The involvement of K+ channels and the possible pathway of EDHF in the rabbit femoral artery.

Experiments were designed to characterize the cellular mechanisms of action of endothelium-derived vasodilator substances in the rabbit femoral artery. Acetylcholine (ACh, 10(-8)-10(-5) M) induced a concentration-dependent relaxation of isolated endothelium-intact arterial rings precontracted with norepinephrine (NE, 10(-6) M). The ACh-induced response was abolished by the removal of endothelium. NG-nitro-L-arginine (L-NAME, 10(-4) M), an inhibitor of NO synthase, partially inhibited ACh-induced endothelium-dependent relaxation, whereas indomethacin (10(-5) M) showed no effect on ACh-induced relaxation. 25 mM KCl partially inhibited ACh-induced relaxation by shifting the concentration-response curve and abolished the response when combined with L-NAME and NE. In the presence of L-NAME, ACh-induced relaxation was unaffected by glibenclamide (10(-5) M) but significantly reduced by apamin (10(-6) M), and almost completely blocked by tetraethylammonium (TEA, 10(-3) M), iberiotoxin (10(-7) M) and 4-aminopyridine (4-AP, 5 x 10(-3) M). The cytochrome P450 inhibitors, 7-ethoxyresorufin (7-ER, 10(-5) M) and miconazole (10(-5) M) also significantly inhibited ACh-induced relaxation. Ouabain (10(-6) M), an inhibitor of Na+, K(+)-ATPase, or K(+)-free solution, also significantly inhibited ACh-induced relaxation. ACh-induced relaxation was not significantly inhibited by 18-alpha-glycyrrhetinic acid (18 alpha-GA, 10(-4) M). These results of this study indicate that ACh-induced endothelium-dependent relaxation of the rabbit femoral artery occurs via a mechanism that involves activation of Na+, K(+)-ATPase and/or activation of both the voltage-gated K+ channel (Kv) and the large-conductance, Ca(2+)-activated K+ channel (BKCa). The results further suggest that EDHF released by ACh may be a cytochrome P450 product.     

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.     

Glycyrrhetinic acid-sensitive mechanism does not make a major contribution to non-prostanoid, non-nitric oxide mediated endothelium-dependent relaxation of rat mesenteric artery in response to acetylcholine.

Pharmacological characteristics of non-prostanoid (PGI2), non-NO mediated endothelium-dependent relaxation in response to acetylcholine (ACh) were examined in the isolated rat mesenteric artery, especially focusing on the possible contribution of the gap junctional communication in the response. ACh produced an endothelium-dependent relaxation of the isolated rat mesenteric artery with functional endothelium in the presence of both indomethacin (3 x 10(-6) M) and N(G)-nitro-L-arginine methyl ester (L-NAME) (10(-4) M), an inhibitor of nitric oxide synthase (NOS). ACh-induced relaxation of the rat mesenteric artery in the presence of indomethacin and L-NAME was strongly attenuated in the solution containing high (80 mM) KCl, tetraethylammonium (TEA) (10(-2) M), which suggests the involvement of endothelium-derived relaxing factor(s) (EDHF(s)) in the response. Non-PGI2, non-NO mediated endothelium-dependent relaxation to ACh was not profoundly affected by glibenclamide (10(-6) M), 4-aminopyridine (4-AP) (10(-4) M), iberiotoxin (10(-7) M), agitoxin-2 (10(-8) M), or apamin (10(-7) M), but was abolished by the treatment with apamin (10(-7) M) plus charybdotoxin (10(-7) M). Non-PGI2, non-NO mediated endothelium-dependent relaxation to ACh was not substantially affected by arachidonic acid (AA) (10(-4) M) or ONO-RS-082 (10(-5) M), an inhibitor of phospholipase A2, which rules out the involvement of AA metabolites in the vascular response. Furthermore, a gap junction inhibitor, 18alpha-glycyrrhetinic acid (18alpha-GA) did not show dramatic inhibitory effect on non-PGI2, non-NO mediated endothelium-dependent relaxation induced by ACh. These findings suggest that 1) metabolites of AA are not involved in non-PGI2, non-NO mediated endothelium-dependent relaxation to ACh in the isolated rat mesenteric artery; 2) Heterocellular gap junctional communication does not mainly account for non-PGI2, non-NO mediated endothelium-dependent relaxation evoked by ACh in this artery.     

Chronic treatment with progesterone but not medroxyprogesterone acetate restores the endothelial control of vascular tone in the mesenteric artery of ovariectomized rats

OBJECTIVE: To examine whether chronic administration of the natural hormone progesterone or a synthetic progestogen, medroxyprogesterone acetate, to ovariectomized rats affects the endothelial control of arterial tone in the isolated mesenteric artery. DESIGN: Sham-operated rats received a daily subcutaneous injection of solvent (sesame oil), whereas ovariectomized rats received either sesame oil, progesterone (22 mg kg/day), or medroxyprogesterone acetate (22 mg kg/day) for 4 weeks, according to their respective group. RESULTS: Phenylephrine-induced contractions were significantly increased (about 200% at 10 microM) by N-nitro-L-arginine, a nitric oxide synthase inhibitor, in intact mesenteric arterial rings from the sham-operated but not from the ovariectomized group. The progesterone but not the medroxyprogesterone treatment restored the potentiating effect of N-nitro-L-arginine on phenylephrine-induced contraction (about 180% at 10 microM). Contractions to phenylephrine were not affected by the combination of charybdotoxin plus apamin, two inhibitors of endothelium-derived hyperpolarizing factor-mediated responses, in all groups. Acetylcholine induced endothelium-dependent relaxations, which were partially inhibited by N-nitro-L-arginine and abolished by the combination of N-nitro-L-arginine plus charybdotoxin and apamin, in all groups. Acetylcholine induced similar charybdotoxin and apamin-sensitive hyperpolarizations in intact mesenteric artery segments from all groups. CONCLUSIONS: Chronic administration of progesterone, but not medroxyprogesterone, to ovarictomized rats restores the endothelium-dependent attenuation of contractile responses to phenylephrine in mesenteric arterial rings through the endothelial formation of nitric oxide. Thus, an enhancement of the protective effect of endothelial cells on the arterial wall might contribute to the beneficial effect of certain progestogen-containing preparations during hormonal treatment.     

Effects of inhibitors of nonselective cation channels on the acetylcholine-induced depolarization of circular smooth muscle from the guinea-pig stomach antrum.

In circular smooth muscle bundles isolated from the guinea-pig stomach antrum, the effects of quinidine, Ni2+, flufenamic acid, niflumic acid, La3+, SKF-96365 and 4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) on acetylcholine (ACh)-induced depolarization were investigated. Recording membrane potentials from smooth muscle cells with intracellular microelectrodes revealed that ACh (1 microM) depolarized the membrane by 5-8 mV and increased the amplitude and frequency of slow potentials. These effects were inhibited by atropine. Quinidine (10 microM) increased the amplitude of ACh-induced depolarization, with no alteration to the properties of slow potentials. Ni2+ (50 microM) transiently (5-10 min) depolarized the membrane by about 5 mV, with an associated increase in frequency and amplitude of slow potentials. In the stabilized condition with Ni2+, the amplitude of ACh-induced depolarization remained unchanged. Flufenamic acid (10 microM) inhibited the generation of slow potentials, with no change in either the amplitude of ACh-induced depolarization or of the amplitude and frequency of slow potentials generated during ACh stimulation. A high concentration of flufenamic acid (100 microM) depolarized the membrane and increased the amplitude of ACh-induced depolarization. Niflumic acid (10 microM) hyperpolarized the membrane and increased the amplitude and frequency of slow potentials and also the amplitude of ACh-induced depolarization. DIDS (100 microM) hyperpolarized the membrane and inhibited the amplitude and frequency of slow potentials, with no alteration to the amplitude of ACh-induced depolarization. SKF-96365 (3-50 microM) depolarized the membrane in a concentration-dependent manner, but did not change the level of ACh-induced depolarization. La3+ (50 microM) did not alter the properties of the slow potentials or the ACh-induced responses. These results provide evidence that ACh-induced depolarization is not inhibited by chemicals known to inhibit non-selective cation channels. We suggest that muscarinic receptor-mediated signal transduction may be different in smooth muscle and interstitial cells.     

Effect of chronic treatment with perindopril on endothelium-dependent relaxation of aorta and carotid artery in SHRSP.

Endothelium-dependent relaxation of aorta and carotid artery from stroke-prone spontaneously hypertensive rats (SHRSP) and the effect of chronic treatment of SHRSP with perindopril, an angiotensin converting enzyme inhibitor, on endothelium-dependent relaxation were studied. Endothelium-dependent relaxation was induced by acetylcholine (ACh) in preparations of SHRSP and normotensive Wistar Kyoto rats (WKY) precontracted with noradrenaline. The ACh-induced relaxation in both preparations was abolished by L-nitroarginine. The ACh-induced relaxation was impaired in preparations from SHRSP and contraction was observed at high concentrations of ACh. In the presence of indomethacin, impairment of endothelium-dependent relaxation in SHRSP was minimized and the contraction was inhibited. The relaxation with sodium nitroprusside did not differ between the preparations from WKY and SHRSP. Treatment of SHRSP with perindopril (2 mg/kg/day) for 6 weeks decreased systolic blood pressure and improved the ACh-induced relaxation of aorta and carotid artery. The treatment inhibited the contraction by higher concentrations of ACh in the presence of L-nitroarginine. These results indicate that the impairment of endothelium-dependent relaxation in aorta and carotid artery of SHRSP may be caused by the reduced availability of nitric oxide. The perindopril-treatment may prevent these changes in SHRSP.     

Influence of oestrous cycle and pregnancy on the reactivity of the rat mesenteric vascular bed

In isolated, perfused mesenteric vascular beds from female rats, it was assessed whether the constrictor response to cirazoline, an alpha(1)-adrenergic agonist, or acetylcholine (ACh)-induced relaxation was altered by oestrous cycle or pregnancy and the ability of nitric oxide (NO), prostanoids and endothelium-derived hyperpolarizing factor (EDHF) to modulate these responses. Mesenteries, removed from female rats on each oestrous cycle day and gestation day 16, were perfused with physiological salt solution. Tone was induced with cirazoline (1 micromol/l), and concentration-response curves to ACh generated. Responsiveness to ACh was tested in the presence of N(omega)-nitro-L-arginine (L-NA), ibuprofen (IBU) and tetrabutylammonium (TBA), to inhibit nitric oxide synthase (NOS), cyclo-oxygenase and K(+) channels respectively. Cirazoline-induced tone was smaller in pro-oestrous and pregnant groups, but the increase in tone to L-NA was larger in pregnant compared with oestrous and dioestrous groups. Control responses to ACh were not different, but L-NA attenuated the response in virgin groups only. IBU did not affect the ACh response, but TBA attenuated it in all groups. When TBA was introduced first, ACh-induced dilatation was significantly reduced and not altered by L-NA addition. These results suggest that in the mesenteric vascular bed from cycling and pregnant rats, EDHF is the major mediator of ACh-induced dilatation and NOS may be up-regulated in pregnant and pro-oestrous rats.     

Mechanisms of the palmitoylcarnitine-induced response in vascular endothelial cells

The mechanisms of Ca2+ mobilization induced by palmitoylcarnitine (Palcar) in rabbit aortic endothelial cells (ETCs) were examined using electrophysiological techniques. The results obtained were compared with those induced by acetylcholine (ACh). When a rabbit aortic muscle preparation with an intact endothelium was treated with 10 microM Palcar, the ACh-induced relaxation was markedly attenuated, whereas endothelium-independent relaxation caused by sodium nitroprusside was not affected. Under perforated-patch whole-cell-clamp conditions, the application of Palcar over the concentration range 0.3 and 10 microM elicited a slowly activating outward current (IPalcar-out), whereas ACh induced a rapidly activating outward current (IACh). A potassium channel blocker, 4-aminopyridine, significantly inhibited both IPalcar-out and IACh. Removal of external Ca2+ almost abolished IPalcar-out. Under the same conditions, however, IACh remained transient. Addition of cation channel blockers SK&F96365 and La3+ inhibited IPalcar-out more effectively than IACh. Application of staurosporine, an inhibitor of protein kinase C, affected neither IACh nor IPalcar-out. In contrast, treatment of ETCs with pertussis toxin (PTX) reduced IACh and almost abolished IPalcar-out. These findings demonstrate that, in ETCs, Palcar induces Ca2+ influx via the activation of PTX-sensitive GTP-binding protein, leading to the activation of Ca(2+)-dependent K+ current and hyperpolarization of the cell.     

Acetylcholine-induced aortic relaxation studied in salbutamol treated rats.

It has been proposed that the acetylcholine (ACh)-induced relaxation of the rat aorta is entirely mediated by endothelium derived-nitric oxide (NO). However, some authors have reported that indomethacin pretreatment attenuates ACh-induced relaxation of rat aortic ring preparations. Moreover, it has also been suggested that cAMP accumulation may regulate either nitric oxide synthase (NOS) or cyclooxygenase (COX) expression in different tissues. Thus, in this in vitro study we have investigated the endothelial mechanisms involved in the ACh-induced relaxation of ring preparations of the rat thoracic aorta, as well as the influence chronic treatment with the selective beta(2)-agonist salbutamol had upon such mechanisms. Results of functional experiments show that N(G)-monomethyl-L-arginine (L-NMMA, 3 x 10(-4) M) considerably inhibited the ACh-induced relaxation of rat aortic ring preparations. However, indomethacin (10(-5) M) was also found to partially attenuate this ACh response, suggesting that although NO is the most important mediator of the ACh-induced relaxation of the rat aortic ring preparations, vasorelaxation may also involve prostanoids. Moreover, the results suggest that treatment with salbutamol failed to produce any change in the ACh-induced relaxation of rat aortic ring preparations.     

Effects of chronic treatment with the spontaneous nitric oxide releaser FK409 on vascular responses in established streptozotocin-induced diabetic rat.

Experiments were designed to investigate the effects of chronic administration of an NO donor, (+/-)-(E)-ethyl-2-[(E)-ethylhydroxyimino]-5-nitro-3-hexeneamide (FK409), on the impairment of the acetylcholine-induced endothelium-dependent relaxations of the aorta, perfused mesenteric arterial bed and perfused kidney that seen in streptozotocin-induced diabetic rats. In aortic strips and in the perfused kidney, the decreased acetylcholine-induced relaxation seen in diabetes was restored to normal by chronic (daily for 4 weeks) administration of FK409 (20 mg/kg or 10 mg/kg, respectively). Acetylcholine increased the NOx (NO2- and NO3-) level in the perfusates from aortic strips, the perfused kidney and the perfused mesenteric arterial bed. These increases were significantly weaker for diabetic rats than for the controls. This effect of diabetes was ameliorated by chronic administration of FK409 (20 mg/kg) in aortic strips and perfused kidney, but not in the perfused mesenteric arterial bed. These results demonstrate that chronic administration of the novel NO releaser FK409 can improve diabetes-impaired endothelium-dependent vasodilatation in the rat aorta and perfused kidney.     

Exercise aggravates cardiovascular risks and mortality in rats with disrupted nitric oxide pathway and treated with recombinant human erythropoietin

Chronic administration of recombinant human erythropoietin (rHuEPO) can generate serious cardiovascular side effects such as arterial hypertension (HTA) in clinical and sport fields. It is hypothesized that nitric oxide (NO) can protect from noxious cardiovascular effects induced by chronic administration of rHuEPO. On this base, we studied the cardiovascular effects of chronic administration of rHuEPO in exercise-trained rats treated with an inhibitor of NO synthesis (L-NAME). Rats were treated or not with rHuEPO and/or L-NAME during 6 weeks. During the same period, rats were subjected to treadmill exercise. The blood pressure was measured weekly. Endothelial function of isolated aorta and small mesenteric arteries were studied and the morphology of the latter was investigated. L-NAME induced hypertension (197 ± 6 mmHg, at the end of the protocol). Exercise prevented the rise in blood pressure induced by L-NAME (170 ± 5 mmHg). However, exercise-trained rats treated with both rHuEPO and L-NAME developed severe hypertension (228 ± 9 mmHg). Furthermore, in these exercise-trained rats treated with rHuEPO/L-NAME, the acetylcholine-induced relaxation was markedly impaired in isolated aorta (60% of maximal relaxation) and small mesenteric arteries (53%). L-NAME hypertension induced an internal remodeling of small mesenteric arteries that was not modified by exercise, rHuEPO or both. Vascular ET-1 production was not increased in rHuEPO/L-NAME/training hypertensive rats. Furthermore, we observed that rHuEPO/L-NAME/training hypertensive rats died during the exercise or the recovery period (mortality 51%). Our findings suggest that the use of rHuEPO in sport, in order to improve physical performance, represents a high and fatal risk factor, especially with pre-existing cardiovascular risk.     

The action of glibenclamide on glycogen catabolism and related parameters in the isolated perfused rat liver

Inhibitory effects on glycogenolysis have been reported for glibenclamide in the presence of insulin after stimulation of glycogenolysis by glucagon. Inhibition of oxidative phosphorylation, which has been equally reported for this drug, however, should stimulate glycogenolysis. The present work aimed to find an answer to the question of how glibenclamide affects glycogen catabolism in the liver of fed rats undergoing substrate- and hormone-free perfusion. The experimental system was the isolated perfused liver of ad libitum fed rats. Metabolites in the outflowing perfusate were assayed enzymatically. Oxygen uptake was measured polarographically. Glibenclamide (25-500 microM) stimulated glucose production and lactate release, with a clear correlation between concentrations and effects. Maximal stimulations were 132 and 127% for lactate production and glucose release, respectively. At low glibenclamide concentrations (up to 100 microM) both oxygen uptake and pyruvate production were stimulated, but at higher concentrations inhibition took place. Uric acid production was stimulated by glibenclamide. All effects of glibenclamide are probably due to decreases in oxidative phosphorylation. Stimulation of glucose release is the opposite of what should be expected for a hypoglycemic drug and it also contrasts with some reports of diminishing effects in the presence of glucagon plus insulin. This means that the stimulatory action on glycogenolysis that was seen as a net effect under the specific conditions of the present work could be counterbalancing inhibitory effects in vivo. This combination of events could eventually diminish the effectiveness of the drug as a hypoglycemic agent in the fed state.     

Estrogen-induced augmentation of endothelium-dependent nitric oxide-mediated vasodilation in isolated rat cerebral small arteries

We examined chronic effects of 17beta-estradiol (E(2)beta) on the responses of isolated rat anterior cerebral small arteries to vasoactive substances with special reference to endothelial function. Female Sprague-Dawley rats were separated into four groups: (1) sham-operated group (Sham), (2) sham-operated plus E(2)beta treated group (Sham+E), (3) ovariectomized group (OVX), (4) ovariectomized plus E(2)beta treated group (OVX+E). 5-Hydroxytryptamine (5-HT) (10(-10)-10(-3) M) and U46619 (10(-15)-10(-8) M) induced concentration-dependent contractions in the cerebral small arteries. The 5-HT- and U46619-induced contractions were not affected by pretreatment with 3 x 10(-5) M N(omega)-nitro-L-arginine methyl ester (L-NAME). No significant difference in high potassium (80 mM)- and the agonists-mediated contractions was observed among the four groups. Administration of acetylcholine (ACh) (10(-9)-10(-3) M) and sodium nitroprusside (SNP) (10(-8)-10(-3) M) caused dose-related relaxations in the cerebral small arteries precontracted by 10(-8) M U46619. Chronic treatment with E(2)beta caused a significant potentiation of the ACh-induced relaxations in the Sham+E and OVX+E groups. The dose-response curve for ACh in the OVX group was quite similar to that obtained with the Sham group. The ACh-induced relaxation was reduced significantly by pretreatment with 3 x 10(-5) M L-NAME, and an additional treatment with 10(-3) M L-arginine reversed significantly the L-NAME-induced inhibition. The removal of endothelial cells produced a significant reduction of the ACh-induced relaxation. Indomethacin (10(-5) M) did not alter the ACh-induced relaxation. The findings suggest that E(2)beta potentiates ACh-induced endothelium-dependent relaxation in rat anterior cerebral arteries and that the potentiation may be, in part, mediated by increasing production and release of endogenous NO from the endothelial cells.     

Effects of vanadate on vascular contractility and membrane potential in the rabbit aorta.

Isolated rabbit aortic ring with intact endothelial cell preparations precontracted with NE (10(-7) M) were relaxed by vanadate in a dose dependent manner (from 0.2 to 2 mM). Application of vanadate and ACh during the tonic phase of high K+(100 mM)-induced contraction showed a slight relaxation in contrast to that in NE-induced contraction, but sodium nitroprusside (10 microM) more effectively relaxed the aortic ring preparations in high K+ contraction than that of vanadate. Vanadate-induced relaxation in NE-contracted aortic rings was reversed by application of BaCl2 (50 microM) or glibenclamide (10 microM). Furthermore, Vanadate hyperpolarized membrane potential of smooth muscle cells in endothelium-intact aortic strips and this effect was abolished by application of glibenclamide. The above results suggest that vanadate release EDHF (Endothelium-Derived Hyperpolarizing Factor), in addition to EDRF (Endothelium-Derived Relaxing Factor) from endothelial cell. This EDHF hyperpolarize the smooth muscle cell membrane potential via opening of the ATP-sensitive K+ channel and close a voltage dependent Ca++ channel. So it is suggested that the vanadate-induced relaxation of rabbit thoracic aortic rings may be due to the combined effects of EDRF and EDHF.     

Regional differences in endothelium-dependent relaxation in the rat: contribution of nitric oxide and nitric oxide-independent mechanisms

Relaxant effects of acetylcholine (ACh), histamine, calcitonin gene-related peptide (CGRP) and the calcium ionophore A23187 were examined in rat femoral (Ø ? 0.2 mm), mesenteric (0.2 mm), intrarenal (0.2 mm) and hepatic (0.3 mm) arteries, and aorta (2 mm). Acetylcholine elicited an endothelium-dependent relaxation in all arteries. Histamine induced an endothelium-dependent relaxation in aorta, and mesenteric and intrarenal arteries, whereas a partly endothelium-dependent and mainly endothelium-independent relaxation was observed in hepatic and femoral arteries, respectively. In hepatic, mesenteric and intrarenal arteries, CGRP induced an endothelium-independent relaxation, whereas either small or no relaxation was obtained in aorta and femoral arteries respectively. A23187 induced an endothelium-dependent relaxation in the aorta and hepatic artery, whereas A23187 had no relaxant effect in femoral, mesenteric and intrarenal arteries. Nω-nitro-l -arginine (l -NOARG, 0.3 mM) reduced the maximum ACh-induced relaxation (in the presence of 10 μM indomethacin) by 66% in the aorta, and abolished the relaxation in femoral and intrarenal arteries. A marked l -NOARG/indomethacin-resistant relaxation was obtained in mesenteric and hepatic arteries. Levcromakalim induced a concentration-dependent and almost complete relaxation in all arteries. When contracted by a 60 mM K⁺ solution, all arteries responded to ACh with a relaxation that was abolished by l -NOARG. These results demonstrate marked regional differences with regard to the vascular effects of ACh, histamine, CGRP and A23187. Whereas nitric oxide appears to mediate endothelium- dependent relaxation regardless of the vascular region, an l -NOARG/indomethacin-resistant relaxation, presumably mediated by an endothelium-derived hyperpolarizing factor, was observed only in mesenteric and hepatic arteries, and aorta.     

葛根素对自发性高血压大鼠肠系膜动脉舒张功能的影响

目的　探究葛根素对自发性高血压大鼠肠系膜动脉舒张功能的影响。 方法　20只自发性高血压大鼠随机分为5组：高血压组,卡托普利组,葛根素低、中、高剂量组,每组4只,另外4只WKY作为正常对照组。于给药前、给药8周后测量体重和血压,检测血清中NO和血浆中ET-1含量,分离肠系膜三级动脉做HE染色并计算管壁厚度/管腔半径（WT/LR）。利用离体血管压力直径测定仪检测葛根素对内皮完整和去内皮动脉环的舒张效应,并观察内皮依赖性途径阻滞剂和非内皮依赖性途径阻滞剂孵育后,葛根素对动脉环舒张作用的影响。 结果　与高血压组相比,葛根素低、中、高剂量组的收缩压差值和舒张压差值均降低。葛根素高剂量组血清NO含量下降、血浆ET-1含量升高。葛根素中、高剂量组肠系膜三级动脉WT/LR均下降。葛根素对内皮完整和去内皮的动脉环均有浓度依赖性舒张作用,但内皮完整动脉环舒张作用更强。内皮依赖性通路阻滞剂和非内皮依赖性通路阻滞剂孵育后,葛根素的舒张效应均下降。 结论　葛根素对自发性高血压大鼠肠系膜动脉的舒张效应同时具备内皮依赖性和非内皮依赖性。其内皮依赖性途径通过NO-sGC-cGMP信号通路途径来实现的,同时也与促进前列腺类物质释放有关。葛根素非内皮依赖性途径可能是与血管平滑肌上K+通道开放有关。     

Difference in effect of inhibitors of energy metabolism on endothelium-dependent relaxation of rat pulmonary artery and aorta

Previous studies have suggested that systemic artery endothelial cell production of the nitrovasodilator endothelium-derived relaxing factor (EDRF) is dependent upon oxidative energy production. This study was undertaken to test if pulmonary artery (PA) EDRF has a similar requirement for oxidative phosphorylation. The effects of inhibitors of oxidative phosphorylation and glycolysis on endothelium-dependent relaxation were studied in rat aortic and PA rings. In aortic rings, 0.1 microM rotenone and 0.1 microM antimycin A, and, to a lesser extent, 50 mM 2-deoxyglucose, inhibited endothelium-dependent relaxation to acetylcholine and adenosine diphosphate. Relaxation to the receptor-independent calcium ionophore A23187 was less severely affected, and relaxation to the direct smooth muscle dilator sodium nitroprusside was unaffected. The inhibitors had much less effect on PA relaxation, decreasing the potency but not the efficacy of the endothelium-dependent dilators. These results suggest that the dependence on oxidative energy production for endothelium-dependent relaxation may differ between the systemic and pulmonary vascular beds, and that in pulmonary arterial endothelium, oxidative energy production may not be required for receptor-mediated production and/or release of EDRF. The resistance of PA endothelium to decreases in oxidative energy production may contribute to the normally low tone maintained in this circuit in vivo.     

超氧阴离子对缺氧大鼠肺内动脉乙酰胆碱舒张反应的影响

本文应用微量生物测定法观察超氧阴离子在慢性缺氧影响肺内动脉乙酰胆硷舒张反应中的作用。发现慢性缺氧可明显减弱大鼠肺内动脉的ACh内皮依赖性舒张,超氧化物歧化酶则可使此舒张反应恢复到正常水平。利用黄嘌呤—黄嘌呤氧化酶系统产生氧自由基(主要为O_2~((?))可削弱正常大鼠肺内动脉的ACh舒张反应,同样SOD可保护其免遭外源性氧自由基的损伤。结果表明慢性缺氧使肺血管氧自由基(尤其是O_2~((?))产生增多是大鼠肺内动脉ACh舒张反应受到损伤的原因之一。     

Angiotensin II-induced modulation of endothelium-dependent relaxation in rabbit mesenteric resistance arteries

The role of local endogenous angiotensin II (Ang II) in endothelial function in resistance arteries was investigated using rabbit mesenteric resistance arteries. First, the presence of immunoreactive Ang II together with Ang II type-1 receptor (AT₁R) and angiotensin converting enzyme (ACE) was confirmed in these arteries. In endothelium-intact strips, the AT₁R-blocker olmesartan (1 μ m ) and the ACE-inhibitor temocaprilat (1 μ m ) each enhanced the ACh (0.03 μ m )-induced relaxation during the contraction induced by noradrenaline (NA, 10 μ m ). Similar effects were obtained using CV-11974 (another AT₁R blocker) and enalaprilat (another ACE inhibitor). The nitric-oxide-synthase inhibitor N ^G-nitro- l -arginine ( l -NNA) abolished the above effect of olmesartan. In endothelium-denuded strips, olmesartan enhanced the relaxation induced by the NO donor NOC-7 (10 n m ). Olmesartan had no effect on cGMP production (1) in endothelium-intact strips (in the absence or presence of ACh) or (2) in endothelium-denuded strips (in the absence or presence of NOC-7). In β-escin-skinned strips, 8-bromoguanosine 3',5' cyclic monophosphate (8-Br-cGMP, 0.01–1 μ m ) concentration dependently inhibited the contractions induced (a) by 0.3 μ m Ca²⁺ in the presence of NA+GTP and (b) by 0.2 μ m Ca²⁺+GTPγS. Olmesartan significantly enhanced, while Ang II (0.1 n m ) significantly inhibited, the 8-Br-cGMP-induced relaxation. We propose the novel hypothesis that in these arteries, Ang II localized within smooth muscle cells activates AT₁Rs and inhibits ACh-induced, endothelium-dependent relaxation at least partly by inhibiting the action of cGMP on these cells.     

Impaired EDHF-mediated vasodilatation in adult offspring of rats exposed to a fat-rich diet in pregnancy

We recently reported vascular dysfunction in adult offspring of rats fed a fat-rich (animal lard) diet in pregnancy. This study reports further characterization of constrictor and dilator function in mesenteric and caudal femoral arteries from 180-day-old offspring of dams fed the high fat diet (OHF). Endothelium-dependent relaxation in response to acetylcholine (10⁻⁹–10⁻⁵ m ) was impaired in mesenteric small arteries from male and female OHF compared with offspring of dams fed normal chow (males (maximum percentage relaxation): OHF 67.92 ± 2.89, n = 8 versus control 92.08 ± 2.19, n = 8, P < 0.01). Substantial relaxation in response to acetycholine in control mesenteric arteries remained after inhibition of nitric oxide synthase, soluble guanylate cyclase and cyclo-oxygenase but was blocked by 25 m m potassium. This component of relaxation, attributed to EDHF, was significantly reduced in OHF mesenteric arteries compared with controls. However, EDHF played a minor role in acetylcholine-induced relaxation in both control and OHF femoral caudal arteries (male and female). In these arteries, in contrast to mesenteric vessels, acetylcholine-induced relaxation was significantly enhanced in OHF but only in males (ACh (maximum percentage relaxation): OHF 58.40 ± 4.39, n = 8 versus male controls 32.18 ± 6.36, P < 0.05). This was attributable to enhanced nitric oxide-mediated relaxation. In conclusion, reduced endothelium-dependent relaxation in OHF mesenteric arteries is due to impaired EDHF-mediated relaxation. This defect was not apparent in femoral arteries in which EDHF has a less prominent role.