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Inhibition of plasma prolactin in the rat by Amantadine
Life Sciences, Vol. 37, pp. 1877-1880 Printed in the U.S.A.
Pergamon Press
INHIBITION OF PLASMA PROLACTIN IN THE RAT BY AMANTADINE 1 M. Fayez 2, H.H. Ahmed 3, and S.K. Quadri 4 Department of Anatomy and Physiology Kansas State University, Manhattan, Kansas
66506
(Received in final form August 291 1985) Summar~ A single iv injection of 15 or 30 but not 7.5 mg/kg BW of an antiviral drug, amantadlne, significantly (P < 0.05) decreased plasma prolactin (PRL) concentrations in male rats. This effect was dosedependent, with the highest dose producing a longer-lasting decrease in plasma PRL. The amantadine-induced decrease was unaffected by a simultaneous injection of 5-hydroxytryptophan (30 mg/kg BW) but was completely blocked by a simultaneous injection of haloperidol (0.05 mg/kg BW). It is concluded that this novel effect of amantadine on PRL is produced by an interaction with the dopaminergic system. Amantadine (l-amlno-adamantan, adamantanamine, Symmetrel) is an amine with an unusual symmetrical structure in which the carbon atoms are arranged like those in a diamond (adamas) molecule. Its biological actions are also unusual and remarkably diverse. Originally, it was introduced as an antlviral drug effective against influenza virus and has been used as a prophylactic agent against this virus in man and animals (I-3). In 1968, during treatment of an influenza patient, it was accidentally found to be effective against Parkinson's disease (4). The latter effect is believed to be due to the dopamine-releasing property of this drug (5). Since dopamine inhibits prolactln (PRL) release (6), it was of interest to determine if amantadlne treatment would decrease circulating levels of PRL in the rat. To our knowledge no such investigation has been undertaken, although in one study serum PRL levels were depressed in psychotic patients under simultaneous treatment with neuroleptics and amantadlne (7). Materials and Methods Adult male Sprague-Dawley rats weighing 250-300 g each were purchased from Charles River, Wilmington, Mass. They were housed in an alr-conditioned (23±2 ° C), light-controlled (lights on from 0700 to 1900 h) room and given rat chow and tap water ad libitum. Each animal was implanted with an atrial cannula under light ether anesthesia. The cannula was made of Silastic tubing (0.025 in id x 0.047 in od; Dow Corning, Midland, Mich.) and inserted into the right external Jugular vein. The free end of the cannula passed subcutaneously and exited near the base of the skull. Heparinized saline was used to rinse the cannula daily. Three days after implantation of the cannulae, extensions made of Silastic tubing were attached to the cannulae and the animals were allowed to remain Contribution 85-396-J from the Kansas Agricultural Experiment Station. Peace Fellow of the University of Alexandria. Peace Fellow of the University of Cairo. 4To whom all correspondence should be addressed. 0024-3205/85 $3.00 + .00 Copyright (c) 1985 Pergamon Press Ltd.
1878
Amantadine and Prolactin
undisturbed for at least one hour
Vol. 37, No. 20, 1985
(8).
In the first experiment, three groups of five animals each were used. A pretreatment blood sample (0.7 ml) was collected at I000 h. This was followed 30 min later by an iv injection of either 7.5, 15, or 30 mg/kg BW of amantadine hydrochlorlde (Sigma) in a volume of 0.5 ml of 0.85% NaCI. Three more blood samples were collected at 0.5, I, and 3 h after amantadlne injection. In the second experiment, five groups of cannulated rats containing eight animals per group were used. After a pretreatment sample, the first group was injected iv with amantadine, 30 mg/kg BW; the second group with haloperidol, 0.05 mg/kg BW in 0.5 ml of 0.3% tartaric acid; and the third group simultaneously with amantadine and haloperidol in the above doses. The fourth group was injected with 5-hydroxytryptophan (5-HTP), 30 mg/kg BW in 0.5 ml of a mixture of 0.5 N HCI and 0.5 N NaOH, pH 2.8 and the fifth group simultaneously with 5-HTP and amantadlne in the above doses. Three posttreatment blood samples were collected at 0.5, I, and 3 h after treatments. Blood samples were centrifuged immediately after collection and cells and plasma separated. The cells were returned to the animals in 0.7 ml of saline, and plasma fractions kept frozen for PRL determinations by radioimmunoassay using reagents supplied by NIADDK (8). The reference preparation for prolactin was NIADDK-rPRL-RP-3 (AFP-4459B) with a potency of 30 l.U./mg. Significance of differences in prolactin levels within and between groups was determined by analysis of variance and Student's t_-test. Results Effects of amantadine on plasma PRL concentrations are shown in fig. 1. The lowest dose of 7.5 mg/kg BW produced no significant change, but 15 mg of amantadine/kg BW produced a significant (P < 0.05) decrease in plasma PRL levels at 0.5 and 1 h after treatment. PRL levels were still depressed at 3 h after the treatment but were not significantly different from the pretreatment levels. After treatment with the highest dose of 30 mg/kg BW, PRL levels decreased significantly (P < 0.05) within 0.5 h and remained significantly depressed for 3 hr. In the second experiment, 30 mg of amantadine/kg BW produced the expected decrease in plasma PRL levels (fig 2, top). This decrease was completely blocked when haloperidol was injected simultaneously with amantadine. The AMANTADINE
7.5 mg/kg S W 15 mg/kg B W 30
40-
mg/kg
BW
FIG. 1 E ~30c: .J a~ L
20-
i
m
~ 10-
TIME
(h)
Effects of a single iv injection of 7.5, 15, or 30 mg/kg BW of amantadine on plasma prolactln (PRL) concentrations in male rats. The injections were given immediately after collection of a pretreatment sample at 0 h. Each bar represents mean ± SEM of five animals.
Vol. 37, No. 20, 1985
Amantadine and Prolactin
1879
400-
FIG. 2
...... A
• ~%
E300-
;
.---HAL --A+HAL
Top:
200-
~ "100.
I 0
I~
I
i
i
150//
E
/
{
c 100..a no. <~
50-
< 0
ii i
...... A --- 5-HTP -- A+5-HTP
~\ \
"x\ ", \
I I
,, \
Counteraction of amantadine (A)-induced decrease in plasma prolactin (PRL) by haloperidol (HAL). The iv injections of A (30 mg/kg BW) and HAL (0.05 mg/kg BW) were given alone or in combination immediately after collection of a pretreatment sample at 0 h. Bottom: Lack of effect of 5-hydroxytryptophan (5-HTP) on A-induced decrease in plasma PRL. A (30 mg/kg BW) and 5-HTP (30 mg/kg BW) were injected alone or in combination immediately after collection of a blood sample at 0 h. Each point represents mean ± SEM (vertical bar) of 8 male rats.
o15 i TIME (h)
PRL profile obtained with simultaneous injections of haloperidol and amantadine was indistinguishable from that obtained from haloperidol alone. Treatment with 5-HTP alone produced significant elevations in plasma PRL levels (fig. 2, bottom). However, 5-HTP was unable to counteract the amantadine-induced decrease in plasma PRL when it was injected simultaneously with amantadine. Discussion
These results demonstrate that amantadine decreases plasma PRL levels in the rat. PRL remained depressed for the longest period after treatment with the highest dose of this amine, whereas the lowest dose had no significant effect, indicating that the duration of this effect is dose-dependent. No report has appeared on the effect of amantadine on PRL release, although in one study serum PRL was depressed and the symptoms of galactorrhea improved in psychotic patients under treatment with neuroleptics and amantadine (7). Most of the available information indicates that amantadine produces its effects through interaction with the dopaminergic system. Although amantadine appears to be less effective than E-dopa in treatment of Parkinson's disease (9,10), the effective dose of E-dopa can be substantially reduced when given in combination with amantadine (II). Amantadine also has been shown to induce potentiation of £-dopa-induced behavioral effects in mice (12). A number of other clinical, pharmacological, and behavioral studies indicate that amantadine interacts with the catecholaminergic system (13-15). Although the exact mechanism of this interaction is not clear, there is evidence that it can inhibit neuronal re-uptake of dopamine (16), stimulate dopamine receptors (17), and increase the release of dopamine from central and peripheral neurons (14, 18-19). There is some evidence, albeit weak, that amantadine also might increase the sensitivity of 5-hydroxytryptamine receptors (20) and increase central levels of this amine (21). In our study, the amantadine-lnduced decrease in plasma PRL was unaffected by 5-HTP but was completely blocked by the dopamine antagonist, haloperidol, indicating that amantadine inhibits PRL release by an interaction with the dopaminergic system. Haloperidol and other
1880
Amantadine and Prolactin
Vol. 37, No. 20, 1985
dopamlne receptor blockers, spiroperidol and plmozide, also have been shown to counter behavioral responses produced by amantadine t r e a t m e n t (5,15). The results of our study can also be explained by assuming that amantadine inhibited plasma PRL by acting as a 5-HT antagonist rather than as a dopamine agonist. However, as discussed above, there is no evidence to support such an assumption. Whatever the exact mechanism of action, the antlviral drug, amantadlne, inhibits plasma PRL and this novel effect is blocked by the dopamine antagonist, haloperidol, but not by the serotonin precursor, 5-HTP. References 1.
W.L. DAVIES, R.R. GRUNERT, R.F. HAFF, J.W. McGAHEN, E.M. NEUMAYER, M. PAULSHOCK, J.C. WATTS, T.R. WOOD, E.C. HERMANN, and C.E. HOFFMAN, Science 144:862-864 (1964). 2, J.J. SKEHEL, A.J. HAY, and J.A. ARMSTRONG, J. Gen Virol 38:97-110 (1977). 3. J.R. LAMONTAGNE, G.J. GALASSO, J Infectious Dis 138:928-931 (1978). 4. R.S. SCHWAB, A.C. ENGLAND, D.C. POSKANER, and R.R. YOUNG, J Am Med Assoc 208:1168-1170 (1969). E.V. BAILEY, and T.W. STONE, Arch Int Pharmacodyn 216:246-262 (1975). 5, 6. J. MEITES and J.A. CLEMENS, Vitamins and Hormones, p. 30 Academic Press, New York (1972). 7o L.J. SIEVER, J Clin Psychopharmacol ~:2-7 (1981). 8. M. FAYEZ, H.H. Ahmed, and S.K. QUADRI, Proc Soc Exp Biol Med 178:606-609 (1985). 9. K.R. HUNTER, G.M. STERN, D.R. LAWRENCE, and P. ARMITAGE, Lancet 1:1127-1133 (1970). I0. V. DALLOS, K. HEATHFIELD, P. STONE, and F.A. ALLEN, Brit Med J 4:24-28
(1970). 11. B.F.B. BIRDWOOD, S.S.B. GILDER, and C.A.S. WINK, Parkinson's Disease - A New Approach to Treatment, p. 189, Academic Press, New York, (1971). 12. T. SVENSSON, and U. STROMBERG, J Pharm Pharmacol 22:639-640 (1970). 13. P. MILLAC, I. HASON, M.L.E. ESPIR and D.G. SLYFIELD, Lancet 1:464-469
(1970). 14. R. GRELAK, R. CLARK, J. STUMP and V. VERNER, Science 169:203-204 (1970). 15. U. STROMBERG, and T.H. SVENSSON, Acta Pharmacol 30:161-171 (1971). 16. R.L.H. HEIMANS, M.J. RAND, and M.R. FENNESSY, J Pharm Pharmacol 24:875-881 (1972). 17. R. PAPESCHI, Neuropharmacol 13:77-83 (1974). 18. B. SCATTON, A. CHERAMY, M.J. BESSON, and J. GLOWINSKI, Europ J Pharmacol 13:131-133 (1970). 19. L. FARNEBO, K. FUXE, M. GOLDSTEIN, B. HAMBERGER and U. UNGERSTEDT, Europ J Pharmacol 16:27-38 (1971). 20. B. COX, and S.J. THA, Europ J Pharmacol 30:344-351 (1975). 21. U. STROMBERG, T.H. SVENSSON and B. WALDECK, J Pharm Pharmacol 22:959-962 (1970).
Pergamon Press
INHIBITION OF PLASMA PROLACTIN IN THE RAT BY AMANTADINE 1 M. Fayez 2, H.H. Ahmed 3, and S.K. Quadri 4 Department of Anatomy and Physiology Kansas State University, Manhattan, Kansas
66506
(Received in final form August 291 1985) Summar~ A single iv injection of 15 or 30 but not 7.5 mg/kg BW of an antiviral drug, amantadlne, significantly (P < 0.05) decreased plasma prolactin (PRL) concentrations in male rats. This effect was dosedependent, with the highest dose producing a longer-lasting decrease in plasma PRL. The amantadine-induced decrease was unaffected by a simultaneous injection of 5-hydroxytryptophan (30 mg/kg BW) but was completely blocked by a simultaneous injection of haloperidol (0.05 mg/kg BW). It is concluded that this novel effect of amantadine on PRL is produced by an interaction with the dopaminergic system. Amantadine (l-amlno-adamantan, adamantanamine, Symmetrel) is an amine with an unusual symmetrical structure in which the carbon atoms are arranged like those in a diamond (adamas) molecule. Its biological actions are also unusual and remarkably diverse. Originally, it was introduced as an antlviral drug effective against influenza virus and has been used as a prophylactic agent against this virus in man and animals (I-3). In 1968, during treatment of an influenza patient, it was accidentally found to be effective against Parkinson's disease (4). The latter effect is believed to be due to the dopamine-releasing property of this drug (5). Since dopamine inhibits prolactln (PRL) release (6), it was of interest to determine if amantadlne treatment would decrease circulating levels of PRL in the rat. To our knowledge no such investigation has been undertaken, although in one study serum PRL levels were depressed in psychotic patients under simultaneous treatment with neuroleptics and amantadlne (7). Materials and Methods Adult male Sprague-Dawley rats weighing 250-300 g each were purchased from Charles River, Wilmington, Mass. They were housed in an alr-conditioned (23±2 ° C), light-controlled (lights on from 0700 to 1900 h) room and given rat chow and tap water ad libitum. Each animal was implanted with an atrial cannula under light ether anesthesia. The cannula was made of Silastic tubing (0.025 in id x 0.047 in od; Dow Corning, Midland, Mich.) and inserted into the right external Jugular vein. The free end of the cannula passed subcutaneously and exited near the base of the skull. Heparinized saline was used to rinse the cannula daily. Three days after implantation of the cannulae, extensions made of Silastic tubing were attached to the cannulae and the animals were allowed to remain Contribution 85-396-J from the Kansas Agricultural Experiment Station. Peace Fellow of the University of Alexandria. Peace Fellow of the University of Cairo. 4To whom all correspondence should be addressed. 0024-3205/85 $3.00 + .00 Copyright (c) 1985 Pergamon Press Ltd.
1878
Amantadine and Prolactin
undisturbed for at least one hour
Vol. 37, No. 20, 1985
(8).
In the first experiment, three groups of five animals each were used. A pretreatment blood sample (0.7 ml) was collected at I000 h. This was followed 30 min later by an iv injection of either 7.5, 15, or 30 mg/kg BW of amantadine hydrochlorlde (Sigma) in a volume of 0.5 ml of 0.85% NaCI. Three more blood samples were collected at 0.5, I, and 3 h after amantadlne injection. In the second experiment, five groups of cannulated rats containing eight animals per group were used. After a pretreatment sample, the first group was injected iv with amantadine, 30 mg/kg BW; the second group with haloperidol, 0.05 mg/kg BW in 0.5 ml of 0.3% tartaric acid; and the third group simultaneously with amantadine and haloperidol in the above doses. The fourth group was injected with 5-hydroxytryptophan (5-HTP), 30 mg/kg BW in 0.5 ml of a mixture of 0.5 N HCI and 0.5 N NaOH, pH 2.8 and the fifth group simultaneously with 5-HTP and amantadlne in the above doses. Three posttreatment blood samples were collected at 0.5, I, and 3 h after treatments. Blood samples were centrifuged immediately after collection and cells and plasma separated. The cells were returned to the animals in 0.7 ml of saline, and plasma fractions kept frozen for PRL determinations by radioimmunoassay using reagents supplied by NIADDK (8). The reference preparation for prolactin was NIADDK-rPRL-RP-3 (AFP-4459B) with a potency of 30 l.U./mg. Significance of differences in prolactin levels within and between groups was determined by analysis of variance and Student's t_-test. Results Effects of amantadine on plasma PRL concentrations are shown in fig. 1. The lowest dose of 7.5 mg/kg BW produced no significant change, but 15 mg of amantadine/kg BW produced a significant (P < 0.05) decrease in plasma PRL levels at 0.5 and 1 h after treatment. PRL levels were still depressed at 3 h after the treatment but were not significantly different from the pretreatment levels. After treatment with the highest dose of 30 mg/kg BW, PRL levels decreased significantly (P < 0.05) within 0.5 h and remained significantly depressed for 3 hr. In the second experiment, 30 mg of amantadine/kg BW produced the expected decrease in plasma PRL levels (fig 2, top). This decrease was completely blocked when haloperidol was injected simultaneously with amantadine. The AMANTADINE
7.5 mg/kg S W 15 mg/kg B W 30
40-
mg/kg
BW
FIG. 1 E ~30c: .J a~ L
20-
i
m
~ 10-
TIME
(h)
Effects of a single iv injection of 7.5, 15, or 30 mg/kg BW of amantadine on plasma prolactln (PRL) concentrations in male rats. The injections were given immediately after collection of a pretreatment sample at 0 h. Each bar represents mean ± SEM of five animals.
Vol. 37, No. 20, 1985
Amantadine and Prolactin
1879
400-
FIG. 2
...... A
• ~%
E300-
;
.---HAL --A+HAL
Top:
200-
~ "100.
I 0
I~
I
i
i
150//
E
/
{
c 100..a no. <~
50-
< 0
ii i
...... A --- 5-HTP -- A+5-HTP
~\ \
"x\ ", \
I I
,, \
Counteraction of amantadine (A)-induced decrease in plasma prolactin (PRL) by haloperidol (HAL). The iv injections of A (30 mg/kg BW) and HAL (0.05 mg/kg BW) were given alone or in combination immediately after collection of a pretreatment sample at 0 h. Bottom: Lack of effect of 5-hydroxytryptophan (5-HTP) on A-induced decrease in plasma PRL. A (30 mg/kg BW) and 5-HTP (30 mg/kg BW) were injected alone or in combination immediately after collection of a blood sample at 0 h. Each point represents mean ± SEM (vertical bar) of 8 male rats.
o15 i TIME (h)
PRL profile obtained with simultaneous injections of haloperidol and amantadine was indistinguishable from that obtained from haloperidol alone. Treatment with 5-HTP alone produced significant elevations in plasma PRL levels (fig. 2, bottom). However, 5-HTP was unable to counteract the amantadine-induced decrease in plasma PRL when it was injected simultaneously with amantadine. Discussion
These results demonstrate that amantadine decreases plasma PRL levels in the rat. PRL remained depressed for the longest period after treatment with the highest dose of this amine, whereas the lowest dose had no significant effect, indicating that the duration of this effect is dose-dependent. No report has appeared on the effect of amantadine on PRL release, although in one study serum PRL was depressed and the symptoms of galactorrhea improved in psychotic patients under treatment with neuroleptics and amantadine (7). Most of the available information indicates that amantadine produces its effects through interaction with the dopaminergic system. Although amantadine appears to be less effective than E-dopa in treatment of Parkinson's disease (9,10), the effective dose of E-dopa can be substantially reduced when given in combination with amantadine (II). Amantadine also has been shown to induce potentiation of £-dopa-induced behavioral effects in mice (12). A number of other clinical, pharmacological, and behavioral studies indicate that amantadine interacts with the catecholaminergic system (13-15). Although the exact mechanism of this interaction is not clear, there is evidence that it can inhibit neuronal re-uptake of dopamine (16), stimulate dopamine receptors (17), and increase the release of dopamine from central and peripheral neurons (14, 18-19). There is some evidence, albeit weak, that amantadine also might increase the sensitivity of 5-hydroxytryptamine receptors (20) and increase central levels of this amine (21). In our study, the amantadine-lnduced decrease in plasma PRL was unaffected by 5-HTP but was completely blocked by the dopamine antagonist, haloperidol, indicating that amantadine inhibits PRL release by an interaction with the dopaminergic system. Haloperidol and other
1880
Amantadine and Prolactin
Vol. 37, No. 20, 1985
dopamlne receptor blockers, spiroperidol and plmozide, also have been shown to counter behavioral responses produced by amantadine t r e a t m e n t (5,15). The results of our study can also be explained by assuming that amantadine inhibited plasma PRL by acting as a 5-HT antagonist rather than as a dopamine agonist. However, as discussed above, there is no evidence to support such an assumption. Whatever the exact mechanism of action, the antlviral drug, amantadlne, inhibits plasma PRL and this novel effect is blocked by the dopamine antagonist, haloperidol, but not by the serotonin precursor, 5-HTP. References 1.
W.L. DAVIES, R.R. GRUNERT, R.F. HAFF, J.W. McGAHEN, E.M. NEUMAYER, M. PAULSHOCK, J.C. WATTS, T.R. WOOD, E.C. HERMANN, and C.E. HOFFMAN, Science 144:862-864 (1964). 2, J.J. SKEHEL, A.J. HAY, and J.A. ARMSTRONG, J. Gen Virol 38:97-110 (1977). 3. J.R. LAMONTAGNE, G.J. GALASSO, J Infectious Dis 138:928-931 (1978). 4. R.S. SCHWAB, A.C. ENGLAND, D.C. POSKANER, and R.R. YOUNG, J Am Med Assoc 208:1168-1170 (1969). E.V. BAILEY, and T.W. STONE, Arch Int Pharmacodyn 216:246-262 (1975). 5, 6. J. MEITES and J.A. CLEMENS, Vitamins and Hormones, p. 30 Academic Press, New York (1972). 7o L.J. SIEVER, J Clin Psychopharmacol ~:2-7 (1981). 8. M. FAYEZ, H.H. Ahmed, and S.K. QUADRI, Proc Soc Exp Biol Med 178:606-609 (1985). 9. K.R. HUNTER, G.M. STERN, D.R. LAWRENCE, and P. ARMITAGE, Lancet 1:1127-1133 (1970). I0. V. DALLOS, K. HEATHFIELD, P. STONE, and F.A. ALLEN, Brit Med J 4:24-28
(1970). 11. B.F.B. BIRDWOOD, S.S.B. GILDER, and C.A.S. WINK, Parkinson's Disease - A New Approach to Treatment, p. 189, Academic Press, New York, (1971). 12. T. SVENSSON, and U. STROMBERG, J Pharm Pharmacol 22:639-640 (1970). 13. P. MILLAC, I. HASON, M.L.E. ESPIR and D.G. SLYFIELD, Lancet 1:464-469
(1970). 14. R. GRELAK, R. CLARK, J. STUMP and V. VERNER, Science 169:203-204 (1970). 15. U. STROMBERG, and T.H. SVENSSON, Acta Pharmacol 30:161-171 (1971). 16. R.L.H. HEIMANS, M.J. RAND, and M.R. FENNESSY, J Pharm Pharmacol 24:875-881 (1972). 17. R. PAPESCHI, Neuropharmacol 13:77-83 (1974). 18. B. SCATTON, A. CHERAMY, M.J. BESSON, and J. GLOWINSKI, Europ J Pharmacol 13:131-133 (1970). 19. L. FARNEBO, K. FUXE, M. GOLDSTEIN, B. HAMBERGER and U. UNGERSTEDT, Europ J Pharmacol 16:27-38 (1971). 20. B. COX, and S.J. THA, Europ J Pharmacol 30:344-351 (1975). 21. U. STROMBERG, T.H. SVENSSON and B. WALDECK, J Pharm Pharmacol 22:959-962 (1970).