An increase in opening of BK(Ca) channels in smooth muscle cells in streptozotocin-induced diabetic mice

INTRODUCTION Diabetes mellitus (DM) is a kind of disease thatmetabolism decompensates with hyperglycemia and re-sults in multi-organ damage[1]. Thus, the risk of coro-nary disease, cerebrovascular disease, and other car-diovascular complications increase. These changes, atleastpartially, due todiabetes functionalchanges inbloodvessels including endothelial cell dysfunction. Simulta-neously, altered ion channelfunction in vascular smoothmuscle are also involved[2,3]. In vascular…     

Lack of endothelium-derived hyperpolarizing factor (EDHF) up-regulation in endothelial dysfunction in aorta in diabetic rats

It is not known whether the impairment of nitric oxide (NO)-dependent vasodilation of the aorta of diabetic rats is associated with any changes in the endothelial production of vasoactive prostanoids and endothelium-derived hyperpolarizing factor (EDHF). Therefore, we analyzed the contribution of NO, vasoactive prostanoids and EDHF to the decreased endothelium-dependent vasorelaxation in Sprague-Dawley rats at 4 and 8 weeks after diabetes mellitus induced by streptozotocin (STZ). The acetylcholine-induced (Ach) endothelium-dependent relaxation was significantly decreased in the thoracic aorta 8 weeks after the STZ-injection (Ach 10(-6) M: 73.1 +/- 7.4% and 56.7 +/- 7.9% for control and diabetic rats, respectively). The sodium nitroprusside-induced (NaNP) endothelium-independent vasodilation was also impaired in the diabetic rats (8 weeks after STZ) (NaNP 10(-8) M: 74.2 +/- 11.4% and 35.9 +/- 9.4% for control and diabetic rats, respectively). In contrast, the basal NO production, as assessed by the N omega-nitro-L-arginine methyl ester (L-NAME)-induced vasoconstriction was not modified in diabetes. Moreover, the amount of 6-keto-PGF(1 alpha) (stable metabolite of prostacyclin / prostaglandin I2 / PGI2 ), 12-L-hydroxy-5,8,10-heptadecatrienoic acid (12-HHT) and thromboxane B2 (TxB2 ) (stable metabolite of thromboxane A2 - TxA2) were significantly increased in the 8 weeks diabetic rat aorta. The EDHF-pathway did not change in the aortic endothelium during the development of STZ-induced diabetes. Our results indicate that STZ-induced diabetes mellitus did not modify the basal NO production, but induced the impairment of acetylcholine- and sodium nitroprusside-induced vasodilation in the thoracic aorta. In parallel with the impairment of NO-dependent vasodilation, the basal PGI2, 12-HHT and TxA2 synthesis were increased. The EDHF-pathway did not contribute to the endothelium-dependent relaxation either in control or diabetic aorta. The above alterations in the endothelial function may play an important role in the development of endothelial dysfunction and vascular complications of diabetes.     

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.     

Persistence of EDHF pathway and impairment of the nitric oxide pathway after chronic mercury chloride exposure in rats: mechanisms of endothelial dysfunction

Chronic mercury exposure impairs vascular function, leading to the depression of endothelium-dependent vasodilatation. Loss of the nitric oxide (NO) pathway has been implicated, but little is known about effects on other endothelial mediators. This study investigated the mechanisms of endothelial dysfunction in rats subjected to chronic mercury chloride exposure. The endothelium-dependent relaxation of rat aorta evoked by acetylcholine (ACh) and isoproterenol was impaired in a dose-dependent manner by chronic mercury chloride exposure. Endothelium-independent responses to sodium nitroprusside (SNP) were not affected by chronic mercury chloride exposure. In healthy vessels, ACh-induced relaxation was inhibited by L-N-nitroarginine methyl ester (L-NAME; 10(-4) M) and partially by glybenclamide (10(-5) M), indicating the involvement of NO and endothelium-derived hyperpolarizing factor (EDHF). In vessels from mercury-exposed rats, responses to ACh were insensitive to L-NAME but were significantly reduced by glybenclamide, indicating selective loss of NO-mediated relaxation. In vessels from mercury-exposed rats, responses to ACh were partially restored after treatment with the antioxidant, superoxide dismutase (SOD) and catalase, this effect was not seen when aorta from exposed group was incubated with L-NAME along with SOD and catalase indicating selective loss of NO-mediated vasodilatation and with no affect the EDHF-mediated component of relaxation. The results imply that chronic mercury exposure selectively impairs the NO pathway as a consequence of oxidative stress, while EDHF is able to maintain endothelium-dependent relaxation at a reduced level.     

Effect of insulin treatment on smooth muscle contractility and endothelium-dependent relaxation in rat aortae from established STZ-induced diabetes.

1. This study involved the chronic administration of low or high insulin to rats with established streptozotocin (STZ)-induced diabetes. We studied the effect of such treatment on smooth muscle contractility and endothelium-dependent relaxation using aortic strips. 2. Aortae from diabetic rats, but not those from high-insulin-treated diabetic rats, showed an impaired endothelium-dependent in response to acetylcholine (ACh) by comparison with untreated controls. 3. Isotonic high K+-induced contractility was impaired in diabetic aortae. This impairment was prevented by high-insulin treatment. 4. Noradrenaline (NA)-induced contractility was enhanced in aortae from high-insulin-treated diabetic rats, but not in those from untreated diabetic or low-insulin treated diabetic rats. 5. In the combined presence of the nitric oxide inhibitor N(G)-nitro-L-arginine and the cyclo-oxygenase inhibitor indomethacin, NA-induced contractility was significantly greater in aortae from high-insulin-treated diabetic rats than in those from controls or untreated diabetic rats. 6. An increased expression of the mRNA for the alpha1D and alpha1B adrenergic receptors was found in aortae from high-insulin-treated diabetic rats. 7. These results demonstrate that in rats with established STZ-induced diabetes, high-insulin treatment prevents the development of an impaired endothelium-dependent relaxation in the aorta, and that such treatment enhances NA-induced contractility. This enhancement may be related to an upregulation in the expression of the mRNA for the alpha1B or alpha1D adrenergic receptor that is secondary to the hyperinsulinaemia.     

Impairment of endothelium-dependent relaxation and changes in levels of cyclic GMP in aorta from streptozotocin-induced diabetic rats.

1. Acetylcholine (ACh)-induced relaxation of aortic strips with endothelium and production of cyclic GMP between streptozotocin-induced diabetic and age-matched control rats were compared. 2. The concentration-response curve for ACh-induced relaxation was shifted to the right in diabetic rats. IC50 values for ACh were 4.57 +/- 0.67 x 10(-8) M and 1.00 +/- 0.87 x 10(-7) M in aortic strips from age-matched control and diabetic rats, respectively (n = 6, P less than 0.05). 3. Relaxations produced by atrial natriuretic peptide (ANP) in diabetic aortae were similar to those in age-matched vessels. 4. Relaxations produced by sodium nitroprusside (SNP) in diabetic aortae were similar to those in age-matched vessels. 5. Basal levels of cyclic GMP and ACh-induced production of cyclic GMP were significantly decreased in diabetic rats. 6. These results suggest that functional changes in endothelium but not in guanylate cyclase activity in the aorta may occur in diabetes, and thus, spontaneous and ACh-induced formation of cyclic GMP may be decreased. This decrease in production of cyclic GMP may be responsible for the decreased response of the aorta to the relaxant effect of ACh.     

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.     

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.     

Impairment of endothelium-dependent ACh-induced relaxation in aorta of diabetic db/db mice—possible dysfunction of receptor and/or receptor–G protein coupling

Diabetes is a risk factor of ischemic heart disease, cerebral ischemia, and atherosclerosis, in which endothelial dysfunction plays a role in the pathogenesis. We examined vascular responses in the aorta of pre-diabetic db/db mice with normoglycemia, hyperlipidemia, and hyperinsulinemia (6 weeks old), and diabetic db/db mice with hyperglycemia, hyperlipidemia, and hyperinsulinemia (11 weeks old) in comparison with age-matched non-diabetic db/+ mice. Prostaglandin F(2alpha) (PGF(2alpha))-induced contraction was significantly enhanced in the aorta of diabetic but not pre-diabetic db/db mice compared to age-matched non-diabetic db/+ mice. Acetylcholine (ACh), adenosine-5'-diphosphate (ADP), NaF, a G protein activator and A-23187, a Ca-ionophore, caused endothelium-dependent and nitric oxide (NO)-mediated relaxation, and sodium nitroprusside (SNP), an NO donor, caused endothelium-independent relaxation in the pre-contracted aorta of db/db mice. Maximal endothelium-dependent ACh-induced relaxation was reduced in diabetic but not pre-diabetic db/db mice compared to age-matched db/+ mice, while maximal SNP-induced relaxation was not different between diabetic and non-diabetic mice. ACh-induced relaxation in diabetic db/db mice was not affected by ozagrel, a thromboxane A(2) (TXA(2)) synthetase inhibitor, or acetylsalicylic acid (aspirin), a cyclooxygenase inhibitor, suggesting no involvement of endogenous TXA(2) or prostanoids in the reduction of relaxation. Maximal endothelium-dependent ADP-, A-23187-, and NaF-induced relaxation was not reduced in diabetic db/db mice. EC(50) values for ACh- and SNP-induced relaxation were increased in diabetic but not pre-diabetic db/db mice, suggesting decreases in sensitivity to NO in diabetic mice. Two-week treatment with KV-5070, a PPARgamma agonist, lowered plasma glucose, triglyceride (TG), and insulin but not cholesterol, and reversed the reduced ACh-induced relaxation. In conclusion, ACh-induced endothelium-dependent relaxation is impaired in diabetic db/db mice, probably due to the dysfunction of ACh receptors and/or receptor-G protein coupling. Endothelial dysfunction was not genetic and was considered to be initiated primarily by hyperglycemia, and was improved by anti-diabetic treatment with a PPARgamma agonist.     

The role of nitric oxide in the responses of the ovine digital artery to vasoactive agents and modification of these responses by endotoxin and cytokines

1. Laminitis, an important cause of lameness in domestic ungulates, occurs as a result of altered digital perfusion. Endotoxin and cytokines may mediate the vascular derangements observed through alterations in nitric oxide production. In this study, the vascular responses of the isolated ovine digital artery were examined and the influence of endotoxin and cytokines investigated. 2. Neither removal of the endothelium nor incubation with N(G)-nitro-L-arginine methyl ester (L-NAME, 300 microM) altered the response to phenylephrine (PE, 1 nM to 300 microM). Indomethacin (10 microM) decreased PE log EC(50) from -6.22+/-0.08 to -6.55+/-0.07. Acetylcholine (1 nM to 1 mM) and bradykinin (BK, 100 pM to 3 microM) induced endothelium-dependent relaxation. Bradykinin-induced relaxation was reduced by L-NAME, E(max) falling from -61.7+/-7.4 to -34.0+/-2.1%. Addition of indomethacin further reduced BK E(max) to -9.6+/-2.8%. Sodium nitroprusside (1 nM to 300 microM) produced endothelium-independent relaxation that was unaffected by L-NAME or indomethacin. 3. Following a 6 h incubation with endotoxin (3 microml(-1)), arterial responses to PE and BK did not differ from polymyxin B-treated controls (10 microg ml(-1)). Arteries incubated for 6 h with interferon-gamma (IFN-gamma, 10 ng ml(-1)) and tumour necrosis factor-alpha (TNF-alpha, 5 ng ml(-1)) exhibited greater relaxation to BK (E(max)-50.0+/-5.1%) than polymyxin B-treated controls (E(max)-33.1+/-4.0%), but did not differ in their response to PE. 4. Prolonged incubation (16 h) with endotoxin (3 microg ml(-1)) did not alter the response to PE, however incubation with IFN-gamma (10 ng ml(-1)), TNF-alpha (5 ng ml(-1)) and interleukin-1beta (20 ng ml(-1)) for 16 h increased PE log EC(50) from -6.44+/-0.09 to -6. 10+/-0.11. 5. Nitric oxide is an important mediator of endothelium-dependent relaxation in ovine digital arteries but does not modulate PE-induced vasoconstriction. Incubation with cytokines decreased the sensitivity of digital arteries to PE.     

洛伐他汀对低密度脂蛋白损伤血管内皮的保护作用

目的：探讨洛伐他汀对低密度脂蛋白所致血管内皮功能损伤的保护作用及可能的机制．方法：一次性从大鼠舌下静脉注射天然低密度脂蛋白(n-LDL 4mg／kg),在舌下静脉注射n-LDL之前大鼠腹腔注射洛伐他汀(2或4mg／kg),每天一次,连续五天．注射n-LDL后48小时检测乙酰胆碱诱导的血管内皮依赖性舒张(EDR)及血清一氧化氮(N0)、丙二醛(MDA)的含量和超氧化物歧化酶(SOD)的活性．结果：一次注射n-LDL导致了EDR、血清NO水平及SOD活性明显降低,MDA的浓度明显增高。预先给予洛伐他汀能明显减轻LDL引起的EDR的抑制和血清NO水平及SOD活性的降低,减少MDA的生成,左旋硝基精氨酸(L-NNA)减弱洛伐他汀对血管内皮的保护作用．结论：洛伐他汀对LDL损伤的血管内皮具有保护作用,可能与保护内皮依赖性松弛因子和抗氧化作用有关。     

Mechanisms underlying the attenuation of endothelium-dependent vasodilatation in the mesenteric arterial bed of the streptozotocin-induced diabetic rat

Experiments were designed to investigate the mechanisms underlying the diabetes-related impairment of the vasodilatations of the perfused mesenteric arterial bed induced by acetylcholine (ACh) and K(+). In streptozotocin (STZ)-diabetic rats, the ACh-induced endothelium-dependent vasodilatation was attenuated. The dose-response curves for ACh in control and diabetic rats were each shifted to the right by N(G)-nitro-L-arginine (L-NOARG) and by isotonic high K(+) (60 mM). The ACh dose-response curves under isotonic high K(+) were not different between control and diabetic rats. We also examined the vasodilatation induced by K(+), which is a putative endothelium-derived hyperpolarizing factor (EDHF). The mesenteric vasodilatation induced by a single administration of K(+) was greatly impaired in STZ-induced diabetic rats. Treatment with charybdotoxin plus apamin abolished the ACh-induced vasodilatation but enhanced the K(+)-induced response in controls and diabetic rats. After pretreatment with ouabain plus BaCl(2), the ACh-induced vasodilatation was significantly impaired and the K(+)-induced relaxation was abolished in both control and diabetic rats. The impairment of the endothelium-dependent vasodilatation of the mesenteric arterial bed seen in STZ-induced diabetic rats may be largely due to a defective vascular response to EDHF. It is further suggested that K(+) is one of the endothelium-derived hyperpolarizing factors and that the vasodilatation response to K(+) is impaired in the mesenteric arterial bed from diabetic rats.     

Changes in superoxide dismutase mRNA expression by streptozotocin-induced diabetes.

1. Experiments were designed to investigate the involvement of superoxide anions in the attenuated endothelium-dependent relaxation of the rat aorta from streptozotocin (STZ)-induced diabetic rats. 2. The endothelium-dependent relaxation responses to acetylcholine (ACh, 10(-7) M) in helical strips of the aorta precontracted with noradrenaline (NA, 5 x 10(-3) approximately 3 x 10(-7) M) were significantly decreased in STZ-induced diabetic rats. The recovery phase of the relaxation after single administration of ACh in the STZ-induced diabetic rats was more rapid than those in control vessels. 3. Preincubation of aortic strips with superoxide dismutase (SOD, 60 u ml-1) normalized the recovery phase of the relaxation of diabetic aorta after single administration of ACh, whereas catalase (150 u ml-1) or indomethacin (10(-5) M) had no effects on the relaxation. 4. SOD (180 u ml-1) caused relaxation in NA precontracted aortic strips and the degree of the SOD-induced relaxation was significantly greater in diabetic aorta as compared with age-matched control vessels. 5. When the changes in mRNA expressions of Mn-SOD or Cu-Zn-SOD were observed, Mn-SOD mRNA expression was markedly decreased, and Cu-Zn-SOD was slightly decreased in diabetic aorta. 6. These results suggest that the rapid destruction of NO by superoxide anions may occur in the STZ-induced diabetic rats, and this may be due to a decrease in mRNA expression of Mn-SOD or Cu-Zn-SOD.     

Endothelium-dependent modulation of resistance vessel contraction: studies with NG-nitro-L-arginine methyl ester and NG-nitro-L-arginine.

1. The effect of NG-nitro-L-arginine methyl ester (L-NAME) and NG-nitro-L-arginine (L-NOARG) on noradrenaline (NA)-induced contractility and acetylcholine (ACh)-induced endothelium-dependent relaxation was studied in rat mesenteric resistance arteries. 2. Third order branches of mesenteric arteries were dissected and mounted on two forty micron wires in a Mulvany myograph. 3. Incubation with L-NAME and L-NOARG (10 microM) caused a time-dependent shift in the 50% response to NA (ED50) (0.01 microM-10 microM) but was not associated with an increase in the maximum contractile response. 4. L-NAME and L-NOARG (10 microM) caused a time-dependent inhibition of ACh (1 microM)-induced relaxation with a maximum effect after 120 min. 5. Following endothelium removal, incubation with either L-NAME or L-NOARG caused no significant shift in the ED50, although the residual relaxation response to ACh (1 microM) was further attenuated. 6. Incubation with the cyclo-oxygenase inhibitor, indomethacin, enhanced the relaxation to ACh and reduced the inhibitory effects of L-NAME and L-NOARG. 7. In conclusion, L-NAME and L-NOARG are potent inhibitors of acetylcholine-induced endothelium-dependent relaxation in mesenteric resistance arteries. The shift in ED50 associated with these inhibitors suggests a probable role for the endothelium in modulating the contractility of the resistance vasculature.     

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

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

Endothelium-derived hyperpolarizing factor does not contribute to the decrease in endothelium-dependent relaxation in the aorta of streptozotocin-induced diabetic rats

• 1.1. We examined the contribution of endothelium-derived hyperpolarizing factor (EDHF) to the impairment of endothelium-dependent relaxation caused by acetylcholine (ACh) in the aorta of streptozotocin-induced diabetic rats, by using N^ω-nitro-l-arginine methylester (L-NAME) and tetraethylammonium chloride (TEA) to inhibit nitric oxide (NO) and EDHF, respectively.
• 2.2. ACh-induced relaxation of the aorta decreased in diabetic rats. In contrast, sodium nitroprusside-induced relaxation was the same in diabetic rats and control rats.
• 3.3. Treatment with 5 × 10⁻⁷ M L-NAME resulted in a right shift of the dose-response curves of ACh-induced relaxation in the aorta. The shift was greater in the control aorta.
• 4.4. Treatment with 5 × 10⁻⁴ M TEA resulted in a similar right shift in both the control and diabetic aorta.
• 5.5. Therefore, while endothelium-derived NO appears to contribute to the impairment of ACh-induced endothelium-dependent relaxation in the aorta of diabetic rats, EDHF does not

.     

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

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

Differential changes of adrenoceptor- and muscarinic receptor-linked prostacyclin synthesis by the aorta and urinary bladder of the diabetic rat.

1. The effect of experimental diabetes mellitus (DM; hyperglycaemic, non-ketototic; 2 months duration) in the rat on receptor-linked prostacyclin (PGI2) synthesis (measured as 6-oxo-PGF1 alpha by radioimmunoassay) was studied in the aorta and urinary bladder using adrenaline, angiotensin II (AII) and acetylcholine (ACh). Signal transduction systems were studied via stimulation of PGI2 synthesis with phorbol ester dibutyrate (PDBU; a protein kinase C activator [PKC]), Ca2+ ionophore A23187 (A23187) and thapsigargin (both elevate intracellular Ca2+, activating phospholipase A2 [PLA2]) and arachidonate (AA; substrate for PGI2 synthesis). 2. In response to adrenaline, AII and phorbol ester, aortic PGI2 release was markedly reduced (all > 75%) in diabetic rats compared to controls. EC50s of the dose-response curves for adrenaline, AII and PDBU were also markedly increased in aortae from DM rats compared to controls. Although there was decreased output of PGI2 in response to A23187 by aortae from diabetic rats compared to controls, there was no difference in the EC50s (mean +/- s.e. mean: diabetic, 2.7 +/- 0.2 x 10(-6) M; controls 2 +/- 0.18 x 10(-6) M). There were no differences in PGI2 release (or in the EC50s) in response to thapsigargin or AA between aortae from diabetic and control rats. 3. In the urinary bladder, there was a marked increase in PGI2 output in response to ACh and a marked decrease in EC50s for the ACh-PGI2 dose-response curves in diabetic rats (EC50 = 5.8 +/- 0.32 x 10(-7) M) compared to controls (EC50 = 2.2 +/- 0.15 x 10(-6) M).(ABSTRACT TRUNCATED AT 250 WORDS)     

Neurotensin potentiates the potassium-induced release of endogenous dopamine from rat striatal slices

The relationship between the renin-angiotensin system (RAS) and prostacyclin (PGI2) biosynthesis was studied in experimental diabetic rats. The group with diabetes induced by streptozotocin (STZ, 3.3 mmol/kg i.v.) showed prolonged hypertension, and plasma renin activity decreased markedly from 8.4 +/- 0.7 to 2.4 +/- 0.3 and 1.2 +/- 0.3 ng angiotensin I/ml per h at 2 and 8 weeks after STZ treatment. Plasma PGI2, determined as 6-keto-PGF1 alpha, decreased significantly at 8 weeks, with the values for the STZ-treated and control groups being 1490 +/- 99 and 2210 +/- 90 pg/ml, respectively. Significant suppression of renin release from renal cortical slices was observed at 8 weeks in the diabetic group, although no significant change was found in the renal renin content when compared with that of the controls. The release of PGI2 from the renal medullary slices of the diabetic group was suppressed at 2 and 8 weeks, with the suppression in aorta and renal cortical slices being apparent only at 8 weeks. These results indicate that suppression of the RAS may be related to PGI2 biosynthesis in diabetes mellitus.     

Beneficial effect of pentaerythrityl tetranitrate on functional and morphological changes in the rat thoracic aorta evoked by long-term nitric oxide synthase inhibition

The present study examined whether pentaerythrityl tetranitrate (PETN), a tolerance-devoid exogenous donor of nitric oxide (NO), could attenuate functional and morphological changes in the rat thoracic aorta evoked by 6-week NO synthase inhibition by NG-nitro-L-arginine methyl ester (L-NAME). Systolic blood pressure in L-NAME + PETN-treated rats (163 +/- 1 mm Hg) was significantly lower than in L-NAME-treated rats (172 +/- 2 mm Hg) but was still higher than in age-matched controls (126 +/- 2 mm Hg). Six weeks of treatment of rats with L-NAME significantly inhibited endothelium-dependent relaxation of the isolated thoracic aorta induced by acetylcholine. The inhibitory effect of L-NAME was entirely reversed by the simultaneous treatment with PETN. The enhancing effect of L-NAME on noradrenaline-induced contraction was antagonised by long-term treatment with PETN. Wall thickness, cross-sectional area and wall/diameter ratio of the thoracic aorta in L-NAME-treated rats were markedly increased. In the L-NAME + PETN-treated rats, the increment of these parameters was significantly lower. The results suggest that PETN administered to rats during development of NO-deficient hypertension prevented functional impairment and at the same time reduced structural changes in the thoracic aorta induced by long-term inhibition of NO synthase.