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B Driessen

Publications and source records attributed to B Driessen.

35 records · Page 2Linked to original sources
PubMed1996

Failure of tyramine to release neuronal ATP as a cotransmitter of noradrenaline in the guinea-pig vas deferens.

Contractions, release of noradrenaline and release of ATP elicited by the indirectly acting sympathomimetic amine tyramine and responses elicited by exogenous noradrenaline were studied in the isolated vas deferens of the guinea pig. Release of noradrenaline was assessed as overflow of tritium after preincubation with [3H]-noradrenaline. ATP was measured by means of the luciferin-luciferase technique. In tissues pretreated with pargyline 1 mM, tyramine 300 microM, when added to the superfusion medium for 2 min, elicited contraction and an overflow of tritium (mainly [3H]-noradrenaline) and ATP. Contraction and ATP overflow responses were prevented and tritium overflow was greatly reduced by desipramine 10 microM. Prazosin 0.3 microM abolished contractions and evoked ATP overflow without changing tritium overflow. Blockade of postjunctional P2-purinoceptors by suramin 300 microM caused a marked decrease of tyramine-evoked contractions and a slight reduction of tritium overflow whereas evoked ATP overflow was markedly increased. The effect on contraction was not shared by two other P2-purinoceptor antagonists, namely pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) 32 microM and diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) 32 microM: PPADS increased contractions about fourfold, whilst DIDS had no effect at all. When the vas deferens was superfused for 24 min with medium containing tyramine 300 microM, evoked contractions and tritium overflow continued throughout whereas ATP overflow faded rapidly to basal values. In the presence of prazosin 0.3 microM, tyramine 300 microM again failed to elicit contractions as well as an overflow of ATP. Application of noradrenaline 10 microM instead of tyramine also resulted in prolonged contraction and an overflow of ATP that declined rapidly. It is concluded that all ATP released by tyramine is non-neuronal in origin, secondary to the activation of postjunctional alpha 1-adrenoceptors by released noradrenaline. The non-neural ATP does not seem to play a functional role in smooth muscle contraction and derives from a postjunctional source which is subject to a rapid depletion upon sustained alpha 1-adrenoceptor activation.

Adenosine Triphosphate↗
PubMed1996

Opposite modulation of cotransmitter release in guinea-pig vas deferens: increase of noradrenaline and decrease of ATP release by activation of prejunctional beta-adrenoceptors.

Effects of isoprenaline on contraction, release of noradrenaline and release of ATP elicited by electrical field stimulation (210 pulses, 7 Hz) as well as on contractions elicited by exogenous noradrenaline and ATP were studied in the isolated vas deferens of the guinea pig. Release of noradrenaline was assessed as overflow of total tritium after preincubation with [3H]-noradrenaline. ATP was measured by means of the luciferin-luciferase technique. In [3H]-noradrenaline-pretreated tissues, electrical stimulation elicited an overflow of tritium and ATP and a biphasic contraction. Isoprenaline (1-100 nM) reduced the contraction, mainly phase I, and enhanced the evoked overflow of tritium: evoked overflow of ATP was not changed significantly. No, or almost no, contraction remained in [3H]-noradrenaline-pretreated tissues exposed to both prazosin (0.3 microM) and suramin (300 microM), and the evoked overflow of ATP was reduced by about 82%. Under these conditions, isoprenaline (1-100 nM) again enhanced the evoked overflow of tritium, but it now decreased the evoked overflow of ATP. Propranolol (1 microM), when added on top of prazosin and suramin, prevented the effects of isoprenaline (1-100 nM). In some tissues not pretreated with [3H]-noradrenaline, purinergic and adrenergic components of the neurogenic contraction (again to 210 pulses, 7 Hz) were isolated by exposure to prazosin (0.3 microM) and suramin (300 microM), respectively. Isoprenaline (1-100 nM) decreased the isolated purinergic component but did not change significantly the isolated adrenergic component. Contractions elicited by ATP (1000 microM) were not changed and contractions elicited by noradrenaline (100 microM) were slightly increased by isoprenaline (1-100 nM). Isoprenaline (100 nM) did not change the degradation of ATP (100 microM) by pieces of the vas deferens. It is concluded that, in the guinea-pig vas deferens, activation of prejunctional beta-adrenoceptors modulates the neural release of noradrenaline and ATP in opposite directions: release of noradrenaline is enhanced, whereas release of ATP is decreased.

Adenosine Triphosphate↗
PubMed1996

Opposite modulation of noradrenaline and ATP release in guinea-pig vas deferens through prejunctional beta-adrenoceptors: evidence for the beta 2 subtype.

Activation of prejunctional beta-adrenoceptors has been suggested to increase the release of noradrenaline but to decrease the neural release of ATP in the guinea-pig vas deferens. Experiments were carried out to determine the subtype of beta-adrenoceptor involved. In [3H]-noradrenaline-preincubated tissues superfused with medium containing prazosin and suramin, isoprenaline (1-100 nM), salbutamol (0.01-1 microM) and terbutaline (0.1-10 microM) increased the overflow of tritium but reduced the overflow of ATP elicited by electrical stimulation (210 pulses/7 Hz). The effects of isoprenaline were blocked by the beta 2-selective antagonist 1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3- [(1-methylethyl)amino]-2-butanol (ICI 118,551; 100 nM). In prazosin- and suramin-free medium, isoprenaline (100 nM) did not change the overflow of ATP elicited by exogenous noradrenaline (10 microM). Isoprenaline (1-100 nM), salbutamol (0.01-1 microM) and terbutaline (0.1-10 microM) reduced the initial twitch contraction elicited by electrical stimulation (210 pulses/7 Hz) in prazosin- and suramin-free medium as well as the isolated purinergic neurogenic contraction obtained by exposure to prazosin. They increased or tended to increase the secondary sustained concentration elicited by electrical stimulation in prazosin- and suramin-free medium as well as the isolated adrenergic neurogenic contraction obtained in the presence of suramin. The inhibition by isoprenaline of the isolated purinergic contraction was attenuated by ICI 118,551 (100 nM) but not by the beta 1-selective antagonist 1-[2-((3-carbamoyl- 4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4- trifluoromethyl-2-imidazolyl)phenoxy]-2-propanol (CGP 20712A; 100 nM). The results confirm the opposite beta-adrenoceptor-mediated modulation of noradrenaline and neural ATP release in the guinea-pig vas deferens. They show that the prejunctional beta-adrenoceptor is of the beta 2-subtype.

Adenosine Triphosphate↗
PubMed1995

Functional consequences of inhibition of nucleotide breakdown in rat vas deferens: a study with Evans blue.

The effect of Evans blue on nucleotide breakdown, nucleotide-evoked contractions and electrically evoked contractions, overflow of ATP and overflow of tritium (after labelling with [3H]-noradrenaline) was studied in rat vas deferens. Pieces of vas deferens degraded 83 to 85% of added ATP, ADP and 2-methyl-thio ATP (all 100 microM) over 30 min. Evans blue (100 microM) reduced this degradation to 22 to 26%. Nucleotides elicited contraction with potency declining in the order alpha,beta-methylene ATP > 2-methylthio ATP > ATP > ADP. Evans blue (100 microM) shifted the concentration-response curve of alpha, beta-methylene ATP to the right and increased the maximum. Concentration-response curves of ATP, ADP and 2-methylthio ATP, in contrast, were shifted to the left and responses were much potentiated. In the presence of Evans blue, the rank order of potency was ATP > 2-methylthio ATP > alpha, beta-methylene ATP > ADP. Electrical field stimulation (100 pulses at 10 Hz) elicited contraction and an overflow of tritium and ATP. Evans blue (100 microM) did not alter the contraction and the evoked overflow of tritium but increased 24-fold the evoked overflow of ATP. The results indicate that Evans blue may serve as an-albeit impure-ecto-nucleotidase inhibitor in functional experiments. Such experiments demonstrate that the low potency of ATP (and also ADP and 2-methylthio ATP) in eliciting contraction, and the small size of the overflow of ATP upon sympathetic nerve stimulation, are due to rapid breakdown.

Adenosine Triphosphate↗
PubMed1995

Comparison of corelease of noradrenaline and ATP evoked by hypogastric nerve stimulation and field stimulation in guinea-pig vas deferens.

Contractions and overflow of tritium and ATP elicited by hypogastric nerve stimulation (HNS) and field stimulation (FS) were studied in the guinea-pig isolated vas deferens preincubated with [3H]-noradrenaline. ATP was measured by means of the luciferin-luciferase technique. HNS and FS elicited contraction, tritium overflow and ATP overflow. HNS at supramaximal current strength produced smaller responses than did FS at supramaximal current strength (210 pulses/7 Hz). Supramaximal HNS and submaximal FS were used in the remainder of the study. Prazosin (0.3 mumol/l) reduced contractions and the overflow of ATP elicited by both HNS and FS; the evoked overflow of tritium was not changed (210 pulses/7 Hz). Combined administration of prazosin (0.3 mumol/l) and suramin (300 mumol/l) abolished contractions and reduced the overflow of ATP elicited by both HNS and FS slightly more than did prazosin alone; tritium overflow again was not changed (210 pulses/7 Hz). Contractions, tritium overflow and ATP overflow increased with the frequency of both HNS and FS (from 7 to 25 Hz; 210 pulses); the increase in ATP overflow with frequency was more marked than the increase in tritium overflow. The preferential increase of ATP overflow with the frequency of HNS and FS persisted in the combined presence of prazosin (0.3 mumol/l) and suramin (300 mumol/l). The study confirms for HNS, a more physiologic way of sympathetic nerve stimulation, several observations previously obtained with FS. First, HNS-evoked ATP release is detectable as an overflow of ATP into the superfusion fluid.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1994

Antinociceptive effect of intrathecally administered P2-purinoceptor antagonists in rats.

To investigate whether ATP participates in spinal nociceptive transmission, effects of intrathecally applied P2-purinoceptor antagonists and agonists in the tail-flick and the formalin test were studied in rats. In the tail-flick assay, the P2 antagonists suramin (12-120 micrograms), Evans blue (0.1-10 micrograms), Trypan blue (1-30 micrograms) and Reactive blue 2 (1-30 micrograms) but not pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 0.03-30 micrograms) caused moderate antinociception up to a doubling of the response latency. In contrast, the P2 agonists alpha,beta-methylene ATP (alpha,beta-mATP, 0.3-30 micrograms) and 2-methylthio-ATP (3-30 micrograms) decreased the tail-flick latency by up to about 50%. When co-injected with alpha,beta-mATP, suramin (120 micrograms) or Evans blue (10 micrograms) prevented the effect of alpha,beta-mATP 3 micrograms but not of alpha,beta-mATP 30 micrograms. In the formalin test, pretreatment with suramin (3-90 micrograms) 60 min prior to testing caused significant antinociception by decreasing the weighted pain intensity score by up to about 80%. alpha,beta-mATP (30 micrograms), applied 30 min prior to testing, was without effect. The results indicate that endogenous ATP, acting through P2-purinoceptors, may contribute to nociceptive information processing in the spinal cord.

Adenosine Triphosphate↗
PubMed1994

Modulation of neural noradrenaline and ATP release by angiotensin II and prostaglandin E2 in guinea-pig vas deferens.

Effects of angiotensin II and prostaglandin E2 on contractions, release of noradrenaline and release of ATP elicited by electrical stimulation (210 pulses, 7 Hz) were studied in the isolated vas deferens of the guinea pig. Release of noradrenaline was assessed as overflow of tritium after preincubation with [3H]-noradrenaline. ATP was measured by means of the luciferin-luciferase technique. In some experiments postsynaptic alpha 1-adrenoceptors and P2X-purinoceptors were blocked by prazosin and suramin, respectively, to isolate the neural fraction of the overflow of ATP. Electrical stimulation elicited an overflow of tritium and ATP and, in the absence of prazosin and suramin, contraction. In the absence of prazosin and suramin, angiotensin II (1-100 nM) enhanced contractions as well as the evoked overflow of tritium and ATP. All parameters were increased by about the same percentage for a given concentration of angiotensin II. The effect of prostaglandin E2 (1-100 nM) was complex. Contractions were mainly enhanced, the evoked overflow of tritium was reduced, whereas the evoked overflow of ATP was predominantly increased. No or almost no contraction remained in the presence of prazosin and suramin, and the evoked overflow of ATP was decreased to about 16%. Angiotensin II (1-100 nM) again enhanced the evoked overflow of tritium and ATP. Both were increased by about the same percentage for a given concentration of angiotensin II and also were increased by about the same percentage as obtained in the absence of prazosin and suramin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1994

The fade of the purinergic neurogenic contraction of the guinea-pig vas deferens: analysis of possible mechanisms.

The purinergic response of the guinea-pig vas deferens to long trains of pulses at high frequency consists of an initial twitch followed by a much lower plateau. Mechanical, neurochemical and electrophysiological techniques were used to examine the reason for the fade. Mechanical measurements. In tissues stimulated by trains of 180 pulses/10 Hz and treated with prazosin to suppress the noradrenergic contraction component, the response to alpha, beta-methylene ATP and to exogenous ATP was as high during the secondary plateau of the purinergic neurogenic contraction as it was outside electrical stimulation periods; the response to 50 pulses/100 Hz was also unchanged during the low plateau. The plateau was not increased by reactive blue 2,8-(p-sulphophenyl)theophylline, propranolol or capsaicin. Neurochemical measurements. In tissues preincubated with [3H]-noradrenaline, electrical stimulation elicited an overflow of tritium and of ATP. In the absence of drugs as well as in the presence of prazosin and suramin to suppress contractions, the overflow of tritium per pulse decreased slightly in the course of trains of 90 pulses/10 Hz; the overflow of ATP per pulse decreased to a greater extent on average, but the decrease was not statistically significant. In the presence of prazosin and nifedipine, also to suppress contractions, the overflow of tritium per pulse again decreased slightly in the course of trains of 105 pulses/10 Hz, but the overflow of ATP per pulse if anything tended to increase. Electrophysiological measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1994

Release of ATP in rat vas deferens: origin and role of calcium.

Release of endogenous ATP elicited by electrical (neural) stimulation and exogenous agonists was studied in the rat isolated vas deferens. The aims were to dissect neural and postjunctional contributions to the nerve activity-evoked overflow of ATP and to clarify the role of transmitter receptors and calcium in postjunctional ATP release. In tissues preincubated with [3H]-noradrenaline, electrical stimulation (100 pulses/10 Hz) elicited contraction and an overflow of tritium and ATP. Contractions as well as ATP overflow were reduced by prazosin 0.3 microM and even more so by prazosin 0.3 microM combined with suramin 300 microM. They were also reduced by nifedipine 10 microM and even more so by nifedipine 10 microM combined with ryanodine 20 microM (the additional effect of ryanodine on ATP overflow was not significant). In tissues not pretreated with [3H]-noradrenaline, exogenous noradrenaline 10 microM and alpha,beta-methylene ATP 10 microM elicited contraction and an overflow of ATP. Responses to noradrenaline were blocked by prazosin 0.3 microM but not suramin 300 microM and were greatly reduced by nifedipine 10 microM and in Ca(2+)-free medium. Responses to alpha,beta-methylene ATP were blocked by suramin 300 microM but not prazosin 0.3 microM, were reduced by nifedipine 10 microM (effect on ATP overflow not significant) and were reduced even more in Ca(2+)-free medium. Neuropeptide Y 0.3 microM caused only very small contraction and ATP overflow. The electrically as well as the agonist-evoked ATP overflow correlated well with the contraction responses except in experiments with suramin which retarded the removal, by vas deferens tissue, of ATP from the medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1994

P1-purinoceptor-mediated modulation of neural noradrenaline and ATP release in guinea-pig vas deferens.

The effect of P1-purinoceptor activation on contractions, release of noradrenaline and release of ATP elicited by electrical field stimulation (210 pulses, 7 Hz) was studied in the superfused vas deferens of the guinea pig. Release of noradrenaline was assessed as overflow of total tritium after preincubation with [3H]-noradrenaline. ATP was measured by means of the luciferin-luciferase technique. Electrical stimulation elicited reproducible contraction, tritium overflow and ATP overflow. In the absence of other drugs, adenosine (10-100 microM) did not change evoked contractions but reduced the evoked overflow of tritium and ATP. In subsequent experiments alpha 1-adrenoceptors were blocked by prazosin, P2-purinoceptors by suramin and alpha 2-adrenoceptors by rauwolscine. No or almost no contraction remained under these conditions. The evoked overflow of tritium was 505% and the evoked overflow of ATP 34% of that observed in the absence of prazosin, suramin and rauwolscine. Adenosine (1-100 microM) again reduced the evoked overflow of tritium and ATP, and so did the A1-selective agonist 2-chloro-N6-cyclopentyladenosine (CCPA; 0.032-0.32 microM). Adenosine and CCPA decreased the evoked overflow of ATP to a greater extent than the evoked overflow of tritium. It is concluded that neural release of both postganglionic sympathetic cotransmitters, noradrenaline and ATP, is decreased upon activation of prejunctional P1- (A1-) purinoceptors in guinea-pig vas deferens. The A1-receptor-mediated inhibition of the release of ATP is more marked than the inhibition of the release of noradrenaline, a pattern opposite to the inhibition produced by activation of prejunctional alpha 2-autoreceptors.

Action Potentials↗
PubMed1994

Presynaptic modulation of the release of the co-transmitters noradrenaline and ATP.

The release of both sympathetic co-transmitters, noradrenaline and ATP, is modulated via presynaptic receptors. However, the degree of the modulation may differ indicating that the ratio of the released co-transmitters changes upon presynaptic receptor activation. For example, alpha 2-autoinhibition affects the release of noradrenaline more markedly than the release of ATP. Some sympathetic axon terminals possess presynaptic P2-purinoceptors which are activated by endogenous ATP. These receptors are a novel kind of auto-receptor: they mediate a presynaptic negative feedback mechanism in which released ATP inhibits subsequent co-transmitter release.

Adenosine Triphosphate↗
PubMed1993

Neural ATP release and its alpha 2-adrenoceptor-mediated modulation in guinea-pig vas deferens.

Contractions, release of previously stored [3H]-noradrenaline (measured as overflow of total tritiated compounds) and release of ATP elicited by electrical field stimulation (210 pulses, 7 Hz) were studied in the superfused vas deferens of the guinea pig. Prazosin and suramin were used to suppress non-neural ATP release, and effects of bromoxidine and rauwolscine on the neural release thus isolated were examined. Electrical stimulation elicited reproducible contraction, tritium overflow and ATP overflow. Both prazosin (0.03-3 microM) and suramin (30-300 microM) reduced contractions as well as the evoked overflow of ATP. No visible contraction remained in 21 of 28 tissues exposed to prazosin 0.3 microM combined with suramin 300 microM. The evoked overflow of ATP under these conditions was about 17% of that observed in the absence of drugs. In the presence of prazosin 0.3 microM and suramin 300 microM, bromoxidine (0.01-1 microM) decreased and rauwolscine (0.1-10 microM) increased the evoked overflow of both tritium and ATP. Rauwolscine increased the evoked overflow of tritium to a significantly greater extent than the overflow of ATP. It is concluded that the overflow of ATP elicited by electrical (neural) stimulation in the presence of prazosin 0.3 microM and suramin 300 microM reflects purely neural release of ATP. This release of ATP, like the release of noradrenaline, is modulated through prejunctional alpha 2-adrenoceptors. The alpha 2-adrenoceptor modulation of the release of noradrenaline seems to be more marked than the modulation of the release of ATP.

Adenosine Triphosphate↗
PubMed1993

Effect of opioid receptor subtype-selective agonists on purinergic and adrenergic components of neurogenic contractions of mouse vas deferens.

1. Effects of opioid agonists on the purinergic and adrenergic components of neurogenic contractions and in some experiments on transmitter overflow were studied in the mouse isolated vas deferens. 2. When the vas deferens was stimulated every 2 min by pairs of pulses 2 s apart in the presence of prazosin 0.3 microM (to isolate the purinergic component) or alpha,beta-methylene-ATP 3 microM (to isolate the adrenergic component), each pulse elicited a separate twitch. The opioid agonists [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO, mu-receptor-selective), [D-Pen2,D-Pen5]enkephalin (DPDPE, delta-selective) and trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]- benzeneacetamide (U-50488, kappa-selective) concentration-dependently reduced both purinergic and adrenergic contractions. For each agonist, maximal effects and concentrations causing half-maximal effects were very similar for inhibition of the purinergic component on the one hand and for inhibition of the adrenergic component on the other hand, although the adrenergic component was inhibited with a slight preference. Moreover, effects on contractions elicited by the first and the second pulse of the pairs were very similar. 3. When vasa deferentia preincubated with [3H]-noradrenaline were stimulated with trains of 100 pulses delivered at 20 Hz, morphine 10 microM reduced significantly both evoked tritium overflow and evoked contractions. Its effect was antagonized by naloxone. 4. It is concluded that, in contrast to drugs acting at some other presynaptic receptors, opioid mu-, delta- and kappa-agonists inhibit purinergic and adrenergic neurogenic contractions of the mouse vas deferens in a similar manner. In contrast to a previous report, no enhancement by morphine of the release of noradrenaline elicited by high frequency pulse trains was observed.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1993

Effects of the central analgesic tramadol on the uptake and release of noradrenaline and dopamine in vitro.

1. The centrally acting analgesic, tramadol, has low affinity for opioid receptors and therefore presumably other mechanisms of analgesic action. Neurotransmitter release and uptake experiments were used to characterize the effects of tramadol on the central noradrenergic and dopaminergic systems. 2. Tramadol inhibited the uptake of [3H]-noradrenaline into purified rat hypothalamic synaptosomes with an IC50 of 2.8 microM; the (-)-enantiomer was about ten times more potent than the (+)-enantiomer. Results with the principal metabolite O-desmethyltramadol were very similar. Inhibition of dopamine uptake into purified rabbit caudate nucleus synaptosomes was very weak with 62% inhibition of 100 microM. 3. Rat occipital cortex slices were preincubated with [3H]-noradrenaline and rabbit caudate nucleus slices with [3H]-dopamine, then superfused and stimulated electrically. Tramadol, 1 and 10 microM, enhanced the stimulation-evoked [3H]-noradrenaline overflow by 25 and 69%, respectively; the (-)-enantiomer was more potent than the racemate or the (+)-enantiomer. Tramadol, 10 microM, had no effect on dopamine release. 4. The effects of tramadol on the stimulation-evoked [3H]-noradrenaline release were abolished when uptake sites were already blocked by a high concentration of cocaine. 5. The metabolite O-desmethyltramadol showed a slight facilitation of the stimulation-evoked noradrenaline release; the effect was more pronounced in the presence of a high concentration of naloxone. In the presence of cocaine, inhibition of the release was observed similar to the effect of morphine but less potent. 6. The results show that tramadol blocks noradrenaline uptake with selectivity as compared to dopamine uptake. The interaction with the noradrenaline transporter is stereoselective. The principal metabolite O-desmethyltramadol shows in addition to noradrenaline uptake inhibition, opioid inhibition of noradrenaline release.

5-Hydroxytryptophan↗
PubMed1993

Effects of the central analgesic tramadol and its main metabolite, O-desmethyltramadol, on rat locus coeruleus neurones.

1. Tramadol is a centrally acting analgesic with low opioid receptor affinity and, therefore, presumably additional mechanisms of analgesic action. Tramadol and its main metabolite O-desmethyltramadol were tested on rat central noradrenergic neurones of the nucleus locus coeruleus (LC), which are involved in the modulation of nociceptive afferent stimuli. 2. In pontine slices of the rat brain the spontaneous discharge of action potentials of LC cells was recorded extracellularly. (-)-Tramadol (0.1-100 microM), (+)-tramadol (0.1-100 microM), (-)-O-desmethyl-tramadol (0.1-100 microM) and (+)-O-desmethyltramadol (0.01-1 microM) inhibited the firing rate in a concentration-dependent manner. (+)-O-desmethyltramadol had the highest potency, while all other agonists were active at a similar range of concentrations. 3. (-)-Tramadol (10, 100 microM) was less inhibitory in brain slices of rats pretreated with reserpine (5 mg kg-1, 5 h before decapitation) than in controls. 4. The effect of (-)-tramadol (10 microM) was abolished in the presence of the alpha 2-adrenoceptor antagonist, rauwolscine (1 microM), whilst that of (+)-O-desmethyltramadol (0.3 microM) virtually disappeared in the presence of the opioid antagonist, naloxone (0.1 microM). (+)-Tramadol (30 microM) and (-)-O-desmethyl-tramadol (10 microM) became inactive only in the combined presence of naloxone (0.1 microM) and rauwolscine (1 microM). 5. In another series of experiments, the membrane potential of LC neurones was determined with intracellular microelectrodes. (-)-Tramadol (100 microM) inhibited the spontaneous firing and hyper-polarized the cells; this effect was abolished by rauwolscine (1 microM). (+)-O-desmethyltramadol (10 microM)had a similar but somewhat larger effect on the membrane potential than (-)-tramadol. The (+)-O-desmethyltramadol-(10 microM) induced hyperpolarization was abolished by naloxone (0.1 microM).6. The hyperpolarizing effect of noradrenaline (30 microM) was potentiated in the presence of (-)-tramadol(100 microM), but not in the presence of (+)-O-desmethyltramadol (10 microM). There was no potentiation of the noradrenaline (30 microM) effect, when the cells were hyperpolarized by current injection to an extent similar to that produced by (-)-tramadol (100 microM).7. Both noradrenaline (100 microM) and (- )-tramadol (100 microM) decreased the input resistance.8. The results confirm that the analgesic action of tramadol involves both opioid and non-opioid components. It appears that (-)-tramadol inhibits the uptake of noradrenaline and via a subsequent increase in the concentration of endogenous noradrenaline indirectly stimulates alpha2-adrenoceptors. (+)-0-desmethyltramadol seems to stimulate directly opioid micro-receptors. The effects of (+)-tramadol and(-)-O-desmethyltramadol consist of combined micro-opioid and alpha2-adrenergic components.

Action Potentials↗
PubMed1992

Interaction of the central analgesic, tramadol, with the uptake and release of 5-hydroxytryptamine in the rat brain in vitro.

1. Tramadol is a centrally acting analgesic with low opioid receptor affinity and therefore presumably other mechanisms of analgesic action. Tramadol inhibits noradrenaline uptake but since 5-hydroxytryptamine (5-HT) is also involved in the modulation of pain perception, we tested the effects of tramadol on 5-HT uptake and release in vitro. 2. Tramadol inhibited the uptake of [3H]-5-HT into purified rat frontal cortex synaptosomes with an IC50 of 3.1 microM. The (+)-enantiomer was about four times more potent than the (-)-enantiomer; the main metabolite of tramadol, O-desmethyltramadol, was about ten times less potent. 3. Rat frontal cortex slices were preincubated with [3H]-5-HT, then superfused and stimulated electrically. Tramadol facilitated the basal outflow of [3H]-5-HT, at concentrations greater than 1 microM, while the uptake inhibitor 5-nitroquipazine enhanced both basal and stimulation-evoked overflow. Effects of the (+)-enantiomer were more potent than either the racemate, the (-)-enantiomer or the principal metabolite. 4. The effects of tramadol on the basal outflow of [3H]-5-HT were almost completely abolished when the superfusion medium contained a high concentration of the selective 5-HT uptake blocker, 6-nitroquipazine. 5. The results provide evidence for an interaction of tramadol with the neuronal 5-HT transporter. An intact uptake system is necessary for the enhancement of extraneuronal 5-HT concentrations by tramadol indicating an intraneuronal site of action.

Animals↗