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Apomorphine antagonism of the elevation of homovanillic acid induced by antipsychotic drugs
Life Sciences Vol . 11, . Part I, pp. 805-613, 1972 . Printed in Great Britain
Pergamon Preen
APOI~RPEIIi~ AIiPAG~QISI~ OF TH8 BLSVATIOü INDIICSD BY AIaTIPSYCHOTIC DRIIGS
OF H~lDVANILLIC ACID
Robert A . Lahti, Barbara McAllister and Jan Wozniak The IIpjohn Company, CNB Research, Ralamazoo, .lüchigan
(Received 23 Mardi 1972; in final form 5 May 1972) su~Rx
Apomorphine was found to be effective in antagonising the homovanillic acid elevating activity of several antipeychotic agents . Increasing doses of chlorpromazine overcame the effect of apomorphine on homovaaillic acid sad demonstrated the competitive nature of these drugs for the dopamiaergic receptors . Several apomorphiaelike compounds, and amaatadine, did not exert the antagonistic effect displayed by apomorphine . The relationship of these effects to the production of extrapyramidal Bide effects and to antipeycho- . tic activity is briefly discussed. Apomorphine has been widely used as a tool in the search for antipeychotic drugs .
These drugs block the apomorphine induced gnawing behavior in mica
(i), the emesis produced in dogs by apomorphine (2), and block apomorphine induced stereotyped behavior is rate
(3) .
Apomorphine ie believed to stimulate dopaminergic receptors in the brain sad support for such activity has recently been provided by the finding that apomorphina is an affective agent in the treatment of Parkinsons disease (4), a disease in which a deficiency of dopamine ie believed to play a significant role .
A great deal of evidence for the apomorphine stimulatory effect oa dopa-
mine receptors -comes from biochemical data .
Apomorphine causes a decrease in
the turnover of dopamine in the brain (5) as well as a decrease in the production of homovanillic acid (6) (HVA), one of the major metabolites of dopamine, in the brain.
These metabolic effects of apomorphine are explained through the
concept that apomorphine stimulates dopaminergic receptors which in turn exert a feedback effect on the utilization and synthesis of dopamine (7) . The antipeychotic agents, on the other: hand, are believed to exertt a
805
808
Eüect ad Apomorphine on HVA Levels
Vol. 11, No. 13
dopaminergic blocking effect, which easily explains their ability to antagonize various behavioral changes brought about by apomorphine .
Biochemically, the
antipsychotice produce effects the opposite of apomorphine, namely an increase in the turnover of striatal dopamine (8) and an increase in HVA levels (9) . These effects are also explained through the concept of a feedback effect from the receptor to the preaynaptic neuron calling for an increased release of transmitter to overcome the blockade of the receptor (LO) .
Along with the in-
creased release of transmitter an increase in the enzyme tyrosine hydroxylase also occurs (11) . The present studies were carried out in an attempt to determine whether or not apomorphine could exert an antagonistic effect on the biochemical changes in dopamine brought about by the antipeychotic agents . Methods Aomovaaillic acid was extracted from four whole mouse braise by homogenizing the frozen brains in 6 ml of O .1N HC1 using a ground glass homogenizer . The homogenates were transferred to a centrifuge tube aad 2 ml of 5X Zn80 4 and 1 ml of 1N NaOH were added to the homogenates, the tubes were shaken and then centrifuged at 10,000g for 10 min .
The suparnataats were transferred to a
60 ml reagent bottle containing 1 .5 g of NaCl and 0 .4 ml of 6N HC1, 20 ml of ether was added and the samples were shaken for 5 min .
After shaking, a 15 ml
aliquot of ether was removed aad placed in a flask containing 3 ml of O .1N Trie buffer at pH 8 .0, samples were shaken for 5 min .
A 1 ml sample of the aqueous
layer was removed and HVA was determined fluorometrically by the method of Anden et al .
(12) .
An internal standard of 0 .5 ug of HVA was added to split
control samples which ware then carried through the entire procedure . covery of added HVA was approximately 80X .
The re-
Apomorphiae was administered sub-
cutaneously and other drugs intraperitoneally . Results and Discussion The data presented is Table 1 indicates that thiothixene at 2 mg/kg causes a profound increase in the amount of HVA present in the môuse brain .
Vol . il, No. 13
SHect ad Apomorphine on HYA Levels TABLE
807
1
$ffect of Various Doses of Apomorphine on the Thiothixene Induced Elevation in Homovanillic Acid .
Treatment
Dose
mg/kg
HVA ~yg/gm f SEM .09 f .05
Saline Thiothiaene
2 .0
.37 f .07
p< .O1
Thiothixene + Apomorphine
2 .0 +
2 .5
.31 f .06
NS*
Thiothixene + Apomorphine
2 .0 +
5 ..0
.24 f .07
.0
Thiothixene + Apomorphine
2 .0 + 10 .0
.20 f .03
p<.05*
Apomorphine
2 .5
.07 f .02
NS
Apomorphine
5 .0
.06 f .02
NS
Apomorphine
10 .0
.05 f .02
NS
*Data from this group was statistically evaluated with respect to thiothixene treated animals . Drugs were administered i .p . 1 hr before apomorphine and mica ware sacrificed 1 hr after apomorphine administration . Four brains were used per determination and 3 determinations were made par schedule . Apomorphine appears to be causing a decrease in HVA ; however, the change does not become statistically significant at any of the dosages used .
When
animals are given thiothixene followed by apomorphine, it becomes apparent that at 5 mg/kg apomorphine begins to exert a significant antagonistic affect on the elevation of HVA produced by thiothixene . The results of an evaluation of the affect of several different chemical classes of antipsychotics are presented in Table 2 .
A butyrophenone derivative
(haloperidol), a propylamine phenothiazine (chlorpromazine), a piperazine phenothiazine (trifluoperazine), and a thioxantheae derivative (thiothixene) were tasted for their effect on brain HVA and the effect of apomorphine on the increased HVA level .
All of the antipsychotice tested produced an increase in
HVA at fairly low doses and is each case apomorphine at 10 mg/kg e .c . antagonized the elevation in HVA . in HVA .
Apomorphine alone caused a significant decrease
These effects are cônsietent with the behavioral studies on the inter-
808
Egect ad Apomorphine on HYA Levels
Vol. 11, No .
is
actions of apomorphine with the antipsychotics (3) . TABLE
2
Effect of Apomorphine on the Elevation in HVA Induced by a Variety of Antipeychotic Agents .
Treatment
Dose mg/kg
HVA ug/gm f SEM 0 .15 f .O1
Saline Haloperidol
0 .25
0 .45 f .O1
p< .O1
Haloperidol + Apomorphine
0 .25 + 10
0 .13 f .04
p< .O1
Chlorpromazine
2 .0
0 .29 f .09
.01~<.05
Chlorpromazine + Apomorphine
2 .0 + 10
0 .14 f .O1
.01~< .05
Trifluoperazine
1 .0
0 .52 f .07
p< .O1
Trifluoperazine + Apomorphine
1 .0 + 10
0 .18 f .05
p< .O1
Thiothixene
2 .0
0 .35 f .14
.05~<.1
Thiothixene + Apomorphine
2 .0 + 10
0 .10 f .03
.01~<.05
0 .02 f .02
p< .O1
10 .0
Apomorphine
Drugs were administered i .p . 1 hr prior to apomorphine and mice were sacrificed 1 hr after apomorphine . Four mouse braise were used per determination and 3 determinations were made per schedule . Data from antipsychotic drug plus apomorphine treated groups were evaluated statistically with respect to the corresponding antipsychotic drug treated group . Attempts were made to determine whether or not other apomorphine-like compounds would also be effective in aatagoniziag the elevation in HVA produced by the antipsychotics .
Amantadine was also tested in this category since
it hoe been found to be effective is the treatment of Parkinsons disease (13) and it is believed to block the reuptake of dopamine into the presynaptic nerve ending (14) .
The data presented in Table 3 suggests that the structural epeci-
ficity is rather critical since morphine and bulbocapniae, which are somewhat similar in structure to apomorphine, did not exert the same antagonistic effect as did apomorphine .
The findings of a recent report showing that bulbocapnine
is similar in its pharmacological properties to the antipsychotic agents (15)
Eüect a~f Apomorphine on HVA Levels
Vol. 11, No . 13
809
would have predicted that bulbocapnine should not have antagonized the HVA effect, but perhaps should 6ava potentiated it .
Amantadine also proved to be
ineffective in reversing the HVA elevating activity of thiothixene . TABLE
Treatment
3
Dose mg/kg
Saline
HVA ug/gm ~ SEM 0 .13 t .10
Thiothixene
2 .0
0 .20 f .04
NS
Thiothixene + Apomorphine
2
+ 10
0 .06 f .05
p~ .05*
Thiothixene + Bulbocapnine
2
+ 10
0 .25 f .03
NS*
Thiothixene + Morphine
2
+ 10
0 .30 f .06
NS*
Thlothizena + Amantadine
2
+ 80
0 .26 f .04
N8*
Apomorphine
10
0 .00
N8
Bulbocapnine
10
0 .04 f .O1
NS
Morphine
10
0 .08 f .04
N3
Amantadine
80
0 .02 f .03
NS
*Evaluated by T-test with respect to thiothizene treated mice . Thiothixene was administered i.p . 1 hr prior to apomorphine-like drugs and all nice were sacrificed 1 hr after apomorphine-like drugs were administered . Four mouse brains were used per dntnrmination and three determinations warn made per schedule . The results presented thus far were obtained in mice in which the antipsychotic drugs ware administered prior to apomorphine.
The results presented
in Table 4 were obtained from mice to which apomorphina was given prior to the antipaychotic .
Increasing doses of chlorpromazine ware utilized to demonstrate
that the antipeychotic agent can overcome the blocking affect of apomorphine on BVA .
A dose of 4 mg/kg of chlorpromazine was able to largely overcome the
antagonistic effect of 10 mg/kg of apomorphine on HVA. The finding that increasing doses of apomorphine can overcome the effect of the antipsychotics on the elevation of HyA is is agreement with the data of VanRossum et al . (I6) who found that large doses of dopaniae injected into the
810
S`üect ~ Apomorphine on HVA Levels
Vol . 11, No . 13
caudate nucleus could overcome some of the behavioral effects of the antipeychotice .
In this study the elevation in HVA produced by the antipeychotice
was used as a measure of dopaminargic blocking activity .
Apomorphine was cap-
able of overcoming this blockade ae shown by decreasing the amount of HVA present in the brain .
Apomorphine could do this by several different mechanisms ;
an inhibition of monoamine oxidase which would block the converaioa of 3methoxy tyramine to HVA, by decreasing the release of dopamine through a feedback mechaaiem from the poet synaptic receptor, or by decreasing the synthesis of dopamine thereby making lees of the transmitter available for release, or apomorphine could have exerted its effect through a combination of these mechamama . TABLE
4
Effect of Various Doses of Chlorpromazine on the Antagonistic Effect Exerted by Apomorphina on Elevations is HVA .
Treatment
Dose mg/kg
Saline
HVA hg/gm f SEM 0 .12 f .04
Chlorpromazine Apomorphine + Chlorpromazine Chlorpromazine Apomorphine + Chlorpromazine Chlorpromazine Apomorphine + Chlorpromazine
1 .0 10
+ 1 .0
2 .0 10
+ 2 .0
4 .0 10
+ 4 .0
0 .28 f .04
p< .05
0 .06 f .02
p< .O1*
0 .29 f .O1
p< .05
0 .08 t .02
p< .O1*
0 .34 f .04
p< .05
0 .21 f .07
p< .5*
*Evaluated by T-test with respect to similar chlorpromazine treated mica . Apomorphine was administered (s .c .) 0 .5 hr prior to chlorpromazine aad all mice were sacrificed 2 hra after chlorpromazine had been administered . Four mice were used per determination and three determinations ware made par schedule . Conviacing evidence has been presented to show that apomorphine decreases the utilization of dopamine by usage of radioactive precursors of dopamine and measuring the rate of decay of radioactive dopamine (5) .
Apomorphine decreased
the rate of decay, which ie suggestive of a decrease utilization or release of
Yol . il, No. 13 the transmitter .
Eäect ad Apomorphine on HVA Levels
811
It has also been shown that apomorphine, at fairly high
doses, can inhibit the synthesis of dopamine is vivo (17) .
Whether this inhi-
bitory effect is through a feedback mechanism or through a direct effect of apomorphina on tyrosine hydroxylase could not be ascertained . In contrast to apomorphine, the aatipsychotics exert their effect oa HVA primarily through a feedback mechanism causing an increased release of dopamine in an attempt to overcome the receptor blocking activity of the antipeychotice . Bvidenca has also base presented elsewhere, which demonstrates that the antipsychotics also produce an increase is tyroeiae hydroxylase activity (11) concomitant with the increased utilization of dopamine .
On this basis, it would
seem that apomorphine's antagonistic effect on HVA may be through a combination of decreased release of dopamine and a decreased synthesis of dopamine .
The
later mechanism is probably not of great significance since it was shows that relatively large doses of apomorphine are needed for the inhibition of tyrosine hydroxylase is vivo (17) . The reversible nature of the effect of the antipsychotics and of apomorphiae . on HVA have been adequately demonstrated in this study .
When thiothixeae
was administered prior to apomorphine, and in all probability thiothixene was occupying the receptor before apomorphine, it was found that apomorphine could overcome the receptor blockade .
On the other hand, whoa apomorphine was admin-
istered first and allowed to occupy the receptor, it was found that chlorpromazine could overcome the effect of apomorphine by increasing the dose of chlorpromazine .
These effects seem to. imply that the observed drug effects are re-
versible and the interactions ~ra of a c.ampetitive nature . The antipsychotic agents have been show to produce an elevation in HVA which in turn can be antagonized by apomorphine, or as shown elsewhere by atropine (18), however it cannot ba determined by these results whether this effect is related to the production of extrapyramidal aide effects or to antipsychotic activity, or to both of these activities .
Presently, it would appear
that the elevation of HVA correlates best with the production of extrapyramidal
812
Sffect .od Apomorphine on HVA Levels
Vol. 11, No . 13
aide effects since thioridazine, which has a low propensity for the production of the extrapyram~dal effects, is not too affective is elevating HVA (18), nor is it very effective in antagonizing the behavioral effects of apomorphine (3) . The finding that atropine will antagonize the HVA elevating activity of the antipaychotica ae well se the production of extrapyramidal effects in mas while apparently not antagonizing the antipaychotic effects in man (19), would seem to imply that the HVA elevating activity and the anti-apomorphine activity of the antipaychotic agents ie batter related to the production of extrapyramidal effects than it is to their antipaychotic activity . Ackaowledgemeat-The following companies are acknowledged for generously supplying drug samples : Pfizer (thiothixeae) ; Smith, Rline and French (trifluoperazine and chlorpromazine) ; and McNeil Laboratories (haloperidol) . ßefereaces 1.
M. FE~TE and A . M . RIIßTI, J . Pharm . Pharmac . 22, 377 (1970) .
2.
& . P . HHARC~VA and 0 . CBANDBA, Brit . J . Pharmacol . 21, 436 (1963) .
3.
P . A . JANSSEN, C . J . F . NIS?fl:GESBB and R . H . L . SCHELLEIDaiS, ArzneimForsch . 15, 104 (1965) .
4.
J . BRAHAM, I . SAßOVA-PINAAS and Y. GOLDHAI~ß, Brit . Med . J . 3, 768 (1970) .
5.
H . NYBAC&, J . SCHUBEßT aad G . SEDVALL, J . Pharm . Pharmac . 22, 622 (1970) .
6.
B . ß00S, J . Pharm . Pharmac . 21, 263 (1969) .
7.
N . E . ANDEN, A, ßiTBBN3BN, R . F~ and T . HOSFSLT, J : Pharm . Pttaxmac . 19, 627 (1967) .
8.
N . NYBAC&, Z . BOßZECQ and G . SEDVALL, EulO~ . J . Pharmacol . 4, 395 (1968) .
9.
D . F . SHAßMAN, Brit . J . Pharmacol . 30, 620 (1967) .
10 .
M . DaPRAnA and A . PLETBCBBß, J . Pharm . Pharmac . 18, 628 (1966) .
11 .
H . MOSACGäIO in Sympoeium on Braie ChemietYV and Mental Diseaae , Houston, Texas Nov . 18-20 (1970) (to be published) .
12 .
N . E . ANDEN, B . E . ß00S and B . WEßDINIIIS, Life Sci . 7, 448 (1963) .
Vol. li, No . 13 13 .
ß.
SCHFiAB, A. C .
Aaeoc . 14 .
ENGLAI~, D . C . POSRANZSß
and
ß. ß . YOUNG,
813 J . Am. Med .
208, 1168 (1969) .
B. SCATTON, A . CHEBAMY, M. J . BBSSOti and Phaxmecol .
15 .
Effect ad Apomorphine on HVA Lévele
J . GLOFTINSRI,
Europ. J .
13, 131 (1970) .
P. SII~N, ß . Cf~ßMOT,
C . LßROUSS$ and J .
ß. HOISSISß,
Therapie
25, 939
(1970) . 16 .
J . M. van1t033UM in Modern Probleme of Pharmacopeychiatry , Ed . Bobon, P . A . J . Janeeen and J . Bobon, Vol . Basel,
17 .
5, p. 65 .
D. P.
3. Rargér A . G .,
(1970) .
M. GOLDBTEIN, L. S . FßSSDMAN and T. BACRSTßOM, J . Pharm . Phax~ac .
22,
715 (1970) . 18 .
ß . O'RSSFB, D. F .
SHAßMAN and M.
VOGT,
Brit . J . Pharmacol .
38, 287
(1970) . 19 .
L . JULOU in Modere Probleme of Pharmaçopevchiatry , 8d . P . A . J. Janseen and J . Bobon, Vol.
(1970) .
5, p . 50,
D.
P . Bobon,
S. Barger A . G., Basel,
Pergamon Preen
APOI~RPEIIi~ AIiPAG~QISI~ OF TH8 BLSVATIOü INDIICSD BY AIaTIPSYCHOTIC DRIIGS
OF H~lDVANILLIC ACID
Robert A . Lahti, Barbara McAllister and Jan Wozniak The IIpjohn Company, CNB Research, Ralamazoo, .lüchigan
(Received 23 Mardi 1972; in final form 5 May 1972) su~Rx
Apomorphine was found to be effective in antagonising the homovanillic acid elevating activity of several antipeychotic agents . Increasing doses of chlorpromazine overcame the effect of apomorphine on homovaaillic acid sad demonstrated the competitive nature of these drugs for the dopamiaergic receptors . Several apomorphiaelike compounds, and amaatadine, did not exert the antagonistic effect displayed by apomorphine . The relationship of these effects to the production of extrapyramidal Bide effects and to antipeycho- . tic activity is briefly discussed. Apomorphine has been widely used as a tool in the search for antipeychotic drugs .
These drugs block the apomorphine induced gnawing behavior in mica
(i), the emesis produced in dogs by apomorphine (2), and block apomorphine induced stereotyped behavior is rate
(3) .
Apomorphine ie believed to stimulate dopaminergic receptors in the brain sad support for such activity has recently been provided by the finding that apomorphina is an affective agent in the treatment of Parkinsons disease (4), a disease in which a deficiency of dopamine ie believed to play a significant role .
A great deal of evidence for the apomorphine stimulatory effect oa dopa-
mine receptors -comes from biochemical data .
Apomorphine causes a decrease in
the turnover of dopamine in the brain (5) as well as a decrease in the production of homovanillic acid (6) (HVA), one of the major metabolites of dopamine, in the brain.
These metabolic effects of apomorphine are explained through the
concept that apomorphine stimulates dopaminergic receptors which in turn exert a feedback effect on the utilization and synthesis of dopamine (7) . The antipeychotic agents, on the other: hand, are believed to exertt a
805
808
Eüect ad Apomorphine on HVA Levels
Vol. 11, No. 13
dopaminergic blocking effect, which easily explains their ability to antagonize various behavioral changes brought about by apomorphine .
Biochemically, the
antipsychotice produce effects the opposite of apomorphine, namely an increase in the turnover of striatal dopamine (8) and an increase in HVA levels (9) . These effects are also explained through the concept of a feedback effect from the receptor to the preaynaptic neuron calling for an increased release of transmitter to overcome the blockade of the receptor (LO) .
Along with the in-
creased release of transmitter an increase in the enzyme tyrosine hydroxylase also occurs (11) . The present studies were carried out in an attempt to determine whether or not apomorphine could exert an antagonistic effect on the biochemical changes in dopamine brought about by the antipeychotic agents . Methods Aomovaaillic acid was extracted from four whole mouse braise by homogenizing the frozen brains in 6 ml of O .1N HC1 using a ground glass homogenizer . The homogenates were transferred to a centrifuge tube aad 2 ml of 5X Zn80 4 and 1 ml of 1N NaOH were added to the homogenates, the tubes were shaken and then centrifuged at 10,000g for 10 min .
The suparnataats were transferred to a
60 ml reagent bottle containing 1 .5 g of NaCl and 0 .4 ml of 6N HC1, 20 ml of ether was added and the samples were shaken for 5 min .
After shaking, a 15 ml
aliquot of ether was removed aad placed in a flask containing 3 ml of O .1N Trie buffer at pH 8 .0, samples were shaken for 5 min .
A 1 ml sample of the aqueous
layer was removed and HVA was determined fluorometrically by the method of Anden et al .
(12) .
An internal standard of 0 .5 ug of HVA was added to split
control samples which ware then carried through the entire procedure . covery of added HVA was approximately 80X .
The re-
Apomorphiae was administered sub-
cutaneously and other drugs intraperitoneally . Results and Discussion The data presented is Table 1 indicates that thiothixene at 2 mg/kg causes a profound increase in the amount of HVA present in the môuse brain .
Vol . il, No. 13
SHect ad Apomorphine on HYA Levels TABLE
807
1
$ffect of Various Doses of Apomorphine on the Thiothixene Induced Elevation in Homovanillic Acid .
Treatment
Dose
mg/kg
HVA ~yg/gm f SEM .09 f .05
Saline Thiothiaene
2 .0
.37 f .07
p< .O1
Thiothixene + Apomorphine
2 .0 +
2 .5
.31 f .06
NS*
Thiothixene + Apomorphine
2 .0 +
5 ..0
.24 f .07
.0
Thiothixene + Apomorphine
2 .0 + 10 .0
.20 f .03
p<.05*
Apomorphine
2 .5
.07 f .02
NS
Apomorphine
5 .0
.06 f .02
NS
Apomorphine
10 .0
.05 f .02
NS
*Data from this group was statistically evaluated with respect to thiothixene treated animals . Drugs were administered i .p . 1 hr before apomorphine and mica ware sacrificed 1 hr after apomorphine administration . Four brains were used per determination and 3 determinations were made par schedule . Apomorphine appears to be causing a decrease in HVA ; however, the change does not become statistically significant at any of the dosages used .
When
animals are given thiothixene followed by apomorphine, it becomes apparent that at 5 mg/kg apomorphine begins to exert a significant antagonistic affect on the elevation of HVA produced by thiothixene . The results of an evaluation of the affect of several different chemical classes of antipsychotics are presented in Table 2 .
A butyrophenone derivative
(haloperidol), a propylamine phenothiazine (chlorpromazine), a piperazine phenothiazine (trifluoperazine), and a thioxantheae derivative (thiothixene) were tasted for their effect on brain HVA and the effect of apomorphine on the increased HVA level .
All of the antipsychotice tested produced an increase in
HVA at fairly low doses and is each case apomorphine at 10 mg/kg e .c . antagonized the elevation in HVA . in HVA .
Apomorphine alone caused a significant decrease
These effects are cônsietent with the behavioral studies on the inter-
808
Egect ad Apomorphine on HYA Levels
Vol. 11, No .
is
actions of apomorphine with the antipsychotics (3) . TABLE
2
Effect of Apomorphine on the Elevation in HVA Induced by a Variety of Antipeychotic Agents .
Treatment
Dose mg/kg
HVA ug/gm f SEM 0 .15 f .O1
Saline Haloperidol
0 .25
0 .45 f .O1
p< .O1
Haloperidol + Apomorphine
0 .25 + 10
0 .13 f .04
p< .O1
Chlorpromazine
2 .0
0 .29 f .09
.01~<.05
Chlorpromazine + Apomorphine
2 .0 + 10
0 .14 f .O1
.01~< .05
Trifluoperazine
1 .0
0 .52 f .07
p< .O1
Trifluoperazine + Apomorphine
1 .0 + 10
0 .18 f .05
p< .O1
Thiothixene
2 .0
0 .35 f .14
.05~<.1
Thiothixene + Apomorphine
2 .0 + 10
0 .10 f .03
.01~<.05
0 .02 f .02
p< .O1
10 .0
Apomorphine
Drugs were administered i .p . 1 hr prior to apomorphine and mice were sacrificed 1 hr after apomorphine . Four mouse braise were used per determination and 3 determinations were made per schedule . Data from antipsychotic drug plus apomorphine treated groups were evaluated statistically with respect to the corresponding antipsychotic drug treated group . Attempts were made to determine whether or not other apomorphine-like compounds would also be effective in aatagoniziag the elevation in HVA produced by the antipsychotics .
Amantadine was also tested in this category since
it hoe been found to be effective is the treatment of Parkinsons disease (13) and it is believed to block the reuptake of dopamine into the presynaptic nerve ending (14) .
The data presented in Table 3 suggests that the structural epeci-
ficity is rather critical since morphine and bulbocapniae, which are somewhat similar in structure to apomorphine, did not exert the same antagonistic effect as did apomorphine .
The findings of a recent report showing that bulbocapnine
is similar in its pharmacological properties to the antipsychotic agents (15)
Eüect a~f Apomorphine on HVA Levels
Vol. 11, No . 13
809
would have predicted that bulbocapnine should not have antagonized the HVA effect, but perhaps should 6ava potentiated it .
Amantadine also proved to be
ineffective in reversing the HVA elevating activity of thiothixene . TABLE
Treatment
3
Dose mg/kg
Saline
HVA ug/gm ~ SEM 0 .13 t .10
Thiothixene
2 .0
0 .20 f .04
NS
Thiothixene + Apomorphine
2
+ 10
0 .06 f .05
p~ .05*
Thiothixene + Bulbocapnine
2
+ 10
0 .25 f .03
NS*
Thiothixene + Morphine
2
+ 10
0 .30 f .06
NS*
Thlothizena + Amantadine
2
+ 80
0 .26 f .04
N8*
Apomorphine
10
0 .00
N8
Bulbocapnine
10
0 .04 f .O1
NS
Morphine
10
0 .08 f .04
N3
Amantadine
80
0 .02 f .03
NS
*Evaluated by T-test with respect to thiothizene treated mice . Thiothixene was administered i.p . 1 hr prior to apomorphine-like drugs and all nice were sacrificed 1 hr after apomorphine-like drugs were administered . Four mouse brains were used per dntnrmination and three determinations warn made per schedule . The results presented thus far were obtained in mice in which the antipsychotic drugs ware administered prior to apomorphine.
The results presented
in Table 4 were obtained from mice to which apomorphina was given prior to the antipaychotic .
Increasing doses of chlorpromazine ware utilized to demonstrate
that the antipeychotic agent can overcome the blocking affect of apomorphine on BVA .
A dose of 4 mg/kg of chlorpromazine was able to largely overcome the
antagonistic effect of 10 mg/kg of apomorphine on HVA. The finding that increasing doses of apomorphine can overcome the effect of the antipsychotics on the elevation of HyA is is agreement with the data of VanRossum et al . (I6) who found that large doses of dopaniae injected into the
810
S`üect ~ Apomorphine on HVA Levels
Vol . 11, No . 13
caudate nucleus could overcome some of the behavioral effects of the antipeychotice .
In this study the elevation in HVA produced by the antipeychotice
was used as a measure of dopaminargic blocking activity .
Apomorphine was cap-
able of overcoming this blockade ae shown by decreasing the amount of HVA present in the brain .
Apomorphine could do this by several different mechanisms ;
an inhibition of monoamine oxidase which would block the converaioa of 3methoxy tyramine to HVA, by decreasing the release of dopamine through a feedback mechaaiem from the poet synaptic receptor, or by decreasing the synthesis of dopamine thereby making lees of the transmitter available for release, or apomorphine could have exerted its effect through a combination of these mechamama . TABLE
4
Effect of Various Doses of Chlorpromazine on the Antagonistic Effect Exerted by Apomorphina on Elevations is HVA .
Treatment
Dose mg/kg
Saline
HVA hg/gm f SEM 0 .12 f .04
Chlorpromazine Apomorphine + Chlorpromazine Chlorpromazine Apomorphine + Chlorpromazine Chlorpromazine Apomorphine + Chlorpromazine
1 .0 10
+ 1 .0
2 .0 10
+ 2 .0
4 .0 10
+ 4 .0
0 .28 f .04
p< .05
0 .06 f .02
p< .O1*
0 .29 f .O1
p< .05
0 .08 t .02
p< .O1*
0 .34 f .04
p< .05
0 .21 f .07
p< .5*
*Evaluated by T-test with respect to similar chlorpromazine treated mica . Apomorphine was administered (s .c .) 0 .5 hr prior to chlorpromazine aad all mice were sacrificed 2 hra after chlorpromazine had been administered . Four mice were used per determination and three determinations ware made par schedule . Conviacing evidence has been presented to show that apomorphine decreases the utilization of dopamine by usage of radioactive precursors of dopamine and measuring the rate of decay of radioactive dopamine (5) .
Apomorphine decreased
the rate of decay, which ie suggestive of a decrease utilization or release of
Yol . il, No. 13 the transmitter .
Eäect ad Apomorphine on HVA Levels
811
It has also been shown that apomorphine, at fairly high
doses, can inhibit the synthesis of dopamine is vivo (17) .
Whether this inhi-
bitory effect is through a feedback mechanism or through a direct effect of apomorphina on tyrosine hydroxylase could not be ascertained . In contrast to apomorphine, the aatipsychotics exert their effect oa HVA primarily through a feedback mechanism causing an increased release of dopamine in an attempt to overcome the receptor blocking activity of the antipeychotice . Bvidenca has also base presented elsewhere, which demonstrates that the antipsychotics also produce an increase is tyroeiae hydroxylase activity (11) concomitant with the increased utilization of dopamine .
On this basis, it would
seem that apomorphine's antagonistic effect on HVA may be through a combination of decreased release of dopamine and a decreased synthesis of dopamine .
The
later mechanism is probably not of great significance since it was shows that relatively large doses of apomorphine are needed for the inhibition of tyrosine hydroxylase is vivo (17) . The reversible nature of the effect of the antipsychotics and of apomorphiae . on HVA have been adequately demonstrated in this study .
When thiothixeae
was administered prior to apomorphine, and in all probability thiothixene was occupying the receptor before apomorphine, it was found that apomorphine could overcome the receptor blockade .
On the other hand, whoa apomorphine was admin-
istered first and allowed to occupy the receptor, it was found that chlorpromazine could overcome the effect of apomorphine by increasing the dose of chlorpromazine .
These effects seem to. imply that the observed drug effects are re-
versible and the interactions ~ra of a c.ampetitive nature . The antipsychotic agents have been show to produce an elevation in HVA which in turn can be antagonized by apomorphine, or as shown elsewhere by atropine (18), however it cannot ba determined by these results whether this effect is related to the production of extrapyramidal aide effects or to antipsychotic activity, or to both of these activities .
Presently, it would appear
that the elevation of HVA correlates best with the production of extrapyramidal
812
Sffect .od Apomorphine on HVA Levels
Vol. 11, No . 13
aide effects since thioridazine, which has a low propensity for the production of the extrapyram~dal effects, is not too affective is elevating HVA (18), nor is it very effective in antagonizing the behavioral effects of apomorphine (3) . The finding that atropine will antagonize the HVA elevating activity of the antipaychotica ae well se the production of extrapyramidal effects in mas while apparently not antagonizing the antipaychotic effects in man (19), would seem to imply that the HVA elevating activity and the anti-apomorphine activity of the antipaychotic agents ie batter related to the production of extrapyramidal effects than it is to their antipaychotic activity . Ackaowledgemeat-The following companies are acknowledged for generously supplying drug samples : Pfizer (thiothixeae) ; Smith, Rline and French (trifluoperazine and chlorpromazine) ; and McNeil Laboratories (haloperidol) . ßefereaces 1.
M. FE~TE and A . M . RIIßTI, J . Pharm . Pharmac . 22, 377 (1970) .
2.
& . P . HHARC~VA and 0 . CBANDBA, Brit . J . Pharmacol . 21, 436 (1963) .
3.
P . A . JANSSEN, C . J . F . NIS?fl:GESBB and R . H . L . SCHELLEIDaiS, ArzneimForsch . 15, 104 (1965) .
4.
J . BRAHAM, I . SAßOVA-PINAAS and Y. GOLDHAI~ß, Brit . Med . J . 3, 768 (1970) .
5.
H . NYBAC&, J . SCHUBEßT aad G . SEDVALL, J . Pharm . Pharmac . 22, 622 (1970) .
6.
B . ß00S, J . Pharm . Pharmac . 21, 263 (1969) .
7.
N . E . ANDEN, A, ßiTBBN3BN, R . F~ and T . HOSFSLT, J : Pharm . Pttaxmac . 19, 627 (1967) .
8.
N . NYBAC&, Z . BOßZECQ and G . SEDVALL, EulO~ . J . Pharmacol . 4, 395 (1968) .
9.
D . F . SHAßMAN, Brit . J . Pharmacol . 30, 620 (1967) .
10 .
M . DaPRAnA and A . PLETBCBBß, J . Pharm . Pharmac . 18, 628 (1966) .
11 .
H . MOSACGäIO in Sympoeium on Braie ChemietYV and Mental Diseaae , Houston, Texas Nov . 18-20 (1970) (to be published) .
12 .
N . E . ANDEN, B . E . ß00S and B . WEßDINIIIS, Life Sci . 7, 448 (1963) .
Vol. li, No . 13 13 .
ß.
SCHFiAB, A. C .
Aaeoc . 14 .
ENGLAI~, D . C . POSRANZSß
and
ß. ß . YOUNG,
813 J . Am. Med .
208, 1168 (1969) .
B. SCATTON, A . CHEBAMY, M. J . BBSSOti and Phaxmecol .
15 .
Effect ad Apomorphine on HVA Lévele
J . GLOFTINSRI,
Europ. J .
13, 131 (1970) .
P. SII~N, ß . Cf~ßMOT,
C . LßROUSS$ and J .
ß. HOISSISß,
Therapie
25, 939
(1970) . 16 .
J . M. van1t033UM in Modern Probleme of Pharmacopeychiatry , Ed . Bobon, P . A . J . Janeeen and J . Bobon, Vol . Basel,
17 .
5, p. 65 .
D. P.
3. Rargér A . G .,
(1970) .
M. GOLDBTEIN, L. S . FßSSDMAN and T. BACRSTßOM, J . Pharm . Phax~ac .
22,
715 (1970) . 18 .
ß . O'RSSFB, D. F .
SHAßMAN and M.
VOGT,
Brit . J . Pharmacol .
38, 287
(1970) . 19 .
L . JULOU in Modere Probleme of Pharmaçopevchiatry , 8d . P . A . J. Janseen and J . Bobon, Vol.
(1970) .
5, p . 50,
D.
P . Bobon,
S. Barger A . G., Basel,