Possible role of prostaglandin E1 on adrenergic neurotransmission in the guinea-pig Taenia coli

The effects of prostaglandin (PG) E₁ were investigated on the responses to adrenergic and non-adrenergic inhibitory nerve stimulation using the perivascular nerve-taenia preparation of the guinea pig. PGE₁ caused a rapid and sustained contraction and markedly inhibited the response to adrenergic but not to non-adrenergic inhibitory nerve stimulation. It was also observed that PGE₁ had some desensitizing action to exogenous noradrenaline on the postjunctional site. Although indomethacin decreased the tone of the preparation, it potentiated the response to adrenergic nerve stimulation without any effects on the response to non-adrenergic inhibitory nerve stimulation. From these observations, it was concluded that endogenous PGE₁ may also play a regulatory role in adrenergic inhibitory neurotransmission, mainly by inhibitory action on noradrenaline release and partly by a similar action on the postjunctional site.     

Effects of prostaglandin E2 and indomethacin on the rebound of the guinea-pig taenia coli.

The effects of prostaglandin E₂ (0.2 μM) and indomethacin (50 μM) on the rebound of smooth muscle cells of the guinea-pig taenia coli were studied. Stimulation of the non-cholinergic, non-adrenergic, intramural nerves caused membrane hyperpolarizaiton, known as the inhibitory junction potential (I.J.P.). This hyperpolarization was followed by a rebound depolarization and a rather small rebound contraction in quiescent preparations; the rebound depolarization was often accompanied by action potentials, resulting in a pronounced rebound contration. The effects of prostaglandin E₂ (PGE₂) on the membrane were comparable with the phenomena observed during the rebound, i.e. membrane depolarization, development of action potentials and contraction of the smooth muscle cells. Furthermore, an increase in amplitude of the I.J.P., enhancement of the spike discharge and a concomitant increase in rebound contraction were observed in the presence of PGE₂. Indomethacin did not modify the membrane potential or the amplitude of the I.J.P., but inhibited the rebound contraction and suppressed the development of action potentials during the rebound. The action of PGE₂ on the smooth muscle cell membrane was not modified by indomethacin, but the rebound contraction in the presence of both compounds was decreased. These experimental results indicate: that the rebound contraction is accompanied by depolarization of the membrane following the hyperpolarization caused by stimulation of the non-cholinergic non-adrenergic nerves; that the rebound activity can be mimicked by PGE₂; that indomethacin does not interfere with the action of PGE₂ applied exogenously and that the observations are consistent with the assumption that prostaglandins might be involved in the rebound.     

Interaction between hemicholinium-3 and edrophonium on the isolated taenia of the guinea-pig caecum

Endrophonium produced a contraction of the taenia of the guinea-pig caecum which was inhibited by hyoscine and by hemicholinium-3 (HC-3) but not by hexamethonium and only slightly by tetrodotoxin or cocaine. Reduced concentrations of Ca²⁺ inhibited contractions produced by edrophonium to a similar extent to contractions produced by acetylcholine. These results suggest that edrophonium directly stimulates hyoscine-sensitive receptors on the taenia and that HC-3 can differentiate between the action of edrophonium and acetylcholine. Endrophonium which selectively inhibits acetylcholinesterase augmented contractions produced by acetylcholine or by transmural stimulation, indicating that acetylcholinesterase is concerned in the inactivation of the transmitter at postganglionic cholinergic nerve endings. HC-3 did not inhibit the anticholinesterase activity of edrophonium or the augmentation of responses to acetylcholine and to transmural stimulation produced by edrophonium.     

Neuronal and non-neuronal components in the overflow of labelled adenyl compounds from guinea-pig taenia coli

Guinea-pig taenia coli preprations were pre-incubated in 3H-adenosine and the overflow of 3H-compounds to a superfusing medium was measured during transmural field stimulation in the presence and absence of tetrodotoxin. The fractional overflow of 3H-compounds on stimulation of taenia coli pre-incubated in 3H-adenosine at 10(-7) M was greater than after incubation at 10(-5) M. About half of the releasable store was blocked by tetrodotoxin. It is proposed that at lower concentrations, there is selective loading of a releasable store, while at higher concentrations thare is a greater loading of non-releasable stores, and that neuronal stores account for about 33% of the 3H-compounds released by transmural stimulation.     

Effect of prostaglandin E1 and its biosynthesis inhibitor indomethacin on drinking in the rat

In the rat, injection of prostaglandin E₁ (PGE₁)0.5, 1.0 or 2.0 μg into the 3rd brain ventricle (3rd b.v.) inhibited the water deprivation-induced water intake in a dose-related fashion. The 1.0 μg dose of PGE₁ also inhibited the intake of 1.8% sodium chloride in rats depleted of body sodium by intraperitoneal dialysis, and of food in food deprived rats during a 60 min test period. Prostaglandin E₁ (1 μg) depressed the dipsogenic effect of angiotensin II (AII) or carbachol injected through the same cannula. Water-deprived rats pretreated with the PG synthetase inhibitor indomethacin, in two different doses, showed enhanced water intake. The pretreatment with indomethacin also enhanced the dipsogenic effect of various doses of AII injected into the 3rd b.v. The antagonistic action of PGE₁ on water-deprivation, or AII-induced water intake, and the enhancement of water intake after blocking PGs synthesis, suggests the involvement of PG in the regulation of thirst.     

Electrophysiological analysis of the actions of pituitary adenylyl cyclase activating peptide in the taenia of the guinea-pig caecum

The actions of pituitary adenylyl cyclase activating peptide (PACAP) on membrane potential and conductance were investigated in the taenia of the guinea-pig caecum. The possible role of PACAP in inhibitory transmission was also investigated. Membrane potentials of smooth muscle cells were measured by intracellular microelectrodes, in the presence of hyoscine and nifidepine (both 10^–6M). To determine conductance changes, current was passed from external plate electrodes using the technique of Abe and Tomita (1968). PACAP-27 caused a concentration dependent hyperpolarization of the muscle with a maximum of 12–15 mV at 10^–6M. The hyperpolarization caused by PACAP was associated with a substantial increase in membrane conductance. The hyperpolarization was abolished by apamin (10^–6M), a blocker of small conductance, calcium-dependent, potassium channels, and was reduced to about 50% by suramin (10^–4M), which is an antagonist of P₂ receptors for purines. The hyperpolarization was not reduced by tetrodotoxin (2 × 10^–6M), suggesting PACAP acts directly on the muscle. With continued exposure to PACAP, the hyperpolarization decayed back to resting membrane potential after several minutes, possibly due to receptor desensitization. Inhibitory junction potentials (IJPs) were markedly reduced in amplitude in the period of presumed receptor desensitization to PACAP, were abolished by tetrodotoxin, but were not affected by suramin. Apamin abolished the UP and revealed a small excitatory junction potential. This study implies that PACAP released from nerve fibres in the taenia caeci hyperpolarizes the muscle via an opening of apamin-sensitive potassium channels. The action is probably through type I PACAP receptors.     

Effects of prostaglandin E2, prostaglandin I2 and 6-keto-prostaglandin F1 alpha on adrenergic neurotransmission in the pulmonary artery of the rabbit.

Strips of the rabbit pulmonary artery were preincubated with 3H-noradrenaline and then superfused and stimulated electrically at 2 or 4 Hz. PGE2 and PGI2 reduced the stimulation-evoked overflow of total tritium and 3H-noradrenaline. PGI2 was about 10 times less potent than PGE2. High concentrations of 6-keto-PGF 1alpha also diminished the evoked overflow, but the effect was small. It is concluded that PGI2, in comparison with PGs of the E series, is a relatively weak inhibitor of noradrenaline release.     

Modulation by prostaglandins of the release of [3H]noradrenaline evoked by potassium and nerve stimulation in the isolated rat heart

In the isolated rat heart perfused with Krebs solution and prelabeled with [³H]noradrenaline, we examined the effect of prostaglandins (PG) I₂, E₂, 6-keto-PGF_1α and their precursor, arachidonic acid, on the overflow of tritium elicited by potassium (K⁺) and by stimulation of cardiac sympathetic nerve plexus. Prostaglandins E₂, I₂ and arachidonic acid but not 6-keto-PGF_1α reduced K⁺ and nerve stimulation-induced overflow of tritium. Administration of indomethacin, an inhibitor of cyclooxygenase, increased tritium overflow elicited by either K⁺ or by nerve stimulation. During infusion of indomethacin, the inhibitory effect of both PGE₂ and PGI₂ on the K⁺ or nerve stimulation-induced overflow of tritium remained unaltered. In contrast, the effect of arachidonic acid to reduce K⁺ or nerve stimulation-induced overflow of tritium was abolished by indomethacin, indicating that the fatty acid inhibits release of tritium by its conversion to a product(s) of cyclooxygenase, presumably PGI₂ and PGE₂. These data suggest that prostaglandins, particularly PGI₂ and PGE₂ sythesized in the isolated rat heart act on prejunctional sites to modulate release of the adrenergic transmitter.     

Effects of indomethacin on plasma homovanillic acid concentration in normal subjects: a study of prostaglandin-dopamine interactions

In laboratory animals, prostaglandins have been shown to act as endogenous neuromodulators of central dopamine (DA) activity. To examine the interaction between prostaglandins and DA in man, the effect of a prostaglandin synthesis inhibitor, indomethacin, was studied on plasma concentrations of the DA metabolite, homovanillic acid (pHVA). Indomethacin (150 mg PO) as compared to placebo significantly elevated mean pHVA concentrations in eight normal subjects. Results of this study support the hypothesis that, as in animals, inhibition of prostaglandin synthesis increases central DA turnover in man.     

Pre- and postjunctional adrenoceptor types in the circular muscle of the guinea-pig caecum

Summary The sucrose gap technique was used to study the effects of applied adrenoceptor agonists on membrane potential and non-adrenergic, non-cholinergic inhibitory junction potentials (IJPs), in the smooth muscle of the circular coat of guinea-pig caecum. Noradrenaline (10 nmol/1–100 mol/l), phenylephrine (1–100 mol/l) and isoprenaline (0.1–100 mol/l) caused hyperpolarisations of the smooth muscle membrane which were rapid in onset and effect. The magnitudes of hyperpolarisations elicited by noradrenaline were significantly reduced by the non-specific -adrenoceptor antagonist phentolamine (10 gmol/l), the₁-adrenoceptor antagonist prazosin (1 mol/l) and the -adrenoceptor antagonist propranolol (5 gmol/1). The ₂-antagonist yohimbine (10 gmol/l) did not significantly reduce the magnitude of the hyperpolarisations induced by noradrenaline. Noradrenaline application caused a reduction in UP amplitude, during hyperpolarisation, by up to 50%. The reduction of the UP amplitude elicited by noradrenaline was significantly antagonised by yohimbine and phentolamine, but not by prazosin or propranolol. Clonidine caused a reduction of UP amplitude by up to 20%, but neither phenylephrine nor isoprenaline caused any significant reduction in UP amplitude. It is concluded that the hyperpolarising responses to exogenous noradrenaline in the circular muscle of guinea-pig caecum are mediated by postjunctional ₁- and -adrenoceptors, and that the inhibition of UP amplitude is mediated by prejunctional ₂-adrenoceptors. Send offprint requests to G. Burnstock at the above address     

The action of prostaglandin E2 on the smooth muscle cell of the guinea-pig taenia coli

The effect of prostaglandin E₂ (PGE₂) on the smooth muscle cell of guinea pig taenia coli was investigated by measuring changes in membrane potential, membrane resistance, muscle contraction and ion fluxes. The action of PGE₂ caused depolarization of the cell membrane, and increased spike activity and muscle contraction. The amplitude of the PGE₂ depolarization was concentration-dependent. The action of PGE₂ could be mimicked by depolarizing the muscle membrane with an external current with as result a decrease in membrane resistance similar to that observed in the presence of PGE₂. The PGE₂ depolarization was not abolished when the sodium pump was inhibited by omitting external potassium or in the presence of K-strophantin, persisted in low chloride Krebs and in low sodium solution, but was reduced in calcium-free solution and in the presence of D600. ⁴⁵Ca influx was enhanced by PGE₂, but ⁴⁵Ca efflux was not affected. The ⁴²K efflux was increased in the presence of PGE₂, but this response was blocked by Ca-free solution. These results indicate that calcium permeability is enhanced by PGE₂, and that this enhancement is associated with a depolarization of the muscle cell membrane of the guinea-pig taenia coli.     

不同剂量前列腺素E1对肺动脉高压犬血流动力学影响的实验研究

目的观察不同剂量前列腺素E1(PGE1)治疗犬血管栓塞性肺动脉高压的效果.方法 15条健康犬随机分为对照组,前列腺素E1P1组(25ng.min-1.kg-1PGE1)、前列腺素E1P2组(50ng.min-1.kg-1PGE1),每组5只.用交联萄聚糖混悬液经股静脉注射复制肺动脉高压,采用Swan-Ganz漂浮导管及西门子960型循环电脑监测仪等方法,观察动物用药前后肺动脉高压模型犬的血流动力学指标.结果 P1组(25ng.min-1.kg-1PGE1)使肺动脉压(PAP)下降,T2,T3,T4,T5时段(P＜0.05),P2组(50ng.min-1.kg-1PGE1)使肺动脉压(PAP)下降,T2,T3,T4,T6时段(P＜0.001)差异显著,T5时段(P＜0.05).两组对心率无明显影响,但两组均影响体循环的平均动脉压,T2时段(P＜0.05).结论 PGE1对心功能无影响.MAP、PCWP、SVR下降但CO、CI无变化,提示PGE1能改善心功能及治疗肺动脉高压,适宜治疗剂量P2组PGE1优于P1组.     

Some properties and mechanisms of thymol-induced release of calcium from the calcium-store in guinea-pig taenia caecum

The properties and mechanisms of Ca release induced by thymol from the intracellular Ca-store in the guinea-pig taenia caecum were investigated and compared with those by carbachol, using an intact muscle and a microsomal fraction. In Ca, Na-free, EGTA-containing K-solution, a transient contraction was evoked by each drug, and carbachol produced the contraction following treatment with thymol; however, a reversed sequence did not. The efflux of preloaded 45Ca in the presence and absence of ATP from taenia microsomes was accelerated by increasing concentrations of Ca ions outside. The minimal concentration to stimulate 45Ca-efflux was below 0.2 microM in both cases, and the Km values for Ca ions in the presence and absence of ATP were estimated to be 0.65 microM and 2.0 microM Ca ions, respectively. Thymol, which has been reported to be one of the most potent stimulators of the Ca-induced Ca release in the sarcoplasmic reticulum of skeletal muscle, enhanced the 45Ca-efflux from the taenia microsomes in the presence of ATP dose-dependently, and its mode of action seemed bimodal. That is, at 0.5 mM, thymol lowered the concentration of Ca ions which are needed to induce stimulation of 45Ca-efflux, whereas, at 1 mM, the stimulative effect of thymol on 45Ca-efflux was to augment the maximum rate of 45Ca-efflux, independent of concentrations of Ca ions. Carbachol (1 mM) did not have an effect on 45Ca-efflux with or without 0.1 mM GTP. In conclusion, the possibility has been suggested that in the guinea-pig taenia caecum, carbachol might release stored Ca ions via unknown pathway(s), whereas thymol directly releases Ca ions in a ATP-regulated fashion. Further, carbachol would be more efficacious for releasing stored Ca ions. Notwithstanding, the Ca-stores and/or the Ca-releasing mechanisms, which are utilized by both thymol and carbachol, seemed to share a common part(s) to some degree.     

Lipo PGE_1在蛛网膜下腔出血中的应用

目的：观察前列腺素E1脂微球载体制剂（Lipo PGE1）对蛛网膜下腔出血的疗效。方法：自发性蛛网膜下腔出血患者65例,随机分为治疗组和对照组。治疗组静脉滴注Lipo PGE1,同时行其他传统治疗方法。对照组不使用LipoPGE1,其余治疗措施同治疗组,观察治疗前后影像学、血浆和脑脊液中生化指标等方面的改变。结果：两组预后存在显著差异,治疗组预后较佳（P〈0.05）;在出血后第3、7天,治疗组内皮素水平也明显低于对照组;两组的再出血发生率及死亡率差异无统计学意义（P〉0.05）。结论：前列腺素E1能减少蛛网膜下腔出血后脑血管痉挛,改善预后。     

On the opioid receptor subtype inhibiting the evoked release of 3H-noradrenaline from guinea-pig atria in vitro

Guinea-pig isolated atria were incubated and loaded with 3H-(-)-noradrenaline. The intrinsic nerves were stimulated with trains of 5 or 35 field pulses (4 Hz), and the evoked efflux of 3H-noradrenaline and of total tritium was determined in the presence of atropine, corticosterone, desipramine, and phentolamine by liquid scintillation spectrometry. Ethylketocyclazocine (1.4 nmol/l, IC50), MR 2033 (9.1 nmol/l), dynorphin A (1-13) (25 nmol/l, peptidase inhibitors present), etorphine (71 nmol/l), and [D-Ala2, D-Leu5]-enkephalin (greater than 10 mumol/l, peptidase inhibitors present) inhibited the stimulation-evoked efflux of 3H-noradrenaline in a concentration-dependent manner, but not morphine up to 10 mumol/l. The inhibition by ethylketocyclazocine, MR 2033, and etorphine was antagonized by naloxone 1 mumol/l. Similarly, the MR 2033 effect was antagonized by SKF 10047 1 mumol/l. All antagonists investigated failed to affect the evoked 3H-noradrenaline efflux when present in the absence of exogenous agonists. Arunlakshana-Schild plots were calculated for the antagonism between ethylketocyclazocine and a pair of stereoisomers, (-)-MR 2266 (20 nmol/l-5 mumol/l) and (+)-MR 2267 (0.3-10 mumol/l) at the presynaptic opioid receptor, and pA2 values were estimated. The isomeric affinity ratio was 60, with pA2 values of (-)-MR 2266, 9.06, and (+)-MR 2267, 7.28, respectively. The results show that the 3H-noradrenaline release can be inhibited via activation of presynaptic opioid receptors. Under the conditions presently investigated endogenous opioids do not modulate the evoked transmitter release. The results favour the idea that a single population (presumably of the kappa-subtype) of opioid receptors is present at guinea-pig atrial noradrenergic nerves.     

Differentiation between the actions of acetylcholine and tetramethylammonium on the isolated taenia of the guinea-pig caecum by hemicholinium-3

1. Contractions of the isolated taenia of the guinea-pig caecum produced by acetylcholine and TMA were examined in the presence of various antagonists and anticholinesterases.2. Hemicholinium-3 (HC-3) (50-400 mug/ml) inhibited contractions or relaxations produced by TMA but not contractions produced by acetylcholine. The inhibition was rapid in onset and readily reversible. Contractions produced by transmural stimulation were unaffected by HC-3 but responses produced by nicotine were inhibited.3. Low concentrations of hyoscine and benzhexol inhibited responses to acetylcholine to a greater extent than those to TMA.4. Morphine, raised concentrations of Mg(++) or reduced concentrations of Ca(++) inhibited contractions produced by TMA and by acetylcholine to a similar extent.5. Edrophonium, in concentrations which preferentially inhibit acetylcholinesterase, increased contractions produced by acetylcholine and converted responses to nicotine or transmural stimulation into contractions or biphasic responses with a marked contraction phase but did not increase contractions produced by TMA.6. Iso-OMPA, in concentrations which preferentially inhibit butyrylcholinesterase, had no effect on responses to acetylcholine, nicotine, transmural stimulation or TMA.7. HC-3 inhibited contractions produced by TMA in the presence of anticholinesterases but had little effect on contractions produced by acetylcholine.8. These results suggest that TMA produces contractions by acting directly on receptors of the smooth muscle. An analysis of possible reasons for HC-3 (in the concentrations used) acting as an antagonist of TMA but not of acetylcholine indicates that the findings do not necessarily contradict the interpretation that both agonists act on the same receptor.     

Central and peripheral effects of bradykinin and prostaglandin E2 on blood pressure in conscious rats

Summary Bradykinin or prostaglandin E2 (PGE2), when injected intravenously, decreased blood pressure of conscious rats in a dose-dependent manner, while intracerebroventricular injections of bradykinin or PGE2 caused a dose-dependent increase in blood pressure. SQ 14,225, an inhibitor of angiotensin converting enzyme, potentiated the central pressor or peripheral depressor effect of bradykinin. Indomethacin, an inhibitor of prostaglandin synthesis, almost completely inhibited the central pressor effect of bradykinin when injected intraventricularly. Indomenthacin, when injected intravenously, failed to inhibit the peripheral depressor effect of bradykinin, whereas it significantly attenuated the peripheral depressor effect of bradykinin when the angiotensin converting enzyme was inhibited with SQ14,225. These results suggest that the central pressor effect of bradykinin is mainly mediated by the synthesis of prostaglandins in the central nervous system, while only a small fraction of peripheral depressor effect of bradykinin is, at least in conscious rats, mediated by the synthesis of prostaglandins in the systemic circulation.     

Effect of prostaglandin E1 and indomethacin on responses of longitudinal muscle of guinea-pig ileum to cholecystokinin.

The effect of prostaglandin E1 (PGE1) and indomethacin (IND) cholecystokinin (CCK)-induced contractions of guinea-pig isolated ileum longitudinal muscle were studied. PGE1 (2.8--28 nM) consistently and dose dependently increased the contractions evoked by CCK (indirect muscle stimulation) or by ACh. IND (2.7 microM) decreased the contractions to both compounds and this was reversed with 2.8--7 nM PGE1. Pretreatment of the preparations with phentolamine (2.6 microM) or pretreatment of the animals with reserpine (2 mg/kg i.p. 24 h before killing) did not affect PGE1 potentiation or IND inhibition of CCK-induced contractions. The results indicated that PGE1 potentiated CCK-induced contractions of the longitudinal muscle of guinea-pig ileum by increasing the response to released ACh. Experiments with IND suggested that endogenous PGs may modulate the effect of CCK or related gastrointestinal hormones.     

(3H)-adenine nucleotide and (3H)-noradrenaline release evoked by electrical field stimulation, perivascular nerve stimulation and nicotine from the taenia of the guinea-pig caecum

1. The release of [(3)H]-noradrenaline and adenine nucleotide evoked by electrical field stimulation (20-60 V, 30 Hz), perivascular nerve stimulation (20-80 V, 60 Hz) and nicotine (10, 100 muM) was studied in the taenia of the guinea-pig caecum under various conditions.2. Electrical stimulation at high intensity (60 V) caused the release of [(3)H]-adenine nucleotide; however, the inhibitory action of electrical stimulation was proportional to [(3)H]-noradrenaline release.3. The intensity of the inhibitory effect of stimulation of the perivascular nerves was directly related to [(3)H]-noradrenaline release and not associated with the release of [(3)H]-nucleotide.4. Cold storage for more than 8 days, cooling (19 degrees C) or tetrodotoxin treatment (1 mug/ml) abolished the inhibitory responses to electrical stimulation and to nicotine. After these treatments, nicotine and electrical stimulation elicited only contractions; the release of [(3)H]-noradrenaline, but not that of [(3)H]-adenine nucleotide, was inhibited.5. The dissociation of the inhibitory effects of electrical stimulation and nicotine from [(3)H]-nucleotide release does not support the hypothesis that ATP or a related nucleotide is the humoral transmitter of the non-adrenergic inhibition in the taenia of the guinea-pig caecum.     

Direct evidence for ATP release from non-adrenergic, non-cholinergic ("purinergic") nerves in the guinea-pig taenia coli and bladder

Demonstration of release of ATP from smooth muscle preparations during stimulation of purinergic nerves is complicated by the difficulty in showing whether it comes from nerve or muscle. ATP released during relaxation of the guinea-pig taenia coli and contraction of bladder strips in response to purinergic nerve stimulation was measured in the superfusate using the luciferin-luciferase ATP assay method. The amount of ATP increased 2-6 fold during isometric responses to purinergic nerve stimulation. This release was blocked by tetrodotoxin but not by adrenergic nerve destruction with 6-hydroxydopamine. No significant release of ATP was detected during comparable responses elicited by direct muscle stimulation. These results provide further support for the purinergic nerve hypothesis.