去甲肾上腺素和脑室内注射甲氧明引起的小鼠排便抑制

去甲肾上腺素（ＮＥ）５ｍｇ·ｋｇ￣（－１）ｉｐ和赛拉嗪１－２ｍｇ·ｋｇ￣（－１）ｓｃ可抑制小鼠排便，而甲氧明（Ｍｅｔ）１５ｍｇ·ｋｇ￣（－１）ｓｃ，异丙肾上腺素１０ｍｇ·ｋｇ￣（－１）ｓｃ多巴酚丁胺２０ｍｇ·ｋｇ￣（－１）ｓｃ和沙丁胺醇５ｍｇ·ｋｇ￣（－１）ｓｃ无效、Ｍｅｔ１５０μｇｉｃｖ也抑制排便。咪唑克生１ｍｇ·ｋｇ￣（－１）ｓｃ可拮抗ＮＥ，赛拉嗪和ｉｃｖＭｅｔ引起的排便抑制，哌唑嗪１ｍｇ·ｋｇ￣（－１）ｓｃ和普萘洛尔１０ｍｇ·ｋｇ￣（－１）ｓｃ则无效。这提示ＮＥ和ｉｃｖＭｅｔ抑制小鼠排便是作用于肠α＿２肾上腺素受体所致。     

Pre- and post-junctional supersensitivity: Differentiation by intraventricular infusions of norepinephrine and methoxamine

Intraventricular infusions of methoxamine, an adrenergic agonist that has a relatively low affinity for the presynaptic uptake mechanism, produces a significant dose-dependent increase in locomotor activity comparable to the increase elicited by infusion of equimolar doses of norepinephrine (NE). The behavioral responsiveness to infusion of both NE and methoxamine was more than doubled 3 weeks after pretreatment with 6-hydroxydopamine (6-OHDA). These results indicate that the increased responsiveness to NE induced by 6-OHDA is due to enhanced postsynaptic receptor sensitivity rather than to a loss of presynaptic uptake inactivation.     

海马胞外钙不依赖去甲肾上腺素释放及蛋白激酶C的调制作用(英文)

在细胞外无钙时,佛波醇基酯能加强3,4-二氨基吡啶、藜芦定或哇巴因所诱发的去甲上腺素(NE)释放,但对莫能星(Mon)诱发的NE释放无作用。河豚毒素能阻断前3种物质诱发的NE释放,但对Mon诱发的释放无作用。钙整合剂BAPTA-AM能抑制这4种物质诱发的NE释放。结果提示蛋白激酶c仅调制由膜去极化因素诱发的NE释放。     

Participation of angiotensin II in pressor response and norepinephrine release to spinal nerve stimulation in pithed rats

Experiments were carried out to examine whether endogenous angiotensin II (A-II) is involved in the regulation of release of norepinephrine (NE) elicited by the stimulation of spinal sympathetic nerves in pithed rats. It was assessed in terms of the alterations in concentrations of arterial blood plasma A-II and NE elicited by nerve stimulation (5 Hz, 50 V, 1 msec for 45 s) in pithed rats under vehicle or captopril (3 mg/kg, i.v.) treatment. Comparative study with pentobarbital anesthetized rats showed that pithing rats have the characteristics of lower basal blood pressure and lower NE level, whereas they have higher basal A-II level. In pithed rats treated with vehicle, pressor response to nerve stimulation was accompanied by increases in both A-II and NE level. In rats treated with captopril, the nerve stimulation caused about 40% lower increases in pressor response and NE level than those observed in rats treated with vehicle. These results suggest that the sympathetic nerve-induced NE release is facilitated by endogenous A-II in pithed rats, and that captopril exerts its inhibitory effect on the pressor response to nerve stimulation through the suppression of this interaction.     

Microiontophoretic release of norepinephrine from micropipettes

Microiontophoretic release of norepinephrine from micropipettes was measured in brain slices and Ringer's solution by radioassay. Transport number (the ratio of drug released to charge passed) was reasonably constant, in Ringer's solution, for a given pipette but varied widely between different pipettes. This variability was unrelated to pipette geometry, or electrical parameters. In the same pipette, the transport number for drug release into brain slices was considerably less than that for ejection into Ringer's solution. Finally, there were a number of conditions under which drug release was minimal despite apparently normal charge passage.     

Inhibition by diltiazem of norepinephrine release from sympathetic nerves in the rabbit pulmonary artery

In order to determine if the calcium blocker diltiazem could alter excitation-secretion coupling in vascular sympathetic nerves, superfused rabbit pulmonary arterial strips were preincubated with 3H-norepinephrine and stimulated electrically (2-8 Hz) and by KCl (60 mM). Diltiazem significantly inhibited tension development with 4 Hz (1.5 X 10(-5) M) and 8 Hz (1.5 X 10(-6), 1.5 X 10(-5) M) stimuli, but only at 1.5 X 10(-5) M did diltiazem inhibit the 3H overflow evoked by an 8-Hz stimulus. No inhibition of 3H overflow was noted with the 2 and 4 Hz stimuli. With an 8-Hz stimulus the inhibition of tension development (45.4%) by diltiazem (1.5 X 10(-5) M) was significantly greater than the inhibition of 3H overflow (33.8%). A similar relationship was noted with 60 mM KCl stimulation. These data suggest that excitation-secretion coupling in vascular sympathetic nerves can be inhibited by diltiazem.     

Effects of beta-endorphin on norepinephrine release in hypertension

Recent studies have suggested an involvement of the endogenous opioid system in blood pressure control. The purpose of the present study was to determine the role of beta-endorphin in the regulation of sympathetic nervous activity in the central nervous system of hypertension. The effects of beta-endorphin on the electrically evoked release of [3H]norepinephrine (NE) were investigated in superfused slices of rat medulla oblongata. Beta-endorphin inhibited the stimulation-evoked NE release in a dose-dependent manner in rat medulla oblongata. In the medulla oblongata of spontaneously hypertensive rats (SHR), the inhibitory effect of beta-endorphin on the stimulation-evoked NE release was significantly smaller than in the medulla oblongata of Wistar-Kyoto rats. These results showed that beta-endorphin might reduce NE release in rat medulla oblongata. Furthermore, the lesser inhibitory effect of beta-endorphin on NE release in SHR might suggest that the opioid peptide could be involved in the regulation of central sympathetic nervous activity in hypertension.     

Roles of purines in synaptic modulation evoked by hypercapnia in isolated spinal cord of neonatal rat in vitro

Background and purpose

The purine compounds, adenosine 5′-triphosphate (ATP) and adenosine, are known to accumulate in the extracellular space and to elicit various cellular responses during hypoxia/ischemia, whereas the roles of purines during hypercapnia are poorly understood. In this study, we examined the effects of various drugs affecting purine turnover on the responses to hypercapnia in the spinal cord.

Experimental approach

Electrically evoked reflex potentials were measured in an in vitro preparation of the isolated spinal cord of the neonatal rat by extracellular recording. Extracellular adenosine concentrations were assayed by high performance liquid chromatography (HPLC) methods.

Key results

Hypercapnia (20% CO₂) depressed the reflex potentials, which were partially reversed by an adenosine A₁ receptor antagonist, 8-cyclopentyl theophylline, but not by a P2 receptor antagonist, pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonic acid. Exogenous adenosine and ATP also depressed the reflex potentials via adenosine A₁ receptors. The hypercapnia-evoked depression was not reversed by inhibitors of gap junction hemichannels, anion channels, P2X₇ receptors or equilibrative nucleoside transporters, all of which might be involved in purine efflux pathways. The adenosine accumulation evoked by hypercapnia was not inhibited by tetrodotoxin, ethylene glycol-bis(β-amino ethyl ether) tetraacetic acid (EGTA) or an ecto-ATPase inhibitor, ARL 67156. Homocysteine thiolactone, used to trap intracellular adenosine, significantly reduced extracellular adenosine accumulation during hypercapnia.

Conclusions and implications:

These results suggest that hypercapnia released adenosine itself from intracellular sources, using pathways different from the conventional exocytotic mechanism, and that this adenosine depressed spinal synaptic transmission via adenosine A₁ receptors.     

Storage,release, uptake,and inactivation of purines

Adenine nucleotides are released into the interstitial space during platelet thrombus formation and neurotransmission. ATP has also been reported to be released from the heart and endothelial cells in some studies. Ecto ATPase, ADPase, and 5′-nucleotidase activities capable of hydrolyzing ATP sequentially to adenosine are present in many cell types and may serve to terminate the actions of the nucleotides. The opposing effects of adenosine and ATP on the same cell types have suggested a modulatory role for adenosine of the actions of extracellular ATP and that the rates of hydrolysis of nucleotides might be regulated. Consistent with this it has been found that the balance between feedforward inhibition of 5′-nucleotidase by ADP and/or ATP and preferential delivery of AMP from ADPase to 5′-nucleotidase determines the rate of adenosine production and that this differs in different cell types. Alternatively, adenosine may be produced intracellularly as a result of an imbalance between energy demand and supply. There are at least two different cytosolic forms of 5′-nucleotidase. Degradation of ATP during increased metabolic activity results in an increase in intracellular AMP concentration. Either cytosolic enzyme has a high KM (2–5 mM) and would thus respond to this increase with a proportional rise in the rate of adenosine production. The nucleoside transporter is essential to allow the diffusion of adenosine to extracellular receptor sites. In general, adenosine must be taken up via the nucleoside transporter before it is inactivated either by phosphorylation by adenosine kinase in the micromolar range or by deamination by adenosine deaminase at higher concentrations. © 1993 Wiley-Liss, Inc.     

Nicorandil stimulates release of adenyl purines from porcine coronary artery

1. To clarify the mechanism of the cardioprotective effect of nicorandil (2-nicotinamidoethyl-nitrate ester), the effects of nicorandil and nitric oxide (NO) donors on the release of ATP, ADP, AMP and adenosine from arterial segments and cultured endothelial cells of the porcine coronary artery were examined. 2. Nicorandil significantly increased the release of total adenyl purines from arterial segments and from cultured endothelial cells. 3. Cromakalim, an ATP-sensitive K+ channel opener, did not affect the release of total adenyl purines from coronary artery segments. 4. s-Nitroso-N-acetyl-D,L-penicillamine and isosorbide dinitrate, NO donors, significantly increased the release of total adenyl purines from coronary artery segments. 5. These results demonstrate that nicorandil stimulates ATP release from the coronary artery by acting not as an ATP-sensitive K+ channel opener, but as a nitrate, thus suggesting the cardioprotective properties of nicorandil.     

Presynaptic regulation of cardiac norepinephrine release in ischemia.

In myocardial ischemia presynaptic regulation of norepinephrine release may be altered either by ischemic effects on presynaptic receptor signaling or by ischemia-evoked accumulation of endogenous agonists. Because presynaptic receptors are targets of several drugs. such alterations may have pharmacotherapeutic implications. We investigated the effect of brief ischemic periods on presynaptic regulation of norepinephrine release by alpha2-adrenoceptors, beta2-adrenoceptors, adenosine A1-, angiotensin AT1-, and bradykinin B2-receptors in isolated perfused rat hearts. Exocytotic norepinephrine release was evoked by electrical field stimulation. Paired stimulations were performed to compare the pharmacologic intervention (S2) with the release under baseline conditions (S1), and the effects of receptor agonists and antagonists were compared under nonischemic and stop-flow conditions. In summary. during brief myocardial ischemia, presynaptic modulation of norepinephrine release is differentially regulated. Autoinhibitory alpha2-adrenoceptors lose their activity, whereas stimulatory beta2-adrenoceptors are sensitized. Inhibitory adenosine A1-receptors gain importance during ischemia owing to endogenous adenosine formation. Bradykinin- and angiotensin-mediated stimulation of norepinephrine release is not affected under ischemic conditions.     

粉防己碱对豚鼠缺氧心脏去甲肾上腺素释放的影响

目的　研究粉防己碱（Ｔｅｔ） 对豚鼠缺氧心脏去甲肾上腺素（ＮＥ）释放的影响。方法　用高压液相色谱电化学法测定不同缺氧条件下豚鼠离体心脏流出液中ＮＥ 含量。结果　Ｔｅｔ 组（ｎ ＝１０） 停灌时心脏ＮＥ释放显著低于对照组（ｎ ＝１２,Ｐ＜ ０－０１） ;在低氧灌注、低氧酸性灌注及低氧高钾灌注下行电场刺激时,Ｔｅｔ 组（ｎ ＝ ９） 心脏ＮＥ释放量明显低于对照组（ｎ＝ １０ ～１２,Ｐ＜ ０－０５,Ｐ＜ ０－０１） ;Ｔｅｔ 在低氧高钾灌注时抑制心脏ＮＥ释放的作用强于在低氧灌注及低氧酸性灌注时（ Ｐ＜ ０－０５） 。结论　Ｔｅｔ 可抑制缺氧心脏ＮＥ的释放     

NMDA-induced hippocampal [3H]norepinephrine release is modulated by glycine

Kynurenic acid (KYN) non-competitively inhibited N-methyl-D-aspartate (NMDA)-induced [3H]norepinephrine ([3H]NE) release from rat hippocampal slices. At 100 microM KYN, the effect on release was primarily on the maximal obtainable response to NMDA. Glycine was able to completely block the inhibitory effects of 100 microM KYN on NMDA-evoked release. This ability to prevent KYN inhibition of release was shared by other amino acids with the following order of potency: glycine greater than D-serine greater than D-alanine much greater than L-serine greater than or equal to L-alanine. Neither isomer of valine or threonine was able to reverse KYN inhibition of NMDA-induced release. These potencies agreed with the relative abilities of these amino acids to displace strychnine-insensitive [3H]glycine binding to rat brain membranes. Glycine and D-serine had no effect on the inhibition of NMDA-stimulated [3H]NE release produced by D-2-amino-5-phosphonovaleric acid, MK-801 or Mg2+. Also, neither amino acid modified KYN inhibition of kainic acid-induced release. These data demonstrate that the glycine regulatory site associated with the NMDA receptor can be demonstrated in whole brain slices by using an antagonist to attenuate the influences of endogenous glycine.     

3,4-二氨基吡啶易化鸡胚交感神经元去甲肾上腺素释放(英文)

目的:用鸡胚交感神经元研究3,4-二氨基吡啶(DAP)易化电刺激诱发[~3H]NE释放的机制. 方法:用[~H]NE或fura-2孵育神经元,测[~H]NE释放或[Ca~(2 )]_i. 结果:电刺激诱发[~3H]NE释放和[Ca~(2 )]_i升高被ω-conotoxine GVIA (CTX)抑制,被(—)isradipine(Isp)减弱,被Bay k 8644加强.当3,4-二氨基吡啶(DAP)存在时,电刺激诱发[~3H]NE释放被易化,这时CTX的作用减弱,Isp的作用增强,Bay k 8644不再显示作用. 结论:DAP对电刺激诱发[~3H]NE释放的易化作用,可能是通过L-型Ca~(2 )通道而实现的.     

Correlation between positive chronotropic effect and norepinephrine release induced by acetone in the rat right atrium

The effects of acetone on contraction rate and norepinephrine (NE) release of rat right atrium were investigated. Acetone, in the concentration range 10-210 mM increased the atrial contraction rate (ACR) in a dose-dependent manner, but in concentrations exceeding 210 mM, caused a gradual reduction in the ACR from the peak. The positive chronotropic effect of acetone on ACR can be reduced by adding 0.002 mM of propranolol (a non-selective beta 1- and beta 2-adrenergic receptor blocker), or by pretreating the rat with reserpine (an NE depleter) (5 mg/kg body weight, i.p., 24 h prior to experiment). These findings lead to the hypothesis that the increase in ACR induced by acetone may be partly due to an increase in NE release from sympathetic nerve endings in the atrium by acetone. To test this speculative hypothesis, the effect of acetone on [14C]NE + cold NE release from the right atrium, preinoculated with 0.25 microM of [14C]NE + cold NE for 20 min at 35 degrees C, was carried out using a simple technique developed in our laboratory. The acetone (10-1000 mM)-stimulated peak of NE release (pmol/g atrium/min) and summed NE release (pmol/g atrium/5 min) in excess of the basal spontaneous NE release were analyzed. The dose-response curves of the effect of 10-210 mM of acetone on the ACR and the peak of NE release were parallel. However, acetone concentrations above 210 mM caused a gradual drop of the curve of the ACR from its maximum while still enhancing the curve of the NE release. This continued gradually up to an acetone concentration of 500 mM. The atrial NE release reached a maximum at acetone concentrations between 500 and 1000 mM. This indicates that the increase in ACR caused by acetone in the range 10-210 mM may be partly due to an increase in NE release from the sympathetic nerve terminals in the atrium. However, an acetone concentration above 210 mM may be too toxic to the muscle fibers and/or the pacemaker and/or the conducting system, and so even though the NE release is still increasing, it can not enhance the ACR any further. It is generally speculated that the release of NE from the sympathetic nerve endings in the heart induced by the great number of organic solvents and general anesthetics contributes to the cause of tachycardia, arrhythmia and fibrillation of the heart.(ABSTRACT TRUNCATED AT 400 WORDS)