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Trifluoperazine antagonizes postsynaptic α1- but not α2-adrenoceptor-mediated pressor responses in the rat
European Journal of Pharmacologr. 105 (1984) 343-346 Elsevier
343
Short communication T R I F L U O P E R A Z I N E A N T A G O N I Z E S P O S T S Y N A P T I C a t- BUT N O T ¢ , z - A D R E N O C E l Y r O R M E D I A T E D P R E S S O R R E S P O N S E S IN T H E RAT I)IDIER PRUNEAU *, YVES MAINGUY and FRANCIS ROY * Dg'partement de Pharmacologte Cardiot'asculatre. ('entre de Recherches, l.ahoratotres Fournier S,A.. 50 rue de Dijon, 21121 Fontaine les Dijon, France Received 1 August 1983, accepted 13 August 1984
D. P R U N E A U , Y. M A I N G U Y a n d F. ROY, Trifluoperazine antagonizes postsynaptic a I- but not ae-adrenoceptorsm e d i a t e d pressor responses in the rat, E u r o p e a n J. Pharmacol. 105 (1984) 3 4 3 - 3 4 6 .
The specificity of the a-adrenergic blockade by trifluoperazine was tested in pithed rats. Trifluoperazine reduced the pressor effects of ( - )-noradrenaline. The log dose-response curve to methoxamine, an a~-agonist, was shifted to the right whereas the vasopressor responses to BHT-920, an a2-agonist, were unaffected by trifluoperazine. It was concluded that trifluoperazine acts as a peripheral vascular an-antagonist in the rat. Trifluoperazine
a~-Adrenoceptors
a2-Adrenoceptors
1. Introduction Trifluoperazine is an antipsychotic drug which binds to the Ca 2~-dependent regulatory protein, calmodulin, and prevents its activation by calcium (Levin and Weiss, 1977). In addition, phenothiazine derivatives have inhibitory effects on the Na ~ - C a 2+ exchange (Caroni et al., 1980) and, as demonstrated with vas deferens (Takayanagi, 1964) and isolated arteries (Asano et al., 1981), trifluoperazine and chlorpromazine antagonize the ( - ) noradrenaline-, serotonin- and histamine-induced contractions. Blockade of a-adrenoceptors by trifluoperazine is also suggested by its ability to displace [3H]WB-4101 (an a~-adrenergic radioligand) in the central nervous system (Peroutka et al., 1977). Recently, trifluoperazine has been found to antagonize a~-adrenergic effects in guinea-pig and rat hepatocytes (Cocks et al., 1981; HuertaBahena et al.. 1983), vas deferens (Cocks et al., 1981) and hamster adipocytes (Huerta-Bahena et al., 1983). No previous report, however, has presented def-
* To whom all correspondence should be addressed, 0014-2999/8,1/$03.00 " 1984 Elsevier Science Publishers B.V.
Pithed rat
inite in vivo evidence that trifluoperazine antagonized selective a-adrenergic receptor subtype effects. The present work investigated the ability of trifluoperazine to antagonize the vasopressor responses induced by ( - )-noradrenaline and selective a~- and az-agonists in the pithed rat.
2. Materials and methods 2.1. General procedure
Normotensive male Wistar rats (250-300 g) were anesthetized with sodium pentobarbitone (50 m g / k g i.p.). The animals were pithed by inserting a steel rod (2 mm in diameter) through the orbit and foramen magnum down into the spinal canal, and immediately respired with room air via a tracheal cannula attached to a Harvard Apparatus model 680 rodent respirator. The rat was artificially ventilated at a frequency of 70 strokes per min with a volume of 1.5 ml/100 g. Body temperature was maintained at 3 7 ° C by means of warming blankets connected to a homeothermic blanket control system (Bioscience CFP 8185). Arterial
344
blood pressure was recorded continuously from the ]eft common carotid artery via a Statham P 23
Db transducer connected to a Gould-Brush 2400 S recorder. Heart rate was recorded with a cardiotachometer triggered by the pulse pressure. The left femoral vein was cannulated for intravenous (i.v.) administration of drugs in a volume of 0.5 m l / k g . Following a 15 min period of equilibration, saline or trifluoperazine (1, 2 and 4 m g / k g ) was injected; 15 min later, increases in diastolic blood pressure were measured in m m H g following i.v. bolus injections of ( - )-noradrenaline. mcthoxamine or BHT-920. In studies with ( - ) noradrenaline the rats were pretreated with DI_,propranolol (1 m g / k g ) injected i,v. together with saline or trifluoperazine. Six doses of agonists were given to each animal. Log dose-response curves were drawn referring to the maximal increase in diastolic pressure.
2.2. Drugs BHT-920 • 2 HCI (Thomae); methoxamine (Pfizer); ( - ) - n o r a d r e n a l i n e bitartrate, DL-propranolol, trifluoperazine hydrochloride (Sigma Chemical Company).
2.3. Statistical analysis Values were expressed as means _+S.E.M. Statistical evaluation was made using Student's t-test, P < 0.05 was considered significant,
3. Results The resting diastolic blood pressure of pithed rats before experimentation was 41.0 + 0.6 m m H g (n = 62) and was unaltered by i.v. injection of trifluoperazine (1, 2 and 4 m g / k g ) or DL-propranolol (1 mg/kg). The maximal pressor effect obtained with ( - ) - n o r a d r e n a l i n e alone (after DLpropranolol pretreatment) amounted to 126.0 + 1.7 m m H g (fig. 1). After i.v. treatment with trifluoperazine 2 and 4 m g / k g the log dose-response curves t o ( - ) - n o r a d r e n a l i n e w a s shifted slightly to the right (2.3 and 4.2 fold respectively; at an increase in blood pressure of 50 mmHg), the maxi-
INCREASE IN DIASTOLIC 13o (mm Hg )
PRESSURE
12o 11o lOO 90 80 70 60 50 40 30 20. 10 0~3
i
:~
lb
3o
16o
360
( - ) NORADRENALINE (#g/kg) Fig. l. Log dose-response curves for the increase in diastolic pressure of pithed rats brought a b o u t by i.v. ( - )-noradrenaline 15 rain after saline (11 II), trifluoperazine ( • • 2 m g / k g ; ,7 • v 4 m g / k g l . Symbols represent mean values _+S.E.M. (n = 5-7).
mal response being significantly ( P < 0 . 0 5 ) decreased to 113.0 + 2.3 m m H g (fig. 1 ). The effect of trifluoperazine pretreatment on the diastolic pressor response to the selective ch-agonist methoxamine is shown in fig. 2A. Trifluoperazine 1, 2 and 4 m g / k g caused a parallel, dose-related shift to the right of the log dose-response curves to methoxamine without significant changes in the maximal responses. Displacements up to 2.3, 3.9 and 13.4 fold were noted after trifluoperazine doses of 1. 2 and 4 m g / k g respectively. Least squares regression analysis was used to determine the relationship between log (dose ratio - 1 ) and log of thc antagonist concentration (M). The experimcntal regression line used to test the degree of parallelism had a slope of 1.16 + 0.02, in agreement with the theoretically determined slope of 1 expected for competitive antagonism for a single class of binding sites. The pA 2 value calculated for trifluoperazine was 5.81 + 0.96. The pressor response elicited by BHT-920, an a:-agonist, was unaffected by trifluoperazine pretreatment at 1, 2 and 4 m g / k g i.v. and the log dose-response curves to BHT-920 were not shifted (fig. 2B).
345
lO0 90 8o zo60"~ 'r- 50 E 40 30 u3 rr 20 co co lo uJ rr a. o _q 12o. 11o. '~ loo 90. z 8o 70 6o 50 z
3 10 50 160 300 1000 13HT_920 2. HCL (po/ko) B
ao-
3o20lO3
10
30
100
300
1000 3 0 0 0
METHOXAMINE (pg/kg) Fig. 2. Log dose-response curves for the increase in diastolic pressure of pithed rats brought about by i.v. BHT-920.2 HCI and methoxamine, 15 min after saline (O ' O), trifluoperazine (,', ,', 1 m g / k g : • .-• 2 mg/kg; C)-© 4 mg/kg). Symbols represent mean values _+S.E.M. (n = 5-7).
4. Discussion In pithed rats, trifluoperazine antagonized the pressor response elicited by ( - ) - n o r a d r e n a l i n e during fl-adrenoceptor blockade. This suggests a possible specific blockade of a-adrenergic effects in the peripheral circulation. Because ( -- )noradrenaline has mixed a J a 2 effects we used methoxamine, an at selective agent resistant to
neuronal uptake, and BHT-920, a drug which has been designed as a potent a 2 agonist (Kobinger and Pichler, 1981) to further explore the selectivity of trifluoperazine. The weaker ability of trifluoperazine to antagonize the response induced by ( - ) - n o r a d r e n a l i n e compared to that elicited by methoxamine may be explained by the a 2 component of the pressor response due to ( - ) noradrenaline; a2-adrenoceptor stimulation being insensitive to trifluoperazine. Neuroleptic drugs act by blocking dopamine receptors and their relative potencies at D 2 dopamine receptors correlate closely with their clinical efficiency (Peroutka and Snyder, 1980). Among the secondary effects observed with phenothiazine treatment are hypotension and the association of arrhythmia and sudden death with long-term therapy (Alexander and Nino, 1969). These associated effects seem to involve neuroleptic receptor sites other than central dopamine receptors. Peroutka et al. (1977) reported that trifluoperazine was a potent competitor of the 3H-labeled al-adrenergic agonist WB-4101 for binding to a-adrenergic receptors in rat brain homogenates. The present data provide evidence that trifluoperazine exerts specific antagonism toward a~-adrenoceptors in the vasculature of the rat and we suggest that the propensity of trifluoperazine to elicit autonomic side-effects such as orthostatic hypotension is due to its peripheral vascular al-adrenergic blockade. As a corollary, the experimental use of trifluoperazine as a calmodulin antagonist (Asano et al., 1981) implies a cautious interpretation of the results in view of the a, blocking properties of that drug.
Acknowledgements ]'he authors are grateful to Dr. Karl Thomae (Biberach, FRG) and Burroughs Wellcome (London, U.K.) for the generous supply of BHT-920 and methoxamine, and thank Dr. J.B. Chazan for his helpful suggestions regarding the manuscript.
References Alexander, C.S. and A. Nino, 1969, Cardiovascular complications in young patients taking psychotropic drugs, Am.
Heart J. 78, 757.
346 Asano, M., Y. Suzuki and I1. Hidaka, 1981, Effects of various calmodulin antagonists on contraction of rabbit aortic strips, J. Pharmacol. Exp. Ther. 220, 191. ('aroni, P., L. Reinlib and E. Carofoli, 1980, charge movements during the N a ~ - C a 2' exchange in heart sarcolemmal vesicles, Proc. Natl. Acad. Sci. U.S.A. 77, 6354. Cocks, T.M,, P. Dilger and l).lf. Jenkinson, 1981, The mechanism of the blockade by trifluoperazine of some actions of phenylephrine on liver and smooth muscle, Biochem. Pharmacol. 30, 28'73. ttuerta-Bahena, J., R. Villalobos-Molina and J.A. Garcia- S'~inz, 1983, Trifluoperazine and chlorpromazine antagonize alpha-1 - but not alpha-2 adrenergic effects, Mol. Pharmacol. 23, 67. Kobinger, ~ . and L. Pithier, 1981, Alpha-1 and Alpha-2 adrenoceptor subtypes: selectivity of various agonists and
relative distribution of receptor,,, as determined in rats, l-uropean J. Pharmacol. 73, 313. Levin. R . M and B. Weiss, 1977, Binding of trifluoperazinc to the calcium-dependent activator of cyclic nucleotide phosphodiesterase, Mol. Pharmacol. 13,690. Peroutka, S.J. and S.H. Snyder. 1980, Relationship of neuroleptic drug effects at brain dopamine, serotonin, a-adrenergic, and histamine receptors to clinical potency, Am. J. Psyehiat. 137, 1518. Peroutka, S.J.. D.C. U'Prichard, D.A. Greenberg and S.lq. Snyder, 1977, Neuroleptic drug interactions with norcpinephrine alpha receptor binding sites in rat brain, Neuropharmacology 16. 549. Takayanagi. 1., 1964, Phenothiazine derivatives. Relationship between peripheral and central actions, Ar;,neim F o r s c h . / I ) r u g Res. 14, 694.
343
Short communication T R I F L U O P E R A Z I N E A N T A G O N I Z E S P O S T S Y N A P T I C a t- BUT N O T ¢ , z - A D R E N O C E l Y r O R M E D I A T E D P R E S S O R R E S P O N S E S IN T H E RAT I)IDIER PRUNEAU *, YVES MAINGUY and FRANCIS ROY * Dg'partement de Pharmacologte Cardiot'asculatre. ('entre de Recherches, l.ahoratotres Fournier S,A.. 50 rue de Dijon, 21121 Fontaine les Dijon, France Received 1 August 1983, accepted 13 August 1984
D. P R U N E A U , Y. M A I N G U Y a n d F. ROY, Trifluoperazine antagonizes postsynaptic a I- but not ae-adrenoceptorsm e d i a t e d pressor responses in the rat, E u r o p e a n J. Pharmacol. 105 (1984) 3 4 3 - 3 4 6 .
The specificity of the a-adrenergic blockade by trifluoperazine was tested in pithed rats. Trifluoperazine reduced the pressor effects of ( - )-noradrenaline. The log dose-response curve to methoxamine, an a~-agonist, was shifted to the right whereas the vasopressor responses to BHT-920, an a2-agonist, were unaffected by trifluoperazine. It was concluded that trifluoperazine acts as a peripheral vascular an-antagonist in the rat. Trifluoperazine
a~-Adrenoceptors
a2-Adrenoceptors
1. Introduction Trifluoperazine is an antipsychotic drug which binds to the Ca 2~-dependent regulatory protein, calmodulin, and prevents its activation by calcium (Levin and Weiss, 1977). In addition, phenothiazine derivatives have inhibitory effects on the Na ~ - C a 2+ exchange (Caroni et al., 1980) and, as demonstrated with vas deferens (Takayanagi, 1964) and isolated arteries (Asano et al., 1981), trifluoperazine and chlorpromazine antagonize the ( - ) noradrenaline-, serotonin- and histamine-induced contractions. Blockade of a-adrenoceptors by trifluoperazine is also suggested by its ability to displace [3H]WB-4101 (an a~-adrenergic radioligand) in the central nervous system (Peroutka et al., 1977). Recently, trifluoperazine has been found to antagonize a~-adrenergic effects in guinea-pig and rat hepatocytes (Cocks et al., 1981; HuertaBahena et al.. 1983), vas deferens (Cocks et al., 1981) and hamster adipocytes (Huerta-Bahena et al., 1983). No previous report, however, has presented def-
* To whom all correspondence should be addressed, 0014-2999/8,1/$03.00 " 1984 Elsevier Science Publishers B.V.
Pithed rat
inite in vivo evidence that trifluoperazine antagonized selective a-adrenergic receptor subtype effects. The present work investigated the ability of trifluoperazine to antagonize the vasopressor responses induced by ( - )-noradrenaline and selective a~- and az-agonists in the pithed rat.
2. Materials and methods 2.1. General procedure
Normotensive male Wistar rats (250-300 g) were anesthetized with sodium pentobarbitone (50 m g / k g i.p.). The animals were pithed by inserting a steel rod (2 mm in diameter) through the orbit and foramen magnum down into the spinal canal, and immediately respired with room air via a tracheal cannula attached to a Harvard Apparatus model 680 rodent respirator. The rat was artificially ventilated at a frequency of 70 strokes per min with a volume of 1.5 ml/100 g. Body temperature was maintained at 3 7 ° C by means of warming blankets connected to a homeothermic blanket control system (Bioscience CFP 8185). Arterial
344
blood pressure was recorded continuously from the ]eft common carotid artery via a Statham P 23
Db transducer connected to a Gould-Brush 2400 S recorder. Heart rate was recorded with a cardiotachometer triggered by the pulse pressure. The left femoral vein was cannulated for intravenous (i.v.) administration of drugs in a volume of 0.5 m l / k g . Following a 15 min period of equilibration, saline or trifluoperazine (1, 2 and 4 m g / k g ) was injected; 15 min later, increases in diastolic blood pressure were measured in m m H g following i.v. bolus injections of ( - )-noradrenaline. mcthoxamine or BHT-920. In studies with ( - ) noradrenaline the rats were pretreated with DI_,propranolol (1 m g / k g ) injected i,v. together with saline or trifluoperazine. Six doses of agonists were given to each animal. Log dose-response curves were drawn referring to the maximal increase in diastolic pressure.
2.2. Drugs BHT-920 • 2 HCI (Thomae); methoxamine (Pfizer); ( - ) - n o r a d r e n a l i n e bitartrate, DL-propranolol, trifluoperazine hydrochloride (Sigma Chemical Company).
2.3. Statistical analysis Values were expressed as means _+S.E.M. Statistical evaluation was made using Student's t-test, P < 0.05 was considered significant,
3. Results The resting diastolic blood pressure of pithed rats before experimentation was 41.0 + 0.6 m m H g (n = 62) and was unaltered by i.v. injection of trifluoperazine (1, 2 and 4 m g / k g ) or DL-propranolol (1 mg/kg). The maximal pressor effect obtained with ( - ) - n o r a d r e n a l i n e alone (after DLpropranolol pretreatment) amounted to 126.0 + 1.7 m m H g (fig. 1). After i.v. treatment with trifluoperazine 2 and 4 m g / k g the log dose-response curves t o ( - ) - n o r a d r e n a l i n e w a s shifted slightly to the right (2.3 and 4.2 fold respectively; at an increase in blood pressure of 50 mmHg), the maxi-
INCREASE IN DIASTOLIC 13o (mm Hg )
PRESSURE
12o 11o lOO 90 80 70 60 50 40 30 20. 10 0~3
i
:~
lb
3o
16o
360
( - ) NORADRENALINE (#g/kg) Fig. l. Log dose-response curves for the increase in diastolic pressure of pithed rats brought a b o u t by i.v. ( - )-noradrenaline 15 rain after saline (11 II), trifluoperazine ( • • 2 m g / k g ; ,7 • v 4 m g / k g l . Symbols represent mean values _+S.E.M. (n = 5-7).
mal response being significantly ( P < 0 . 0 5 ) decreased to 113.0 + 2.3 m m H g (fig. 1 ). The effect of trifluoperazine pretreatment on the diastolic pressor response to the selective ch-agonist methoxamine is shown in fig. 2A. Trifluoperazine 1, 2 and 4 m g / k g caused a parallel, dose-related shift to the right of the log dose-response curves to methoxamine without significant changes in the maximal responses. Displacements up to 2.3, 3.9 and 13.4 fold were noted after trifluoperazine doses of 1. 2 and 4 m g / k g respectively. Least squares regression analysis was used to determine the relationship between log (dose ratio - 1 ) and log of thc antagonist concentration (M). The experimcntal regression line used to test the degree of parallelism had a slope of 1.16 + 0.02, in agreement with the theoretically determined slope of 1 expected for competitive antagonism for a single class of binding sites. The pA 2 value calculated for trifluoperazine was 5.81 + 0.96. The pressor response elicited by BHT-920, an a:-agonist, was unaffected by trifluoperazine pretreatment at 1, 2 and 4 m g / k g i.v. and the log dose-response curves to BHT-920 were not shifted (fig. 2B).
345
lO0 90 8o zo60"~ 'r- 50 E 40 30 u3 rr 20 co co lo uJ rr a. o _q 12o. 11o. '~ loo 90. z 8o 70 6o 50 z
3 10 50 160 300 1000 13HT_920 2. HCL (po/ko) B
ao-
3o20lO3
10
30
100
300
1000 3 0 0 0
METHOXAMINE (pg/kg) Fig. 2. Log dose-response curves for the increase in diastolic pressure of pithed rats brought about by i.v. BHT-920.2 HCI and methoxamine, 15 min after saline (O ' O), trifluoperazine (,', ,', 1 m g / k g : • .-• 2 mg/kg; C)-© 4 mg/kg). Symbols represent mean values _+S.E.M. (n = 5-7).
4. Discussion In pithed rats, trifluoperazine antagonized the pressor response elicited by ( - ) - n o r a d r e n a l i n e during fl-adrenoceptor blockade. This suggests a possible specific blockade of a-adrenergic effects in the peripheral circulation. Because ( -- )noradrenaline has mixed a J a 2 effects we used methoxamine, an at selective agent resistant to
neuronal uptake, and BHT-920, a drug which has been designed as a potent a 2 agonist (Kobinger and Pichler, 1981) to further explore the selectivity of trifluoperazine. The weaker ability of trifluoperazine to antagonize the response induced by ( - ) - n o r a d r e n a l i n e compared to that elicited by methoxamine may be explained by the a 2 component of the pressor response due to ( - ) noradrenaline; a2-adrenoceptor stimulation being insensitive to trifluoperazine. Neuroleptic drugs act by blocking dopamine receptors and their relative potencies at D 2 dopamine receptors correlate closely with their clinical efficiency (Peroutka and Snyder, 1980). Among the secondary effects observed with phenothiazine treatment are hypotension and the association of arrhythmia and sudden death with long-term therapy (Alexander and Nino, 1969). These associated effects seem to involve neuroleptic receptor sites other than central dopamine receptors. Peroutka et al. (1977) reported that trifluoperazine was a potent competitor of the 3H-labeled al-adrenergic agonist WB-4101 for binding to a-adrenergic receptors in rat brain homogenates. The present data provide evidence that trifluoperazine exerts specific antagonism toward a~-adrenoceptors in the vasculature of the rat and we suggest that the propensity of trifluoperazine to elicit autonomic side-effects such as orthostatic hypotension is due to its peripheral vascular al-adrenergic blockade. As a corollary, the experimental use of trifluoperazine as a calmodulin antagonist (Asano et al., 1981) implies a cautious interpretation of the results in view of the a, blocking properties of that drug.
Acknowledgements ]'he authors are grateful to Dr. Karl Thomae (Biberach, FRG) and Burroughs Wellcome (London, U.K.) for the generous supply of BHT-920 and methoxamine, and thank Dr. J.B. Chazan for his helpful suggestions regarding the manuscript.
References Alexander, C.S. and A. Nino, 1969, Cardiovascular complications in young patients taking psychotropic drugs, Am.
Heart J. 78, 757.
346 Asano, M., Y. Suzuki and I1. Hidaka, 1981, Effects of various calmodulin antagonists on contraction of rabbit aortic strips, J. Pharmacol. Exp. Ther. 220, 191. ('aroni, P., L. Reinlib and E. Carofoli, 1980, charge movements during the N a ~ - C a 2' exchange in heart sarcolemmal vesicles, Proc. Natl. Acad. Sci. U.S.A. 77, 6354. Cocks, T.M,, P. Dilger and l).lf. Jenkinson, 1981, The mechanism of the blockade by trifluoperazine of some actions of phenylephrine on liver and smooth muscle, Biochem. Pharmacol. 30, 28'73. ttuerta-Bahena, J., R. Villalobos-Molina and J.A. Garcia- S'~inz, 1983, Trifluoperazine and chlorpromazine antagonize alpha-1 - but not alpha-2 adrenergic effects, Mol. Pharmacol. 23, 67. Kobinger, ~ . and L. Pithier, 1981, Alpha-1 and Alpha-2 adrenoceptor subtypes: selectivity of various agonists and
relative distribution of receptor,,, as determined in rats, l-uropean J. Pharmacol. 73, 313. Levin. R . M and B. Weiss, 1977, Binding of trifluoperazinc to the calcium-dependent activator of cyclic nucleotide phosphodiesterase, Mol. Pharmacol. 13,690. Peroutka, S.J. and S.H. Snyder. 1980, Relationship of neuroleptic drug effects at brain dopamine, serotonin, a-adrenergic, and histamine receptors to clinical potency, Am. J. Psyehiat. 137, 1518. Peroutka, S.J.. D.C. U'Prichard, D.A. Greenberg and S.lq. Snyder, 1977, Neuroleptic drug interactions with norcpinephrine alpha receptor binding sites in rat brain, Neuropharmacology 16. 549. Takayanagi. 1., 1964, Phenothiazine derivatives. Relationship between peripheral and central actions, Ar;,neim F o r s c h . / I ) r u g Res. 14, 694.