L－精氨酸二肽对大鼠异丙肾上腺素心肌损伤的影响

在大鼠异丙肾上腺素（ＩＳＯ）心肌坏死模型上发现心肌环─磷酸鸟苷（＿ｃＧＭＰ）含量明显减少，冠脉流量降低，冠血管对乙酰胆碱（Ａｃｈ）扩血管反应（内皮依赖性）减弱，而对硝普钠（ＮＰＳ）的扩血管反应（非内皮依赖性）无明显改变。用内皮衍生松驰因子（ＥＤＲＦ）前体Ｌ－精氨酸二肽（Ｌ－Ａｒｇ－Ａｒｇ－ＯＨ）治疗可明显减轻ＩＳＯ心肌损伤，增加心肌＿ｃＧＭＰ含量，增加冠脉灌流量，改善冠血管对Ａｃｈ的舒张反应。实验结果表明，ＩＳＯ心肌坏死时冠脉内皮ＥＤＲＰ生成减少，应用Ｌ－精氨酸二肽具有防治意义。     

BN3C对缺血性心肌损伤的保护作用

观察ＢＮ３Ｃ对缺血性心肌损伤的影响。方法：大鼠皮下注射大剂量异丙肾上腺素造成缺血性,心肌损伤模型;结果：ＢＮ３Ｃ可明显降低血中ＣＰＫ,ＦＦＡ及心肌组织中的ＭＤＡ,升高ＧＳＨ－Ｐｘ活性,并使ＥＣＧ抬高的Ｊ点下降;结论ＢＮ３Ｃ对ＩＳＯ诱发的大鼠缺血性心有肌损伤有明显的保护作用。     

Further studies on the extraneuronal uptake and metabolism of isoprenaline in the perfused rat heart

Summary To simultaneously determine the kinetics of removal, O-methylation and accumulation of ³H-isoprenaline, isolated rat hearts were perfused for 4 min with various concentrations of ³H-isoprenaline. The apparent K _m for the O-methylation of ³H-isoprenaline (3.3±0.5 M) was more than one order of magnitude lower than the corresponding value for the accumulation of unchanged amine (71.3±7.1 M). The apparent K _m for removal was very similar to that for accumulation (63.2±5.9 M). At perfusion concentrations higher than 25 M, i.e. when O-methylation was saturated, removal virtually equalled accumulation. However, at low substrate concentrations removal of ³H-isoprenaline was overwhelmingly followed by O-methylation; this led to a marked difference between rates of removal and those of accumulation.When initial rates of uptake of ³H-isoprenaline were determined after 1.5 min of perfusion of the hearts by the method of Graefe et al. (1978), the uptake of ³H-isoprenaline consisted of two components: a nonsaturable and a saturable (after subtraction of the nonsaturable component from the total uptake).The kinetic constants of the saturable component of uptake were higher than those obtained after 4 min perfusion (see above) (K _m : 110±19 M; V _max: 80±4 nmoles·g^–1·min^–1).Corticosterone competitively inhibited the saturable component of uptake of ³H-isoprenaline (K _m : 1.2 M).During wash out of accumulated ³H-isoprenaline, O-methylation took place predominantly in one of the two extraneuronal compartments. The efflux of 3-O-methyl-³H-isoprenaline (³H-OMI), the O-methylated metabolite of ³H-isoprenaline, was characterized by a half time of about 1.2 min. O-methylation accelerated the loss of radioactivity from the tissue during wash out.The extraneuronal uptake of ³H-isoprenaline was characterized as a pump and leak system by means of steady-state kinetics of accumulation of ³H-isoprenaline. Half saturation of the steady-state accumulation was observed at a concentration of 104.5 ±18.5 M ³H-isoprenaline; the leak component was characterized by a rate constant of 0.0359 min^–1.This study was supported by the Deutsche Forschungsge-meinschaftA preliminary account was presented at the 6th International Congress of Pharmacology (Graefe et al., 1975)     

Lack of presynaptic modulation by isoprenaline of 3H-noradrenaline release from rabbit isolated ear artery

Summary The aim of the present investigation was to examine whether or not presynaptic facilitatory -adrenoceptors are detectable on the postganglionic nerves in the rabbit isolated ear artery. Strips of rabbit central ear artery were incubated with ³H-noradrenaline (10^–7 mol/l; 30 min or 10^–6 mol/l; 60 min). Subsequently, they were washed repeatedly with physiological salt solution. The strips were subjected to electrical-field stimulation (S₁–S₈) and the resultant ³H-overflow was determined.When the ear artery was stimulated with 150 pulses (0.5 ms; 3 Hz; 225 mA), isoprenaline (10^–9–10^–6 mol/l) either alone or in the presence of either rauwolscine (10^–6 mol/l) or phentolamine (10^–6 mol/l) did not alter the stimulation-evoked ³H-overflow. This was also the case in the presence of rauwolscine (10^–6 mol/l) plus either the selective phosphodiesterase inhibitor ICI 63 197 (3 × 10^–5 mol/l) or forskolin (10^–6 mol/l). When the ear artery was stimulated with 300 pulses (1 ms; 5 Hz; 225 mA), isoprenaline had no effect on the stimulation-evoked ³H-overflow. This was also the case when phentolamine (10^–6 mol/l) was present. Propranolol (10^–7–10^–5 mol/l) did not alter the stimulation-evoked ³H-overflow. In some experiments, the stimulation current was reduced to 175 mA in order to obtain similar reference release (S₃) values despite the presence of rauwolscine (150 pulses; 0.5 ms; 3 Hz). Even then, isoprenaline (10^–9–10^–6 mol/l) did not change stimulation-evoked ³H-overflow. The results suggest that postganglionic sympathetic nerves in rabbit central ear artery do not possess presynaptic facilitatory -adrenoceptors. Send offprint requests to J. Abrahamsen at the above address     

Adrenoceptor-mediated effects on calcium channel currents are antagonized by 5′-(N-ethyl)-carboxamido-adenosine in guinea-pig atrial cells

Summary In guinea-pig atrial myocytes, the effects of the adenosine analogue 5-(N-ethyl)-carboxamido-adenosine (NECA) in the presence of isoprenaline (ISO) on Ca²⁺ channel activity were analyzed. Single Ca²⁺ channel currents were recorded from cell-attached patches by application of several hundred 100 ms depolarizing steps. Under control conditions, burstlike activity of channel openings during some depolarizing steps were followed by variably long periods of quiescence (blank sweeps). During superfusion with ISO (100 nmol/l), ensemble-averaged (mean) current was increased by about 150%. The underlying mechanism was found to be a significant increase in the channel availability, defined as the ratio of current-containing sweeps to the total number of sweeps. In addition, the ISO-induced reduction of blank sweeps was combined with slightly but not significantly higher values of the open probability in the current-containing sweeps. Open time and shut time histograms could be fitted by single and double exponential curves, respectively, which remained rather unaffected in the presence of ISO; accordingly, mean open time and mean shut time of the channel were not significantly changed by ISO. After the addition of NECA (1 mol/l) in the presence of ISO, the ISO-induced increase in mean current was abolished. This effect of NECA on mean current was due to a reduction of the channel availability and a slight decrease in the open probability. The purinoceptor blocking agent 8-phenyltheophylline (10 mol/l) antagonized the inhibitory action of NECA on the ISO-induced increase in Ca²⁺ channel activity. These results indicate that -adrenoceptor-induced changes in Ca²⁺ channel activity are counteracted by stimulation of, presumably, A₁ adenosine receptors. This may be explained by the fact that purinoceptors, beside their stimulating action on K⁺ channels, mediate an additional inhibitory effect on the adenylate cyclase system in the atrium. Subsequently, purinoceptor activation reverses the ISO-induced increase in Ca²⁺ channel activity due to a reduction in cAMP content leading to a decrease in the number of phosphorylated Ca²⁺ channels. Send offprint requests to U. Jahnel at the above address     

Isoprenaline increases brain concentrations of administered l-dopa and l-tryptophan in the rat

A small dose of isoprenaline or saline was administered intraperitoneally to rats 20 min before the administration of one of the amino acids l-dopa or l-tryptophan. Isoprenaline caused a marked increase in the brain concentration of the administered amino acid. Isoprenaline has previously been shown to cause a decrease in at least some of those plasma amino acids which compete with l-dopa and tryptophan for carrier-mediated transport into the brain. The effect of isoprenaline on the concentrations of dopa and tryptophan in the brain is suggested to be at least partly caused by a change in the relationship between endogeneous and administered amino acids. It is also possible that a direct effect of isoprenaline on the blood-brain barrier transport system contributes to the effect.The reported finding might be of clinical interest in view of the therapeutic importance of aromatic amino acids with a central site of action.     

银杏内酯对异丙肾上腺素致心肌损伤的影响

目的观察银杏内酯对小鼠耐缺氧能力以及对大鼠心肌缺血损伤的影响.方法按文献方法制备小鼠耐缺氧模型,观察小鼠常压密闭条件下的存活时间.用大剂量异丙肾上腺素(8mg/kg)造成大鼠心肌缺血性损伤模型,注射异丙肾上腺素前连续4 d灌胃给予银杏内酯(10、20、40mg/kg)、银杏叶提取物(EGb,300mg/kg)、普萘洛尔(5 mg/kg)或溶媒,比较各组大鼠心肌组织学变化、血清磷酸肌酸激酶(CPK)、乳酸脱氢酶(LDH)活性及心肌超氧化物岐化酶(SOD)、丙二醛(MDA)含量.结果银杏内酯明显延长小鼠在缺氧条件下的存活时间,显著减轻异丙肾上腺素所致大鼠心肌组织损伤,抑制损伤大鼠血清CPK、LDH活性及心肌组织中MDA含量的升高,提高大鼠心肌组织中SOD的活性.结论银杏内酯能提高小鼠的耐缺氧能力,保护大鼠心肌缺血损伤,该作用可能与抗血小板活化因子及氧自由基有关.     

A comparison of the actions of ICI66082 and propranolol on cardiac and peripheral beta-adrenoceptors.

The relative blocking potencies of ICI66082 and propranolol with respect to heart rate contractility, diastolic blood pressure and peripheral vascular conductance were compared in anaesthetized dogs. Peripheral blood flow was measured with an electromagnetic flow-probe around the descending aorta with retrograde cannulation of the inferior mesenteric artery for intra-arterial injections of isoprenaline. Cardiac and peripheral vascular effects of ICI66082 and propranolol were compared in terms of the shifts in the dose--response curves after i.v. and intra-arterial injections of isoprenaline. Propranolol was twice as potent as an equimolar dose of ICI66082 on cardiac beta-adrenoceptors. It was 70--130 times more potent in its action on the peripheral vascular receptors. Propranolol itself was 3 times more potent in blocking peripheral vascular receptors than cardiac beta-receptors. ICI66082 was 17--21 times more active in blocking the myocardial beta-adrenoceptors than those in the peripheral vessels. Electrophysiological studies showed that ICI66082 is devoid of membrane-depressant properties in concentrations up to 100 mg/l.     

Inhibition of fluid transport in the isolated gall bladder of the guinea pig by isoprenaline,theophylline and cyclic adenosine 3′,5′-monophosphate

Summary The isolated gall bladder of guinea pigs was used to study the effects of isoprenaline and orciprenaline on fluid transport. Both drugs in the range 10^–8 M to 10^–4 M inhibited fluid transport 20–50 min after application, when applied to the serosal side. The maximum inhibition observed was 49±3.9% by a concentration of 10^–5 M. After this inhibitory phase the transport rate returned to control values. Doubling the concentration did not evoke a new inhibitory response, but washing gall bladders with fresh Ringer's solution restored the sensitivity to isoprenaline. Isoprenaline was ineffective when added to the mucosal side. Propranolol but not practolol, prevented the action of isoprenaline. Theophylline inhibited fluid transport in the range 10^–3 M to 10^–2 M. Cyclic adenosine 3,5-monophosphate (cyclic AMP) 3.3×10^–3 M decreased fluid transport only when added to the serosal side. In contrast to isoprenaline, both theophylline and cyclic AMP caused a prolonged decrease in fluid transport. The results are in accordance with the assumption that the inhibition of fluid transport in the gall bladder by -sympathomimetic drugs may be caused by an increase of the intracellular cyclic AMP level.Part of this work was presented at the 14th meeting of the Deutsche Pharmakologische Gesellschaft in Mainz, 1973.This work was supported by a grant from the Deutsche Forschungsgemeinschaft given to the Sonderforschungsbereich 160, Eigenschaften biologischer Membranen, Projekt T.     

二氮嗪对异丙肾上腺素诱导的大鼠心肌细胞凋亡相关基因表达的影响

目的研究线粒体ATP敏感性钾通道开放剂二氮嗪对异丙肾上腺素诱导的大鼠心肌细胞凋亡相关基因表达的影响。方法采用完全随机化设计,将32只雄性SD大鼠随随机分为4组：A.正常对照组;B.异丙肾上腺素组;C.二氮嗪组;D.格列本脲组。采用半定量RT-PCR法检测各组大鼠心肌Bcl-2、Caspase-3相对表达量;采用TUNEL法检测各组大鼠心肌凋亡,计算凋亡指数（apopticindex,AI）。结果各组大鼠心肌Bcl-2、Caspase-3相对表达量之间存在差异（P〈0.01）。C组Bcl-2、Caspase-3相对表达量与A,B,D组均有差异（P〈0.05）;B组、D组与A组之间有差异（P〈0.05）;B组、D组之间无明显差异（P=0.134,0.297）。A组大鼠心肌TUNEL染色未见阳性细胞;B、B、D各组AI上存在差异（P=0.001）;C组和B、D组织间存在差异（P〈0.01）;B组、D组之间无明显差异（P=0.156）。结论二氮嗪可以减少异丙肾上腺素诱导的大鼠心肌细胞凋亡;减少凋亡的原因可能与其能上调Bcl-2的表达,下调Caspase-3表达有关。