Modulation of release of ATP in the major pelvic ganglion of rats

用荧光素－荧光素酶方法测定大鼠盆总神经节腺苷三磷酸（ＡＴＰ）释放．钠通道阻断剂河豚毒素（１μｍｏｌ·Ｌ－１）抑制电刺激诱发的盆总神经节ＡＴＰ的释放．灌流液中去除Ｃａ２＋并加入ＥＧＴＡ（１ｍｍｏｌ·Ｌ－１）后消除ＡＴＰ的释放．腺苷（１００μｍｏｌ·Ｌ－１），Ａ１腺苷受体激动剂环戊腺苷（０．１μｍｏｌ·Ｌ－１），毒蕈碱性受体激动剂氧化震颤素（１μｍｏｌ·Ｌ－１）和５－羟色胺（１００μｍｏｌ·Ｌ－１）减少ＡＴＰ的释放．Ａ１腺苷受体拮抗剂８－环戊基－１，３－二丙基黄嘌呤（１０ｎｍｏｌ·Ｌ－１），α２肾上腺素受体拮抗剂育亨宾（３μｍｏｌ·Ｌ－１），Ｄ２多巴胺受体拮抗剂舒必利（２０μｍｏｌ·Ｌ－１）和组胺（１００μｍｏｌ·Ｌ－１）增加ＡＴＰ的释放．结果提示，在大鼠盆总神经节存在着作为神经递质参与突触传递的ＡＴＰ释放．Ａ１腺苷受体，毒蕈碱性受体，α２肾上腺素受体，Ｄ２多巴胺受体，５－羟色胺受体及Ｈ１组胺受体激动剂或拮抗剂可以通过节前机制影响ＡＴＰ的释放     

Comparison of in vitro-in vivo release of Risperdal(®) Consta(®) microspheres

The objective was to investigate the relationship between in vitro and in vivo release of commercial Risperdal(?) Consta(?) microspheres. A modified USP apparatus 4 method was used for accelerated and real-time in vitro release testing. The in vivo plasma profile (clinical data) reported for the product was deconvoluted for comparison with the in vitro release profiles. The in vivo profile differed from the real-time in vitro profile and was faster initially and then slower after approximately 30 days. This effect is considered to be due to differences in the in vivo conditions such as small interstitial volume, low pH and immune response. Accelerated in vitro release profiles obtained at temperatures (50°C and 54.5°C) above the microsphere glass transition temperature (Tg～48°C) overlapped with the in vivo profile after time scaling. A linear in vitro-in vivo relationship was observed with correlation coefficients of 0.97 and 0.99 at 50°C and 54.5°C, respectively. The accelerated test performed below the Tg had a similar release profile to that of the real-time in vitro test. The accelerated tests performed above the Tg of the microspheres showed the potential to be used for in vivo performance prediction as well as for quality control purposes.     

β-Endorphin-induced release of 5-hydroxytryptamine from human platelets

Platelets of healthy human subjects were incubated with 5-hydroxytryptamine (5-HT) followed by a second incubation with either -endorphin (-end) or the combination of -end and naloxone. -End (300 pg/ml) reduced the levels of 5-HT to 50% of initial values within 15–40 min. After 40–80 min incubation, the levels of 5-HT decreased to approximately zero. Addition of increasing amounts of -end (up to 300 pg/ml) produced increasing releases of 5-HT with increasing doses of -end. The response was dose-related, however variable, across subjects. Addition of either 28.7 or 57.4 pg naloxone to 300 pg -end did not antagonize the effects of -end on 5-HT.     

Influence of ethanol on swelling and release behaviors of Carbopol®-based tablets

The aim of this work was to investigate the effect of ethanol on the in vitro swelling and release behaviors of Carbopol^®-based tablets. The swelling behavior of drug-free compacts and the release of model drugs (metformin HCl, caffeine and theophylline) from matrix tablets were evaluated in acidic and buffered media with 0, 20 and 40% (v/v) ethanol. Release data were analyzed by fitting to Higuchi and Peppas models and calculation of similarity factor (f₂). ANOVA tests were performed to determine significant factors on swelling and release. It was found that ethanol affects swelling and erosion of drug-free Carbopol^® compacts, and the effect was highly dependent on medium pH. For matrix tablets, no dose dumping due to ethanol was manifested. The release rate and mechanism, however, were significantly affected by ethanol concentration as indicated by ANOVA applied to the constant, K_H, from Higuchi model and the exponent, n, from Peppas model, respectively. The effect of ethanol on release was further confirmed by similarity factor results, which indicated that ethanol led to different release profiles (f₂ < 50) in seven of eight cases for matrices containing metformin HCl and in three of eight cases for matrices containing caffeine and theophylline.     

Influence of neuronal uptake on the presynaptic α-adrenergic modulation of noradrenaline release

Summary Conditions required for the inhibitory feedback modulation of noradrenergic neurotransmission were studied in isolated atria of the rat.The alpha adrenergic antagonist, yohimbine, 0.8 M, or phentolamine, 1 M, did not affect the chronotropic response to 4 or 8 shocks at 0.8 Hz but increased it when a higher number of shocks was applied. When neuronal uptake was inhibited by cocaine, 2.9 M, or desipramine, 0.1 M, the enhancement of neurotransmission by yohimbine or phentolamine was higher than that observed in the presence of -adrenergic antagonists alone.In atria preincubated with ³H-noradrenaline, the effect of the drugs on the ³H-overflow evoked by 240 shocks at 2.0 Hz was studied. Cocaine 2.9 M, did not increase the evoked overflow but yohimbine, 0.8 M, did. The ³H-overflow obtained in the group of yohimbine plus cocaine was significantly higher than was expected from the effects of both drugs alone.It is concluded that yohimbine or phentolamine enhance the chronotropic response in rat atria only when the concentration of noradrenaline in the biophase is sufficiently high to activate presynaptic receptors. In this tissue, the efficiency of the neuronal uptake influences the degree of -adrenergic autoinhibition.     

Impairment of contraction and release of nitric oxide in rat arota by levothyroxine

AIM: To study the influence of levothyroxine on rat aorta contraction and nitric oxide (NO) release. METHODS: levothyroxine was administered 0.75 mg·g~(-1)×8d sc,and responses of isolated rat aorta rings were recorded and compared in the absence and presence of L-Argnine (LArg) and N~ω-Nitro-L-Argnine(L-NOARG) on norepinephrine (NE)-induced contraction. RESULTS: AUC     

Is there feedback regulation of neurotransmitter release by autoreceptors?

Neurotransmitter release does not seem to be regulated by neuronal receptors mediating feedback and the mechanism of action of presynaptically active agents is still uncertain. In a recent set of papers [27, 82], experiments were described in which major modifications were made to the amount of neurotransmitter released per impulse, with all other parameters of field stimulation, such as pulse number, voltage and frequency, fully controlled. These studies done with a number of sympathetically innervated tissues give some insight into an antagonist action presynaptically which is independent of the ambient concentration of extracellular transmitter. It appears to involve, instead, the gating mechanisms which control neuronal membrane depolarization and repolarization. It was found that the effects of yohimbine and also of phenoxybenzamine on stimulation-induced efflux appeared to be essentially "all or none". That is, the absolute total release of tritiated transmitter with 100 pulses was elevated to roughly the same dpm value by the presynaptic antagonist at each of the pulse durations between 50 and 1000 microsec, in a variety of test tissues. The declining percentage effect of the antagonist on tritium efflux, as the pulse duration was enlarged between 50 and 1000 microsec, referred to earlier (Fig. 3), was due to rising values for transmitter release in the controls not matched by proportionally similar increases in the antagonist-treated tissues. Values for the amount of transmitter released during stimulation in the presence of yohimbine, at pulse lengths between 50 and 1000 microsec, were all in the range of values achieved in the absence of yohimbine with long pulse lengths (1000-2000 microsec). In other words, prolongation of the pulse duration from 50 to 1000 microsec and the exposure of tissues to a presynaptic antagonist, such as yohimbine or phenoxybenzamine, may involve a common mechanism, and the effects of these two procedures are not additive. In fact, with much prolonged pulse durations (2000-5000 microsec), the presynaptic antagonists are virtually ineffective. It is known that the release of transmitter from sympathetic nerves is directly related to the duration of the action potential. If it is prolonged, the calcium channels stay open longer leading to greater entry of calcium and to an increased release of transmitter [45, 46]. Yohimbine and phenoxybenzamine may prolong the duration of depolarization by indirect modification of the calcium gating mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)     

Kinetics of drug release from polylactic acid—hydrocortisone microcapsules

Abstract

Polylactic acid microcapsules of similar particle size distribution containing various drug loadings of hydrocortisone were prepared. The microcapsules, which contained randomly dispensed drug particles, showed a dissolution pattern which consists of a fast first-stage and a slow second-stage drug release. Our studies showed that the kinetics of drug release from the microcapsules can be adequately described by a spherical matrix model based on a flux mechanism involving the diffusion of dissolved drug at the penetrating front of the dissolution medium. Drug loading played an important role in the control of drug release rate. An empirical relationship between drug loading and drug diffusi-bility through the polymeric matrix was developed and showed that the rate of drug release increased exponentially with the increase in drug loading. The microcapsules were further shown to exhibit increased rate of drug release in dissolution medium containing either cetylpyridium chloride or aerosol OT. The effect of the surfactants was attributed to surface tension lowering and improved wetting of the microcapsule particles.     

Further study of prerequisites for the enhancement by α-adrenoceptor antagonists of the release of noradrenaline

Summary Segments of the rabbit ear artery were preincubated with (–)-³H-noradrenaline and then perfused/superfused and stimulated by transmural electrical pulses. The outflow of ³H-noradrenaline and total tritium was determined.In the first series of experiments, stimulation periods of approximately constant length (50 s) were used (cocaine 5 M present). Thirteen pulses (0.25 Hz) elicited an overflow of ³H-noradrenaline of 0.024% of tissue tritium; 26 pulses (0.5 Hz) elicited an overflow of 0.059%, and 52 pulses (1 Hz) of 0.166%. Rauwolscine 1 M did not change the overflow evoked by 13 pulses, increased that evoked by 26 pulses and increased most markedly that evoked by 52 pulses. Phentolamine 1 M decreased the overflow at 13, did not change the overflow at 26, and increased the overflow at 52 pulses. Corynanthine 1 M decreased the overflow at 13, and did not change the overflow at 26 and 52 pulses. The effect of tetraethylammonium (TEA) 100 M was opposite to that of rauwolscine; it increased most markedly the overflow evoked by 13 pulses, increased less that evoked by 26 pulses, and least the overflow at 52 pulses.In the second series of experiments, the frequency of stimulation was kept constant (2 Hz). In the absence of cocaine, 10 pulses elicited an overflow of ³H-noradrenaline of 0.023% of tissue tritium; 20 pulses elicited an overflow of 0.043%, and 40 pulses of 0.089%. Phentolamine 1 M did not change the overflow evoked by 10 pulses, increased that evoked by 20 pulses, and increased most markedly that evoked by 40 pulses. TEA 100 M increased the evoked overflow at all pulse numbers. Similar results were obtained in the presence of cocaine 5 M.The results demonstrate that the enhancement by -adrenoceptor antagonists of the release of noradrenaline depends on the biophase concentration of noradrenaline. Under the present conditions, graded increases in biophase noradrenaline concentration led to graded increases in the effect of the antagonists. A second prerequisite for the release-enhancing effect appears to be a sufficient length of the pulse train. Under the present conditions, graded increases in train length up to about 20s led to graded increases in the effect of the antagonists, even though the average biophase concentration of noradrenaline did not change with the pulse train length. This pattern of effects of the -antagonists is not shared by at least one other release-enhancing drug, namely TEA.     

Suitability of κ-carrageenan pellets for the formulation of multiparticulate tablets with modified release

κ-Carrageenan is a novel pelletisation aid with high formulation robustness and quick disintegration leading to fast drug release unlike the matrix-like release from non-disintegrating microcrystalline cellulose pellets. Compression of pellets into tablets is cost effective. The feasibility of formulating multiparticulate tablets with coated κ-carrageenan pellets was investigated. Pellets containing a highly soluble drug in acid, namely bisacodyl and κ-carrageenan or MCC as pelletisation aid were prepared, enteric coated with a mixture of Kollicoat(?) MAE 30 DP and Eudragit(?) NE 30 D and compressed using silicified microcrystalline cellulose as embedding powder. The effect of coating level, type of pellet core, compression force and punch configurations on drug release were studied. A sufficient coating thickness for κ-carrageenan pellets was necessary to obtain multiparticulate tablets with adequate resistance in the acid stage regardless of the compression pressure used. While κ-carrageenan pellets and their tablets released over 80% of the drug during the neutral stage only about 20-24% was released from MCC pellets and their tablets. The type of punches used (oblong or round) did not significantly influence the drug release from the prepared tablets. Moreover, sufficient prolonged release properties were obtained with κ-carrageenan pellets containing theophylline as a model drug and coated with Kollicoat(?) SR 30 D using Kollicoat(?) IR as pore former. A lower coating level and higher amount of pore former were needed in case of theophylline pellets formulated with MCC as pelletisation aid. The sustained release properties of both coated pellet formulations were maintained after compression at different compression pressures.     

PKC and PKA mediate LPS-induced release of CGRP in DRG neurons of neonatal rats

Calcitonin gene-related peptide (CGRP), a 37-amino acid neuropeptide, is produced in dorsal root ganglia (DRG) neurons, which extend nerves peripherally to different organs and centrally to the spinal cord.We have previously reported that plasma levels of CGRP are significantly elevated in rats after injection of lipopolysaccharide (LPS) in vivo.LPS triggers CGRP release from capsaicin-sensitive sensory nerves in the isolated mesenteric arteial bed of the rats.In this work, we used the cultured DRG neurons of neonatal mrs to detemine whether or not LPS could trigger CGRP release and if it did so, what cellular signaling pathway was involved in the CGRP release.Neurons were disassociated from the DRG of 5- 7-d neonatal rat using     

Effect of Kollidon? SR on the release of Albuterol Sulphate from matrix tablets

The objective of this study was to evaluate Kollidon SR for the development of extended release Albuterol Sulphate matrix tablets in comparison with other polymers as Hydroxypropylmethylcellulose K15M, Carbopol 71G NF, and Eudragit L100-55. The mechanical properties of the tablets were improved as concentration of Kollidon SR or other polymers increased. It was found that Kollidon SR 30% (w/w) and HPMC 30% (w/w) tablets have f₂ similarity factor of 83.5 in their Albuterol Sulphate dissolution profile. The marketed product was found to release 99.7% of drug content within 8 h, while Kollidon SR and HPMC tablets with 30% (w/w) polymer concentration level released 92.7% and 92.9% respectively of drug content within 8 h. Kollidon SR has a unique character of maintaining tablets geometric shape until the end of dissolution test, this is mainly due to the water insoluble content, polyvinyl acetate, forming 80% (w/w) of Kollidon SR, while the remaining content 20% (w/w) is the water soluble, polyvinylpyrrolidone, responsible for pore formation causing a diffusion controlled release. Drug release from all previous formulations is best described to be controlled by more than one kinetic mechanism of release.In conclusion, Kollidon SR and HPMC and Carbopol were found to be potential candidates for the development of extended release of Albuterol Sulphate tablets.     

α-Adrenoceptor-mediated inhibition of noradrenaline release in rabbit brain cortex slices

Summary Brain cortex slices from rabbits were preincubated with [³H]noradrenaline and then superfused and stimulated electrically at 3Hz. In the presence of cocaine 30 M, unlabelled noradrenaline, -methylnoradrenaline, clonidine, oxymetazoline, xylazine and guanabenz decreased, whereas yohimbine, corynanthine, phentolamine, tolazoline and azapetine increased the stimulation-evoked overflow of tritium. Phenylephrine and prazosin had no effect on the evoked overflow except at concentrations that greatly accelerated the basal outflow of tritium. The results indicate that the noradrenergic axons of rabbit brain cortex are endowed with presynaptic -adrenoceptors which are exclusively of the ₂-type. Addition of various concentrations of cocaine, addition of pargyline, or stimulation at different current strengths was used to obtain either a high or a low stimulation-evoked overflow of tritium. Independently of the method used, a low evoked overflow coincided with a large percentage inhibition produced by 0.1M clonidine, whereas a high evoked overflow coincided with a smaller percentage inhibition produced by clonidine. The results indicate that drugs which block the re-uptake of noradrenaline diminish the presynaptic inhibitory effect of -adrenergic agonists by increasing the biophase concentration of released noradrenaline.     

A kinetic study of the release of noradrenaline by electrical stimulation: influence of presynaptic α-adrenoceptors

Summary Dog saphenous vein strips were incubated with 1.4 mol/l ³H-(-)-noradrenaline for 60 min, after inhibition of the noradrenaline-metabolizing enzymes and of extraneuronal uptake. At the end of the incubation period the strips were perifused for 150 min; cocaine (10 mol/l) was added to the perifusion fluid from t=75 min onwards. In some experiments either phentolamine (10 mol/l) or clonidine (0.1 mol/l) was also added at this time. Some strips were subjected to electrical stimulation from t=100 to 150 min of perifusion (t=0 being the start of perifusion), with frequencies ranging from 0.5 to 13.5 Hz. A compartmental analysis of spontaneous or electrically-induced efflux of ³H-noradrenaline was made. The spontaneous efflux had a long half time (t/2=124 min) and most of the ³H-noradrenaline which had accumulated in the strips did not participate in the efflux (bound fraction, representing 90% of tissue activity at t=100 min of perifusion). Neither phentolamine nor clonidine modified the half time or the bound fraction observed for spontaneous efflux. Electrical stimulation (>0.5 Hz) mobilized only one compartment of noradrenaline, which represented about 50% of the noradrenaline accumulated in the strips. The half time of ³H-efflux induced by electrical stimulation decreased when the frequency increased from 0.5 Hz up to 13.5 Hz. Phentolamine increased the rate of efflux for all frequencies of stimulation and decreased the half time of efflux. However, the releasable pool of noradrenaline was only increased by phentolamine at 0.5 Hz, but not at higher frequencies. Clonidine was used only at two frequencies of stimulation, 1.5 and 4.5 Hz. For the low frequency clonidine decreased the releasable pool, but no change was observed at 4.5 Hz.The results support the view that there is a norarenaline pool which is resistant to electrical stimulation and that its magnitude is not dependent on the activity of presynaptic -adrenoceptors.Results presented in part to the 13th Annual Meeting of the Portuguese Pharmacological Society (Porto, December 1982) and to the 5th Meeting on Adrenergic Mechanisms (Porto, October 1983)Work supported by a grant from Instituto Nacional de Investigação Científica (FmPl)     

β Adrenoceptor-mediated facilitation of endogenous noradrenaline release from rat isolated trachea

Overflow of endogenous noradrenaline from rat isolated tracheae was evoked by electrical field stimulation (3 Hz, 540 pulses) in the presence of yohimbine, desipramine and tyrosine. Isoprenaline 100 nmol/l increased the evoked overflow of noradrenaline by about 65%. This effect was antagonized by propranolol (100 nmol/l) and the ₂-selective adrenoceptor antagonist ICI 118,551 (100 nmol/l), but not by the ₁-selective adrenoceptor antagonist CGP 20712 A (100 nmol/l). The ₂-selective adrenoceptor agonist formoterol (1–100 nmol/l) also facilitated the evoked overflow of noradrenaline, but maximally by only about 25% at 10 nmol/l, i.e. formoterol behaved as a partial agonist at these facilitatory -adrenoceptor. This assumption is also supported by the observation that formoterol (10 nmol/l) acted as antagonist against isoprenaline (100 nmol/l). Mechanical removal of the mucosa resulted in a 30% decrease in tissue noradrenaline and a 55% reduction of the evoked overflow of noradrenaline. In mucosa-denuded preparations isoprenaline failed to facilitate noradrenaline overflow. In the presence of indomethacin (3 mol/l) the evoked overflow of noradrenaline from mucosa containing preparations was increased by about 50%, but isoprenaline still further facilitated the evoked noradrenaline overflow by about 40%. In conclusion, the overflow of noradrenaline in the rat trachea is facilitated via ₂-adrenoceptors, an effect which requires an intact air-way mucosa. Correspondence to: K. Racké at the above address     

β-Adrenoceptor activates endothelium-dependent release of nitric oxide in rat aorta

AIM:To examine the possible role of agents elevating cAMP to release NO from aortic en-dothelial cells. METHODS:NG-nitro-L-arg inine methylester (L-NAME) , an inhibitor of NO synthase, partially inhibited endothelium-dependent relaxation evoked in phenylephrine-precontracted rings by isoproterenol and abolished relaxation mediated by forskolin 0. 2 umol L-1.RESULTS: In rings without en-dothelium, isoproterenol and forskolin were less effective relaxants and L-NAME had no effect on the responses. In methylene blue-treated rings isoproterenol- and forskolin-induced relaxation were prevented in both en-dothelium-intact and -denuded rings, but the inhibitory effects of methylene blue were significantly more in rings with endothelium than in those without. On the other hand, relaxation induced by sodium nitroprusside was not inhibited by L-NAME, but was inhibited by methylene blue in both the endothelium-intact and -denuded rings. The concentration relaxation curves to sodium nitroprusside after methylene bl     

In-vivo evaluation of prolonged release bilayer tablets of anti-Parkinson drugs in Göttingen minipigs

Objectives Patients with Parkinson's disease can benefit from controlled released levodopa dosage forms since there is a clear clinical advantage in obtaining sustained plasma concentrations. The purpose of this study was to obtain a tablet that prolonged the release of levodopa. Methods A novel bilayer tablet, consisting of an immediate release layer containing nebicapone (100 mg) and an erosion‐matrix type prolonged release layer containing levodopa (100 mg) and carbidopa (25 mg) was developed (LCN PR). A pharmacokinetic study in Göttingen minipigs was performed to evaluate this formulation. Key findings LCN PR tablets prolonged the in‐vitro release of levodopa in HCl 0.1 m for more than 3 h. In‐vivo plasma levodopa levels peaked at a later time point with LCN PR tablets as compared with that obtained with Sinemet 100/25 (2.7 vs 0.5 h). Nebicapone increased the maximum plasma concentration and area under the plasma concentration–time curve values for levodopa. Conclusions The results obtained suggested that LCN PR tablets may have decreased the number of tablets and daily intake in the treatment of patients with Parkinson's disease.     

Controlled release from a coated particle — Effects of initial conditions and methods of solution

The exact effects of three initial conditions - time lag, burst release, and steady state concentration profile - on drug release from a coated spherical matrix containing dissolved drug into a finite amount of well stirred elution liquid have been analyzed. The degree of the effect of initial conditions on drug release depends on the diffusivity ratio of coating layer to core matrix and the radius ratio of the coated particle to the core. For the case where drug concentration in the core is dependent on time only, the differences between the exact and the pseudo-steady state solutions are computed, therefore, pros and cons for the pseudo-steady state solution, which is simple and direct, can be anchored on exact comparison.     

Effect of ω-conotoxin GVIA on release of 3H-γ-aminobutyric acid from slices of rat neostriatum

Summary -Conotoxin GVIA (-CT) diminished the potassium-induced in vitro release of ³H--aminobutyric acid (³H-GABA) from slices of rat neostriatum in a manner which depended on the concentration of potassium. -CT (0.1 nmol/l) decreased the release of ³H-GABA induced by 25 mmol/l K⁺ from 11.6% to 6.1% of tissue content, ie. by 48%, while it did not affect the release of ³H-GABA caused by 20 mmol/l K⁺, which was 4.8% of tissue content. However, in the presence of a polyclonal antiserum or cysteamine (600 mol/l), both of which diminish the effects of endogenous somatostatin, 0.1–10 nmol/l -CT decreased the release of ³H-GABA induced by 20 mmoles/l K⁺ by 40%. It is concluded that -CT did not only inhibit GABA-neurones, but had an additional inhibitory effect on somatostatin neurones which are known to depress the release of ³H-GABA. It is further concluded that neuronal interactions, which are possible in brain slice preparations, may impede the interpretation of effects of drugs, especially if agents are used which affect basic mechanisms of transmitter release and thus the release of various transmitters from neurones. Send offprint requests to D. K. Meyer at the above address