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On the mechanism of amphetamine potentiation by desipramine (DMI)
Vol . 5, pp . 2005-2010, 1966 " Life Sciences Printed in Great Britain.
Pergamon Preßs Ltd .
ON THE MECHANISM OF AMPHETAMINE POTENTIATION HY DESIPRAMINE (DMI)* Fridolin Sulser, Mary Langloia Ovens and James V. Dingen Department of Pharmacology, Vanderbilt University Sc~tool of Medicine and Paychopharmacology Research Center, Central State Hospital, Nashville, Tennessee
(Received 9 August 1966 ; in final form 31 August 1966) AMPHETAMINE appears to activate central adrenergic mechanisms .
It is, thus,
of interest that imipramine-like antidepressants enhance and prolong the behavioral effects of amphetamine in a variety of experimental situations (1, 2, .3, 4, 5, 6) .
These properties of imipramine-like drugs have been used
to formulate or support various hypotheses on the mode of their antidepressant action .
It is impossible, however, to draw meaningful conclusions on the
mechanism of action of a particular drug fran drug interaction studies, unless it is first established that one drug does not interfere with the distribution of metabolism of the other . The results of the present studies show that pretreatment with desipramine (DMI) leads to a marked and prolonged elevation of the levels of d-amphetamine in brain .
Consequently, the enhancement of the central actions of d-amphetamine
by DMI cannot be explained solely on the basis of a "sensitization" of central adrenergic mechanisms .
Methode and Materials Male Sprague-Dawley rata (180-2008) were used in all experiments . motor stimulation was measured in Williamson activity cages .
Psycho-
Since DMI inter-
feres in the determination of amphetamine by the methyl orange procedure of Axelrod (7) amphetamine-H3 sulfate was used in these studies .
*
D-amphetamine-H3
Supported by NIH Research Grant MH11468-01 from the United States Public Health Service . 2005
2006
AMPHÉTAMINE POT~TIATION
Vol .
5,
No .
21
sulfate (generally labeled, 4.28 c/mmol .) was obtained from New England Nuclear Corporation.
The drug was asagyed by a modification of the method of
Axelrod (7, 8) . Amphetamine-H3 was isolated fran alkalinized homogenates by extraction into benzene .
The benzene extract was washed with alkali to remove phenolic
metabolites and the amphetamine-H8 was returned to an aqueous phase by shaking the benzene extract with 1 N HC1.
An aliquot of the acid extract was
alkalinized and the amphetamine-H3 extracted into toluene .
The radioactivity
in the toluene was measured in a scintil7.ation spectrometer after the addition of phosphor (Liquifluor Concentrate, obtained from Nuclear Chicago Corp .) .
Results A single dose of DMI enhances and strikingly prolongs the psychomotor activity elicited by d~amphetamine (Fig . 1) .
For example, in rata pretreated
with DMI, d-amphetamine (3 mg/kg i .p .) elicits marked psychomotor stimulation as long as ten hours after its administration .
In contrast, in normal animals
the action of d~emphetamine persists onlvy about 3 hours with the maximum activity occuring at one hour . stimulation.
DMI, given alone, does not evoke a measurable
It is noteworthy that the potentiation of d-amphetamine action
by DMI is more striking when lower doses of d-amphetamine are used, whereas the prolongation by DMI is more pronounced when higher doses of the central stimulant are administered . To determine if this effect of DMI was a central phenomenon, rats were ir~jected with d-amphetamine-H8 sulfate .
The animals were killed at various
times after the administration of the drug and the brains analyzed for d~amphetamine ae described in Methode.
In both control and DMI pretreated
animals the levels of d-amphetamine in brain decreased logarithmically (Fig . 2) .
In animals pretreated with DMI, however, the brain levels of
d-amphetamine were not on>,vy higher than those of control animals but oleo
VoI . 5, No . 2I
AMPHETAMINE POTENTIATION
200
36 32 26 24 F 20 F 16 U a 12
F F v a
8 4 1
2
3
4 5 6 HOURS
7
8
9 10
1
2
3
4 3 6 HOURS
7
8
9 b
FIG . 1 Effect of DMI on Psychomotor Stimulation Elicited by D-Amphetamine (a) d-amphetamine alone (b) DMI + d-amphetamine The activity is expressed as integrated counts hour . mean of 6 to 20 animals .
0 declined at a slower rate .
0
Each value represents the
3 .0 mg/kg d-amphetamine 1.5 mg/kg d-amphetamine 0.75 mgJkg d-amphetamine
It is noteworthy that 6 hours after the
administration of d-amphetamine the levels of the drug in the brains of DMI pretreated rats are approximately the same as those in the brains of control rats at 1 hour .
Analysis of homogenates of the bodies of these animals
revealed that pretreatment with DMI also results in the maintenance of higher body levels of d-amphetamine (Table 1) .
Other tricyclic antidepressants can
also prolong the central actions of amphetamine .
Preliminary studies from this
laboratory have shown that protriptyline enhances the action of d-amphetamine and elevates its levels in brain .
Discussion It has been thought that the amphetamine enhancing action of imi.praminelike drugs reflects a "sensitization" at central adrenergic effector sites.
Vol . 5, No . 21
AMPHETAIdINE POTENTIATION
2006
~~
10 .00
AMPNETAIi11NE
o-~-a DMI +AMPNETANINE
W
Q W
L00
tI7 W _Z
a w x D.
a
.10 0
ao1 ~ 0
2
4 6 HOURS
B
10
FIG . 2 Effect of DMI (10 mg/kg i .p .) on Levels of D-Amphetamine in Brain DMI was given intraperitoneally 45 minutes before the administration of d-amphetamine (3 mg/kg i .p .) . Each point represents the average value from 6 rats . Vertical bare indicate the standard deviation.
TABLE 1 Effect of Pretreatment with DMI on Body Levels of D-Amphetamine DMI (10 mg/kg i.p .) was given 45 minutes before the administration of d-amphetamine (4,1 mg/kg i .p . as the sulfate salt). d-amphetamine sulfate I+g/g rat* 3 hr .
6 hr .
D-amphetamine
0 .33 + 0,13 (5)
0 .10 + 0 .01 (6)
DMI + d-amphetamine
2 .56 + 0 .56 (6)
0 .88 + 0 .22 (3)
* The values are expressed se the mean _+ S .D . parentheses .
The number of animals is in
Vol . 5, No . 21
AMPHETA~GINE POTENTIATION
2009
Since synthesis of brain norepinephrine appears to be a prerequisite for the central action of amphetamine (9,,10), it has been suggested that DMI blocks the reuptake of newly synthesized norepinephrine released by amphetamine and thus potentiates the central action of amphetamine .
The results of the present
studies call for a reinterpretation of some of the previous conclusions on the mechanism of the potentiation of amphetamine by imipramine derivatives . DMI is potent in enhancing and prolonging the central action of amphetamine .
This action of DMI is associated with a striking and sustained increase
in the concentration of d-amphetamine in brain .
Since pretreatment with DMI
also results in a striking increase in the body levels of d-amphetamine these findings suggest that DMI inhibits the metabolism of d-amphetamine in vivo . Valzelli et al . (11) assayed amphetamine by the methyl orange procedure or measured the total radioactivity in brain following the administration of amphetamine-H8 ,
The results of their studies also suggest that DMI prolongs
the action of d-amphetamine by inhibiting its metabolism in vivo . It is noteworthy that DMI appears to impair the metabolism of other drugs . For example, Sjtfgviat and Gillette (12) have presented data which suggest that DMI counteracts the effects of tremorine by decelerating the foxmation of oxotremorine and enhances the action of oxotremorine by inhibiting its inactivation . In conclusion, the reaulta of the present studies emphasise the importance of metabolic considerations in the proper interpretation of drug interaction studies . Acknowledgements-We thank Dr . Gertrude P . Quine, Geigy Research Laboratories, Ardsley, New York, for the generous supply of desipramine and Dr . Clement A . Stone, Merck Institute for Therapeutic Research, West Point, Pennsylvania, for a sample of protriptyline .
References l.
P .L . CARLTON, Paychopharmacolol~ia 2, .864 (1961) .
2.
R.T . HILL, I . KOOSIS, N.W . MINOR and E .B . SIGG~ Phaxmacologist 3, 75 (1961) .
2010
A]I~IiETAMINE POTENTIATION
Vol .
5, No . 21
3.
L, STEIN and T . SEIFTER, Science 134, 286 (1961) .
4.
A, WEISSMAN, Phazmacologist 3, 60 (1961) .
5.
C,L . SCHECKEL and E . HOFF, Psychophaxroacolottia 5, 198 (1964) .
6.
F . SUISER M,H, BICKEL and B,B . BRODIE, J . Phaxmacol . Exp . Therap . 144, 321 (1964 .
7.
J . AXELROD, J . Phaxmacol . Exp . Therap . 110, 315 (1954) .
8.
R .P . MAICKEL, Personal Cosmunication .
9.
A, WEISSMAN, H .K . KOE and ST .S . TENEN, J . Pharmacol . Exp . Therap . 151, 339 (1966) .
10 .
F . SUISER P . D'ENCARNACAO, M .L, OWENS and J .V . DINGELL, Pharmacologist 8, 214 (1966 . -
11 .
L . VALZELLI~ S, CONSOLO and C . MORPURGO, Int . Symp . on Antidepressant Drugs, Milan 1966 (in press) .
12 .
F . SJSQVIST and J, GILLETTE, Life Sci . 4, 1031,(1965) .
Pergamon Preßs Ltd .
ON THE MECHANISM OF AMPHETAMINE POTENTIATION HY DESIPRAMINE (DMI)* Fridolin Sulser, Mary Langloia Ovens and James V. Dingen Department of Pharmacology, Vanderbilt University Sc~tool of Medicine and Paychopharmacology Research Center, Central State Hospital, Nashville, Tennessee
(Received 9 August 1966 ; in final form 31 August 1966) AMPHETAMINE appears to activate central adrenergic mechanisms .
It is, thus,
of interest that imipramine-like antidepressants enhance and prolong the behavioral effects of amphetamine in a variety of experimental situations (1, 2, .3, 4, 5, 6) .
These properties of imipramine-like drugs have been used
to formulate or support various hypotheses on the mode of their antidepressant action .
It is impossible, however, to draw meaningful conclusions on the
mechanism of action of a particular drug fran drug interaction studies, unless it is first established that one drug does not interfere with the distribution of metabolism of the other . The results of the present studies show that pretreatment with desipramine (DMI) leads to a marked and prolonged elevation of the levels of d-amphetamine in brain .
Consequently, the enhancement of the central actions of d-amphetamine
by DMI cannot be explained solely on the basis of a "sensitization" of central adrenergic mechanisms .
Methode and Materials Male Sprague-Dawley rata (180-2008) were used in all experiments . motor stimulation was measured in Williamson activity cages .
Psycho-
Since DMI inter-
feres in the determination of amphetamine by the methyl orange procedure of Axelrod (7) amphetamine-H3 sulfate was used in these studies .
*
D-amphetamine-H3
Supported by NIH Research Grant MH11468-01 from the United States Public Health Service . 2005
2006
AMPHÉTAMINE POT~TIATION
Vol .
5,
No .
21
sulfate (generally labeled, 4.28 c/mmol .) was obtained from New England Nuclear Corporation.
The drug was asagyed by a modification of the method of
Axelrod (7, 8) . Amphetamine-H3 was isolated fran alkalinized homogenates by extraction into benzene .
The benzene extract was washed with alkali to remove phenolic
metabolites and the amphetamine-H8 was returned to an aqueous phase by shaking the benzene extract with 1 N HC1.
An aliquot of the acid extract was
alkalinized and the amphetamine-H3 extracted into toluene .
The radioactivity
in the toluene was measured in a scintil7.ation spectrometer after the addition of phosphor (Liquifluor Concentrate, obtained from Nuclear Chicago Corp .) .
Results A single dose of DMI enhances and strikingly prolongs the psychomotor activity elicited by d~amphetamine (Fig . 1) .
For example, in rata pretreated
with DMI, d-amphetamine (3 mg/kg i .p .) elicits marked psychomotor stimulation as long as ten hours after its administration .
In contrast, in normal animals
the action of d~emphetamine persists onlvy about 3 hours with the maximum activity occuring at one hour . stimulation.
DMI, given alone, does not evoke a measurable
It is noteworthy that the potentiation of d-amphetamine action
by DMI is more striking when lower doses of d-amphetamine are used, whereas the prolongation by DMI is more pronounced when higher doses of the central stimulant are administered . To determine if this effect of DMI was a central phenomenon, rats were ir~jected with d-amphetamine-H8 sulfate .
The animals were killed at various
times after the administration of the drug and the brains analyzed for d~amphetamine ae described in Methode.
In both control and DMI pretreated
animals the levels of d-amphetamine in brain decreased logarithmically (Fig . 2) .
In animals pretreated with DMI, however, the brain levels of
d-amphetamine were not on>,vy higher than those of control animals but oleo
VoI . 5, No . 2I
AMPHETAMINE POTENTIATION
200
36 32 26 24 F 20 F 16 U a 12
F F v a
8 4 1
2
3
4 5 6 HOURS
7
8
9 10
1
2
3
4 3 6 HOURS
7
8
9 b
FIG . 1 Effect of DMI on Psychomotor Stimulation Elicited by D-Amphetamine (a) d-amphetamine alone (b) DMI + d-amphetamine The activity is expressed as integrated counts hour . mean of 6 to 20 animals .
0 declined at a slower rate .
0
Each value represents the
3 .0 mg/kg d-amphetamine 1.5 mg/kg d-amphetamine 0.75 mgJkg d-amphetamine
It is noteworthy that 6 hours after the
administration of d-amphetamine the levels of the drug in the brains of DMI pretreated rats are approximately the same as those in the brains of control rats at 1 hour .
Analysis of homogenates of the bodies of these animals
revealed that pretreatment with DMI also results in the maintenance of higher body levels of d-amphetamine (Table 1) .
Other tricyclic antidepressants can
also prolong the central actions of amphetamine .
Preliminary studies from this
laboratory have shown that protriptyline enhances the action of d-amphetamine and elevates its levels in brain .
Discussion It has been thought that the amphetamine enhancing action of imi.praminelike drugs reflects a "sensitization" at central adrenergic effector sites.
Vol . 5, No . 21
AMPHETAIdINE POTENTIATION
2006
~~
10 .00
AMPNETAIi11NE
o-~-a DMI +AMPNETANINE
W
Q W
L00
tI7 W _Z
a w x D.
a
.10 0
ao1 ~ 0
2
4 6 HOURS
B
10
FIG . 2 Effect of DMI (10 mg/kg i .p .) on Levels of D-Amphetamine in Brain DMI was given intraperitoneally 45 minutes before the administration of d-amphetamine (3 mg/kg i .p .) . Each point represents the average value from 6 rats . Vertical bare indicate the standard deviation.
TABLE 1 Effect of Pretreatment with DMI on Body Levels of D-Amphetamine DMI (10 mg/kg i.p .) was given 45 minutes before the administration of d-amphetamine (4,1 mg/kg i .p . as the sulfate salt). d-amphetamine sulfate I+g/g rat* 3 hr .
6 hr .
D-amphetamine
0 .33 + 0,13 (5)
0 .10 + 0 .01 (6)
DMI + d-amphetamine
2 .56 + 0 .56 (6)
0 .88 + 0 .22 (3)
* The values are expressed se the mean _+ S .D . parentheses .
The number of animals is in
Vol . 5, No . 21
AMPHETA~GINE POTENTIATION
2009
Since synthesis of brain norepinephrine appears to be a prerequisite for the central action of amphetamine (9,,10), it has been suggested that DMI blocks the reuptake of newly synthesized norepinephrine released by amphetamine and thus potentiates the central action of amphetamine .
The results of the present
studies call for a reinterpretation of some of the previous conclusions on the mechanism of the potentiation of amphetamine by imipramine derivatives . DMI is potent in enhancing and prolonging the central action of amphetamine .
This action of DMI is associated with a striking and sustained increase
in the concentration of d-amphetamine in brain .
Since pretreatment with DMI
also results in a striking increase in the body levels of d-amphetamine these findings suggest that DMI inhibits the metabolism of d-amphetamine in vivo . Valzelli et al . (11) assayed amphetamine by the methyl orange procedure or measured the total radioactivity in brain following the administration of amphetamine-H8 ,
The results of their studies also suggest that DMI prolongs
the action of d-amphetamine by inhibiting its metabolism in vivo . It is noteworthy that DMI appears to impair the metabolism of other drugs . For example, Sjtfgviat and Gillette (12) have presented data which suggest that DMI counteracts the effects of tremorine by decelerating the foxmation of oxotremorine and enhances the action of oxotremorine by inhibiting its inactivation . In conclusion, the reaulta of the present studies emphasise the importance of metabolic considerations in the proper interpretation of drug interaction studies . Acknowledgements-We thank Dr . Gertrude P . Quine, Geigy Research Laboratories, Ardsley, New York, for the generous supply of desipramine and Dr . Clement A . Stone, Merck Institute for Therapeutic Research, West Point, Pennsylvania, for a sample of protriptyline .
References l.
P .L . CARLTON, Paychopharmacolol~ia 2, .864 (1961) .
2.
R.T . HILL, I . KOOSIS, N.W . MINOR and E .B . SIGG~ Phaxmacologist 3, 75 (1961) .
2010
A]I~IiETAMINE POTENTIATION
Vol .
5, No . 21
3.
L, STEIN and T . SEIFTER, Science 134, 286 (1961) .
4.
A, WEISSMAN, Phazmacologist 3, 60 (1961) .
5.
C,L . SCHECKEL and E . HOFF, Psychophaxroacolottia 5, 198 (1964) .
6.
F . SUISER M,H, BICKEL and B,B . BRODIE, J . Phaxmacol . Exp . Therap . 144, 321 (1964 .
7.
J . AXELROD, J . Phaxmacol . Exp . Therap . 110, 315 (1954) .
8.
R .P . MAICKEL, Personal Cosmunication .
9.
A, WEISSMAN, H .K . KOE and ST .S . TENEN, J . Pharmacol . Exp . Therap . 151, 339 (1966) .
10 .
F . SUISER P . D'ENCARNACAO, M .L, OWENS and J .V . DINGELL, Pharmacologist 8, 214 (1966 . -
11 .
L . VALZELLI~ S, CONSOLO and C . MORPURGO, Int . Symp . on Antidepressant Drugs, Milan 1966 (in press) .
12 .
F . SJSQVIST and J, GILLETTE, Life Sci . 4, 1031,(1965) .