exposure to the diabetic milieu increases, factors that suppress NO bioavailability gradually prevail. Increasing accumulations of advanced glycation end products may be one of the culprits in this process. In addition, this balance is continuously modified by actual metabolic control and the degree of insulinopenia.

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

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

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.

Histamine-induced vasodilatation in the perfused mesenteric arterial bed of diabetic rats

In this study, we have examined the contribution of endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) to histamine-induced endothelium-dependent relaxation in the perfused mesenteric arterial bed of rats treated with streptozotocin (STZ) to induce diabetes. Histamine (10(-10) to 5 x 10(-6) mol) produced dose-dependent vasodilator response in the perfused mesenteric arterial bed of both control and diabetic animals. In order to isolate the EDHF component of histamine-induced vasodilator response, NG-nitro-L-arginine-methyl ester hydrochloride (L-NAME) (10(-4) M) and indomethacin (10(-6) M) were added to the Krebs solution throughout the experiment. Histamine induced vasodilatation in the perfused mesenteric bed in preparations from both control and diabetic rats. The vasodilator response to histamine was slightly potentiated in the diabetic rat preparations. Sodium nitroprusside (SNP)-induced relaxation was similar in diabetic and control rats. The role of EDNO in histamine-induced vasodilatation was also examined. Vascular preparations were perfused with 20 mM K(+)-Krebs solution to inhibit the EDHF contribution to histamine-induced vasodilatation. Under this condition, histamine induced a vasodilator response in preparations from both control and diabetic rats. However, relative to nondiabetic control animals, histamine-induced maximal response was significantly reduced in preparations from diabetic animals. Pretreatment with L-NAME (10(-4) M) attenuated histamine-induced vasodilatation in both preparations, indicating an NO-mediated vasodilator response. There was a significant attenuation in histamine-induced vasodilatation in the vascular preparations from diabetic rats. The vasodilator effect of calcium ionophore A23187 was investigated in preparations from control and diabetic rats to investigate receptor dysfunction associated with diabetes. A23187 (10(-11) to 10(-7) mol)-induced vasodilator response was not significantly different in the preparations from control and diabetic animals. In conclusion, our results indicated that histamine-induced vasodilation in the perfused mesenteric arterial bed of the STZ-induced diabetic rats is mediated by two vasodilator components, namely EDHF and EDNO. Under diabetic conditions, the EDHF component was potentiated, while histamine-induced vasodilation mediated by the EDNO component was attenuated.

Endothelium-dependent relaxation in isolated renal arteries of diabetic rabbits

1 In this study, we have investigated the vasodilator response to acetylcholine under diabetes conditions in isolated renal arteries of rabbits. We have also examined the contribution of endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) to the endothelium-dependent relaxation caused by acetylcholine in the renal arteries of alloxan-induced diabetic rabbits. 2 Acetylcholine (10(-10) - 10(-4) M) produced cumulative concentration-response curve in the renal arteries of both control and diabetic rabbits. The EC50 values and maximal responses to acetylcholine were not significantly different relative to diabetic conditions. In order to isolate the EDHF component of acetylcholine-induced vasodilator response, L-nitro-methyl arginine ester (L-NAME, 10(-4) M) and indomethacin (10(-6) M) were added to the Krebs' solution throughout the experiment. Under these conditions, acetylcholine induced vasodilatation in the isolated renal arteries from both control and diabetic rabbits. The vasodilator response to acetylcholine was not affected under diabetic conditions. 3 Sodium nitroprusside (SNP)-induced relaxation was increased in the diabetic rabbits compared with the control animals. 4 Tetrabutyl ammonium (TBA, 0.5 mM) produced a significant reduction in acetylcholine-induced vasodilatation in both preparations from control and diabetic animals, consistent with involvement of K+ channels in mediating this response. Glibenclamide (1 microM) attenuated acetylcholine-induced vasodilatation in preparations from control animals only, while iberiotoxin (0.05 microM) significantly reduced the vasodilator response to acetylcholine in preparations from both control and diabetic animals. 5 The role of EDNO in mediating acetylcholine-induced vasodilatation was examined. The vascular preparations were incubated with 20 mM K(+)-Krebs' solution to inhibit the EDHF contribution to acetylcholine-induced vasodilatation. Under this condition, acetylcholine induced a vasodilator response in both preparations from control and diabetic rats. Pretreatment with L-NAME (10(-4) M) attenuated acetylcholine-induced vasodilatation in both preparations, indicating an nitric oxide-mediated vasodilator response. 6 Our results indicated that acetylcholine-induced vasodilatation in the isolated renal arteries of alloxan-induced diabetic rabbits was not affected under diabetic conditions. Acetylcholine-induced vasodilatation is mediated by two vasodilator components; namely, EDHF and EDNO. The contribution of EDHF and EDNO to acetylcholine-induced vasodilatation was not affected under diabetic conditions and there was no indication of endothelial dysfunction associated with diabetes. EDHF component was found to act mainly through high conductance Ca(2+)-activated K+ channels under normal and diabetic conditions, while the adenosine triphosphate-dependent K+ channels were involved in mediating acetylcholine vasodilator response in the control preparations only.

Experimental diabetes induces hyperreactivity of rabbit renal artery to 5-hydroxytryptamine

The influence of diabetes on the response of isolated rabbit renal arteries to 5-hydroxytryptamine (5-HT) was examined. 5-HT induced a concentration-related contraction that was higher in arteries from diabetic rabbits than in arteries from control rabbits. Endothelium removal did not significantly modify 5-HT contractions in arteries from control rabbits but enhanced the response to 5-HT in arteries from diabetic rabbits. Incubation with N(G)-nitro-L-arginine (L-NA) enhanced contractions to 5-HT in arteries from control and diabetic rabbits. In arteries with endothelium, this L-NA enhancement was lower in diabetic rabbits than in control rabbits. In arteries without endothelium, incubation with L-NA enhanced the maximal contractions to 5-HT in control rabbits but did not in diabetic rabbits. Indomethacin inhibited 5-HT-induced contraction of arteries from control rabbits and enhanced the maximal contraction to 5-HT of arteries from diabetic rabbits. In summary, diabetes enhances contractile response of rabbit renal artery to 5-HT. In control animals, this response is regulated by both endothelial and non-endothelial (neuronal) nitric oxide (NO) and by a vasoconstrictor prostanoid. Diabetes impairs the release of non-endothelial NO and the vasoconstrictor prostanoid.

Renal vascular reactivity to vasopressin in rats with diabetes mellitus

We evaluated how renal vascular reactivity to vasopressin changes when nitric oxide (NO) synthesis varies, as has been reported to occur in the course of insulin-dependent diabetes mellitus. Renal vasoconstrictor responses to vasopressin were obtained in young and older Sprague-Dawley control rats (3 and 10 months old) and in age-matched diabetic rats that had been treated with streptozotocin (60 mg/kg i.v.) at the age of 2 months. In young rats, vasopressin (3-1000 ng/kg/min i.v.) induced in vivo a dose-dependent decrease in renal blood flow, which was diminished in streptozotocin diabetic rats (P<0.05). Similarly, in in vitro perfused kidneys, the concentration-response curve for vasopressin (0.03-10 nM) was shifted 3-fold to the right in kidneys isolated from young diabetic rats (P<0.05). This shift was abolished in the presence of an inhibitor of nitric oxide synthesis, N(G)-nitro-L-arginine (100 microM), in the perfusate. In 10-month-old rats, the in vivo renal vasoconstrictor dose-response curve to vasopressin was shifted 10-fold to the left as compared to that for young rats (P<0.001). This shift was similar in both control and diabetic rats. In conclusion, the present study documented the existence of hyporesponsiveness to vasopressin in the early stage of diabetes, possibly related to nitric oxide overproduction. In contrast, renal vascular hyperreactivity to vasopressin occurs with aging, whether the rats are diabetic or not.

Influence of gender and diabetes on vascular and myocardial contractile function

Premenopausal women have a lower cardiovascular risk than men or postmenopausal women. However, this "female advantage" is lost in diabetes, a condition characterized by cardiac and vascular contractile dysfunction. This study was designed to compare the influence of diabetes on vascular and myocardial contractile function between genders. Adult male and female rats were made diabetic with streptozotocin (55 mg/kg) and maintained for 8 weeks. Tension development was examined in thoracic aortic rings and left ventricular papillary muscles. KCl-induced vasoconstriction, acetylcholine (ACh)-induced endothelium dependent or sodium nitroprusside (SNP)-induced endothelium-independent vasorelaxation, duration and maximal velocity of myocardial contraction and relaxation duration (TPT/RT90 and +/- VT) were similar between males and females. Diabetes augmented KCl-induced vasoconstriction at low doses, reduced SNP-induced vasorelaxation and had little effect on ACh-induced vasorelaxation in aortic rings from both genders. Diabetes prolonged TPT and RT90 in both genders, and reduced +/- VT in males but not females. Acute increase in extracellular Ca2+ (2.7 mM to 5.4 mM) shortened TPT in diabetic myocardium from both genders, whereas it had no effect on other myocardial mechanical indices in normal or diabetic groups of either gender. In addition, acute exposure to the Na+/K(+)-ATPase inhibitor ouabain shortened TPT/RT90 and enhanced +/- VT in myocardium from normal female, whereas it had no effect on male or diabetic myocardium. In conclusion, these data suggest that in the vasculature, there is no difference in diabetes-induced contractile dysfunction between genders, however several gender-specific differences are evident in the myocardium.

A brief report on some physiological parameters of streptozocin-diabetic rat

Several biological changes occur when streptozocin is given to experimental animals. The rat streptozocin (STZ) model is extensively used in diabetic experiments. In this brief report, the main physiological characteristics of rats injected with streptozocin are presented. These characteristics are manifested by weight loss, organ weight reduction, serum glucose elevation, decrease in serum insulin level, and other enzyme and hormonal changes. A collection of these parameters may be helpful in establishing a database to describe this model.

Diabetes potentiates acetylcholine-induced relaxation in rabbit renal arteries

The response of rabbit renal arteries to acetylcholine and its endothelial modulation in diabetes were investigated. Acetylcholine induced concentration-related endothelium-dependent relaxation of renal arteries that was significantly more potent in diabetic rabbits than in control rabbits. Pretreatment with N(G)-nitro-L-arginine (L-NOArg), indomethacin, or L-NOArg plus indomethacin induced partial inhibition of acetylcholine-induced relaxation. Inhibition induced by L-NOArg plus indomethacin was significantly higher in arteries from diabetic rabbits than in arteries from control rabbits. In renal arteries depolarised with KCl 30 mM and incubated with L-NOArg plus indomethacin, acetylcholine-induced relaxation was almost abolished in both groups of rabbits and this response was not different from that obtained in arteries without endothelium. Sodium nitroprusside induced concentration-dependent relaxation of renal arteries from control and diabetic rabbits without significant differences between the two groups of animals. These results suggest that diabetes potentiates the acetylcholine-induced relaxation in rabbit renal arteries. Increased release of nitric oxide and prostacyclin could be responsible for the enhanced relaxant potency of acetylcholine in diabetes.

Diabetes-induced changes in endothelial mechanisms implicated in rabbit carotid arterial response to 5-hydroxytryptamine

The influence of diabetes on endothelial mechanisms implicated in the response of isolated rabbit carotid arteries to 5-hydroxytryptamine (5-HT) was studied. 5-HT induced a concentration-dependent contraction that was potentiated in arteries from diabetic rabbits with respect to that in arteries from control rabbits. Endothelium removal potentiated 5-HT contractions in arteries from both control and diabetic rabbits but increased the maximum effect only in arteries from diabetic rabbits. Incubation of arterial segments with N(G)-nitro-L-arginine (L-NA) enhanced the contractile response to 5-HT. This L-NA enhancement was greater in arteries from diabetic rabbits than in arteries from control rabbits. Aminoguanidine did not modify the 5-HT contraction in arteries from control and diabetic rabbits. Indomethacin inhibited the 5-HT-induced response, and this inhibition was higher in arteries from control rabbits than in arteries from diabetic rabbits. In summary, diabetes enhances the sensitivity of the rabbit carotid artery to 5-HT. In control animals, the endothelium modulated the arterial response to 5-HT by the release of both nitric oxide (NO) and a vasoconstrictor prostanoid. Diabetes enhances endothelial constitutive NO activity and impairs the production of the endothelial vasoconstrictor.

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.

Time course of changes in endothelium-dependent and -independent relaxation of chronically diabetic aorta: role of reactive oxygen species

In the present study, the role of reactive oxygen species and the contribution of antioxidant defence in the time course of changes in acetylcholine-stimulated endothelium-dependent and sodium nitroprusside-stimulated endothelium-independent relaxation were investigated in aortic rings isolated from 6-month streptozotocin-diabetic and age-matched control rats. Although there were no significant differences in the degree of the peak relaxations produced by a single administration of acetylcholine (1 microM) or sodium nitroprusside (0.01 microM) between control and diabetic rings, the endothelium-dependent and -independent relaxant responses were more transient and the time required to reach a peak relaxation after addition of acetylcholine was shorter in diabetic vessels. Pretreatment of diabetic vessels with superoxide dismutase (100 U/ml) normalized the recovery phases of endothelium-dependent and -independent relaxations, but had no effect on the peak responses to acetylcholine and sodium nitroprusside. In the presence of diethyldithiocarbamate (5 mM), an inhibitor of superoxide dismutase, the transient nature of the relaxant response to acetylcholine or sodium nitroprusside was more marked and the peak relaxations were inhibited; these effects of diethyldithiocarbamate were more pronounced in diabetic than in control rings. Catalase, 160 U/ml, decreased the peak relaxant response to acetylcholine and accelerated fading of the relaxation in diabetic aorta. Similar results were obtained for control aorta with a higher concentration of catalase (550 U/ml). Pretreatment with 3-amino-1,2,4 triazole (5 mM), a catalase inhibitor, inhibited the peak relaxant response to acetylcholine in diabetic rings. The combination of superoxide dismutase (100 U/ml) plus 3-amino-1,2,4 triazole (5 mM) produced an increase of the transient nature of endothelium-dependent relaxation of diabetic rings greater than that with 3-amino-1,2,4 triazole alone. Neither catalase nor 3-amino-1,2,4 triazole affected the characteristics of sodium nitroprusside-induced relaxation. Desferrioxamine, an inhibitor of hydroxyl radical (.OH) production, or mannitol, a.OH scavenger, had no effect on the characteristics of either acetylcholine- or sodium nitroprusside-induced relaxation in control and diabetic rings. Biochemical measurements revealed an inhibited superoxide dismutase activity in diabetic aorta together with activated catalase. Our findings suggest that, during the chronic phase of streptozotocin-diabetes, excess superoxide (O(2)(. -)) is responsible for the enhanced transient nature of endothelium-dependent and -independent relaxation of aorta via a reduction in bioavailable concentrations of nitric oxide (NO). However, the involvement of hydrogen peroxide (H(2)O(2)) in the establishment of acetylcholine-stimulated relaxation may be increased, which is likely to account for the maintenance of the relaxant effect of acetylcholine in chronically diabetic vessels.

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.

Effect of early stage of experimental diabetes on vascular functions in isolated perfused kidneys

The present study investigates the renal vascular responsiveness to vasoactive agents in diabetic rats which present an early stage of renal failure. Adult male Wistar rats were administered alloxan (150 mg kg(-1), s.c.). Seven days later the right kidneys were isolated and perfused. Renal perfusion pressure was measured continuously. Concentration-response curves were plotted for noradrenaline (NA), sodium nitroprusside (SNP) and carbachol. In basal conditions, kidneys from diabetic rats presented a decreased vascular resistance compared with those from control rats. The vasoconstrictor response to NA showed decreased EC50 values in preparations from diabetic rats compared with control ones (EC50 nmols, control: 2.03 +/- 0.44, n = 8; diabetic: 0.84+/-0.18, n = 6, P < 0.05). This enhanced sensitivity to NA could be in line with the decreased glomerular filtration rate and cortical renal plasma flow previously described in vivo in our laboratory (Garcia, Girardi, Ochoa, Torres & Elias, 1998). Vasoconstrictor responses to phenylephrine were not however, different between diabetic and control rat kidneys. This suggests that the increased sensitivity to NA was due to impaired neuronal uptake since phenylephrine is not a substrate for neuronal uptake. After precontraction with phenylephrine, both endothelium-dependent (carbachol) and endothelium independent (SNP) vasodilator agents caused similar response in the preparations taken from the two groups of animals. So, the enhanced sensitivity to NA is not associated with a deficient dilator responsiveness of the renal vasculature. The vasodilator response to carbachol was the same in absence or presence of L-arginine in the perfusate, suggesting no alteration in its availability at this stage of diabetes. Diabetic animals showed increased plasma level of fructosamine and glycosylated haemoglobin (Hb A1c), indicating the presence of early glycated products at this stage of diabetes, which could be involved in a possible structural alteration of the vessels.

Relaxing effect of insulin in renal arteries from diabetic rats

Abnormal renal vasomotor tone exists in the early stages of diabetes mellitus. Insulin has been proposed to modulate renal function and to possess vasodilatory effects. The present study was initiated in order to evaluate the direct effect of insulin on isolated renal arteries. Twelve insulin-treated streptozotocine diabetic rats with diabetes for 50 days were compared with 15 weight-matched control rats. The contractile responses to 60 mM K+ and 10(-4) M noradrenaline, and the insulin- (0.8-6.4 I.U./ml) induced relaxation of vessels precontracted with noradrenaline, were similar in diabetic and control rats. There was a tendency towards greater relaxation in diabetic (71%) than in control rats (54%). Nw-nitro-L-arginine methyl ester (L-NAME) (10(-4) M) given before noradrenaline tended to attenuate the insulin-induced relaxation, while addition of L-arginine (10(-6) M) to L-NAME attenuated the relaxation in diabetic but increased it in control rats (P < 0.05). The effect of insulin was tested further in control rats and was not influenced by administration of a single dose (10(-6) M) of indomethacin or propranolol given instead of L-NAME. The effect of a single dose of methylene-blue, given before noradrenaline, was tested in control rats in varying doses between 2 x 10(-6) and 2 x 10(-4) M. In the highest concentration it made no difference whether insulin was given or not and there was a similar relaxing effect in diabetic and control arteries. In conclusion, the present study showed that insulin per se has a relaxing effect on renal arteries. There was a tendency to greater relaxation in diabetic than in control rats, an effect which was attenuated by in-vitro-pretreatment with L-NAME as well as with L-NAME and L-arginine in diabetic vessels, while relaxation was increased in control vessels. This may indicate that the effect of insulin may be mediated through nitric oxide in diabetic but not in control rats. The effects of insulin in control vessels were not modified in vitro by indomethacin, propranolol or methylene-blue.

Renal arterial reactivity to potassium, noradrenaline, and neuropeptide Y and association with urinary albumin excretion in the diabetic rat

A changed vasomotor reactivity of renal arteries may lead to defect autoregulation of renal hemodynamics with damage of diabetic kidneys. Eleven streptozotocin-induced diabetic male Wistar rats were daily treated with insulin in order to achieve a blood glucose of 21 mmol/L. Seventeen age and gender-matched rats served as controls. After 50 days, the kidneys were rapidly removed, arteria renalis and the first branches of the intrarenal arteries were dissected free. The arterial reactivity was tested with a sensitive in vitro method. The reactivity to noradrenaline was tested by cumulative application (10(-9) to 3 x 10(-4) M) before and after a single concentration of neuropeptide Y (NPY). Potassium (60 mM) and noradrenaline induced a strong contraction of all arteries with similar response in diabetic and control rats. The effect of noradrenaline after NPY was unchanged in renal vessels of control rats, whereas it was diminished in intrarenal vessels for both diabetic and control rats. Similarly, a diminished response was found for renal arteries in diabetic rats, an effect which was related to the level of blood glucose (r = 0.62, 2p = 0.04). The urinary excretion rate of albumin in the diabetic rats was related to the largest noradrenaline induced contraction (r = 0.71, 2p = 0.01) of renal but not of intrarenal arteries. In conclusion, there was no difference in potassium and noradrenaline evoked contractions in renal and intrarenal arteries in diabetic and control rats. NPY decreased the contractile response to noradrenaline. The high blood glucose slightly increased this effect of NPY.

Effects of diabetes on reactivity of sciatic vasa nervorum in rats

The aim was to investigate the effects of 2 months of streptozotocin-induced diabetes mellitus in rats on the responses of sciatic vasa nervorum to vasoactive drugs. Changes in perineural blood flow were monitored by laser-Doppler flowmetry during drug superfusion in vivo. Laser-Doppler flux was reduced by 53.3% after 2 months of diabetes. A 38-fold increase in norepinephrine sensitivity was found in diabetic compared to nondiabetic rats. Co-superfusion of norepinephrine and a high dose (100 microM) of the nitric oxide synthase inhibitor, NG-nitro-L-arginine, resulted in 116-fold and 3.6-fold increases in norepinephrine sensitivity in nondiabetic and diabetic rats, respectively, such that dose-response curves for changes in vascular conductance were superimposed. This suggests that the increased norepinephrine sensitivity in diabetes was caused by defective endothelial nitric oxide production or action. After norepinephrine preconstriction, acetylcholine caused dose-dependent increases in vascular conductance, sensitivity being 8.1-fold greater in nondiabetic than diabetic rats. In contrast, endothelium-independent responses to the nitrovasodilator, glyceryl trinitrate, were relatively unaffected by diabetes. Thus, diabetes causes a deficit in nitric oxide mediated endothelium-dependent relaxation of vasa nervorum, resulting in increased vasoconstrictor sensitivity which is likely to impair perfusion and contribute to the pathogenesis of neuropathy.

The effect of insulin treatment and of islet transplantation on the resistance artery function in the STZ-induced diabetic rat

1. This study was designed to investigate the influence of insulin treatment and islet transplantation on the smooth muscle contractility and endothelium-dependent and independent relaxation of resistance arteries in the chemically induced streptozotocin (STZ) diabetic rat after 6-8 weeks, and 12-14 weeks of diabetes, compared to non-diabetic age-matched controls. 2. The morphology, and contractile responses to high potassium physiological salt solution (KPSS), KPSS containing 10(-5) M noradrenaline (NAK), and concentration-response curves to noradrenaline (NA) of mesenteric resistance arteries were recorded, along with the endothelium-dependent relaxation responses to acetylcholine (ACh) and bradykinin (BK), and endothelium-independent relaxation to sodium nitroprusside (SNP). Concentration-response curves were then repeated in the presence of a nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NOARG). 3. Insulin-treated diabetic rats in the 12 week study demonstrated enhanced vascular contractility to KPSS, NAK and NA, compared to age-matched non-diabetic controls. 4. Incubation with L-NOARG resulted in both a significant increase in maximum contractile response, and sensitivity (pD2) to NA in the untreated diabetic group (6 weeks). A significant shift in sensitivity was also seen in the insulin-treated diabetic group. In the 12 week study, incubation with L-NOARG resulted in an increased maximum contractile response and sensitivity to NA in the insulin-treated diabetics. An increase in sensitivity was also observed in the untreated diabetic group. 5. Endothelium-dependent relaxation to ACh was significantly augmented in the untreated diabetics (6-weeks), compared to the control group. In the 12-week study, relaxation to both ACh and BK was not significantly different in any of the experimental groups when compared to the sham-operated non-diabetic controls. 6. Incubation with L-NOARG resulted in a significant attenuation of the maximum relaxation response to ACh and BK in all of the experimental groups, in the 6- and the 12-week study. 7. There was no significant difference in the maximum relaxation response or sensitivity to sodium nitroprusside between the diabetic groups and their age-matched controls in either the 6-week or the 12-week study. 8. The results of this study suggest an enhanced release of nitric oxide in the early stages of diabetes, which is more evident in the untreated diabetic rats than the insulin treated, and appears to normalize as the duration of diabetes progresses. This study also shows that the alteration in vascular reactivity of the resistance arteries can be restored to within normal limits by the transplantation of islets of Langerhans, and that islet transplantation is an effective strategy in the correction of the metabolic abnormalities associated with insulin-dependent diabetes.

Drug-induced endothelium-dependent and -independent relaxations in isolated resistance vessels taken from simultaneously hypertensive and streptozotocin-diabetic rats

Hypertension and diabetes mellitus often co-exist and both conditions may be expected to cause synergistic vascular damage. Our group has introduced an animal model for simultaneously occurring hypertension and diabetes mellitus by treating spontaneously hypertensive rats with streptozotocin (STZ). We investigated the drug-induced endothelium-independent and -dependent relaxation in isolated mesenteric small arteries (resistance vessels). Concerning the influence of hypertension, the responses to sodium nitroprusside, methacholine, histamine and nifedipine proved unchanged, the vasodilator response to bradykinin was diminished, whereas that to the K(+)-channel opener cromakalim was enhanced. With respect to the influence of STZ-induced diabetes we found that the responses to sodium nitroprusside, methacholine and nifedipine were unchanged, and that to cromakalim was enhanced, also when the preparations were pretreated with glibenclamide. The responses to histamine (STZ WKY versus control WKY) and bradykinin (STZ SHR versus control SHR) proved enhanced in the isolated vessels taken from diabetic animals. These findings suggest that the influence of the diabetic state is more pronounced than that of hypertension. However, our findings do not indicate that either hypertension or diabetes is associated with generalised endothelial damage in the resistance arteries.

Role of EDRF (nitric oxide) in diabetic renal hyperfiltration

In order to study the role of EDRF in diabetic hyperfiltration, the concentrations of NO2-/NO3-, the stable products of nitric oxide (NO), were measured in arterial plasma, urine, and renal venous blood in streptozotocin diabetic rats and normal control rats. In additional experiments, the renal hemodynamic and blood pressure responses to graded doses of an inhibitor of NO synthesis (Nitro-L-arginine; NLA) were measured. We found that plasma and urinary levels of NO2/NO3 are significantly higher in STZ diabetic rats (10 to 15 days) than in normal rats. Renal blood flow and GFR fell comparably in diabetic and normal rats in response to NLA infusion, although the absolute levels of RBF and GFR remained significantly higher in the diabetic rats at all doses of the inhibitor. Mean arterial blood pressure (MAP) rose in response to NLA administration, but the increase in the diabetic rats was significantly blunted as compared with the normal rats. Similarly, renal vascular resistance (RVR) increased less in the diabetic than in the normal rats at comparable doses of NLA. The blunted vasoconstrictor responses to NLA were accompanied by a smaller reduction in the levels of NO2-/NO3- in the urine of the diabetic versus the normal rats. These findings suggest that NO synthesis is increased in diabetic rats manifesting hyperfiltration and are consistent with the view that excess NO synthesis contributes to renal hyperfiltration.

Duration-dependent attenuation of acetylcholine--but not histamine--induced relaxation of the aorta in diabetes mellitus

1. The relaxations of aortic preparations from 1, 4 and 12 week diabetic rats to acetylcholine and histamine were studied. 2. The relaxation to acetylcholine but not to histamine was significantly attenuated in the 4th and 12th weeks of the disease. In addition, the tissues became less sensitive to acetylcholine but not to histamine with increasing duration of the disease. 3. The results show that there is differential alteration in the responsiveness of the aorta from diabetic rats to both agents.

Endothelium-dependent vasodilator responses of the isolated mesenteric bed are preserved in long-term streptozotocin diabetic rats

Endothelium-dependent and endothelium-independent responses to exogenous vasoactive substances were compared in isolated, perfused mesenteric beds from control rats and in rats subjected to prolonged (15-17 weeks) streptozotocin induced diabetes. The main aim of the study was to determine whether the prolonged period of diabetes altered vascular endothelial function, and thereby modified vascular responsiveness to vasoconstrictors or vasodilators. Noradrenaline induced vasoconstriction was not significantly altered in preparations from diabetic rats compared to control. Vasodilator responses to acetylcholine (ACh) and ATP were endothelium-dependent, since they were greatly reduced or abolished after endothelium removal by perfusion with 0.1% Triton-X 100. The vasodilator action of these agents was fully preserved in the diabetic animals. Sodium nitroprusside produced a vasodilation which was endothelium-independent, this vasodilation was also preserved in the diabetic animal. We conclude that prolonged streptozotocin-induced diabetes does not reduce the ability of the mesenteric vascular endothelium to release vasodilator substances, nor does it alter the responsiveness of the bed to exogenous endothelium-independent vasodilator sodium nitroprusside or vasoconstrictor noradrenaline.

Increased sensitivity to endothelin-1 in isolated Krebs'-perfused kidneys of streptozotocin-diabetic rats

1. Vascular responses to endothelin-1 (ET-1) and noradrenaline (NA) were measured in isolated Krebs'-perfused kidneys of 2 week old streptozotocin-diabetic and non-diabetic rats. 2. Bolus injections of either ET-1 or NA caused dose-dependent increases in perfusion pressure. Responses to ET-1 (10-60 ng/g kidney), but not to NA (0.001-10 micrograms/g kidney), were significantly potentiated in kidneys of diabetic rats compared with non-diabetics. 3. Indomethacin significantly attenuated responses to NA (0.3-10 micrograms/g kidney) in kidneys of both diabetic and non-diabetic rats. 4. Neither indomethacin (1 mumol/L) nor the cyclo-oxygenase/lipoxygenase inhibitor BW755C (1 mumol/L) had any significant effect on the log dose-response curve to ET-1 in either group of kidneys. 5. Perfusion with N-nitro-L-arginine (NOLA; 10 mumol/L) had no effect on basal perfusion pressures, but potentiated responses to ET-1 in both groups of kidneys. However, the difference in responses to ET-1 between kidneys from diabetic and non-diabetic rats remained significant in the presence of NOLA. 6. ET-1 responses were inhibited in Ca(2+)-free Krebs' solution (plus 1 mmol/L EGTA). 7. The results of the present study indicate an increased sensitivity to ET-1 in isolated Krebs'-perfused kidneys of diabetic rats. Responses to ET-1 were unaffected by cyclo-oxygenase and/or lipoxygenase inhibitors, but were potentiated by an endothelium-derived relaxing factor (EDRF) synthesis inhibitor.

The effects of endothelin-1 and NG-nitro-L-arginine methyl ester on regional haemodynamics in conscious rats with streptozotocin-induced diabetes mellitus

1. Resting haemodynamic status and responses to endothelin-1 (0.0004, 0.04, 0.4 nmol kg-1) and NG-nitro-L-arginine methyl ester (L-NAME, 10 mg kg-1) were assessed in conscious, Wistar rats treated with streptozotocin (STZ) to induce diabetes mellitus, and in control animals treated with saline. 2. In the resting state, STZ-treated rats had a bradycardia relative to control animals (291 +/- 13 and 337 +/- 10 beats min-1, respectively), but mean arterial blood pressures were the same in the two groups (STZ-treated 109 +/- 3; control 114 +/- 4 mmHg). However, the STZ-treated rats had raised renal (105 +/- 9 units) and mesenteric (114 +/- 16 units) vascular conductances and reduced hindquarters vascular conductance (26 +/- 4 units) relative to control rats (renal, 80 +/- 6; mesenteric, 75 +/- 7; hindquarters, 37 +/- 3 units). 3. Increasing doses of endothelin-1 caused similar, early falls and subsequent rises in mean arterial blood pressures in both groups of rats. Although there were initial hindquarters vasodilatations with endothelin-1 that were not different in STZ-treated and control rats, there were subsequent renal and mesenteric vasoconstrictions that were greater in the former. Hence, the similar rises in mean arterial blood pressures must have been accompanied by a greater reduction in cardiac output in the STZ-treated rats. 4. L-NAME caused similar renal and mesenteric vasoconstrictions in control and STZ-treated rats, but there was a smaller pressor effect and an attenuated hindquarters vasoconstrictor response to L-NAME in STZ-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective impairment of hindquarters vasodilator responses to bradykinin in conscious Wistar rats with streptozotocin-induced diabetes mellitus

1. Male, Wistar rats were treated with streptozotocin (STZ, 70 mg kg-1, i.p.) or saline and chronically instrumented with pulsed Doppler probes and intravascular catheters (implanted under sodium methohexitone anaesthesia) to allow assessment of haemodynamics in the conscious state 28 days later. 2. Control and STZ-treated rats received bolus doses of glyceryl trinitrate (10-80 nmol kg-1), acetylcholine (0.1-5 nmol kg-1) and bradykinin (0.3-30 nmol kg-1). 3. Although, as reported previously, STZ-treated rats had normal mean arterial blood pressure together with renal and mesenteric vasodilatations and hindquarters vasoconstriction relative to control rats, both groups showed similar hypotensive and regional haemodynamic responses to glyceryl trinitrate and acetylcholine. However, while the depressor effects of bradykinin were similar in control and STZ-treated rats, the former showed a hindquarters vasodilator response to bradykinin that was absent in the STZ-treated rats. 4. A loss of bradykinin-mediated vasodilatation in the hindquarters vascular bed in STZ-treated rats in the presence of normal, hindquarters vasodilator responses to other agents and normal bradykinin-mediated vasodilator responses in other vascular beds is consistent with existing evidence that the vasodilatation elicited by bradykinin in the hindquarters vascular bed is particularly dependent on nitric oxide synthesis and that this is impaired selectively in STZ-treated rats.

Augmented potentiation of renal vasoconstrictor responses by thromboxane A2 receptor stimulation in the alloxan-diabetic rat

Dose-response curves were obtained to bolus injections of noradrenaline (NA) and 5-hydroxytryptamine (5-HT) in blood and Krebs-perfused kidneys of male Wistar rats. Vasoconstrictor responses to both NA and 5-HT were significantly attenuated in blood-perfused kidneys of alloxan-treated 14 day diabetic rats compared with non-diabetic animals. Responses to low doses of NA were also significantly attenuated in Krebs-perfused kidneys from diabetic rats but responses to 5-HT were augmented. Dose-dependent potentiation of vasoconstrictor responses to NA and 5-HT in Krebs-perfused kidneys of both non-diabetic and diabetic rats occurred during infusion of the thromboxane A2 (TxA2)-mimetic U46619 [15S)-hydroxy-11 alpha, 9 alpha-(epoxymethano) prosta-5Z, 13E-dienoic acid). The potentiation by U46619 (11 ng mL-1) was inhibited in both groups during infusion of the thromboxane receptor antagonist AH23848 [( 1 alpha(Z), 2 beta, 5 alpha]-(+/-)-7-[5[[(1,1'-biphenyl)-4-yl]methoxyl]-2-(4- morpholinyl)-3-oxocyclopentyl]-4-heptenoic acid). Infusion of 5-HT in Krebs-perfused kidneys of non-diabetic rats, causing a rise in perfusion pressure of similar magnitude to that produced by infusion of 111ng mL-1 U46619, did not significantly affect responses to bolus injections of NA. Potentiation of vasoconstrictor responses to low concentrations of 5-HT by U46619 was significantly greater in Krebs-perfused kidneys of diabetic rats than kidneys from non-diabetic animals. Activation of vascular TxA2 receptors augments the vasoconstrictor effects of 5-HT in Krebs-perfused diabetic rat kidneys to a greater extent than in non-diabetic kidneys.