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.     

A high-sodium diet in streptozotocin-induced diabetic rats impairs endothelium-derived hyperpolarizing factor-mediated vasodilation

We examined endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation of mesenteric arteries in high-sodium loaded streptozotocin (STZ)-induced diabetic rats. The study shows that acetylcholine (ACh)-induced, EDHF-mediated relaxation is relatively maintained in STZ-induced diabetic rats, but after a high-sodium diet was given, the function was significantly impaired in STZ-induced diabetic rats.     

Mechanism underlying enhanced endothelium-dependent vasodilatation in thoracic aorta of early stage streptozotocin-induced diabetic mice

AIM: To investigate the mechanism of the enhanced endothelium-dependent vasodilatation in thoracic aorta of the early stage streptozotocin (STZ)-induced diabetic C57BL/6J mice. METHODS: Radioimmunity was used to detect the metabolite of prostaglandin I2 (PGI2), 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), in the blood serum. Vascular muscle tension and phenylephrine (PE)-induced rhythmic activity in the isolated thoracic aorta of mice were also compared. RESULTS: 6-Keto-PGF1 alpha in the serum was significantly higher in STZ-induced diabetic mice than age-matched controls [(1.8+/-1.0) microg./L vs (0.5+/-0.3) microg/L, P<0.01]. PE induced rhythmic activity in both diabetic and control mouse aorta but the amplitude was markedly higher in diabetic mice than in controls [(4.9+/-1.7) % vs (12+/-5) %, P<0.01]. PE, high K+ solution-induced contraction, and acetylcholine (ACh)-induced relaxation [(56+/-10) % vs (81+/-8) %, P<0.01] were notably enhanced in diabetic mice than those in controls. Alone NG-nitro-L-arginine methyl ester (L-NAME) or 6-(phenylamino)-5,8-quinolinedione (LY-83583) abolished the rhythmic activity and ACh-induced relaxation in controls but only partially inhibited them in diabetic mice. Indomethacin did not affect rhythmic activity but depressed ACh-induced relaxation. L-NAME plus indomethacin significantly depressed the rhythmic activity and ACh-induced relaxation than L-NAME alone (P<0.01). Furthermore tetraethylammonium plus L-NAME abolished them in diabetic mice. CONCLUSION: The mechanism that enhanced endothelium-dependent vasodilatation in STZ-induced diabetic mice is due to enhanced production of PGI2 and endothelium-derived hyperpolarizing factor (EDHF). The phenomena maybe only take place in early stage of diabetic mice.     

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

.     

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.     

Acrolein induces vasodilatation of rodent mesenteric bed via an EDHF-dependent mechanism

Acrolein is generated endogenously during lipid peroxidation and inflammation and is an environmental pollutant. Protein adducts of acrolein are detected in atherosclerotic plaques and neurons of patients with Alzheimer's disease. To understand vascular effects of acrolein exposure, we studied acrolein vasoreactivity in perfused rodent mesenteric bed. Acrolein induced endothelium-dependent vasodilatation that was more robust and more sensitive than dilation induced by 4-hydroxy-trans-2-nonenal, trans-2-hexenal, or propionaldehyde. Acrolein-induced vasodilatation was mediated by K(+)-sensitive components, e.g., it was abolished in 0 [K(+)](o) buffer or in 3 mM tetrabutylammonium, inhibited 75% in 50 microM ouabain, and inhibited 64% in 20 mM K(+) buffer. Moreover, combined treatment with the Ca(2+)-activated K(+) channel inhibitors 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34, 100 nM) and apamin (5 microM) significantly reduced vasodilatation without altering sensitivity to acrolein. However, acrolein-induced % dilation was unaffected by l-NAME or indomethacin pretreatment indicating mechanistic independence of NO and prostaglandins. Moreover, acrolein induced vasodilatation in cirazoline-precontracted mesenteric bed of eNOS-null mice confirming eNOS independence. Pretreatment with 6-(2-propargyloxyphenyl) hexanoic acid (PPOH 50 microM), an epoxygenase inhibitor, or the superoxide dismutase mimetic Tempol (100 microM) significantly attenuated acrolein-induced vasodilatation. Collectively, these data indicate that acrolein stimulates mesenteric bed vasodilatation due to endothelium-derived signal(s) that is K(+)-, ouabain-, PPOH-, and Tempol-sensitive, and thus, a likely endothelium-derived hyperpolarizing factor (EDHF). These data indicate that low level acrolein exposure associated with vascular oxidative stress or inflammation stimulates vasodilatation via EDHF release in medium-sized arteries--a novel function.     

Critical role of gap junctions in endothelium-dependent hyperpolarization in rat mesenteric arteries

1. Acetylcholine (ACh) evokes endothelium-dependent hyperpolarization in arterial cells, presumably through endothelium-derived hyperpolarizing factor (EDHF). The identity of EDHF is still elusive; however, several recent studies suggest the possible involvement of myoendothelial gap junctions in the EDHF response. 2. To elucidate the role of gap junctions in endothelium-dependent hyperpolarization, we examined the effects of the gap junction inhibitors 18 alpha-glycyrrhetinic acid (18 alpha-GA; 10(-4) mol/L) and carbenoxolone (3 x 10(-4) mol/L), a water-soluble form of 18 beta-GA, on hyperpolarization and relaxation to ACh in rat proximal and distal mesenteric arteries. Experiments were performed in the presence of indomethacin (10(-5) mol/L) and N(G)-nitro-L-arginine (10(-4) mol/L). 3. In both proximal and distal mesenteric arteries, ACh-induced hyperpolarization and relaxation were partially inhibited by 18 alpha-GA and abolished by carbenoxolone. 4. Endothelium-independent hyperpolarization to levcromakalim, an ATP-sensitive K+ channel opener, were unaffected by 18 alpha-GA or carbenoxolone in both arteries. 5. Relaxations to levcromakalim were unaffected by 18 alpha-GA, but were inhibited somewhat by carbenoxolone in proximal mesenteric arteries. 6. These findings suggest that myoendothelial gap junctions play a critical role in EDHF-mediated responses in both proximal and distal mesenteric arteries of the rat.     

Endothelium-derived relaxing, contracting and hyperpolarizing factors of mesenteric arteries of hypertensive and normotensive rats

Differences in the acetylcholine (ACh)-induced endothelium-dependent relaxation and hyperpolarization of the mesenteric arteries of Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were studied. Relaxation was impaired in preparations from SHRSP and tendency to reverse the relaxation was observed at high concentrations of ACh in these preparations. Relaxation was partly blocked by NG-nitro-L-arginine (L-NOARG, 100 microM) and, in the presence of L-NOARG, tendency to reverse the relaxation was observed in response to higher concentrations of ACh, even in preparations from WKY. The relaxation remaining in the presence of L-NOARG was also smaller in preparations from SHRSP. The tendency to reverse the relaxation observed at higher concentrations of ACh in preparations from SHRSP or WKY in the presence of L-NOARG were abolished by indomethacin (10 microM). Elevating the K+ concentration of the incubation medium decreased relaxation in the presence of both indomethacin and L-NOARG. Relaxation in the presence of L-NOARG and indomethacin was reduced by the application of both apamin (5 microM) and charybdotoxin (0.1 microM). This suggests that the relaxation induced by ACh is brought about by both endothelium-derived relaxing factor (EDRF, nitric oxide (NO)) and hyperpolarizing factor (EDHF), which activates Ca2+-sensitive K+ channels. Electrophysiological measurement revealed that ACh induced endothelium-dependent hyperpolarization of the smooth muscle of both preparations in the presence of L-NOARG and indomethacin; the hyperpolarization being smaller in the preparation from SHRSP than that from WKY. These results suggest that the release of both NO and EDHF is reduced in preparations from SHRSP. In addition, indomethacin-sensitive endothelium-derived contracting factor (EDCF) is released from both preparations; the release being increased in preparations from SHRSP.     

Calcium dobesilate potentiates endothelium-derived hyperpolarizing factor-mediated relaxation of human penile resistance arteries

1 We have evaluated the participation of endothelium-derived hyperpolarizing factor (EDHF) in the endothelium-dependent relaxation of isolated human penile resistance arteries (HPRA) and human corpus cavernosum (HCC) strips. In addition, the effect of the angioprotective agent, calcium dobesilate (DOBE), on the endothelium-dependent relaxation of these tissues was investigated. 2 Combined inhibition of nitric oxide synthase (NOS) and cyclooxygenase (COX) nearly abolished the endothelium-dependent relaxation to acetylcholine (ACh) in HCC, while 60% relaxation of HPRA was observed under these conditions. Endothelium-dependent relaxation of HPRA resistant to NOS and COX inhibition was prevented by raising the extracellular concentration of K(+) (35 mM) or by blocking Ca(2)(+)-activated K(+) channels, with apamin (APA; 100 nM) and charybdotoxin (CTX; 100 nM), suggesting the involvement of EDHF in these responses. 3 Endothelium-dependent relaxation to ACh was markedly enhanced by DOBE (10 micro M) in HPRA but not in HCC. The potentiating effects of DOBE on ACh-induced responses in HPRA, remained after NOS and COX inhibition, were reduced by inhibition of cytochrome P450 oxygenase with miconazole (0.3 mM) and were abolished by high K(+) or a combination of APA and CTX. 4 In vivo, DOBE (10 mg kg(-1) i.v.) significantly potentiated the erectile responses to cavernosal nerve stimulation in male rats. 5 EDHF plays an important role in the endothelium-dependent relaxation of HPRA but not in HCC. DOBE significantly improves endothelium-dependent relaxation of HPRA mediated by EDHF and potentiates erectile responses in vivo. Thus, EDHF becomes a new therapeutic target for the treatment of erectile dysfunction (ED) and DOBE could be considered a candidate for oral therapy for ED.     

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.     

Type 1 diabetes and hypercholesterolaemia reveal the contribution of endothelium-derived hyperpolarizing factor to endothelium-dependent relaxation of the rat aorta

1. The present study evaluated the effect of diabetes, hypercholesterolaemia and their combination on the contribution of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) to relaxation of rat isolated aortic rings and the potential contribution of oxidant stress to the disturbance of endothelial function. 2. Thoracic aortic rings from control, diabetic, hypercholesterolaemic and diabetic plus hypercholesterolaemic rats were suspended in organ baths for tension recording. Generation of superoxide by the aorta was measured using lucigenin-enhanced chemiluminescence. 3. The maximal response to acetylcholine (ACh) was significantly reduced in diabetic or hypercholesterolaemic rats compared with control rats. In rats with diabetes plus hypercholesterolaemia, both the sensitivity and maximal response to ACh was impaired. In control rats, the response to ACh was abolished by the NO synthase inhibitor N(G)-nitro-L-arginine (L-NNA) or inhibition of soluble guanylate cyclase with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). In contrast, in rats with diabetes, hypercholesterolaemia or both, relaxation to ACh was resistant to inhibition by L-NNA or ODQ, but abolished by additional inhibition of K(Ca) channels with charybdotoxin plus apamin. 4. The generation of superoxide was not significantly enhanced in aortic rings from either diabetic or hypercholesterolaemic rats, but was significantly increased in aortic rings from rats with diabetes plus hypercholesterolaemia. 5. These results suggest that when diabetes and hypercholesterolaemia impair endothelium-dependent relaxation, due to a diminished contribution from NO, a compensatory contribution of EDHF to endothelium-dependent relaxation of the aorta is revealed. The attenuation of NO-mediated relaxation, at least in the presence of both diabetes and hypercholesterolaemia, is associated with enhanced superoxide generation.     

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.     

Elevated plasma endothelin-1 level in streptozotocin-induced diabetic rats and responsiveness of the mesenteric arterial bed to endothelin-1

1. Both the plasma endothelin-1 (ET-1) levels and the plasma glucose levels were markedly elevated in streptozotocin (STZ)-induced diabetic rats.
2. The maximum contractile response of the mesenteric arterial bed to ET-1 was significantly reduced, and the vasodilatation induced by the ET_B-receptor agonist IRL-1620 in the mesenteric arterial bed was significantly reduced in STZ-induced diabetic rats.
3. ET-1 (10⁻⁸ M) caused a transient vasodilatation followed by a marked vasoconstriction in methoxamine-preconstricted mesenteric arterial beds. The ET-1-induced vasodilatation was significantly larger in beds from diabetic rats than in those from age-matched controls. By contrast, the ET-1-induced vasoconstriction was significantly smaller in STZ-induced diabetic rats than in the controls.
4. Both removal of the endothelium with Triton X-100 and preincubation with BQ-788 (10⁻⁶ M) (ET_B-receptor antagonist) abolished the ET-1-induced vasodilatation. Preincubation with BQ-485 (10⁻⁶ M) or BQ-123 (3×10⁻⁶) (ET_A-receptor antagonist) significantly augmented the ET-1-induced vasodilatation in control mesenteric arterial beds, but not that in beds from diabetic rats.
5. These results demonstrate that marked increases not only in plasma glucose, but also in plasma ET-1 occur in STZ-induced diabetic rats. We suggest that the decreased contractile response and the increased vasodilator response of the mesenteric arterial bed to ET-1 may both be due to desensitization of ET_A receptors, though ET_B receptors may also be desensitized. This desensitization may result from the elevation of the plasma ET-1 levels seen in STZ-induced diabetic rats.

     

内皮依赖性超极化因子在血管舒张中的作用

目的研究内皮依赖性超极化因子(EDHF)在血管舒张中的作用及机制。方法测定各种内皮依赖性舒张因子抑制剂、钾通道抑制因子、细胞色素P450单氧化酶抑制剂作用下的血管环张力。结果EDHF的血管舒张作用在大鼠肠系膜微动脉明显大于胸主动脉。一氧化氮(NO)合成受到慢性抑制时,胸主动脉的EDHF作用有增加趋势,在肠系膜微动脉投药后3 d和1周的EDHF作用明显增加。ChTx部分抑制、TBA明显抑制EDHF在肠系膜微动脉的舒张作用。结论EDHF在大鼠肠系膜微动脉的内皮依赖性舒张反应中起主要作用;在NO合成受抑制时其作用明显增加;其作用介导于K_Ca通道。     

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.     

Effects of chronic in vivo administration of nitroglycerine on ACh-induced endothelium-dependent relaxation in rabbit cerebral arteries

BACKGROUND AND PURPOSE: In the setting of nitrate tolerance, endothelium-dependent relaxation is reduced in several types of peripheral vessels. However, it is unknown whether chronic in vivo administration of nitroglycerine modulates such relaxation in cerebral arteries. EXPERIMENTAL APPROACH: Isometric force and smooth muscle cell membrane potential were measured in endothelium-intact strips from rabbit middle cerebral artery (MCA) and posterior cerebral artery (PCA). KEY RESULTS: ACh (0.1-10 microM) concentration-dependently induced endothelium-dependent relaxation during the contraction induced by histamine in both MCA and PCA. Chronic (10 days) in vivo administration of nitroglycerine reduced the ACh-induced relaxation in PCA but not in MCA, in the presence of the cyclooxygenase inhibitor diclofenac (3 microM). In the presence of the NO-synthase inhibitor N (omega)-nitro-L-arginine (L-NNA, 0.1 mM) plus diclofenac, in MCA from both nitroglycerine-untreated control and -treated rabbits, ACh (0.1-10 microM) induced a smooth muscle cell hyperpolarization and relaxation, and these were blocked by the small-conductance Ca(2+)-activated K(+)-channel inhibitor apamin (0.1 microM), but not by the large- and intermediate-conductance Ca(2+)-activated K(+)-channel inhibitor charybdotoxin (0.1 microM). In contrast, in PCA, ACh (<3 microM) induced neither hyperpolarization nor relaxation under these conditions, suggesting that the endothelium-derived relaxing factor is NO in PCA, whereas endothelium-derived hyperpolarizing factor (EDHF) plays a significant role in MCA. CONCLUSIONS AND IMPLICATIONS: It is suggested that in rabbit cerebral arteries, the function of the endothelium-derived relaxing factor NO and that of EDHF may be modulated differently by chronic in vivo administration of nitroglycerine.     

Acetylcholine-induced vasodilation may depend entirely upon NO in the femoral artery of young piglets

1 To characterize agonist-induced relaxation in femoral artery rings from young piglets, we compared the effect of a NOS-inhibitor N(omega)-nitro-L-arginine (L-NOARG), an NO-inactivator oxyhaemoglobin (HbO) and a soluble guanyl cyclase(sGC)-inhibitor 1H-[1,2,4]Oxadiazolo-[4,3,-alpha]quinoxalin-1-one (ODQ) on acetylcholine(ACh)-induced relaxation. The involvement of K(+) channel activation was studied on relaxations induced by ACh, the two NO donors sodium nitroprusside (SNP) and diethylamine (DEA) NONOate, and the cell membrane permeable guanosine 3'5' cyclic monophosphate (cGMP) analogue 8-Br-cGMP. 2 Full reversal of phenylephrine-mediated precontraction was induced by ACh (1 nM-1 microM) (pD(2) 8.2+/-0.01 and R(max) 98.7+/-0.3%). L-NOARG (100 microM) partly inhibited relaxation (pD(2) 7.4+/-0.02 and R(max) 49.6+/-0.8%). The L-NOARG/indomethacin(IM)-resistant response displayed characteristics typical for endothelium-derived hyperpolarizing factor (EDHF), being sensitive to a combination of the K(+) channel blockers charybdotoxin (CTX) (0.1 microM) and apamin (0.3 microM). 3 ODQ (10 microM) abolished relaxations induced by ACh and SNP. L-NOARG/IM-resistant relaxations to ACh were abolished by HbO (20 microM). 4 Ouabain (1 microM) significantly inhibited ACh-induced L-NOARG/IM-resistant relaxations and relaxations induced by SNP (10 microM) and 8-Br-cGMP (0.1 mM). A combination of ouabain and Ba(2+) (30 microM) almost abolished L-NOARG/IM-resistant ACh-induced relaxation (R(max) 7.7+/-2.5% vs 23.4+/-6.4%, with and without Ba(2+), respectively, P<0.05). 5 The present study demonstrates that in femoral artery rings from young piglets, despite an L-NOARG/IM-resistant component sensitive to K(+) channel blockade with CTX and apamin, ACh-induced relaxation is abolished by sGC-inhibition or a combination of L-NOARG and HbO. These findings suggest that relaxation can be fully explained by the NO/cGMP pathway.     

Mechanisms of relaxing response induced by rat/mouse hemokinin-1 in porcine coronary arteries: roles of potassium ion and nitric oxide

Rat and mouse hemokinin-1(r/m hemokinin-1) is a recently described member of the tachykinin family whose cardiovascular functions are not fully understood. In this study, we investigated the mechanisms of the relaxing response induced by r/m hemokinin-1 in isolated porcine coronary arteries by using a specific antagonist of tachykinin NK(1) receptor (SR140333), a nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NNA), and 1H-[1,2,4] Oxadiazolo [4,3-a] quinoxalin-1-one (ODQ), a blocker of cGMP production. r/m Hemokinin-1 (10(-12)-10(-6 )M) evoked a marked endothelium-dependent vasodilatation (E(max)=121.12+/-10.6% and 91.79+/-2.39% in 10(-6) M PGF(2)alpha and 30 mM KCl precontracted arterial rings, respectively) of coronary arteries mediated by activation of endothelial tachykinin NK(1) receptors. Two components contributed to this r/m hemokinin-1-elicited vasodilatation, the first of which was endothelium-derived hyperpolarizing factor (EDHF), which played a major role. This EDHF was identified as a potassium current through certain kinds of potassium channels on the endothelial cell membrane of porcine coronary arteries. Specific antagonists of Ca(2+)-activated K(+) channels (dequalinium and clotrimazole) did not have an inhibitory effect on the r/m hemokinin-1-induced vasodilatation, whereas they did on the substance P-induced vasodilatation. When potassium ion efflux was impaired by a high K(+) concentration (30 mM) or removal of K(+) from the surroundings, NO synthesis was triggered by r/m hemokinin-1 to produce an equivalent EDHF (K(+))-independent vasorelaxation as a compensatory mechanism.     

DIFFERENT RESPONSES TO ACETYLCHOLINE IN THE PRESENCE OF NITRIC OXIDE INHIBITOR IN RAT AORTAE AND MESENTERIC ARTERIES

1. This study compared the relaxation induced by acetylcholine (ACh) in aortic and mesenteric arterial rings from Sprague-Dawley (SD) rats in the presence and absence of inhibitors of the known endothelium-derived relaxing factors. 2. ACh-induced relaxations were completely blocked by methylene blue and N”-nitro-L-arginine (LNNA) in aortae, whereas these were only partially attenuated by methylene blue and LNNA in mesenteric arteries. 3. This methylene blue-resistant relaxation of ACh was partly attenuated by potassium channel blockers (tetraethylammonium and barium) but not affected by LNNA, indomethacin and calcium-free solution. 4. These results suggest that there may be another endothelial relaxing factor which is not nitric oxide (NO), prostanoids or endothelium-derived hyperpolarizing factor (EDHF) in mesenteric arteries but not in aortae. This unknown factor seems to be extracellular calcium ([Ca²⁺]_o)-independent.     

Alteration of endothelium-mediated vasodilator response in the rat hindlimb vasculature consecutive to chronic hypoxic stress: NO and EDHF involvement

The previously documented impairment of hindlimb blood flow consecutive to chronic hypoxia might be related to endothelial vasomotor dysfunction. The aim of this study was to assess in-vivo the effect of chronic hypoxic stress on endothelium-mediated vasodilator response of hindlimb vascular bed, especially as regards to endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide (NO) pathway contribution. Dark Agouti rats were randomly assigned to live at barometric pressure ≈ 760 mmHg (N rats) or ≈ 550 mmHg (CH rats). Under anesthesia, catheters were placed in the carotid artery for arterial pressure measurement, and in the saphenous vein and iliac artery for drug delivery. Hindlimb blood flow (HBF) was measured by transit-time ultrasound flowmetry, at baseline and during endothelium-dependent vasodilator response induced by intra-arterial injection of acetylcholine (0.75 ng and 7.5 ng) with and without specific blockers of NOS (L-NAME) and EDHF (Charybdotoxin + Apamin). HBF and hindlimb vascular conductance changes in response to ACh infusion were significantly lower in CH than in N rats. The mechanisms responsible for this blunted response involved impairment in both NO pathway and EDHF. The chronic hypoxia-induced alteration of NO pathway was mainly related to the bioavailability of its substrate l-Arginine, since the infusion of l-Arginine restored the endothelial response to ACh in CH rats to the level of N rats. These results demonstrate that the impairment in endothelium-mediated vasodilator response of the hindlimb vascular tree induced by chronic hypoxic stress involves both NO and EDHF.