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Analgesic effect of metoclopramide and its mechanism
Life Sciences, Vol. 38, pp. 1289-1292 Printed in the U.S.A.
Pergamon Press
ANALGESIC EFFECT OF METOCLOPRAMIDE AND ITS MECHANISM S. R a m a s w a m y and J.S. Bapna
D e p a r t m e n t of Pharmacology, 3awaharlal Institute of Postgraduate Medical Education and Research, Pondicherry 605 006, INDIA (Received in final form January 29, 1986)
Summary M e t o c l o p r a m l d e produced a s i g n i f i c a n t analgesic e f f e c t when t e s t e d by both a c e t i c acid induced w r i t h i n g and hot p l a t e test. Th:s e f f e c t was reduced by naloxone suggesting oplold i n v o l v e m e n t . F u r t h e r , b r o m o c r l p t m e which inhibits the release o l PRL a t t e n u a t e d the e l f e c t of m e t o c l o p r a m l d e i n d i c a t i n g t h a t this drug could a c t by releasing PRL. The unaltered analgesic e f f e c t of m e t o c l o p r a m l d e by yohlmbine reveals t h a t alpha-2 adrenoceptors may not be involved in this action.
A number of reports substantiate the view that the pituitary peptide hormones p a r t i c i p a t e significantly m the analgesic action of morphine (1,2). We have r e c e n t l y d e m o n s t r a t e d opioid mediated analgesic e f f e c t for prolaetm (PRL) ('). It is e s t a b l i s h e d t h a t d u r m g stress the PRL level increases similar to that of endogenous opioid peptioes (4). All these evidences favour a close interaction between PRL and opimd system. It Is known that dopammergic system controls PRL release. Dopammergic agomsts like b r o m o c r i p t m e inhibited PRL release while antagonists enhanced the same. The aim of the present study was to investigate whether the elevation of endogenous PRL level by drugs result m analgesic e f f e c t . Metoclopramide, a dopammergic antagonist (5) increased PRL level in animal models as well as m humans (6). Hence, this drug was chosen to e l e v a t e endogenous PRL level. The analgesm a c t i v i t y of metoclopramide and the possible role of PRL was tested.
METHODS Swlss male albmo n~me (20-25 g) were used for this study. Analgesic assay: Analgesla was examined by c h e m i c a l and t h e r m a l methods. In c h e m i c a l assay 0.6% a c e t i c acld (I0 m l / k g ) was rejected m t r a p e r l t o n e a l l y and the number of wri~hmgs during I0 m m perlod was noted. If there was a s l g m f i c a n t decrease m number of w r l t h m g s i t was considered as d e v e l o p m e n t of analgeslc e f f e c t . In the t h e r m a l assay. Eddy's hot p l a t e (7) was used. The animals were placed over "his plate (55 _+ 0.5°C) and the r e a c t i o n t i m e taken to llck the forepaws was observed. lhls was noted prior to and at 15, 30, 60 and 120 m m a f t e r drug t r e a t m e n t . A graph was drawn w i t h t i m e a f t e r durg a d m m l s t r a t l o n against the increase in the reaction t i m e and the arlalgesla was expressed as the area under the curve (AUC m cm2.) In both t h e assays, each animal was subjected to analgesic test once only.
Drug t r e a t m e n t : C o n t r o l animals recelved sahne. M e t o c l o p r a m l d e was a d m m l s t e r e d 0.p.) m varying doses f r o m 1.25 to 40 rag. In the w r , t h m g assay, the a c e t i c acld challenge was made at 15 m m a f t e r drug m l e c t l o n . The e f f e c t l v e 0024-3205/86 $3.00 + .00 Copyright (c) 1986 Pergamon Press Ltd.
1290
Analgesic Effect of Metoclopramide
Vol. 38, No. 14, 1986
dose t h a t produced 50% of the m a x i m a l response (EDS0) was calculated log dose response curve for m e t o c l o p r a m i d e . To analyse the possible exposed to naloxone (5 mg/kg; ~l mg/kg; l.p.) 15 min prior to w r i t h i n g test was carried out 15
from
the
mechanism of action, another group of animals were l.p.) or b r o m o c r i p t i n e (2 mg/kg; s.c.) or y o h l m b m e 5 m g / k g of m e t o c l o p r a m l d e . In these animals, the rain a f t e r metoclopram~de a d m i n i s t r a t i o n .
The i n t e r a c t i o n between PRL and m e t o c l o p r a m i d e was studied by p r e - t r e a t i n g the animals w i t h m e t o c l o p r a m i d e (1.25 mg/kg) l0 min prior to PRL (20 or 100lJg/kg). The w r i t h i n g test was done 30 min a f t e r PRL a d m i n i s t r a t i o n . Dunnet's
' t ' test was used to analyse the results.
RESULTS In the w r i t h i n g assay, m e t o c l o p r a m l d e produced a dose dependent i n h i b i t i o n of w r i t h i n g response (Table I). The ED 50 of m e t o c l o p r a m i d e was found to be 2.6 mg/kg i n t h i s t e s t . A t 20 mg dose almost t o t a l i n h i b i t i o n of w r i t h i n g was observed. The o n s e t of analgesia in this assay using 5 m g / k g of m e t o c l o p r a m i d e was found t o be 5 n~tn (number of w r i t h m g s -- 16.5 _+ 2.1). The e f f e c t lasted upto 30 mm (no. = 7.9 _+ 1.g) while at 60 min there was no s i g n i f i c a n t e f f e c t (no. - 21.9 * 2.L~). In the hot plate assay, there was a s i g n i f i c a n t increase in the AUC w i t h increase in dose of m e t o c l o p r a m i d e . M a x i m a l e f f e c t was observed at 20 mg since t h e r e was no further increase w i t h dose i n c r e m e n t (Table I). The ED 50 was found to be 12 mg. The decrease ~ t h e number of w r i t h i n g produced by m e t o c l o p r a m i d e was a t t e n u a t e d by e i t h e r n a l o x o n e (5 mg) or b r o m o c r t p t i n e (2 mg) p r e - t r e a t m e n t . However, y o h i m b m e failed co a l t e r the e f f e c t of m e t o c l o p r a m i d e (Table ll). The i n t e r a c t i n g durgs per s e m the doses employed did not produce any change m the w r i t h i n g response as compared w i t h saline t r e a t e d animals (not shown). Subthreshold doses of m e t o c l o p r a m i d e (1.25 mg) when combined w i t h 20 lJg/kg of PRL enhanced i n h i b i t i o n of w r i t h i n g (Table II). However, m e t o c l o p r a m i d e ~vhen given w i t h 100 IJg/kg of PRL, failed to produce this e f f e c t (Table 11).
DISCUSSION The present study shows that m e t o c l o p r a m l d e per se e x h i b i t potent analgeslc a c t l v l t y when tested by both c h e m i c a l and t h e r m a l assays. Thls analgesic e f f e c t was found to be m e d i a t e d through oplold mechanism as opiate r e c e p t o r antagonist a t t e n u a t e d the e f f e c t . It is established t h a t serum PRL levels are elevated during m e t o c l o p r a m l d e t r e a t m e n t (6). In our e a r l i e r study, we r e p o r t e d that PRL per se e x h i b i t e d oplold mediated analgesic e f f e c t (3). The posslbdlty that m e t o c l o p r a m l d e could act via the release of PRL was tested using b r o m o c r l p t l n e . Bromocrlptme, a d o p a m m e r g i c agomst, is known to m h l b l t the release of PRL. The reduced analgesic response to m e t o c l o p r a m i d e In b r o m o c r l p t m e p r e - t r e a t e d animals indicates that metoclopram~de may possibly act by releasing PRL. C o m b l n a t l o n of subthreshold dose of m e t o c l o p r a m l d e (1.25 mg) and submaxlmal dose of PRL (20 ~Jg) resulted m a d d l t l v e e f f e c t . Since both PRL and m e t o c l o p r a m l d e is known to a f f e c t the dopamLnergic system, ]t can be suggested that both these agents may involve d o p a m l n e r g l c receptors to e f f e c t analgesia. C l o m d m e an alpha-2 r e c e p t o r agomst w, 3 found to produce analgesia (g). The role of alpha-2 r e c e p t o r m m e t o c l o p r a m l d e induced analgesia was stud~ed using y o h m b i n e a r e l a t i v e l y specLflc alpha-2 r e c e p t o r antagomst. The f a d u r e of y o h m b i n e
Vol. 38, No. 14, 1986
Analgesic Effect of Metoclopramide
t o a l t e r t h e e f f e c t of m e t o c l o p r a m l d e i n d i c a t e t h a t r e v o l v e d m t h e a n a l g e s i a p r o d u c e d by m e t o c l o p r a m i d e .
TABLE Analgesic
effect
of
metoclopramide
Treatment mg/kg
alpha-2 receptors
25.0
Metoclopramide 1.25
m a y n o t be
I in
writhing
and
hot
Number of a wr i t h i n g s
Saline
1291
±
1.7
plate
AUCb cm 2 1.9
±
1.1
21.2
±
0.8
5.1
_+ 2.1
2.50
13.5
±
1.3"*
6.0
±
1.8"
5.00
6.7
±
0.9**
7.3
±
0.7*
10.00
3.0
±
0.8**
16.3
±
1.7"*
?-0.00
0.2
±
0.2**
23.2
±
3.9**
30.1
+
1.1"*
40.00
--
assay
a w r i t h i n g assay; b h o t p l a t e assay ; n = 6 Each v a l u e r e p r e s e n t s t h e mean ± SEM * P <0.05 and * * P < 0.01 as c o m p a r e d w i t h saline v a l u e
TABLE
II
E f f e c t of PRL, b r o m o c n p t l n e (BRO), n a l o x o n e (NAL) a n d (YOH) on m e t o c l o p r a m i d e (MET) a n a l g e s i a in w r i t h i n g t e s t Treatment rng/kg
Number of wr I th lngs
Saline Metoclopramide 1.25
25.9 18.9
5.00
6.7
P R L 20]Jg 100~ag
±
yohimbme
Percent inhibi t ion
1.7
--
±
2.1
27.1
±
0.9**
74.2
17.8
±
1.9"
31.3
9.1
±
2.5**
64.9
MET 1.25 ± P R L 20 ~g
9.0
±
4.6 **+
65.3
MET 1.25 ± P R L 100~ag
11.5
±
1.9"*
55.6
N A L 5 m g + MET 5 m g
14.5
±
1.6 *$
44.1
B R O 2 m g + MET 5 m g
15.8
±
0.7*$
39.0
YOH I m g ~ MET 5 m g
6.0
±
0.9**
76.9
Each v a l u e r e p r e s e n t s t h e mean ± SEM of a t l e a s t six e x p e r i m e n t s * P < 0.05 and * * P < 0.01 as c o m p a r e d w i t h saline v a l u e * P < 0.05 c o m p a r e d w i t h M E T 1.25 mg v a l u e and ~t p < 0.05 c o m p a r e d w i t h NET 5 mg v a l u e
1292
Analgesic Effect of Metoclopramide
Vol. 38, No. 14, 1986
ACKNOWLEDGEMENT
The authors wish to thank Mr. A.V. Royalu for typing the manuscript. The generous supphes of Prolactm (Ovme, batch 13) by NIH, Bethseda, Naloxone by Endo Laboratorms and Bromocriptme by Sandoz are gratefully acknowledged. REFERENCES
S.AMIR AND Z.AMIT, Life Scl. 23 1143-1152 (1978). S.AMIR and Z.AMIT, Life Sct. 2tl- /4-39-448 (1979). S.RAMASWAMY, N.P.PILLAI and 3.S.BAPNA, Eur. 3. Pharmacol. 96 171-173 (1983). L.GRANDISON and A.GUIDOTTI, Nature 270 357-359 (1977). E.PERINGER, P.3ENNER, I.M.DONALDSON, C.D.MARSDEN and R. MILLER, Neuropbarmacology 15 463 (1976). A. KUPPILA, P.LEINOMEN, R.VITIKO and P.YLOSTALO, 3. Chn. Endo. Met. 5# 955-960(1982). N.B. EDDY ard D.LEIMBACH, 3. Pharmacol. Exp. Ther. 107 385-393 (1953). S.FIELDING, 3.WILKER, M.HYNES, M.SZEWEZAK, W.3. NOVIK and H. LAL, J. Pharmacol. Exp. Ther. 207 899-905 (1978).
Pergamon Press
ANALGESIC EFFECT OF METOCLOPRAMIDE AND ITS MECHANISM S. R a m a s w a m y and J.S. Bapna
D e p a r t m e n t of Pharmacology, 3awaharlal Institute of Postgraduate Medical Education and Research, Pondicherry 605 006, INDIA (Received in final form January 29, 1986)
Summary M e t o c l o p r a m l d e produced a s i g n i f i c a n t analgesic e f f e c t when t e s t e d by both a c e t i c acid induced w r i t h i n g and hot p l a t e test. Th:s e f f e c t was reduced by naloxone suggesting oplold i n v o l v e m e n t . F u r t h e r , b r o m o c r l p t m e which inhibits the release o l PRL a t t e n u a t e d the e l f e c t of m e t o c l o p r a m l d e i n d i c a t i n g t h a t this drug could a c t by releasing PRL. The unaltered analgesic e f f e c t of m e t o c l o p r a m l d e by yohlmbine reveals t h a t alpha-2 adrenoceptors may not be involved in this action.
A number of reports substantiate the view that the pituitary peptide hormones p a r t i c i p a t e significantly m the analgesic action of morphine (1,2). We have r e c e n t l y d e m o n s t r a t e d opioid mediated analgesic e f f e c t for prolaetm (PRL) ('). It is e s t a b l i s h e d t h a t d u r m g stress the PRL level increases similar to that of endogenous opioid peptioes (4). All these evidences favour a close interaction between PRL and opimd system. It Is known that dopammergic system controls PRL release. Dopammergic agomsts like b r o m o c r i p t m e inhibited PRL release while antagonists enhanced the same. The aim of the present study was to investigate whether the elevation of endogenous PRL level by drugs result m analgesic e f f e c t . Metoclopramide, a dopammergic antagonist (5) increased PRL level in animal models as well as m humans (6). Hence, this drug was chosen to e l e v a t e endogenous PRL level. The analgesm a c t i v i t y of metoclopramide and the possible role of PRL was tested.
METHODS Swlss male albmo n~me (20-25 g) were used for this study. Analgesic assay: Analgesla was examined by c h e m i c a l and t h e r m a l methods. In c h e m i c a l assay 0.6% a c e t i c acld (I0 m l / k g ) was rejected m t r a p e r l t o n e a l l y and the number of wri~hmgs during I0 m m perlod was noted. If there was a s l g m f i c a n t decrease m number of w r l t h m g s i t was considered as d e v e l o p m e n t of analgeslc e f f e c t . In the t h e r m a l assay. Eddy's hot p l a t e (7) was used. The animals were placed over "his plate (55 _+ 0.5°C) and the r e a c t i o n t i m e taken to llck the forepaws was observed. lhls was noted prior to and at 15, 30, 60 and 120 m m a f t e r drug t r e a t m e n t . A graph was drawn w i t h t i m e a f t e r durg a d m m l s t r a t l o n against the increase in the reaction t i m e and the arlalgesla was expressed as the area under the curve (AUC m cm2.) In both t h e assays, each animal was subjected to analgesic test once only.
Drug t r e a t m e n t : C o n t r o l animals recelved sahne. M e t o c l o p r a m l d e was a d m m l s t e r e d 0.p.) m varying doses f r o m 1.25 to 40 rag. In the w r , t h m g assay, the a c e t i c acld challenge was made at 15 m m a f t e r drug m l e c t l o n . The e f f e c t l v e 0024-3205/86 $3.00 + .00 Copyright (c) 1986 Pergamon Press Ltd.
1290
Analgesic Effect of Metoclopramide
Vol. 38, No. 14, 1986
dose t h a t produced 50% of the m a x i m a l response (EDS0) was calculated log dose response curve for m e t o c l o p r a m i d e . To analyse the possible exposed to naloxone (5 mg/kg; ~l mg/kg; l.p.) 15 min prior to w r i t h i n g test was carried out 15
from
the
mechanism of action, another group of animals were l.p.) or b r o m o c r i p t i n e (2 mg/kg; s.c.) or y o h l m b m e 5 m g / k g of m e t o c l o p r a m l d e . In these animals, the rain a f t e r metoclopram~de a d m i n i s t r a t i o n .
The i n t e r a c t i o n between PRL and m e t o c l o p r a m i d e was studied by p r e - t r e a t i n g the animals w i t h m e t o c l o p r a m i d e (1.25 mg/kg) l0 min prior to PRL (20 or 100lJg/kg). The w r i t h i n g test was done 30 min a f t e r PRL a d m i n i s t r a t i o n . Dunnet's
' t ' test was used to analyse the results.
RESULTS In the w r i t h i n g assay, m e t o c l o p r a m l d e produced a dose dependent i n h i b i t i o n of w r i t h i n g response (Table I). The ED 50 of m e t o c l o p r a m i d e was found to be 2.6 mg/kg i n t h i s t e s t . A t 20 mg dose almost t o t a l i n h i b i t i o n of w r i t h i n g was observed. The o n s e t of analgesia in this assay using 5 m g / k g of m e t o c l o p r a m i d e was found t o be 5 n~tn (number of w r i t h m g s -- 16.5 _+ 2.1). The e f f e c t lasted upto 30 mm (no. = 7.9 _+ 1.g) while at 60 min there was no s i g n i f i c a n t e f f e c t (no. - 21.9 * 2.L~). In the hot plate assay, there was a s i g n i f i c a n t increase in the AUC w i t h increase in dose of m e t o c l o p r a m i d e . M a x i m a l e f f e c t was observed at 20 mg since t h e r e was no further increase w i t h dose i n c r e m e n t (Table I). The ED 50 was found to be 12 mg. The decrease ~ t h e number of w r i t h i n g produced by m e t o c l o p r a m i d e was a t t e n u a t e d by e i t h e r n a l o x o n e (5 mg) or b r o m o c r t p t i n e (2 mg) p r e - t r e a t m e n t . However, y o h i m b m e failed co a l t e r the e f f e c t of m e t o c l o p r a m i d e (Table ll). The i n t e r a c t i n g durgs per s e m the doses employed did not produce any change m the w r i t h i n g response as compared w i t h saline t r e a t e d animals (not shown). Subthreshold doses of m e t o c l o p r a m i d e (1.25 mg) when combined w i t h 20 lJg/kg of PRL enhanced i n h i b i t i o n of w r i t h i n g (Table II). However, m e t o c l o p r a m i d e ~vhen given w i t h 100 IJg/kg of PRL, failed to produce this e f f e c t (Table 11).
DISCUSSION The present study shows that m e t o c l o p r a m l d e per se e x h i b i t potent analgeslc a c t l v l t y when tested by both c h e m i c a l and t h e r m a l assays. Thls analgesic e f f e c t was found to be m e d i a t e d through oplold mechanism as opiate r e c e p t o r antagonist a t t e n u a t e d the e f f e c t . It is established t h a t serum PRL levels are elevated during m e t o c l o p r a m l d e t r e a t m e n t (6). In our e a r l i e r study, we r e p o r t e d that PRL per se e x h i b i t e d oplold mediated analgesic e f f e c t (3). The posslbdlty that m e t o c l o p r a m l d e could act via the release of PRL was tested using b r o m o c r l p t l n e . Bromocrlptme, a d o p a m m e r g i c agomst, is known to m h l b l t the release of PRL. The reduced analgesic response to m e t o c l o p r a m i d e In b r o m o c r l p t m e p r e - t r e a t e d animals indicates that metoclopram~de may possibly act by releasing PRL. C o m b l n a t l o n of subthreshold dose of m e t o c l o p r a m l d e (1.25 mg) and submaxlmal dose of PRL (20 ~Jg) resulted m a d d l t l v e e f f e c t . Since both PRL and m e t o c l o p r a m l d e is known to a f f e c t the dopamLnergic system, ]t can be suggested that both these agents may involve d o p a m l n e r g l c receptors to e f f e c t analgesia. C l o m d m e an alpha-2 r e c e p t o r agomst w, 3 found to produce analgesia (g). The role of alpha-2 r e c e p t o r m m e t o c l o p r a m l d e induced analgesia was stud~ed using y o h m b i n e a r e l a t i v e l y specLflc alpha-2 r e c e p t o r antagomst. The f a d u r e of y o h m b i n e
Vol. 38, No. 14, 1986
Analgesic Effect of Metoclopramide
t o a l t e r t h e e f f e c t of m e t o c l o p r a m l d e i n d i c a t e t h a t r e v o l v e d m t h e a n a l g e s i a p r o d u c e d by m e t o c l o p r a m i d e .
TABLE Analgesic
effect
of
metoclopramide
Treatment mg/kg
alpha-2 receptors
25.0
Metoclopramide 1.25
m a y n o t be
I in
writhing
and
hot
Number of a wr i t h i n g s
Saline
1291
±
1.7
plate
AUCb cm 2 1.9
±
1.1
21.2
±
0.8
5.1
_+ 2.1
2.50
13.5
±
1.3"*
6.0
±
1.8"
5.00
6.7
±
0.9**
7.3
±
0.7*
10.00
3.0
±
0.8**
16.3
±
1.7"*
?-0.00
0.2
±
0.2**
23.2
±
3.9**
30.1
+
1.1"*
40.00
--
assay
a w r i t h i n g assay; b h o t p l a t e assay ; n = 6 Each v a l u e r e p r e s e n t s t h e mean ± SEM * P <0.05 and * * P < 0.01 as c o m p a r e d w i t h saline v a l u e
TABLE
II
E f f e c t of PRL, b r o m o c n p t l n e (BRO), n a l o x o n e (NAL) a n d (YOH) on m e t o c l o p r a m i d e (MET) a n a l g e s i a in w r i t h i n g t e s t Treatment rng/kg
Number of wr I th lngs
Saline Metoclopramide 1.25
25.9 18.9
5.00
6.7
P R L 20]Jg 100~ag
±
yohimbme
Percent inhibi t ion
1.7
--
±
2.1
27.1
±
0.9**
74.2
17.8
±
1.9"
31.3
9.1
±
2.5**
64.9
MET 1.25 ± P R L 20 ~g
9.0
±
4.6 **+
65.3
MET 1.25 ± P R L 100~ag
11.5
±
1.9"*
55.6
N A L 5 m g + MET 5 m g
14.5
±
1.6 *$
44.1
B R O 2 m g + MET 5 m g
15.8
±
0.7*$
39.0
YOH I m g ~ MET 5 m g
6.0
±
0.9**
76.9
Each v a l u e r e p r e s e n t s t h e mean ± SEM of a t l e a s t six e x p e r i m e n t s * P < 0.05 and * * P < 0.01 as c o m p a r e d w i t h saline v a l u e * P < 0.05 c o m p a r e d w i t h M E T 1.25 mg v a l u e and ~t p < 0.05 c o m p a r e d w i t h NET 5 mg v a l u e
1292
Analgesic Effect of Metoclopramide
Vol. 38, No. 14, 1986
ACKNOWLEDGEMENT
The authors wish to thank Mr. A.V. Royalu for typing the manuscript. The generous supphes of Prolactm (Ovme, batch 13) by NIH, Bethseda, Naloxone by Endo Laboratorms and Bromocriptme by Sandoz are gratefully acknowledged. REFERENCES
S.AMIR AND Z.AMIT, Life Scl. 23 1143-1152 (1978). S.AMIR and Z.AMIT, Life Sct. 2tl- /4-39-448 (1979). S.RAMASWAMY, N.P.PILLAI and 3.S.BAPNA, Eur. 3. Pharmacol. 96 171-173 (1983). L.GRANDISON and A.GUIDOTTI, Nature 270 357-359 (1977). E.PERINGER, P.3ENNER, I.M.DONALDSON, C.D.MARSDEN and R. MILLER, Neuropbarmacology 15 463 (1976). A. KUPPILA, P.LEINOMEN, R.VITIKO and P.YLOSTALO, 3. Chn. Endo. Met. 5# 955-960(1982). N.B. EDDY ard D.LEIMBACH, 3. Pharmacol. Exp. Ther. 107 385-393 (1953). S.FIELDING, 3.WILKER, M.HYNES, M.SZEWEZAK, W.3. NOVIK and H. LAL, J. Pharmacol. Exp. Ther. 207 899-905 (1978).