Life Sciences Vol . 18, pp . 1459-1466, 1976 . Priated in the U .S .A .
Pergamon Preas
SELECTIVE IrTHIBITION OF SEROTONIN UPTAKE BY TRAZODONE, A NEW ANTIDEPRESSANT AGENT Snnio Stefanini, Fabfo Fadda*, Lucio Medda# and Gien Luigi Gessa Institute of Pharmacology, University of Cagliari, 09100 Cagliari, Italy # Institute of Physiology, IIniversity of Cagliari, 09100 Cagliari, Italy (Received in final form May 17, 1976)
Summary
The inh ibitory effect of trazodone, a non tricyclic antidepressant, on $-HT and catecholamiae uptake into the synaptosomal preparation from the rat brain was compared with that of chlorimipramine, The inhibition of $-HT uptake by trazodone is competitive with a Ki of 1,6 x 10'6 M, Trazodone inh ibits 3H-$-HT, 3H-N8 and 3H-DA uptake with an IC$0 of 1,4 x 10 -6 , 3,1 x 10-4 and $,2 x 10 -4 M, respectively, Therefore trazodone is 220 and 3~0 times more potent in inh ibiting $-HT than NE aad DA uptake, respectively, The respeetiv6 IC$0 values o~ chlorimipramine were 0,9 x 10 -~, 3,6 x 10 - and 4,0 x 10- M for 3H-$-HT, 3H-NE and 3H-DA, Trazodone 2- ~3- C4(m-chlorophenyl)1-piperazinyl~ -propyl} e-triazolo ~4,3-] -pirydin-3-(2H)one (Fig, 1), is a new antidepressant agent with analgetic and aaxiolytic properties (1-~),
HC~C ~CH
C
Hz H z
H
H ~N~ ~N H H H /C-C` yC-C,+ .HCI N-Ct ~H N-~r -C -C -N 0 H H H ~Ç- Ç Ç= ; H2 HZ 1i Cl
HC
1459
1460
Trazodona: Serotoaia Uptake Inhibitor
Vol . 18, No . 12
The mechanism of the anti depressant effect of tricyclic anti depressants has been explained with their inhibitory action on the neuronal membrane transport of norepinephrine (NE) (8-11) or serotonin ($-HT) (12-1$) is brain, $-HT uptake is less sensitive than NE uptake to the inhibition by tricyclic anti depressants (13-16) except for chlorimipramine which is more active in inhibiting $-HT uptake than NE uptake (16-18), Trazodone shares with imipramine and chlorimipramine several pharmacological actions : it potentiates the central effects of $-hydroxytryptophan (19-20), decreases brain $-hydroxyindoleacetic acid levels (21-22), prevents brain $-HT decrease produced by fenfluramine and blocks the uptake of $-HT by the rat platelets (23), These results led us to investigate whether trazodone might share with tricyclic anti depressants the property of inhibiting the uptake of 5-HT~ NE and dopamine (DA) into brain synaptosomes, Methods $-hydroxy G-3H tryptamine (11,1 Ci/mmol), 3H dopamine ($,6 Ci/mmol) and 1- ~-3H norepinephrine (9,$ Ci/mmol) were obtained from Radiochemical Centre, Ameraham, Trazodone HC1 was kindly donated by prof, Silvestrini of Angelini S,p,A,, Rome, Male Sprague-Dawley rata, weighing 200-2$0 g, users-eacx3 (iced by decapitation and the brain-stem (medulla oblongata, pons, mesencephalon), the basal ganglia and the cortex were rapidly dissected, Synaptosomes isolated from brain-stem basal ganglia and çortex were used for the uptake of 3H-$_~~3H-DA + 3H-$-HT and a H-NE respectively, Crude synaptosomel preparations Praction (P 2 ) were prepared from a 10~ homogenate of brain tissue in 0,32 M sucrose, as described by Gray and Whittaker (24), After preparation, the fraction (P 2 ) was resuspended in Krebs-Henseleit (2$) solution, containing 0,2 mg/ml ascorbic acid and 1,2$ x 10- $ M pargyüne, saturated with 9$% 02 and $~ C0 2 , A 0.1 ml suspension containing synaptosomes, corresponding to 0,2-0,3 mg protein, was added to each incubation vial containing 0 .~ ml Krebs-Henseleit solution and varying concentrations of the drugs under study to reach a volume of 0,9 ml, The pH of the mixture was 7,4, The synaptosomel suspension was the last component added, after which the incubation mixture was pre-incubated for ~ min at 37° C in a Dubnoff metabolic shaker, The radioactive monoamines were then added in a proper dilution to reach a final volume of 1 ml arsd the incubation continued for ~ min for the experiments with :SH-$HT and 3H-DA; and for 4 min for 3H-NE uptake experiments, The samples were then chilled with the addition of $ ml of ice-cold saline and the synaptosomes were isolated by filtration under vacuum on 0,4$ um Millipor filters, by using a Millipor manyfold sampling set, The filters were then washed with two $ ml volumes of ice-cold saline and placed in counting vials containing 10 ml mats-gel, The radioactivity was measured in a Packard Tri-Carb liquid scintillation spectrometer, Samples were also incubated at
Vol . 18, No . 12
1461
Trazodone : Sarotonin IIptalce Inhibitor
0°C for q.-~ min to correct for " non specific uptake of monoamines to synaptosomes, Results are expressed as the difference between amine uptake at 37 ° C and absorption at 0°C, Values at 0°C account for about 1/5 of the radioactivity present at 37 °C, Proteins were determined by tie method of Lowry (26), Results The inhibitory effect of trazodone on $-HT and catechola~ni ne uptake into the synaptosomal preparation was compared with that of chlo.rimipramine, Trazodone blocked the uptake of 3H-5-HT into brain stem and stristal sinaptosomes exhibiting the same IC50 of 1,4 x 10 -6M, In comparison s the ICAO of chlorimipramine was 0,9 x 10-~M, Therefore trazodone was 1/15 as potent than chlorimipramine in inhibiting $-HT uptake, Moreover, trazodone was much less effective in inhibitiog the uptake of DA and of NE, Thus the IC~0 of trazodone for H-NE uptake was 3,1 x 10 M and the IC50 for .sH-DA uptake was 5,2 x 10 -4M, On the other hand, the IC59 values of chlorimipramine for NE and DA uptake were 3,6 x 10-~M~ respectively (Table 1), It appears that trazodone inhibits the uptake of $-HT 3~0 and 220 more effectively than that of DA and NE, respectively, In this respect s trazodone is much more selective than chlorimipramine, TABLE 1 Drug
Brain-Stem 3H- 5-f1T Ic So 6
Cortex 3H-NE IcSo
Trazodone
1,¢ x 10
Chlorimipramiae
0,9 x 10 ~ M
M
3,1x 3,6
10 4 M
x 10 6 M
Corpus-Striatum 3H-DA IcSo
5,2x 5,O X
10 4 M 10 6 M
Inhibition of 5-HT and catecholamines uptake into brain syaaptoeomes by trazodone and chlorimipramine, Synaptosomes from the striatum brain stem or cortex were incubated with drugs in concentration ranging from $,0 x 10-4 M to 5,0 x 10-8 M and with 1,8 x 10- ~~ 2,9 x 10-7 M concentrations of 3H-NE B 3H-5-HT and 3HDA~ respectively, Values are presented as the molar concentration of drugs that produced $0 percent inhibition of amine accumulation and were calculated on log, probability paper, Data presented are the means of 3 independent determinations made in triplicate for which the S,E, of the means were not greater than 10 percent of the IC50 value, In order to determine the nature of the inhibition of 5-~ uptake by trazodone we performed kinetic experiments using the Lineweaver-Burk plot (2~) and s/v s plot, The inhibition
1462
Traaodona : Serotonia Uptake Inhibitor
Vol . 18, No . 12
constant (Ki) was determined as described by Dixon and Webb (28), In our experimental conditiona l in the presence of 3H-$-HT concentrations ranging from 0,1 to 1,0 x- 10-~ M~ 5-HT uptake process was characterized by a Km of 0,8q x 10 M and a Vmax of ¢1,6 nmol/g/~ min, The inhibition by trazodone was competitive (Fig, 2-3) with an apparent Ki of 1,6 x 10-6 M,
c É w
v _e Z
i/~
+/s-FIT " 1d'
FIG, 2 Liaeweaver-Bark kinetic analysis of the effect of trazodone on the transport of 3H-5-HT into rat brain-stem synaptosomes, Synaptosomes were preincubated with 1,0 x 10-6 M of trazodone for min prior to the addition of various concentrations of 3H-5-HT, The incubation was continued for ~ min and then terminated as described in the "Methodsn, Amine uptake (v) is expressed as nmol of 3H/g pellet/q min, The various points are means of at least five experiments performed in triplicate, Standard errors are ~q~ for the means of all points, Discussion The results show that trazodone is a specific and competitive inhibitor of 5-HT uptake into brain synaptosomes , Although the compound is 1/15 as potent than chlorimipramine in inhibiting $-HT uptake s it is much more selective than the latter is inhibiting the uptake of this amine in respect to that of catecholamines, In fact, trazodone inhibits 5-HT uptake 3~0 and 220 times more effectively than that of DA and N8~ respectively, The ratio of potency of chlorimipramine for inhibiting 5-HT versus catecholamine uptake is ¢0 for NB and ¢¢ for DA, 6 Concentrations~of trazodone ranging from 5 x 10 to
Vol .
18,
No .
12
Trazodone :
146 3
3arotonia IIptake Inhibitor
a~a
asr
,
,~s .
sw
FIG, 3 s/v s plot to determine the influence of trazodoae on the 3H-$-HT uptake into rat brain-ate~m synaptosomes, The amine uptake (v) is expressed as nmol of 3H/g pellet/7 min, Experimental details are presented in "Methods", Each point represents the mean of four experiments performed in triplicate, Standard errors are ~9~ for the means of all points, 6 0,4 x 10 M have been shown to be present in the rat brain from 20 min to 6 hours after a single oral dose of 20 mgfICg (29), Therefore, it is likely that trazodoae blocks $-HT uptake in vivo as well as in vitro, The finding, that this compound potentiates the central actions of 5-hydroxytryptophan ($-HTP) and protects against 5-HT depletion by fenfluramine supports this view, The ability of trazodoae to inhibit 5-HT uptake by the serotoain nerve terminals in vivo might be involved in the anti depressant or the analgetic action of the drug, In fact, indirect evidence suggests that a deficiency in brain $-HT activity plays a role in the patho genesis of mental depression (30, 31) and brain 5-HT seems to be 3sivolved in the control of pain perception (32-34) and in the action of narcotic analgetics (35, 36), Recently, it has bean suggested that endogenous depressed patients might be divided in two subgroups with deficiency of noradreneraic and serotoninergic function, respectively (30), It might be worthwhile to study whether patients helped by trazodoae belong to the second group Finally, the use of such a specific inhibitor of the 5-HT uptake system might be'helpful is studies aimed at elucidating the role of $-HT in the CNS and the mechanisms of its inactivation, Aclmowledgements This study was supported by Angelini S,p,A,, Rome, Italy, References 1, C, ALTISSIDiI, M,P, MASTROSTEFANO and L, 3IGNORE, Acta Aaeathesiol, 22, 587-598 (1971) .
1464
Vol . 18, No . 12
Trazodone : Serotoain IIptake Inhibitor
2, A, REGGIANI, G. MARTINI and A, DIONISIO, Clinica Europea _11, 293-309 (1972), 3, C, CIANCHETTI and G, GIANOTTI, Gazzetta Later, Medicina e Chirurgia ~, 24 bis, 1-10 (1969), 4 . T,A, BAN, M,M, AMIN, N,P,V, NAIR and F, ENGELSON, in Trazodone, Proceedings of the First International Symposium Montreal 4, 110-126, Edit, : T,A, Ban, Montreal, and B, Silvestrini, Rome, (1974) . 5. F, CIOFFI, G . MATTIOLI, 0, POZZI and F, R~TALDI, Rassegna Intern, di Clinica e Terapia 4Q, 1 483-1487 (1969) .
6, L,E, HOLLISTER and J,E, OVERALL, Psychosomatics 6, (1965) .
361-36$
7 . B, SILYESTRINI and B,E, QUADRI, Europ, J, Pharmacol, 12, 231235 (1970) . 8, H,J, DENGLER, H,E, SPIEGEL and E,o, TTTUS, Nature (1961), 9, J, GLOWINSKI and J, AXELROD, Nature ~,
~1, 816-817
1318-1319 (1964) .
10, A,I, SALAMA, J,R, INSALACO and R,A, MAXWELL, J, Pharmacol, Exp, Therap, ~, 474-481 (1971), il, S,B, ROSS and A,L, RENYI, Europ, J, Pharmacol, 2, 181-186 (1967), 12, S,B, ROSS and A,L, RENYI, Life Sciences 6, 1407-141$ (1967), 13, S,B, ROSS and A,L, RENYI, Europ, J, Pharmacol, Z, 270-277 (1969), 14, E, SHASKAN and S,H, SNYDER, J, Pharmacol, Exp, Therap, 404-418 (1970) . 1$, A, CARLSSON, J, Pharm, Pharmacol, 22, 729-732 (1970), 16, A, CARLSSON, H, CORRODI, K, FUXE and T, HOKFELT, Europ, J, Pharmacol, ~, 357-3b6 (1969), 17, A, CARLSSON, K, FUäE and U, UNGERSTEDT, J, Pharm, Pharmacol, 20, 1,50 (1968), 18, S,B, ROSS and A,L, RENYI, Europ, J, Pharmacol, ~., 107-112 (1972) . 19, V,G, LONGO and A, SCOTTI DE CAROLIS, in Trazodone : Mod, Probl, Pharmacopsychiat, 4, 4-10, Edit, : Th,A, Ban, Montreal, and B, Silvestrini, Rome (1974), 20 . J.B, BOISSIER, E, PORTMAN-CRISTESCO, P, SOUBRIE~ and J, FICHEL LE, in Trazodone : Mod . Probl, Pharmacopsychiat, 4, 18-22, Edit, Th,A, Ban, Montreal, and B, Silvestrini, Rome (1974),
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Trasodoae : Serotonia Uptake Inhibitor
1465
21, K, YAMATSU, T, KANEKO, Y, YAMANISHI, A, KITAHARA and S, OHTAKE in Trazodone : Mod, Probl, Pharmacopsychiat, 4, 11-17, Edit, : Th,A, Ban, Montreal, and B, Silvestrini, Rome (1974),
22 . L . ANGELUCCI and P, BOLLE, in Trazodone : Mod, Probl, Pharmacopsychiat, 4, 65-75 . Edit, : Th,A, Ban, Montreal, and B, Silvestrini, Rome (1974), 23 . S, GARATTINI, G, DE GAETANO, R, SAMANIN, S, BERNASCONI and M, C, RONCAGLIONI, Biochem, Pharmacol, 2~, 13-16 (1976), 24 . E,G, GRAY and V,P, WHITTAKER, J, Anat, 46, 79-85 (1962) " 25, H,A, KREBS and K, HENSELEIT, Hoppe-Syler~s Z, Physiol, Chem, 2~, 193 (1964) . 26 . O .H, LOWRY, N, ROSEBROUGH, A, FARR and E, RANDALL~ J, Biol, Chem, ~3., 265-276 (i9$1),
27, H, LINEWEAVER and D, BURK, J . Amer, Chem, Soc, ~, 685 (1934) . 28, M. DIZON and E,C, WEBB, °Enzymes New York (1964),
327-329, Academic Preen,
29, T, FUJITA, C, YAMATO, T, TAKAHASHI and S, OHTAKS, in Trazodone,( Mod ; Probl, Pharmacopsychiat, 4, 56-64, Edit, : Th,A, Ban, Montreal, and B . Silvestrini, Rome (1974), 30, H,M, VAN PRAAG, Advances in Biochem, Psychopharm, 11, 357-368, Raven Press, New York (1974) . 31, M, ASBERG, L . BERTILSSON, D, TUCK S B, CRONHOLM and F, SJOQVIST, Clin, Pharmacol, and Therap, 1~, 277 (1973), 32, R. SAMANIN, W, GOMULKA and L, VALZSLLI, Europ, J, Pharmacol, 10, 339-343 (1970) .
33 . R. SAMANIN and L, VALZELLI, Europ, J, Pharmacol, 16, 298-302 (1971) " 34 . S . TENEN, Psychopharmacologia 12, 278-28$ (1968),
35 . S . TENEN, Peychopharmacologia 10, 204-219 (19b7) . 36 . E,L, WAY, Fed, Proc, ~1, 113-120 (1g72),
Pergamon Preas
SELECTIVE IrTHIBITION OF SEROTONIN UPTAKE BY TRAZODONE, A NEW ANTIDEPRESSANT AGENT Snnio Stefanini, Fabfo Fadda*, Lucio Medda# and Gien Luigi Gessa Institute of Pharmacology, University of Cagliari, 09100 Cagliari, Italy # Institute of Physiology, IIniversity of Cagliari, 09100 Cagliari, Italy (Received in final form May 17, 1976)
Summary
The inh ibitory effect of trazodone, a non tricyclic antidepressant, on $-HT and catecholamiae uptake into the synaptosomal preparation from the rat brain was compared with that of chlorimipramine, The inhibition of $-HT uptake by trazodone is competitive with a Ki of 1,6 x 10'6 M, Trazodone inh ibits 3H-$-HT, 3H-N8 and 3H-DA uptake with an IC$0 of 1,4 x 10 -6 , 3,1 x 10-4 and $,2 x 10 -4 M, respectively, Therefore trazodone is 220 and 3~0 times more potent in inh ibiting $-HT than NE aad DA uptake, respectively, The respeetiv6 IC$0 values o~ chlorimipramine were 0,9 x 10 -~, 3,6 x 10 - and 4,0 x 10- M for 3H-$-HT, 3H-NE and 3H-DA, Trazodone 2- ~3- C4(m-chlorophenyl)1-piperazinyl~ -propyl} e-triazolo ~4,3-] -pirydin-3-(2H)one (Fig, 1), is a new antidepressant agent with analgetic and aaxiolytic properties (1-~),
HC~C ~CH
C
Hz H z
H
H ~N~ ~N H H H /C-C` yC-C,+ .HCI N-Ct ~H N-~r -C -C -N 0 H H H ~Ç- Ç Ç= ; H2 HZ 1i Cl
HC
1459
1460
Trazodona: Serotoaia Uptake Inhibitor
Vol . 18, No . 12
The mechanism of the anti depressant effect of tricyclic anti depressants has been explained with their inhibitory action on the neuronal membrane transport of norepinephrine (NE) (8-11) or serotonin ($-HT) (12-1$) is brain, $-HT uptake is less sensitive than NE uptake to the inhibition by tricyclic anti depressants (13-16) except for chlorimipramine which is more active in inhibiting $-HT uptake than NE uptake (16-18), Trazodone shares with imipramine and chlorimipramine several pharmacological actions : it potentiates the central effects of $-hydroxytryptophan (19-20), decreases brain $-hydroxyindoleacetic acid levels (21-22), prevents brain $-HT decrease produced by fenfluramine and blocks the uptake of $-HT by the rat platelets (23), These results led us to investigate whether trazodone might share with tricyclic anti depressants the property of inhibiting the uptake of 5-HT~ NE and dopamine (DA) into brain synaptosomes, Methods $-hydroxy G-3H tryptamine (11,1 Ci/mmol), 3H dopamine ($,6 Ci/mmol) and 1- ~-3H norepinephrine (9,$ Ci/mmol) were obtained from Radiochemical Centre, Ameraham, Trazodone HC1 was kindly donated by prof, Silvestrini of Angelini S,p,A,, Rome, Male Sprague-Dawley rata, weighing 200-2$0 g, users-eacx3 (iced by decapitation and the brain-stem (medulla oblongata, pons, mesencephalon), the basal ganglia and the cortex were rapidly dissected, Synaptosomes isolated from brain-stem basal ganglia and çortex were used for the uptake of 3H-$_~~3H-DA + 3H-$-HT and a H-NE respectively, Crude synaptosomel preparations Praction (P 2 ) were prepared from a 10~ homogenate of brain tissue in 0,32 M sucrose, as described by Gray and Whittaker (24), After preparation, the fraction (P 2 ) was resuspended in Krebs-Henseleit (2$) solution, containing 0,2 mg/ml ascorbic acid and 1,2$ x 10- $ M pargyüne, saturated with 9$% 02 and $~ C0 2 , A 0.1 ml suspension containing synaptosomes, corresponding to 0,2-0,3 mg protein, was added to each incubation vial containing 0 .~ ml Krebs-Henseleit solution and varying concentrations of the drugs under study to reach a volume of 0,9 ml, The pH of the mixture was 7,4, The synaptosomel suspension was the last component added, after which the incubation mixture was pre-incubated for ~ min at 37° C in a Dubnoff metabolic shaker, The radioactive monoamines were then added in a proper dilution to reach a final volume of 1 ml arsd the incubation continued for ~ min for the experiments with :SH-$HT and 3H-DA; and for 4 min for 3H-NE uptake experiments, The samples were then chilled with the addition of $ ml of ice-cold saline and the synaptosomes were isolated by filtration under vacuum on 0,4$ um Millipor filters, by using a Millipor manyfold sampling set, The filters were then washed with two $ ml volumes of ice-cold saline and placed in counting vials containing 10 ml mats-gel, The radioactivity was measured in a Packard Tri-Carb liquid scintillation spectrometer, Samples were also incubated at
Vol . 18, No . 12
1461
Trazodone : Sarotonin IIptalce Inhibitor
0°C for q.-~ min to correct for " non specific uptake of monoamines to synaptosomes, Results are expressed as the difference between amine uptake at 37 ° C and absorption at 0°C, Values at 0°C account for about 1/5 of the radioactivity present at 37 °C, Proteins were determined by tie method of Lowry (26), Results The inhibitory effect of trazodone on $-HT and catechola~ni ne uptake into the synaptosomal preparation was compared with that of chlo.rimipramine, Trazodone blocked the uptake of 3H-5-HT into brain stem and stristal sinaptosomes exhibiting the same IC50 of 1,4 x 10 -6M, In comparison s the ICAO of chlorimipramine was 0,9 x 10-~M, Therefore trazodone was 1/15 as potent than chlorimipramine in inhibiting $-HT uptake, Moreover, trazodone was much less effective in inhibitiog the uptake of DA and of NE, Thus the IC~0 of trazodone for H-NE uptake was 3,1 x 10 M and the IC50 for .sH-DA uptake was 5,2 x 10 -4M, On the other hand, the IC59 values of chlorimipramine for NE and DA uptake were 3,6 x 10-~M~ respectively (Table 1), It appears that trazodone inhibits the uptake of $-HT 3~0 and 220 more effectively than that of DA and NE, respectively, In this respect s trazodone is much more selective than chlorimipramine, TABLE 1 Drug
Brain-Stem 3H- 5-f1T Ic So 6
Cortex 3H-NE IcSo
Trazodone
1,¢ x 10
Chlorimipramiae
0,9 x 10 ~ M
M
3,1x 3,6
10 4 M
x 10 6 M
Corpus-Striatum 3H-DA IcSo
5,2x 5,O X
10 4 M 10 6 M
Inhibition of 5-HT and catecholamines uptake into brain syaaptoeomes by trazodone and chlorimipramine, Synaptosomes from the striatum brain stem or cortex were incubated with drugs in concentration ranging from $,0 x 10-4 M to 5,0 x 10-8 M and with 1,8 x 10- ~~ 2,9 x 10-7 M concentrations of 3H-NE B 3H-5-HT and 3HDA~ respectively, Values are presented as the molar concentration of drugs that produced $0 percent inhibition of amine accumulation and were calculated on log, probability paper, Data presented are the means of 3 independent determinations made in triplicate for which the S,E, of the means were not greater than 10 percent of the IC50 value, In order to determine the nature of the inhibition of 5-~ uptake by trazodone we performed kinetic experiments using the Lineweaver-Burk plot (2~) and s/v s plot, The inhibition
1462
Traaodona : Serotonia Uptake Inhibitor
Vol . 18, No . 12
constant (Ki) was determined as described by Dixon and Webb (28), In our experimental conditiona l in the presence of 3H-$-HT concentrations ranging from 0,1 to 1,0 x- 10-~ M~ 5-HT uptake process was characterized by a Km of 0,8q x 10 M and a Vmax of ¢1,6 nmol/g/~ min, The inhibition by trazodone was competitive (Fig, 2-3) with an apparent Ki of 1,6 x 10-6 M,
c É w
v _e Z
i/~
+/s-FIT " 1d'
FIG, 2 Liaeweaver-Bark kinetic analysis of the effect of trazodone on the transport of 3H-5-HT into rat brain-stem synaptosomes, Synaptosomes were preincubated with 1,0 x 10-6 M of trazodone for min prior to the addition of various concentrations of 3H-5-HT, The incubation was continued for ~ min and then terminated as described in the "Methodsn, Amine uptake (v) is expressed as nmol of 3H/g pellet/q min, The various points are means of at least five experiments performed in triplicate, Standard errors are ~q~ for the means of all points, Discussion The results show that trazodone is a specific and competitive inhibitor of 5-HT uptake into brain synaptosomes , Although the compound is 1/15 as potent than chlorimipramine in inhibiting $-HT uptake s it is much more selective than the latter is inhibiting the uptake of this amine in respect to that of catecholamines, In fact, trazodone inhibits 5-HT uptake 3~0 and 220 times more effectively than that of DA and N8~ respectively, The ratio of potency of chlorimipramine for inhibiting 5-HT versus catecholamine uptake is ¢0 for NB and ¢¢ for DA, 6 Concentrations~of trazodone ranging from 5 x 10 to
Vol .
18,
No .
12
Trazodone :
146 3
3arotonia IIptake Inhibitor
a~a
asr
,
,~s .
sw
FIG, 3 s/v s plot to determine the influence of trazodoae on the 3H-$-HT uptake into rat brain-ate~m synaptosomes, The amine uptake (v) is expressed as nmol of 3H/g pellet/7 min, Experimental details are presented in "Methods", Each point represents the mean of four experiments performed in triplicate, Standard errors are ~9~ for the means of all points, 6 0,4 x 10 M have been shown to be present in the rat brain from 20 min to 6 hours after a single oral dose of 20 mgfICg (29), Therefore, it is likely that trazodoae blocks $-HT uptake in vivo as well as in vitro, The finding, that this compound potentiates the central actions of 5-hydroxytryptophan ($-HTP) and protects against 5-HT depletion by fenfluramine supports this view, The ability of trazodoae to inhibit 5-HT uptake by the serotoain nerve terminals in vivo might be involved in the anti depressant or the analgetic action of the drug, In fact, indirect evidence suggests that a deficiency in brain $-HT activity plays a role in the patho genesis of mental depression (30, 31) and brain 5-HT seems to be 3sivolved in the control of pain perception (32-34) and in the action of narcotic analgetics (35, 36), Recently, it has bean suggested that endogenous depressed patients might be divided in two subgroups with deficiency of noradreneraic and serotoninergic function, respectively (30), It might be worthwhile to study whether patients helped by trazodoae belong to the second group Finally, the use of such a specific inhibitor of the 5-HT uptake system might be'helpful is studies aimed at elucidating the role of $-HT in the CNS and the mechanisms of its inactivation, Aclmowledgements This study was supported by Angelini S,p,A,, Rome, Italy, References 1, C, ALTISSIDiI, M,P, MASTROSTEFANO and L, 3IGNORE, Acta Aaeathesiol, 22, 587-598 (1971) .
1464
Vol . 18, No . 12
Trazodone : Serotoain IIptake Inhibitor
2, A, REGGIANI, G. MARTINI and A, DIONISIO, Clinica Europea _11, 293-309 (1972), 3, C, CIANCHETTI and G, GIANOTTI, Gazzetta Later, Medicina e Chirurgia ~, 24 bis, 1-10 (1969), 4 . T,A, BAN, M,M, AMIN, N,P,V, NAIR and F, ENGELSON, in Trazodone, Proceedings of the First International Symposium Montreal 4, 110-126, Edit, : T,A, Ban, Montreal, and B, Silvestrini, Rome, (1974) . 5. F, CIOFFI, G . MATTIOLI, 0, POZZI and F, R~TALDI, Rassegna Intern, di Clinica e Terapia 4Q, 1 483-1487 (1969) .
6, L,E, HOLLISTER and J,E, OVERALL, Psychosomatics 6, (1965) .
361-36$
7 . B, SILYESTRINI and B,E, QUADRI, Europ, J, Pharmacol, 12, 231235 (1970) . 8, H,J, DENGLER, H,E, SPIEGEL and E,o, TTTUS, Nature (1961), 9, J, GLOWINSKI and J, AXELROD, Nature ~,
~1, 816-817
1318-1319 (1964) .
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