Contribution of prostaglandins in hypoxia-induced vasodilatation in isolated rabbit hearts. Relation to adenosine and KATP channels

The mechanism of hypoxia-induced coronary vasodilatation was studied in isolated, saline-perfused rabbit hearts under constant flow conditions. Reduction in the perfusion solution PO₂ (from 520±6 to 103±9 mm Hg) under control conditions halved the coronary resistance and was accompanied by a significant release of the prostaglandin (PG) 6-keto-PGF₁ (from 1.8±0.3 to a maximum of 4.4±0.9 pmol min^–1 g^–1). The cyclooxygenase inhibitor, diclofenac (1 M), blocked the release of PGI₂ and reduced hypoxia-induced vasodilatation (from 47±8% to 25±5%, P<0.05). The relative contribution of adenosine, prostaglandins, and adenosine triphosphate (ATP)-sensitive K⁺ channel (K_ATP channel) activation in hypoxia-induced vasodilatation was assessed by comparing the differential change (control response minus response after treatment) in coronary perfusion pressure (CPP) during infusion of 8-phenyltheophylline (8-PT), diclofenac, and glibenclamide, respectively. The differential change in CPP with 8-PT and diclofenac given together (–48 ±7%) was found to be equivalent to the sum of their respective effects (–24±7 and –19±4%, respectively). Glibenclamide (0.3 M) reduced significantly hypoxia-induced vasodilatation (differential change in CPP of –27±6%) as well as the dilator response to 10 M adenosine and to the stable PGI₂-analogue, iloprost. Forskolin-induced coronary vasodilatation in arrested hearts was slightly, but significantly, reduced by glibenclamide. Our results suggest that both cyclooxygenase products and adenosine, acting independently and concomitantly, contribute to the dilator response of coronary resistance vessels to hypoxia, in part through the activation of K_ATP channels. K_ATP channel activation by prostacyclin and adenosine may involve both cyclic adenosine monophosphate-dependent and independent pathways.     

Changes in the infectivity, pyruvate kinase activity, acid phosphatase activity and P-glycoprotein expression in glibenclamide-resistant Leishmania mexicana

We previously demonstrated susceptibility of Leishmania sp. to glibenclamide, a K⁺-ATP transport blocker which interacts with members of the superfamily of adenosine 5′ triphosphate-binding cassette transporters. In order to characterize the molecular differences between a sensitive Leishmania strain, NR(Gs), and an experimentally selected glibenclamide-resistant strain, NR(Gr), specific biochemical and functional parameters have been evaluated both in the wild type and in the resistant strain. Most noteworthy, NR(Gr) exhibit an increased expression of P-glycoprotein and a decreased activity of functional key enzymes such as acid phosphatase, a prominent virulent factor of the parasite, and pyruvate kinase, a key control enzyme for both carbohydrate and protein metabolism. The specific biochemical, metabolic and functional changes observed in the resistant strain correlated with a reduced infectivity of stationary phase NR(Gr) in J774 macrophages and suggested a mechanism to overcome the effect of glibenclamide. Received: 21 January 2000 / Accepted: 1 March 2000     

Effect of depolarizing and hyperpolarizing agents on the membrane potential difference of primary cultures of rabbit aorta vascular smooth muscle cells

Vascular smooth muscle cells of rabbit aorta were enzymatically dispersed, kept in primary culture, and studied between days 1 and 7 in a bath rinsed with Ringer-like solution at 37°C. The electrical membrane potential difference (PD) was measured with microelectrodes. The mean value of PD was –50±0.4 mV (n=53). Cromakalim (BRL 34915), 1 mol/l and 10 mol/l, hyperpolarized the membrane potential by 9±1 mV (n=11) and 15±1 mV (n=53) respectively. Glibenclamide (10 mol/l) abolished the hyperpolarizing effect of cromakalim (n=6). Simultaneous addition of cromakalim and glibenclamide (both 10 mol/l, n=11) and glibenclamide itself (10 mol/l, n=7) had no effect on PD. In patch-clamp experiments in outside-out-oriented Ca²⁺-sensitive K⁺ channels, cromakalim increased the open probability (P _o) only slightly and only with a cytosolic Ca²⁺ activity of 1 mol/l. In all other series cromakalim had no effect on the P _o of these channels. Forskolin (10 mol/l) hyperpolarized PD by 6±1 mV (n=13). The nucleotides UTP, ATP and ITP (10 mol/l) depolarized PD by 12±1 mV (n=7), 8±1 mV (n=65) and 5±1 mV (n=6) respectively. GTP, [,-methylene]ATP and adenosine had no significant effect. Mn²⁺ (1 mmol/l, n=18), Ni²⁺ (1 mmol/l, n=13), Co²⁺ (1 mmol/l, n=11), Zn²⁺ (1 mmol/l, n=6) and the Ca²⁺-channel blockers verapamil and nifedipine (both 0.1 mmol/l, n=6) did not attenuate the depolarization induced by 10 mol/l ATP. Fetal calf serum (100 ml/l, n=7) depolarized PD by 11±2 mV. This effect was not abolished by nifedipine or by replacing NaCl by choline chloride. The data indicate that PD of vascular smooth muscle cells is depolarized by P₂ agonists and hyperpolarized by the K⁺-channel opener cromakalim. The effect of cromakalim is antagonized by glibenclamide. The effect of cromakalim is probably not mediated by the K⁺ channel identified in excised patches.Supported by DFG Gr 480/10     

Ba2+ differentially inhibits the Rb+ efflux promoting and the vasorelaxant effects of levcromakalim and minoxidil sulfate in rat isolated aorta

The K⁺ channel openers activate ATP-sensitive K⁺ channels (K_ATP) in vascular smooth muscle and induce relaxation. In this study, the relationship between these two effects was examined in rings of rat aorta using levcromakalim and minoxidil sulfate as the openers and Ba²⁺ as the K⁺ channel blocker; K⁺ channel opening was assessed by determining the rate constant of ⁸⁶Rb⁺ efflux from the preparation.Ba²⁺ inhibited the ⁸⁶Rb⁺ efflux stimulated by levcromakalim in a noncompetitive manner with an IC₅₀ value of 29 M and a Hill-coefficient of 1.2. At concentrations > 300 M, Ba²⁺ increased the tension of rat aortic rings concentration-dependently. Levcromakalim relaxed contractions to Ba²⁺ (0.5 and 1 mM) with potencies similar to those determined against KCl (25 mM) or noradrenaline as spasmogens (EC₅₀ values 15–40 nM). The vasorelaxant effect against Ba²⁺ was inhibited by the K_ATP channel blockers, glibenclamide and tedisamil, and abolished in depolarizing medium (55 mM KCl). At 3 mM Ba²⁺, levcromakalim was still able to transiently induce complete relaxation; however, within 1 h oscillations in tension developed, leading to a stable level of only 15% relaxation. A similar level of relaxation was achieved against 10 mM Ba²⁺ whereas the combination of 0.5 mM Ba²⁺ and 3 M tedisamil blocked the relaxant effect of levcromakalim completely. With minoxidil sulfate as the K_ATP channel opener the results of the ⁸⁶Rb⁺ efflux and tension experiments were similar to those obtained with levcromakalim.It is concluded that Ba²⁺ is more potent in inhibiting the K⁺ channel opening than the vasorelaxant effects of the openers. On the basis of the ⁸⁶Rb⁺ efflux experiments it is estimated that at least 97% of the channels opened by the activators can be blocked without major effects on vasorelaxation suggesting a dissociation between the two effects. However, if the block is pushed to extremes ( 99.95%) the vasorelaxant effect of the openers is also abolished suggesting a link between both effects. This paradoxon remains to be solved.     

Propagation of impulses in the guinea-pig ureter and its blockade by calcitonin gene-related peptide (CGRP)

The guinea-pig ureter was placed in a three-compartment organ bath to enable the application of electrical stimuli or drugs to its renal end (R site), the middle region (M-site) or the bladder end (B-site) while recording mechanical activity at the R- and B-sites. All experiments were performed in ureters pre-exposed to capsaicin (10 M for 15 min) to prevent the release of sensory neuropeptides from afferent nerves. Electrical field stimulation (EFS, 5–25 ms pulse width, 20 V) produced a phasic contraction at the site of stimulation (direct response to EFS) which propagated to the other end of the ureter. Section of the ureter at the M-site abolished the propagated response to EFS; after section, EFS applied at the M-site induced a phasic contraction at both the R-and B-sites. Likewise, the application of KCl at the M-site produced phasic contractions at both the R- and B-sites. Tetrodotoxin (1 M), nifedipine (1 M) or Bay K 8644 (1 M) applied at the M-site had no influence on the direct or propagated responses to EFS; nifedipine (10 M) applied at the M-site abolished the propagated responses without affecting the direct responses to EFS. Bay K 8644 (1 M) applied at the R-site produced a marked enhancement of the direct response (EFS applied at R-site) while having no effect on the amplitude of the propagated response to EFS. Nifedipine (1 M), applied at the R-site, produced a graded, time-dependent, inhibition of the direct response (EFS applied at R-site) and eventually suppressed it; the propagated response was unaffected until suppression of the direct response, when an allor-none blockade of the propagated response was observed. When applied at the B-site (EFS at Rsite), 1 M nifedipine produced a graded, time-dependent, inhibition of the propagated response and eventually suppressed it, without affecting the direct response to EFS. For further pharmacological analysis of drug action on the propagated activity, EFS was applied at the R-site and drugs were applied at the M-site. Human CGRP (CGRP, 0.1 M) or cromakalim (1-3 M) were applied in superfusion at the M-site in the absence or presence of glibenclamide (1 M). Neither drug affected the direct response to EFS; both CGRP and cromakalim produced a reversible suppression of the propagated response. Glibenclamide suppressed the inhibitory activity of 1 M cromakalim and partly antagonized the effect of CGRP; the blockade by glibenclamide was partly overcome by 3 M cromakalim. The present findings are consistent with the idea that propagation of excitation occurs because of the spread of electrical activity between smooth muscle cells of the ureter and that conduction of impulses is independent of local changes in contractility. The present results also demonstrate that CGRP induced a conduction block along the ureter and that this effect involves activation of glibenclamide-sensitive K channels. Therefore, a local release of CGRP in response to pathophysiological stimuli is, in principle, capable of suppressing ureteral peristalsis and antiperistalsis.     

Phosphate and thiophosphate group donating adenine and guanine nucleotides inhibit glibenclamide binding to membranes from pancreatic islets

Summary In microsomes obtained from mouse pancreatic islets, the Mg complex of adenosine 5-triphosphate (MgATP) increased the dissociation constant (K _D) for binding of [³H]glibenclamide by sixfold. In the presence of Mg²⁺, not only ATP but also adenosine 5-0-(3-thiotriphosphate) (ATPS), adenosine 5-diphosphate (ADP), guanosine 5-triphosphate (GTP), guanosine 5-diphosphate (GDP), guanosine 5-0-(3-thiotriphosphate) (GTPTS) and guanosine 5-0-(2-thiodiphosphate) (GDP S) inhibited binding of [³H]glibenclamide. These effects were not observed in the absence of Mg²⁺. Half maximally effective concentrations of the Mg complexes of ATP, ADP, ATPS and GDP were 11.6, 19.0, 62.3 and 90.1 mol/l, respectively. The non-hydrolyzable analogues adenosine 5-(,-imidotriphosphate) (AMP-PNP) and guanosine 5-(,-imidotriphosphate) (GMP-PNP) did not alter [³H]glibenclamide binding in the presence of Mg²⁺. MgADP acted much more slowly than MgATP and both MgADP and MgADP did not inhibit [³H]glibenclamide binding when the concentrations of MgATP and MgATP were kept low by the hexokinase reaction. Development of MgATP-induced inhibition of [³H]glibenclamide binding and dissociation of [³H]-glibenclamide binding occurred at similar rates. However, the reversal of MgATP-induced inhibition of [³H]glibenclamide binding was slower than the association of [³H]glibenclamide with its binding site. Exogenous alkaline phosphatase accelerated the reversal of MgATP-induced inhibition of [³H]glibenclamide binding. MgATP enhanced displacement of [³H]glibenclamide binding by diazoxide. The data suggest that sulfonylureas and diazoxide exert their effects by interaction with the same binding site at the sulfonylurea receptor and that protein phosphorylation modulates the affinity of the receptor.Some of the results described here are part of the medical theses of S. Löser and I. Rietze Send offprint requests to M. Schwanstecher at the above address     

复方盐酸二甲双胍片在人体内药物动力学和生物等效性研究

目的 建立人血浆中盐酸二甲双胍的反相离子对高效液相色谱和格列本脲的液相色谱-质谱测定方法,研究复方盐酸二甲双胍片(盐酸二甲双胍250mg/格列本脲1.25mg×2片)相对于联合使用的盐酸二甲双胍片(500mg)和格列本脲片(2.5mg)在男性健康志愿者体内的药物动力学行为,评价其生物利用度和生物等效性。方法 采用双交叉随机实验设计:20名受试者交叉口服复方盐酸二甲双胍片2片或口服盐酸二甲双胍片与格列本脲片各1片,服药后于0.5、1.0、1.5、2.0、2.5、3.0、3.5、4.0、5.0、6.0、8.0、12、24、36h分别取血,分离血浆,分别依法测定盐酸二甲双胍和格列本脲的血药浓度。结果 测得口服复方盐酸二甲双胍片或联合使用盐酸二甲双胍片与格列本脲片后,盐酸二甲双胍的达峰时间分别为(2.0±0.7)h和(2.1±0.9)h,峰浓度分别为(1402.4±349.2)μg·L^-1和(1329.7±315.4)μg·L^-1,消除半衰期分别为(3.84±0.61)h和(4.26±0.96)h,AUC_0-24分别为(7292.7±1967.5)μg·L^-1和(7416.2±1843.9)μg·h·L^-1；格列本脲的达峰时间分别为(3.1±0.9)h 和(3.0±0.8)h，峰浓度(71.7±22.7)μg·L^-1和(70.3±20.7)μg·L^-1,消除半衰期分别为(5.05±2.01)h 和(4.78±1.64)h，AUC_0-24分别为(367.6±168.7)μg·L^-1和(352.6±144.7)μg·h·L^-1；以联合服用等剂量的盐酸二甲双胍片与格列本脲片为参比，以AUC_0-24计算得复方盐酸二甲双胍片之盐酸二甲双胍和格列本脲的相对生物利用度，分别为101.1%±28.5%和123.7%±82.9%。结论 建立的分析方法准确灵敏，测得数据可靠。统计学分析表明复方盐酸二甲双胍片与联合使用盐酸二甲双胍片和格列本脲片显生物等效。     

Anti-Diabetic Activities of the Methanol Leaf Extracts of Hymenocardia Acida (Tul.) in Alloxan-Induced Diabetic Rats

The effect of methanolic extract of Hymenocardia acida leaves on diabetes and associated lipidemia were investigated on experimentally-induced diabetic rats. The extract did not demonstrate any acutely toxic effect in rats within the dose range (250 mg/kg – 2000 mg/kg) employed in the study; hence it was well tolerated by the rats. In all experiments, the anti-diabetic effects were dose-dependent and comparable to that of glibenclamide (2 mg/kg) standard. At a dose of 500 mg/kg, lipid profile markers such as the serum total cholesterol (TC) levels, LDL-C, triglycerides and HDL-C were significantly lower (p <0.05) than those of both the treated and untreated controls.     

Antidiabetic activity of Syzygium calophyllifolium in Streptozotocin-Nicotinamide induced Type-2 diabetic rats

The study was initiated to determine the antidaibetic activity of Syzygium calophyllifolium in Streptozotocin-Nicotinamide (STZ-NA) induced diabetic rats. The rats were treated with 100 and 200 mg/kg of the Syzygium calophyllifolium bark methanol extract (SCBM) and compared with the diabetic, normal and standard glibenclamide groups. The blood glucose level and body weight of the rats in different groups were monitored at regular intervals. The serum, blood biochemical and histopathological parameters of liver, kidney and pancreas were also analyzed. In vivo antioxidants like SOD, CAT, GST, GSH and GR levels were estimated in liver and kidney. SCBM (100 mg/kg) extract could reduce the blood glucose level from the 15th day itself (213.67 mg/dL) and the best reduction was observed till the end of the study with 259.25 mg/dL (200 mg/kg). Initial decrease in body weight was recovered after drug treatment and an increase in body weight was observed on the 4th week. The haematological parameters like total haemoglobin, packed cell volume percentage, total WBC and RBC content were found normal compared to that of normal untreated rats. Glibenclamide was also equally effective. The higher dose of SCBM extract could normalize the triglycerides, HDL, cholesterol and VLDL constituents in blood serum to the levels almost similar to that of normal rats. The results of the in vivo antioxidant levels showed that there are no significant difference in SOD, GSH and GR levels in all the groups compared to the normal control. SCBM and SMBM at 200 mg/kg dose were much effective over the lower dose. The histology revealed that SCBM 200 mg/kg could protect the cellular architecture of liver kidney and pancreas. The results from the study confirm ethnopharmacological significance of the plant and could be taken further for the development of an effective pharmaceutical drug against diabetes.     

2例新生儿糖尿病患者致病基因型及疗效分析

目的：分析2例新生儿糖尿病患者的致病基因型及探讨格列苯脲的疗效。方法选取2013年4月至2014年10月本院收治并确诊的新生儿糖尿病患儿2例,对其进行常见致病基因KCNJ11、ABCC8、INS和GCK 4个基因测序分析,并复习相关文献,根据基因结果给予硫脲类药物试验性治疗。结果病例1的KCNJ11基因检测到3个杂合突变,其中Arg201His为已报道的永久性新生儿糖尿病致病突变,余2个位点为无致病性的单核苷酸多态性,ABCC8、INS和GCK基因检测未发现突变;病例2的KCNJ11基因检测到2个杂合突变,位点与病例1非致病性突变位点相同,余基因测序未发现异常。给予病例1格列苯脲口服疗效满意,胰岛素减停后随访血糖平稳;给予病例2格列苯脲试验性用药,疗效不佳。结论新生儿糖尿病的遗传发病机制复杂,KCNJ11基因突变可导致新生儿糖尿病的发生,格列苯脲适于用治疗KCNJ11基因突变阳性病例。