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CARDIOVASCULAR
Department of Pharmacology, School of Medicine, University of Southern Denmark, Odense, Denmark
Received March 28, 2003; accepted May 8, 2003.
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Abstract |
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 Top Abstract Materials and MethodsResultsDiscussionReferences |
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[2-ethoxyphenoxy]benzyl]-morpholine], is a
nontricyclic antidepressant drug (Melloni
et al., 1985
). It is reputedly clinically effective in the
treatment of major depressive illness, well tolerated, and has a wide margin
of safety (Burns, 2000;
Scates and Doraiswamy, 2000;
Wong et al., 2000). Reboxetine
is a highly selective inhibitor of the norepinephrine transporter (NET) in rat
brain synaptosomes (Melloni et al.,
1984; Riva et al.,
1989; Wong et al.,
2000). The inhibition of norepinephrine reuptake in central
neurons is believed to be responsible for its antidepressive activity
(Scates and Doraiswamy, 2000).
Reboxetine has low affinity to 1-adrenoceptors, and
histaminergic and muscarinic receptors
(Riva et al., 1989;
Wong et al., 2000), which
could explain why reboxetine only has mild to moderate cardiovascular side
effects (Burrows et al., 1998).
The overall frequency of adverse effects of reboxetine was similar with
comparative drugs. Reboxetine seems to be relatively well tolerated with a
good safety profile (Scates and
Doraiswamy, 2000).
Desipramine, a tricyclic antidepressant, is a potent inhibitor of
norepinephrine reuptake at central noradrenergic nerve endings
(Sánchez and Hyttel,
1999). Desipramine is a potent antagonist at histamine
H1-receptors (Green and Maayani,
1977) and has weak antagonistic actions at 1-
and 2-adrenoceptor (Hall
and ögren, 1981) and at muscarinic receptors
(Golds et al., 1980). Cocaine
is an inhibitor of norepinephrine uptake
(Maxwell et al., 1969) without
any direct effect on -adrenoceptors and muscarinic receptors.
The action of reboxetine on vascular neuroeffector transmission has not
been studied. The aim of the present study was therefore to examine the pre-
and postsynaptic actions of reboxetine on sympathetic neuroeffector
transmission in the isolated rabbit carotid artery. The actions of reboxetine
were compared with those of desipramine and cocaine. A preliminary report of
some of the results in this article was presented to the 44th Annual Meeting
of the Western Pharmacology Society in Vancouver, British Columbia, Canada
(Rasmussen and Nedergaard,
2001), and the International Congress of Pharmacology in San
Francisco, CA (Rasmussen and Nedergaard,
2002).
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Materials and Methods |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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[2-ethoxyphenoxy]benzyl]-morpholine hydrochloride
(synthesized in the Department of Medicinal Chemistry, H. Lundbeck A/S,
Copenhagen, Denmark). Stock solutions were prepared in twice-distilled water (bretylium, cocaine, desipramine, norepinephrine, [3H]norepinephrine, and pargyline). The stock solutions were diluted with physiological salt solution (PSS) to the concentration required. Stock solutions were stored at 4°C.
Rabbit Isolated Carotid Artery. New Zealand White rabbits of either sex were obtained from Harlan AD (Horst, The Netherlands). Their weight was 1.8 to 2.7 kg. The rabbits were sacrificed by cervical dislocation and exsanguinated. All procedures conformed with Danish national guidelines for the care and handling of animals. The common carotid arteries on each side were divided into four to six rings (4 mm in width).
In Vitro Experiments. All isolated tissue experiments were carried out in equipment made from glass rather than plastic. In preliminary experiments, we found that rods (containing platinum electrodes), tissue holders, and isolated tissue baths made of plastic were not suitable. In spite of repeated and careful washing with soap and water of these plastic utensils, they retained reboxetine. During subsequent experiments, reboxetine leaked from the plastic into the PSS and thereby compromised the experiments. Even when all glass utensils were used, the removal of reboxetine required careful washing and soaking (8-12 h) with 40% (v/v) ethanol.
Salt Solution. The composition of the PSS was as follows: Na+, 1.442 x 10-1 M; K+, 4.9 x 10-3 M; Ca2+, 1.3 x 10-3 M; Mg2+, 1.2 x 10-3 M; Cl-, 1.267 x 10-1 M; HCO3-, 2.5 x 10-2 M; SO42-, 1.2 x 10-3 M; H2PO42-, 1.2 x 10-3 M; and D-(+)-glucose, 1.11 x 10-2 M. The solution also contained calcium disodium EDTA (3 x 10-5 M) and L-(+)-ascorbic acid (10-4 M). The solution was maintained at 37°C, equilibrated before and during the experiment with O2 containing 5% (v/v) CO2 (pH 7.4).
Electrical Field Stimulation-Evoked Release of
[3H]Norepinephrine. The method described by Jensen and
Nedergaard (1999) was used.
Each ring was incubated in 6-ml test tubes containing PSS (2.0 ml). After an
equilibration period (20 min), the rings were incubated with
[3H]norepinephrine (10-7 M) for 30 min. They
were washed three times for 5 min each with salt solution by transferring them
to new test tubes. The rings were then mounted in isolated tissue baths, which
were automatically emptied and refilled with PSS (2.0 ml) every 5 min for the
remainder of the experiments. The fractions (5 min) were collected 135 min
after the onset of washout directly in a counting vial by means of a fraction
collector. At the end of each experiment, each ring was treated with Solvable
(DuPont de Nemours, Dreieich, Germany) for 16 h at room temperature
(18-22°C). The 3H content in each 5-min fraction and tissue was
determined by liquid scintillation spectrometry (Tri-Carb 2100TR; PerkinElmer
Life Sciences). The spectrometer automatically corrected for quenching and
determined the counting efficiency by mean of an external standard.
Electrical field stimulation was applied to the vessels using a stimulator
(model S48; Grass Instruments, Quincy, MA) in connection with a constant
current unit. Electrical field stimulation was applied at various times
(minutes) after onset of washout: 80 (S1) and then every 35 min
(S2-S7). Each period of stimulation consisted of 300
pulses (200 mA, 0.5 ms, 3 Hz). S1 and S2 were
disregarded, and S3 used as an initial control value (
100%).
The 3H overflow evoked by electrical field stimulation was
calculated by summation of the 3H overflow in the three fraction
(F3-F5), which entered in the formation of the peak less
the estimated basal 3H outflow during this period. The latter was
calculated for each stimulation period (S3-S7) by
assuming a linear decline of the basal 3H outflow between the two
fractions (F1-F2) just preceding the stimulation and the
fraction (F6) collected 20 min after the onset of stimulation. The
tritium in each 5-min fraction was expressed as a percentage of the
3H content in the tissue at the time of sampling. This calculation
was done by summation of the assayed tritium in each 5-min fraction and the
3H content in the tissue at the end of the experiment. The
calculated stimulation-evoked 3H overflow was expressed as a
percentage of the initial S3 control stimulation (100%). In
some experiments, the 3H overflow evoked by stimulation
(S3-S7) was corrected for time-dependent changes. This
was done by stimulating untreated tissue in parallel with tissue exposed to
the drug being examined.
Electrical Field Stimulation of Isolated Carotid Artery.
Each ring was subjected to electrical field stimulation using a stimulator (model S48; Grass Instruments) connected to a constant current unit. Each period of stimulation consisted of 300 monophasic pulses (200 mA, 3 Hz, 0.5 ms) followed by a 15-min rest period. The contraction evoked by the sixth stimulation was designated the "control" response. If the stimulation (S6)-evoked tension was less than 1 g, the artery was discarded. The isometric mechanical tension response was recorded by means of a transducer (type SG 4-180; Swema, Stockholm, Sweden) connected to a data acquisition and analysis unit (Powerlab/800; AD Instruments, Castle Hill, New South Wales, Australia), which registered the converted signal in grams of tension.
Effects of drugs added cumulatively on stimulation-evoked contraction were studied in the following manner. Ten minutes after the control response, the lowest concentration of the test drug to be used was added; the response after 20-min incubation was recorded. The next higher concentration was then added 10 min later and the response again recorded after 20 min. The procedure was continued until a total of six or seven drug concentrations had been tested. In all experiments, the contractions evoked by electrical stimulation (S6-S11) were corrected for time-dependent changes. This was done by stimulating untreated tissue in parallel with tissue exposed to the test drug being examined. These data were used to correct the former results. The mean control tension (grams) for the untreated and drug-treated preparations did not differ (p > 0.05).
Effect of Reboxetine on the Contractions of Carotid Artery Evoked by Various Agonists and Potassium. Rings of carotid artery were mounted suitably in an isolated tissue bath filled with 20 ml of salt solution, and a resting tension of 6 g was applied. The rings were washed twice with salt solution during a 1-h equilibration period. The rings were then primed once with norepinephrine (10-6 M). After washout, the respective agonist was added cumulatively. Additions were made whenever a steady contractile response was obtained to the preceding administration. The effect of the agonist was considered to be maximal when at least a 3-fold increase in its concentration failed to cause a further increase in tension. After the maximal response was obtained, the artery was washed repeatedly with PSS until the tension returned to the resting tension value. The tissues were then equilibrated for 30 min before the agonist in question was added cumulatively. The contractions thus evoked were expressed as a percentage of the maximal contraction response developed by the initial addition of the agonist in question. Experiments designed to measure the effect of reboxetine on the contractions evoked by various agonists or K+ were carried out in the following manner: reboxetine was added to the bath 30 min before the second addition of the lowest concentration of the agonist in question and maintained in the bath for the remainder of the experiment. Only one concentration-response curve determination was made per preparation.
Uptake of [3H]Norepinephrine. The method described by
Nedergaard (1989) was used.
Four to six rings (each 8 mm width) of carotid artery were equilibrated for 30
min with PSS and washed once. Monoamine oxidase (MAO) and
catechol-O-methyltransferase (COMT) were blocked by pargyline and
U-0521, respectively, in the following manner: rings were incubated with
pargyline (5 x 10-5 M) for 30 min with subsequent
washout of this agent. U-0521 (10-4 M) was then added to
the bath at least 1 h before the incubation with 3H-amine and was
present throughout the experiment. Each ring was transferred to a separate
bath filled with 20 ml of PSS. After at least 30 min further equilibration,
the tissues were incubated with [3H]norepinephrine
(10-8 M) for 1 h.
In experiments designed to examine the ability of a drug to alter the uptake of [3H]norepinephrine, the former was added 1 h before the latter and maintained in the bath for the remainder of the experiment.
After incubation with [3H]norepinephrine, the rings were cut open into rectangular strips. They were blotted between two pieces of moistened filter paper under pressure (30 g) for 10 s in a standard manner, and their net weight (5.8-12.0 mg) was determined. Each sample was transferred to a 25-ml polyethylene liquid scintillation counting vial and treated with Solvable (DuPont de Nemours) for 16 h at room temperature (18-22°C) in closed vials. Radioactivity was measured by liquid scintillation spectrometry (Tri-Carb 2100 TR; PerkinElmer Life Sciences). Aliquots (100 µl) of the bath fluid were counted also. The uptake of [3H]norepinephrine is expressed as milliliters of fluid cleared per gram (milliliters per gram); also referred to as clearance ratio.
Statistical Analysis. Data are expressed as mean ± S.E.M. Log concentration-response curves were plotted. Differences between mean values were evaluated using an unpaired t test. In the case of unequal variance between the mean values compared (evaluated with a variance ratio test), an unpaired t test for unequal variance was used. When one control value was compared with a set of different concentrations of test drugs, t test with a Bonferonni's correction was used. When multiple comparisons between groups of data were analyzed, two-way analysis of variance (ANOVA) was used. Only the overall treatment effect was analyzed by two-way ANOVA. Significance was accepted at the 0.05 level of probability. Analysis of data were performed with Excel 97 (Microsoft, Redmond, WA).
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Results |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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Effect of Reboxetine and Cocaine on the Inhibitory Action of Bretylium. Bretylium (10-6 M) blocked the stimulation-evoked contractions of carotid artery (Fig. 3). Reboxetine (10-7 M) and cocaine (10-5 M) prevented the bretylium-induced block (Fig. 3).
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Effect of Reboxetine, Desipramine, and Cocaine on Basal 3H Outflow and Stimulation-Evoked 3H Overflow. Reboxetine (10-8-10-5 M), desipramine (10-8-10-5 M), and cocaine (10-7-3 x 10-5 M) had no effect on the basal 3H outflow from carotid artery preincubated with [3H]norepinephrine (data not shown; n = 6). Reboxetine (10-8-10-5 M), desipramine (10-7-10-5 M), and cocaine (10-6-10-5 M) concentration dependently increased the stimulation-evoked 3H overflow from carotid artery preincubated with [3H]norepinephrine (Fig. 4). Emax (percentage) was as follows: 87 (reboxetine), 45 (desipramine), and 23 (cocaine). Reboxetine (10-7 M), desipramine (10-7 M), and cocaine (10-6 M) rapidly enhanced the stimulation-evoked 3H overflow (Fig. 5). The reboxetine-evoked enhancement increased with time, whereas the enhancement seen with desipramine and cocaine remained unchanged (Fig. 5).
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Influence of Pargyline on the Action of Reboxetine and Cocaine on Stimulation-Evoked 3H Overflow. Pargyline (5 x 10-4 M) augmented the facilitatory effect of reboxetine (3 x 10-9-10-6 M) and cocaine (10-7-3 x 10-5 M) (Fig. 6). Effect of Reboxetine, Desipramine, and Cocaine on the Uptake of [3H]Norepinephrine. Reboxetine (10-8-10-6 M), desipramine (10-8-10-6 M), and cocaine (3 x 10-8-10-5 M) reduced the uptake of 3H by carotid artery incubated with [3H]norepinephrine (10-8 M) (Fig. 7). The rank order of inhibitory potency (IC50) was reboxetine > desipramine > cocaine.
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The 3H uptake by carotid artery treated with cocaine (3 x 10-5 M) recovered fully after a short washout period (0.5 h). In contrast, after incubation with reboxetine (10-6 M) the 3H uptake only recovered partially after longer washout periods: 55% (1 h) and 75% (2 h) (Fig. 8).
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Effect of Reboxetine and Cocaine on Contractions of Carotid Artery Evoked by Agonists and Potassium. Reboxetine (10-7 M) and cocaine (10-5 and 2 x 10-4 M) enhanced the contractions of carotid artery evoked by either phenylephrine (10-7-2 x 10-6 M) or norepinephrine (10-7-2 x 10-6 M) (Fig. 9). Higher concentrations of reboxetine (3 x 10-5-6 x 10-5 M) antagonized in a noncompetitive manner the contractions evoked by either phenylephrine or norepinephrine (Fig. 9).
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Reboxetine (10-5-6 x 10-5 M) antagonized noncompetitively the contractions evoked by potassium (Fig. 10). Cocaine (3 x 10-4 M) also reduced the K+-evoked contractions (Fig. 10). However, lower concentrations of cocaine (10-5-10-4 M) had no effect. The contractions of carotid artery evoked by tyramine (3 x 10-6-10-3 M) was markedly reduced by reboxetine (3 x 10-8-10-6 M) and by cocaine (10-7-10-5 M) (Fig. 11).
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Discussion |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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).
Agents that release norepinephrine, even if they do not interact with the
amine pump (uptake-1), would seem to be inhibitors of amine uptake and thus
erroneously be classified as amine pump inhibitors
(Maxwell et al., 1976).
Reboxetine at concentrations higher than 10-5 M caused
an increase in basal3H outflow from the carotid artery preloaded
with [3H]norepinephrine, i.e., reboxetine had no releasing action
at 10-5 M and at lower concentrations. The maximum
inhibition (IC100) of 3H uptake was seen with
10-6 M reboxetine
(Fig. 7). Therefore, it is most
unlikely that the reboxetine-induced inhibition of 3H uptake is due
to a releasing action on norepinephrine stored in the sympathetic neurons.
Reboxetine reduced the uptake of [3H]norepinephrine
(Fig. 7), which confirms
findings in rat hypothalamic synaptosomes
(Wong et al., 2000) and rat
hippocampal synaptosomes (Miller et al.,
2002). This reduction is most likely due to an inhibition of the
neuronal amine pump (uptake-1 mechanism) because cocaine and desipramine also
reduced the uptake (Fig. 7).
Furthermore, this in line with the view that reboxetine is a selective
norepinephrine reuptake inhibitor (Wong et
al., 2000).
The inhibition of [3H]norepinephrine uptake by reboxetine was
only partially reversed after a 2-h washout period
(Fig. 8). In contrast, the
cocaine-induced inhibition was reversed fully after 0.5 h
(Fig. 8). This indicates that
reboxetine is bound rather tightly to the tissue, perhaps the NET transporter
itself. This suggests that there may be a dissociation between plasma
concentration of reboxetine and its concentration in the biophase. This is
also in line with the observation that there are no defined plasma
concentrations of reboxetine that correlate with its therapeutic effect
(Scates and Doraiswamy, 2000).
Clinical studies have demonstrated that the mean plasma concentration of
reboxetine is 3 x 10-7 M
(Scates and Doraiswamy, 2000).
The correlation between the concentration of drugs in salt solution in
isolated tissue experiments and their therapeutic plasma concentration is a
matter of conjecture. However, our findings with reboxetine in concentrations
up to 10-6 M can probably be considered therapeutically
relevant.
Inactivation of norepinephrine release by sympathetic nerve stimulation in
blood vessels is mainly carried out by neuronal (uptake-1) and extraneuronal
uptake (uptake-2) of the transmitter and subsequent inactivation by MAO and
catechol-O-methyltransferase
(Osswald and Guimarães,
1983). The uptake mechanisms for norepinephrine can thus regulate
the amount of transmitter in the junctional cleft.
Reboxetine in low concentrations (up to 10-6 M)
enhanced the contractions of carotid artery evoked by electrical field
stimulation (Fig. 1). This is
probably due to an inhibition of the uptake-1 mechanism. This view is
supported by the finding that reboxetine was a potent inhibitor of
[3H]norepinephrine uptake (Fig.
7) and that cocaine, a well known uptake-1 inhibitor, also
enhanced the neurogenic contractions (Fig.
1). In contrast to reboxetine and cocaine, desipramine did not
enhance the stimulation evoked contraction
(Fig. 1). The reason for this
is that desipramine, besides being an uptake-1 inhibitor, is a weak
-adrenoceptor antagonist (McCulloch
and Story, 1972; Hall and
ögren, 1981). At a high concentration
(10-4 M), reboxetine markedly reduced the
stimulation-evoked contractions (Fig.
1). This is most likely due to a postjunctional nonspecific
inhibitory action, because reboxetine noncompetitively reduced the
contractions evoked by phenylephrine, norepinephrine, and K+ (Figs.
9 and
10).
Reboxetine enhanced the [3H]norepinephrine release evoked by electrical field stimulation (Fig. 4). The enhancement is probably due to an inhibition of the uptake-1 mechanism. This is supported by the finding that reboxetine was a potent inhibitor of [3H]norepinephrine uptake by carotid artery (Fig. 7) (vide supra). Furthermore, the uptake-1 inhibitors cocaine and desipramine also enhanced the stimulation-evoked [3H]norepinephrine release (Fig. 4).
Reboxetine caused a more marked enhancement of
[3H]norepinephrine release than desipramine and cocaine
(Fig. 4). The rank order of the
maximum effect (Emax) was reboxetine > desipramine >
cocaine. The differences in the ability of these three drugs to enhance
[3H]norepinephrine release may well be related to the strength of
their binding to the uptake-1 mechanism. Cocaine and desipramine are both
competitive inhibitors of NET (Buck and
Amara, 1995). Both of these inhibitors can therefore be displaced
by the neurogenic norepinephrine. The more easily they can be displayed by
norepinephrine, the less enhancement will be observed. We have presented
evidence for the view that reboxetine is bound much more tightly to the
uptake-1 mechanism than cocaine (Fig.
8). This would therefore result in a more efficient inhibition of
uptake-1 with a resultant higher amount of norepinephrine in the junctional
gap leading to an increase in the 3H overflow.
All postganglionic sympathetic neurons are endowed with prejunctional
inhibitory 2-adrenoceptors (autoreceptors) that are
activated by released norepinephrine
(Starke, 1977). Inhibition of
uptake-1 in carotid artery by reboxetine most likely leads to an increase in
the junctional cleft concentration of norepinephrine with a correspondingly
increased activation of the autoreceptors. The reboxetine-induced enhancement
of stimulation-evoked [3H]norepinephrine release
(Fig. 4) may therefore have
been dampened. This would probably be more so at high concentrations of
reboxetine. The ability of cocaine to modulate the depolarization-evoked
norepinephrine release via prejunctional 2-adrenoceptors
depended inter alia on the concentration of cocaine, the stimulation intensity
(frequency and length of pulse train) and the geometry of the junctional cleft
(Nedergaard, 1986). This
conclusion was based on a study of the interaction between cocaine and
2-adrenoceptor antagonists. A similar interaction study
using reboxetine instead of cocaine remains to be done. Inhibition of
prejunctional 2-adrenoceptors located on vascular
sympathetic neurons by 2-adrenoceptor antagonists, such as
e.g., rauwolscine, enhances the stimulation-evoked
[3H]norepinephrine release
(Nedergaard, 1986). Because
reboxetine has poor affinity to 2-adrenoceptors
(Wong et al., 2000), it is
most unlikely that the reboxetine-evoked enhancement of
[3H]norepinephrine release (Fig.
4) could be due to 2-adrenoceptor
antagonism.
Desipramine and cocaine rapidly enhanced the stimulation-evoked [3H]norepinephrine release which was then maintained unchanged (Fig. 5). This indicates that the cumulative concentration-response curves for each of these two drugs (Fig. 4) represent equilibrium responses. In contrast, because the reboxetine-induced enhancement increased with time (Figs. 2 and 5), the cumulative concentration-response curve for reboxetine (Figs. 1 and 4) probably does not represent equilibrium responses.
In series with neuronal and extraneuronal uptake, MAO participates in the
metabolism of norepinephrine. Pargyline, a nonselective and irreversible
inhibitor of MAO, augmented the facilitatory effect of reboxetine and cocaine
(Fig. 6). The simplest
explanation for this is that pargyline removed an inactivation pathway for
released [3H]norepinephrine, both pre- and postjunctionally, which
resulted in an increased 3H overflow. It has been suggested that
concomitant therapy with reboxetine and a MAO inhibitor may increase the risk
of a hypertensive crisis (Scates and
Doraiswamy, 2000). This is supported by the positive interaction
between pargyline and reboxetine with regard to norepinephrine release.
The adrenergic neuron blocking agent bretylium reduced the contractions of
carotid artery evoked by electrical field stimulation
(Fig. 3). Bretylium is taken up
into the adrenergic neuron, presumably via the uptake-1 mechanism
(Nedergaard and Bevan, 1967;
Ross and Gosztong, 1975). The
ability of reboxetine and cocaine to prevent the bretylium-induced block
(Fig. 3) further supports the
view that reboxetine is an uptake-1 inhibitor and has a cocaine-like
action.
Reboxetine enhanced the contractions of carotid artery evoked by either
phenylephrine or norepinephrine (Fig.
9). The enhancement is most likely due to an inhibition of the
uptake-1 mechanism. Both norepinephrine
(Iversen, 1967) and
phenylephrine (Rawlow et al.,
1980) are substrates for this neuronal membrane carrier.
Furthermore, cocaine likewise caused an enhancement
(Fig. 9). High concentrations
of reboxetine antagonized in a noncompetitive manner the contractions evoked
by phenylephrine and K+ (Figs.
9 and
10). This suggests that
reboxetine in high concentrations has a nonspecific inhibitory action; the
mechanism of which remains to be explored.
Observations in a family with a genetic form of orthostatic intolerance
suggest that impairment in norepinephrine clearance can result from NET
dysfunction (Shannon et al.,
2000). Selective NET blockade by reboxetine in healthy subjects
created a phenotype that resembled idiopathic orthostatic intolerance
(Schroeder at al., 2002). In
this model reboxetine markedly increased sensitivity to phenylephrine;
probably as a result of central and peripheral effects of NET inhibition. The
sensitivity increase could in part be due a reduced elimination of
phenylephrine via the uptake-1 mechanism. This view is supported by our
finding that reboxetine enhanced the contractions of carotid artery evoked by
phenylephrine (Fig. 9).
Reboxetine markedly reduced the contractions evoked by tyramine
(Fig. 11). Tyramine is an
indirectly acting sympathomimetic amine that enters the neuron via the
uptake-1 mechanism (Trendelenburg,
1972). Reboxetine most likely blocked the ability of tyramine to
release norepinephrine from sympathetic neurons by preventing the entry of the
latter through the neurilemma, i.e., a cocaine-like action. This view is
supported by the finding that cocaine also reduced the tyramine-evoked
contractions (Fig. 11). This
was also the case with rabbit pulmonary artery
(Nedergaard, 1973).
In summary, the results suggest that reboxetine is a potent norepinephrine reuptake inhibitor of peripheral sympathetic neurons in rabbit carotid artery. Reboxetine probably inhibits the uptake-1 mechanism in the same manner as cocaine.
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Acknowledgements |
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Footnotes |
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
ABBREVIATIONS: NET, norepinephrine transporter; U-0521, 1-(3,4-dihydroxyphenyl)-2-methyl-1-propanone; PSS, physiological salt solution; MAO, monoamine oxidase; ANOVA, analysis of variance.
Address correspondence to: Dr. Ove A. Nedergaard, Department of Pharmacology, University of Southern Denmark, Winslowparken 21, DK-5000 Odense C, Denmark. E-mail: oanedergaard{at}health.sdu.dk
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References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Buck KJ and Amara SG (1995) Structural domains of catecholamine transporter chimeras involved in selective inhibition by antidepressants and psychomotor stimulants. Mol Pharmacol 48: 1030-1037.[Abstract]
Burns MJ (2000) The pharmacology and toxicology of atypical antipsychotic agents. J Toxicol Clin Toxicol 39: 1-14.
Burrows GD, Maguire KP, and Norman TR (1998) Antidepressant efficacy and tolerability of the selective norepinephrine reuptake inhibitor reboxetine: a review. J Clin Psychiatry 59 (Suppl 14): 4-7.
Golds PR, Przyslo FR, and Strange PG (1980) The binding of some antidepressant drugs to brain muscarinic acetylcholine receptors. Br J Pharmacol 68: 541-549.[Medline]
Green JP and Maayani S (1977) Tricyclic antidepressants block histamine H2 receptors in the brain. Nature (Lond) 269: 163-165.[CrossRef][Medline]
Hall H and ögren SO (1981) Effects of antidepressant drugs on different receptors in the brain. Eur J Pharmacol 70: 393-407.[CrossRef][Medline]
Iversen LL (1967) The Uptake and Storage of Noradrenaline in Sympathetic Nerves, Cambridge University Press, Cambridge.
Jensen TJ and Nedergaard OA (1999) Modulation of
norepinephrine release from sympathetic neurons of the rabbit aorta by
prejunctional prostanoid receptors. J Pharmacol Exp
Ther 291:
7-11.
Maxwell RA, Ferris RM, and Burscu JE (1976) Structural requirements for inhibition of noradrenaline uptake by phenylethylamine derivatives, desipramine, cocaine and other compounds, in The Mechanism of the Neuronal and Extraneuronal Transport of Catecholamines (Paton DM ed) pp 95-153, Raven Press, New York.
Maxwell RA, Keenan D, Chaplin E, Roth B, and Eckhardt SB
(1969) Molecular features affecting the potency of tricyclic
antidepressants and structurally related compounds as inhibitors of the uptake
of tritiated norepinephrine by rabbit aortic strips. J Pharmacol
Exp Ther 166:
320-329.
McCulloch MW and Story DF (1972) Antagonism of noradrenaline and histamine by desipramine in the isolated artery of the rabbit ear. Br J Pharmacol 46: 140-150.[Medline]
Melloni M, Carniel G, Torre AD, Bonsignori A, Buonamici M, Pozzi O,
Ricciardi S, and Rossi AC (1984) Potential antidepressant agents.
-Aryloxy-benzyl derivatives of ethanolamine and morpholine.
Eur J Med Chem 3:
235-242.
Melloni M, Torre AD, Lazzari E, Mazzini G, and Meroni M
(1985) Configurational studies on
2-[-(2-ethoxyphenoxy)benzyl]morpholine FCE 20124.
Tetrahedron 41:
1391-1399.
Miller DK, Wong EHF, Chesnut MD, and Dwaskin LP (2002)
Functional inhibition of monoamine transporters and nicotinic acetylcholine
receptors. J Pharmacol Exp Ther
302:
687-695.
Nedergaard OA (1973) Cocaine-like effect of ketamine on vascular adrenergic neurones. Eur J Pharmacol 23: 153-161.[CrossRef][Medline]
Nedergaard OA (1986) Presynaptic -adrenoceptor
control of transmitter release from vascular sympathetic neurons in vitro, in
New Aspects of the Role of Adrenoceptors in the Cardiovascular
System (Grobecker H, Philippu A, and Starke K eds) pp
24-32, Springer Verlag, Berlin.
Nedergaard OA (1989) Inhibition of 3H-noradrenaline accumulation by dopexamine hydrochloride in the isolated aorta of the rabbit. Naunyn-Schmiedeberg's Arch Pharmacol 340: 270-273.[Medline]
Nedergaard OA and Bevan JA (1967) Common mode of action of DMPP and bretylium on the response of vascular smooth muscle to transmitter nerve stimulation. Fed Proc 26: 293.
Nedergaard OA and Bevan JA (1971) Neuronal and extraneuronal uptake of adrenergic transmitter in the blood vessel, in Physiology and Pharmacology of Vascular Neuroeffector Systems (Bevan JA, Furchgott RF, Maxwell RA, and Somlyo AP eds) pp 22-34, S Karger, Basel.
Osswald W and Guimarães S (1983) Adrenergic mechanisms in blood vessels: morphological and pharmacological aspects. Rev Physiol Biochem Pharmacol 96: 53-122.[CrossRef][Medline]
Rasmussen LE and Nedergaard OA (2001) Effect of reboxetine on vascular sympathetic neuroeffector transmission in rabbit carotid artery. Proc West Pharmacol Soc 44: 269.
Rasmussen LE and Nedergaard OA (2002) Action of reboxetine on vascular sympathetic neuroeffector transmission. Pharmacologist 44 (Suppl 1): A151.
Rawlow A, Fleig H, Kurahashi K, and Trendelenburg U (1980) The neuronal and extraneuronal uptake and deamination of 3H-(-)-phenylephrine in the perfused rat heart. Naunyn-Schmiedeberg's Arch Pharmacol 314: 237-247.[CrossRef][Medline]
Riva M, Brunello N, Rovescalli AC, Galimberti R, Carfagna N, Carminati P, et al. (1989) Effect of reboxetine, a new antidepressant drug, on the central noradrenergic system: behavioural and biochemical studies. J Drug Rev 1: 243-253.
Ross SB and Gosztong T (1975) On the mechanism of the accumulation of 3H-bretylium in peripheral sympathetic nerves. Naunyn-Schmiedeberg's Arch Pharmacol 288: 283-293.[CrossRef][Medline]
Sánchez C and Hyttel J (1999) Comparison of the effect of antidepressants and their metabolites on reuptake of biogenic amines and on receptor binding. Cell Mol Neurobiol 19: 467-489.[CrossRef][Medline]
Scates AC and Doraiswamy PM (2000) Reboxetine: a selective norepinephrine reuptake inhibitor for the treatment of depression. Ann Pharmacother 34: 1302-1312.[Abstract]
Schroeder C, Tank J, Boschmann M, Diedrich A, Sharma AM, Biaggioni
I, Luft FC, and Jordan J. (2002) Selective norepinephrine
reuptake inhibition as a human model of orthostatic intolerance.
Circulation 105:
347-353.
Shannon JR, Flattem NL, Jordan J, Jacob G, Black BK, Biaggioni I,
et al. (2000) Orthostatic intolerance and tachycardia associated
with norepinephrine-transporter deficiency. N Engl J
Med 342:
541-549.
Starke K (1977) Regulation of noradrenaline release by presynaptic receptor systems. Rev Physiol Biochem Pharmacol 77: 1-124.[CrossRef][Medline]
Trendelenburg U (1972) Classification of sympathomimetic amines, in Catecholamines, Handbook of Experimental Pharmacology (Blaschko H and Muscholl E eds), vol 33, pp 336-362, Springer Verlag, Berlin.
Wong EHF, Sonders MS, Amara SG, Tinholt PM, Piercey MFP, Hoffmann
WP, Hyslop DK, Franklin S, Porsolt RD, Bonsignori A, et al.
(2000) Reboxetine: a pharmacologically potent, selective and
specific norepinephrine reuptake inhibitor. Biol
Psychiatry 47:
818-829.[CrossRef][Medline]
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,
reboxetine; 
desipramine; 
, cocaine. Vertical lines represent
± S.E.M. (n = 6; *, p < 0.05;
**, p < 0.01; ***, p < 0.001,
compared with untreated tissue).
,
10-7 M; 
, untreated. C, reboxetine: 
, cocaine alone; 
