- Email: [email protected]
Treatment with antidepressants and histamine receptor mediated 3H-cyclic AMP formation in guinea pig cortex
Life Sciences, Vol. 30, pp. 921-927 Printed in the U.S.A.
Pergamon Press
TREATMENT~WITH ANTIDEPRESSANTS AND HISTAMINE RECEPTORMEDIATED JH-CYCLIC AMP FORMATION IN GUINEA PIG CORTEX Ghanshyam N. Pandey, Alan Krueger, Puppala Sudershan, and John M. Davis Research Department, l l l i n o i s State Psychiatric I n s t i t u t e , 1601 West Taylor Street, Chicago, l l l i n o i s 60612 and Department of Psychiatry, University of l l l i n o i s at the Medical Center (Received in final form January 13, 1982)
Summary I t has been recently reported that most of the antidepressant drugs block histamine HI and Hp receptors in the brain under in v i t r o conditions and i t has be~n suggested that this may be related in part to t h e i r therapeutic e f f e c t . Since the in v i t r o and in vivo e f f e c t s of these drugs may d i f f e r , we studied the e f f e c t of t r e a t ment with antidepressant drugs on histamine receptor s e n s i t i v i t y in the guinea pig brain and observed that chronic treatment with t r i c y c l i c antidepressants or phenelzine (an MAO i n h i b i t o r ) causes a reduction in histamine receptor s e n s i t i v i t y . This reduction is probably mediated through two d i f f e r e n t mechanisms, since only t r i c y c l i c antidepressants cause a reduction a f t e r acute treatment. Although some of the side effects of antidepressant treatment may be related to the blockade of histamine receptors, these results do not support the assumption that this e f f e c t of antidepressant treatment c o n t r i butes to t h e i r c l i n i c a l e f f e c t s . Several antidepressant drugs have been shown to block histamine receptors in the brain under in v i t r o conditions (1,2). These observations have led to the suggestion that some therapeutic e f f e c t s of antidepressant drugs may be related in part to t h e i r capacity to block histamine receptors in the brain (1,2). However, to our knowledge, the in vivo effects of antidepressant drugs ( i . e . e f f e c t of treatment with antidepressants) on histamine receptors in the brain have not been studied. I t has been observed that in vivo effects of drugs on receptor s e n s i t i v i t y may d i f f e r from those observed in v i t r o . Fo~ example, antidepressant drugs that are potent blockers of alpha receptors (3HB4101 binding) in v i t r o (3), do not produce any s i g n i f i c a n t a l t e r a t i o n s in H-WB4101 binding a f t e r t h e i r administration in vivo (4). I t is of i n t e r e s t , therefore, to examine the effects of antidepressant treatment on histamine receptor s e n s i t i v i t y in the guinea pig brain, since the results of such studies could provide f u r t h e r evidence for or against the suggested mode of action of antidepressants.
~
Methods Groups of male guinea pigs (weighing about 250-300g at the s t a r t of the treatment) were injected I.P. with the drugs (as indicated) or with normal saline e i t h e r once daily f o r 15 days for chronic studies or once f o r acute studies. The animals were then s a c r i f i c e d e i t h e r one hour or 24 hours a f t e r the last treatment and the cerebral cortex was immediately removed from the brain. 0024-3205/82/110921-07503.00/0 Copyright (c) 1982 Pergamon Press Ltd.
922
Antidepressant and Histamine Receptors
Vol. 30, No. Ii, 1982
Histamine-stimulated accumulatioq of 3H-cyclic AMP in slices of guinea pig cortex that had been prelabeled with OH-adenine was used as an index of adenylate cyclase-coupled histamine receptor s e n s i t i v i t y (receptor responsivity). This pulse-labeling technique has been used previously for the determination of adenylate cyclase a c t i v i t y in several tissues, including the guinea pig brain (5). The procedure used for the determination of 3H-cyclic AMP accumulation in the slices prepared from the cortex was e s s e n t i a l l y similar to that described by Frazer et al. (6), the major modification being the use of phosphodiesterase i n h i b i t o r R0-20-1724 instead of caffeine in the medium. In short, i t is as follows: slices of cerebral cortex from male guinea pigs were prepared using a Mcllwain tissue chRpper and were washed with Kreb's-Ringer bicarbonate medium. For labeling with JH-adenine, the slices were incubated with 3H-adenine (5uci/ml suspension) at 37oc for 30 minutes in Kreb's-Ringer bicarbonate medium (gassed continuously with 95% Op, 5% C02). The slices were then washed 5 times with the buffer, and aliquot~ of labeled slices were incubated in Kreb's-Ringer medium (gassed throughout incubation) with R0-20-1724 (0.25 mM) for 30 minutes at 37oc at which time histamine was added to make the f i n a l concentrations as indicated, and the slices were incubated for an additional I0 minutes. The reaction was terminated by boiling a f t e r the addition of non-radioactive c y c l i c AMP. The 3H-cyclic AMP formed was isolated by column chromatography and by the Ba (OH)2-ZnSOaprecipitation method as described by Kr~shna et al. (7)R. The results-a~e eRpressed as percent conversion of total °H-incorporated ~ucleotides~to JH-cyclic AMP. R0-20-1724 was a g i f t from Hoffman-LaRoche, Nutley, N.J. ~H-adenine was obtained from New England Nuclear and histamine from Sigma.
2
Z
'~ .u > "r
8~.~ o
L.~
-6
10-5 Histamine
10-4 (M)
FIG. 1 Effect of various concentrations of histamine on accumulation of VH-cyclic AMP in c o r t i c a l slices from untreated guinea pigs.
Vol. 30, No. ii, 1982
Antidepressant and Histamine Receptors
923
Results
The characteristics of histamine stimulated increase in 3H-cyclic AMP in the cortical slices obtained from untreated guinea pigs was found to be similar to those reported in the literature (5,8). The addition of histamine to the slices in vitro produced a dose dependent increase in 3H-cyclic AMP accumulation as shown in Fig. 1. The effects of chronic treatment (15 days) with antidepressant drugs on histamine-stimulated accumulation of JH-cyclic AMP in the guinea pig cortex obtained when the animals were k i l l e d one hour after the last injection are shown in Figure 2. For the purpose of graphical display, histamine stimulated JH-3 cyclic AMP accumulation in treated animals has been expressed as percent of Hcyclic AMP accumulation of control animals. However, statistical analysis was done with the original data preserving control group v a r i a b i l i t y • The d i f f e r ences between control and treated animals were not significant in the basal accumulation of 3H-cyclic AMP (without histamine) although i t tended to be ~ower in treated animals. Histamine (lO-5M, lO-4M)-stimulated accumulation of ~H-cyc l i c AMP in the cortical slices obtained from guinea pigs that were chronically treated with amitriptyline, desipramine, or phenelzine was significantly lower than that in the control animals• The increasing order ~'~ ~'{ _ '~ .~ ~ ~. 0~ ~.~ • -
8
°_
c
8
u
D.
o_
-
(3-
100
T °. 8. o. - ~ v v v..T._
._u o .~ 5o
ii'
"r
~
, • -=
~ BASAL
HISTAMINE (10-5 M)
STIMULATED (1o -4
M)
_FIG. 2
Effect of chronic treatment with antidepressants on 3H-cyclic AMP accumulation in cortical slices obtained from guinea pigs sacrificed one hour after last injection• Groups of guinea pigs (n=7 in each group) were injected I.P. with amitriptyline (8 mg/kg),phenelzine (15 mg/kg), desipramine (lO mg/kg), chlorpromazine (lOmg/kg), or normal saline (equal volume once dally for 15 days). One hour after the last treatment, the animals were k i l l e d , and the cereral cortex was immediately removed from the brain. Accumulation of H-cyclic AMP in the absence (basal) or presence of histamine was then determined for each animal. In each set of experiments, treated guinea pigs were paired with control guinea pigs. Since the experiments were conducted in different sets, th~ results for treated animals have been expressed as percent of ~H-cyclic AMP accumulation relative to the controls. The data were analyzed by a t - t e s t for two independent groups; p values (two-tailed) expressed above are those compared to control animals.
b
924
Antidepressant and Histamine Receptors
Vol. 30, No. ii, 1982
of i n h i b i t i o n was amitriptyline-phenelzine-desipramine. All of these drugs produced i n h i b i t i o n in the range of 35 to 55 percent of the control value. However, histamine-stimulated accumulation of 3H-cyclic AMP in the slices obtained from guinea pigs treated with chlorpromazine, which has been shown to be a potent blocker of histamine H9 receptors in v i t r o (2), was not s i g n i f i c a n t l y d i f f e r e n t from that in the contgol animals.
cO .I.O
'- -~ ":-
E
u~
u
u
a_
c~
1O0-
8oo8
-
Q_
.0.
<
.._
._~
g
--
v vv
~
VVV n
CL O_ O_
U
U
.
!i IIF;! ~ ]
I:1:
:::::r;* :I :~
If
50. Fi;ii!;I~ I~
L
• c-
13
.~ o ¢-
u
i!!i[i!i!fi!i~t I~
l~_
0 BASAL
HISTAMINE ( 10 -5 M)
STIMULATED ( 10-4 M)
FIG. 3 Effect of chronic treatment with antidepressants on 3H-cyclic AMP accumulation in c o r t i c a l slices obtained from guinea pigs s a c r i f i c e d 24 hours a f t e r last i n j e c t i o n . Another set of experiments was performed to determine i f the reduction in 3H-cyclic AMP accumulation in the guinea pigs treated with antidepressant drugs is related to the blockade or s u b s e n s i t i v i t y of histamine receptors. In this set of experiments groups of guinea pigs were treated for 15 days with the drugs ~nd were s a c r i f i c e d 24 hours a f t e r the last i n j e c t i o n . Histamine stimulated ~H-cyclic AMP accumulation was then determined in the c o r t i c a l slices in each animal. The r e s u l t s , which ~re shown in Fig. 3, indicated a s i g n i f i c a n t decrease in histamine-stimulated ~H-cyclic AMP accumulation in the slices obtained from animals treated with a m i t r i p t y l i n e , desipramine, and phenelzine as compared to the control animals. These results are thus similar to those obtained when animals were s a c r i f i c e d one hour a f t e r the last treatment, indicating that the effects persist at least up to 24 hours. I t has been shown that the e f f e c t of acute treatment (single i n j e c t i o n ) with antidepressants d i f f e r s from the e f f e c t of chronic treatment on betaadrenergic receptor s e n s i t i v i t y in the rat brain (9). We, therefore, also examined the e f f e c t s of acute treatment with antidepressants on accumulation of 3H-cyclic AMP in the guinea pig cortex. For acute studies, groups of guinea pigs (n=6 in each group) were injected once with a m i t r i p t y l i n e (8 mg/kg),
Vol. 30, No. ii, 1982
Antidepressant and Histamine Receptors
925
desipramine (I0 mg/kg), phenelzine (5 mg/kg), or saline and were k i l l e d one hour after injection for JH-cyclic AMP accumulation studies The basal accumulation of JH-cyclic AMP in the slices obtained from guinea pigs treated acutely with antidepressants was similar to that in control animals, as shown in Fig. 4.
°_
¢z °O _ O
0
E U U
<
0
.VV O_
0-
I00
(==
._u -~ ,~
• --
~5o ~
)
I U t-"
BASAL
HISTAMINE ( I0-5 M )
STIMULATED
(10-4M)
FIG. 4 Effect of 3acute treatment (single injection) with antidepressants on H-cyclic AMP accumulation in guinea pig cortical slices. Groups of guinea pigs (n=6 in each group) were injected once I.P. with amitriptyline (8 mg/kg), desipramine (I0 mg/kg), phenelzine (5 mg/kg), or normal saline. The animals were k i l l e d one hour after the injection, at which time the cortex was removed from the brain. The JH-cyclic AMP accumulation in the cortical slices was determined in the absence (basal) or presence of various concentrations of histamine in control and drug-treated animals. The figure shows comparisons of control and treated animals in the basal and histamine stimulated accumulation of 3H-cyclic AMP by the pro cedure indicated in Fig. 2. 4 The accumulation of 3H-cyclic AMP in the presence of histamine (IO-5M, I0- M) was s i g n i f i c a n t l y lower in the slices obtained from the animals acutely treated with amitriptyline and desipramine, but not in animals treated with phenelzine, indicating that the effect of acute treatment with phenelzine d i f fers from i t s effect under chronic conditions.
Discussion These results have some important implications. Since i t has been shown that in the guinea pig brain a histamine-stimulated increase in cyclic AMP production is related to the interaction of histamine with both histamine HI and
926
Antidepressant and Histamine Receptors
Vol. 30, No. ii, 1982
H~ receptors (10,11), i t is reasonable to assume that treatment with antidepressants causes s u b s e n s i t i v i t y of both HI and H2 receptors in the guinea pig brain although t h e i r r e l ~ t i v e e f f e c t s couId not be ascertained. The decrease in histamine-stimulated H-cyclic AMP accumulation in guinea pigs treated with a m i t r i p t y l i n e or desipramine under chronic and acute conditions is probably related at least in part to the blockade of histamine receptors by these drugs. I t has been shown that t r i c y c l i c antidepressants are potent blockers of histamine receptors (1,2), and the level of these drugs in the brain a f t e r a single dose is reported to be similar to the level observed a f t e r chronic treatment (12). This explanation appears to be consistent with the recent observation of i f f l e y et al. (13) that t r i c y c l i c antidepressants competed with the binding of H-mepyramine to histamine HI receptors in the mouse brain in vivo. However, the observation that t h i s decrease in histamine receptor responsiveness persists 24 hours a f t e r the last administration of drugs may suggest that mechanisms other than blockade of receptors are associated with reduced response of histamine receptors.
~
The antidepressant drug phenelzine, is a weak blocker of histamine receptors and reduces histamine receptor s e n s i t i v i t y a f t e r chronic treatment, but not a f t e r acute treatment. This observation f u r t h e r suggests that mechanisms other than blockade of histamine receptors may be associated with the observed reduction of histamine receptor responsiveness a f t e r chronic treatment with phenelzine. I n h i b i t i o n of methyl histamine metabolism by treatment with phenelzine probably results in increased postsynaptic concentrations of histamine receptor agonists (methyl histamine, histamine). Overexposure of histamine receptors to increased concentrations of agonists results in s u b s e n s i t i v i t y of histamine receptors. This explanation appears to be consistent with the reports of Taylor and Richelson (14) who observed desensitization of histamine HI receptors by agonists in mouse neuroblastoma c e l l s . This mechanism of desensitization of histamine receptors is also similar to those suggested for beta-adrenergic receptors (9). Whether or not a similar mechanism is associated with the decreased response to histamine in the animals treated with t r i c y c l i c antidepressants is unclear, since the effects of these drugs on histamine uptake, release or metabolism is not known. Two d i f f e r e n t mechanisms may thus be associated in decreasing histamine sensitive accumulation of ~H-cyclic AMP in the guinea pig cortex. Whereas under acute treatment, the decrease in histamine sensitive 3Hcyclic AMP f~rmation may be caused by the blockade of histamine receptors, the decrease in JH-cyclic AMP formation in chronically treated animals may be related to adaptive changes in the histamine receptor-adenylate cyclase system. The f a i l u r e of chlorpromazine to cause histamine receptor s u b s e n s i t i v i t y suggests that such effects may be specific to antidepressant drugs. However, the effects of several other phenothiazines, which have been shown to be morepetent blockers of histamine H2 receptors (2), should be studied before such a conclusion is drawn. I t is possible that the doses of chlorpromazine used in this study are low. The in v i t r o e f f e c t s of antidepressant drugs on histamine receptor sensit i v i t y has been studied by several investigators. Palmer et al. (15) observed that imipramine, desipramine and t h e i r metabolites i n h i b i t e d in v i t r o the histamine stimulated adenylate cyclase in the slices and homogenates obtained from rabbit cerebral cortex. Green and Mayaani ( I ) and Kanof and Greengard (2) reported that antidepressant drugs and neuroleptics were potent i n h i b i t o r s of histamine H2 receptor mediated cyclic AMP formation in the homogenates obtained from guinea pig hippocampus, whereas Richelson (16) found that these drugs were potent blockers of histamine HI receptors in neuroblastoma c e l l s . Althoygh D i f f l e y et al. (13) showed that t r i c y c l i c antidepressants competed with ~Hmepyramine for binding to HI receptors in vivo, to our knowledge the e f f e c t of treatment with antidepressant drugs on histamine receptor mediated c y c l i c AMP formation in the brain has not been reported before.
Vol. 30, No. ii, 1 9 8 2
~tidepressant and Histamine Receptors
927
Our observation that treatment with antidepressants but not with phenothiazines causes a reduction in histamine receptor response may suggest that certain therapeutic effects of antidepressant drugs may be related to t h e i r a b i l i t y to block histamine receptors in the brain. This assumption is also supported by the observations of Green and Mayaani ( I ) , and of Kanof and Greengard (2) that antidepressant drugs are potent blockers of histamine receptors and that they compete with JH-mepyramine for binding to the HI receptor sites in the brain under in vivo conditions (13). However, antidepressant treatment causes a reduction in the histamine receptor response a f t e r both acute (one administration) and chronic treatment, whereas the c l i n i c a l e f f e c t s of the antidepressant drugs are manifested only a f t e r prolonged treatment (at least I-3 weeks). Furthermore there is generally a poor correlation between the potency of antidepressant drugs as i n h i b i t o r s of histamine receptors in v i t r o and the average c l i n i c a l dose used in the treatment of depression (2). I t appears therefore that although histamine may play a role in the pathophysiology of a f f e c t i v e i l l n e s s and that some of the pharmacologic and side effects of the antidepressant drugs may result as a consequence of the blockade of histamine receptors, the results obtained thus far do not support the assumption that blockade of histamine receptors contribute to the c l i n i c a l e f f e c t s of the antidepressant drugs. Further work is therefore needed to elucidate the role of histaminergic mechanisms in a f f e c t i v e i l l n e s s .
References I. 2. 3. 4. 5. 6. 7. 8. 9. I0. II. 12. 13. 14. 15. 16.
J.P. GREEN and S. MAYAANI, Nature 269 163-169 (1977). P.D. KANOF and P. GREENGARD, Nature 272 329-333 (1978). D.C. U'PRICHARD, D.A. GREENBERGand S.H. SNYDER, Science 199 197-198 (1978). J.E. ROSENBLATT, C.B. PERT, J.F. TALLMAN, A. PERT and W.E. BUNNEY, Brain Res. 160 186-191 (1979). S. PSYCHOYOS, Life Sci. 23 2155-2162 (1978). A. FRAZER, G.N. PANDEY, J__MENDELS, A. NEELEY, M. KANE and M.E. HESS, Neuropharmacology 13 1131-1140 (1974). G. KRISHNA, B. WEISS and B.B. BRODIE, J. Pharmacol. Exp. Ther. 163 379-385 (1968). M. HUANG, H. SHIMIZU and J. DALY, Mol. Pharm. 7 155-162 (1971). G.N. PANDEY, W.J. HEINZE, B.W. BROWNand J.M. DAVIS, Nature 280 234-235 (1979). J.C. SCHWARTZ, Life Sci. 25 895-912 (1978). M. BAUDRY, M.P. MARTRESan~J.C. SCHWARTZ, Nature 253 362-364 (1975). K. SARAI, A. FRAZER, D. BRUNSWICKand J. MENDELS, Biochem. Pharmacol. 2_]_7 2179-2181 (1978). D. DIFFLEY, V.T. TRAN and S.H. SNYDER, Euro. J. Pharmacol. 64 177-181 (1980). J.E. TAYLOR and E. RICHELSON, Mol. Pharmacol. 15 462-471 (1979). G.C. PALMER, H.R. WAGNER, S.J. PALMERand A.A. M--ANIAN, Comm. Psychopharmacol. 1 61-69 (1977). E. RICHELSON, Nature 276 176-177 (1978).
Pergamon Press
TREATMENT~WITH ANTIDEPRESSANTS AND HISTAMINE RECEPTORMEDIATED JH-CYCLIC AMP FORMATION IN GUINEA PIG CORTEX Ghanshyam N. Pandey, Alan Krueger, Puppala Sudershan, and John M. Davis Research Department, l l l i n o i s State Psychiatric I n s t i t u t e , 1601 West Taylor Street, Chicago, l l l i n o i s 60612 and Department of Psychiatry, University of l l l i n o i s at the Medical Center (Received in final form January 13, 1982)
Summary I t has been recently reported that most of the antidepressant drugs block histamine HI and Hp receptors in the brain under in v i t r o conditions and i t has be~n suggested that this may be related in part to t h e i r therapeutic e f f e c t . Since the in v i t r o and in vivo e f f e c t s of these drugs may d i f f e r , we studied the e f f e c t of t r e a t ment with antidepressant drugs on histamine receptor s e n s i t i v i t y in the guinea pig brain and observed that chronic treatment with t r i c y c l i c antidepressants or phenelzine (an MAO i n h i b i t o r ) causes a reduction in histamine receptor s e n s i t i v i t y . This reduction is probably mediated through two d i f f e r e n t mechanisms, since only t r i c y c l i c antidepressants cause a reduction a f t e r acute treatment. Although some of the side effects of antidepressant treatment may be related to the blockade of histamine receptors, these results do not support the assumption that this e f f e c t of antidepressant treatment c o n t r i butes to t h e i r c l i n i c a l e f f e c t s . Several antidepressant drugs have been shown to block histamine receptors in the brain under in v i t r o conditions (1,2). These observations have led to the suggestion that some therapeutic e f f e c t s of antidepressant drugs may be related in part to t h e i r capacity to block histamine receptors in the brain (1,2). However, to our knowledge, the in vivo effects of antidepressant drugs ( i . e . e f f e c t of treatment with antidepressants) on histamine receptors in the brain have not been studied. I t has been observed that in vivo effects of drugs on receptor s e n s i t i v i t y may d i f f e r from those observed in v i t r o . Fo~ example, antidepressant drugs that are potent blockers of alpha receptors (3HB4101 binding) in v i t r o (3), do not produce any s i g n i f i c a n t a l t e r a t i o n s in H-WB4101 binding a f t e r t h e i r administration in vivo (4). I t is of i n t e r e s t , therefore, to examine the effects of antidepressant treatment on histamine receptor s e n s i t i v i t y in the guinea pig brain, since the results of such studies could provide f u r t h e r evidence for or against the suggested mode of action of antidepressants.
~
Methods Groups of male guinea pigs (weighing about 250-300g at the s t a r t of the treatment) were injected I.P. with the drugs (as indicated) or with normal saline e i t h e r once daily f o r 15 days for chronic studies or once f o r acute studies. The animals were then s a c r i f i c e d e i t h e r one hour or 24 hours a f t e r the last treatment and the cerebral cortex was immediately removed from the brain. 0024-3205/82/110921-07503.00/0 Copyright (c) 1982 Pergamon Press Ltd.
922
Antidepressant and Histamine Receptors
Vol. 30, No. Ii, 1982
Histamine-stimulated accumulatioq of 3H-cyclic AMP in slices of guinea pig cortex that had been prelabeled with OH-adenine was used as an index of adenylate cyclase-coupled histamine receptor s e n s i t i v i t y (receptor responsivity). This pulse-labeling technique has been used previously for the determination of adenylate cyclase a c t i v i t y in several tissues, including the guinea pig brain (5). The procedure used for the determination of 3H-cyclic AMP accumulation in the slices prepared from the cortex was e s s e n t i a l l y similar to that described by Frazer et al. (6), the major modification being the use of phosphodiesterase i n h i b i t o r R0-20-1724 instead of caffeine in the medium. In short, i t is as follows: slices of cerebral cortex from male guinea pigs were prepared using a Mcllwain tissue chRpper and were washed with Kreb's-Ringer bicarbonate medium. For labeling with JH-adenine, the slices were incubated with 3H-adenine (5uci/ml suspension) at 37oc for 30 minutes in Kreb's-Ringer bicarbonate medium (gassed continuously with 95% Op, 5% C02). The slices were then washed 5 times with the buffer, and aliquot~ of labeled slices were incubated in Kreb's-Ringer medium (gassed throughout incubation) with R0-20-1724 (0.25 mM) for 30 minutes at 37oc at which time histamine was added to make the f i n a l concentrations as indicated, and the slices were incubated for an additional I0 minutes. The reaction was terminated by boiling a f t e r the addition of non-radioactive c y c l i c AMP. The 3H-cyclic AMP formed was isolated by column chromatography and by the Ba (OH)2-ZnSOaprecipitation method as described by Kr~shna et al. (7)R. The results-a~e eRpressed as percent conversion of total °H-incorporated ~ucleotides~to JH-cyclic AMP. R0-20-1724 was a g i f t from Hoffman-LaRoche, Nutley, N.J. ~H-adenine was obtained from New England Nuclear and histamine from Sigma.
2
Z
'~ .u > "r
8~.~ o
L.~
-6
10-5 Histamine
10-4 (M)
FIG. 1 Effect of various concentrations of histamine on accumulation of VH-cyclic AMP in c o r t i c a l slices from untreated guinea pigs.
Vol. 30, No. ii, 1982
Antidepressant and Histamine Receptors
923
Results
The characteristics of histamine stimulated increase in 3H-cyclic AMP in the cortical slices obtained from untreated guinea pigs was found to be similar to those reported in the literature (5,8). The addition of histamine to the slices in vitro produced a dose dependent increase in 3H-cyclic AMP accumulation as shown in Fig. 1. The effects of chronic treatment (15 days) with antidepressant drugs on histamine-stimulated accumulation of JH-cyclic AMP in the guinea pig cortex obtained when the animals were k i l l e d one hour after the last injection are shown in Figure 2. For the purpose of graphical display, histamine stimulated JH-3 cyclic AMP accumulation in treated animals has been expressed as percent of Hcyclic AMP accumulation of control animals. However, statistical analysis was done with the original data preserving control group v a r i a b i l i t y • The d i f f e r ences between control and treated animals were not significant in the basal accumulation of 3H-cyclic AMP (without histamine) although i t tended to be ~ower in treated animals. Histamine (lO-5M, lO-4M)-stimulated accumulation of ~H-cyc l i c AMP in the cortical slices obtained from guinea pigs that were chronically treated with amitriptyline, desipramine, or phenelzine was significantly lower than that in the control animals• The increasing order ~'~ ~'{ _ '~ .~ ~ ~. 0~ ~.~ • -
8
°_
c
8
u
D.
o_
-
(3-
100
T °. 8. o. - ~ v v v..T._
._u o .~ 5o
ii'
"r
~
, • -=
~ BASAL
HISTAMINE (10-5 M)
STIMULATED (1o -4
M)
_FIG. 2
Effect of chronic treatment with antidepressants on 3H-cyclic AMP accumulation in cortical slices obtained from guinea pigs sacrificed one hour after last injection• Groups of guinea pigs (n=7 in each group) were injected I.P. with amitriptyline (8 mg/kg),phenelzine (15 mg/kg), desipramine (lO mg/kg), chlorpromazine (lOmg/kg), or normal saline (equal volume once dally for 15 days). One hour after the last treatment, the animals were k i l l e d , and the cereral cortex was immediately removed from the brain. Accumulation of H-cyclic AMP in the absence (basal) or presence of histamine was then determined for each animal. In each set of experiments, treated guinea pigs were paired with control guinea pigs. Since the experiments were conducted in different sets, th~ results for treated animals have been expressed as percent of ~H-cyclic AMP accumulation relative to the controls. The data were analyzed by a t - t e s t for two independent groups; p values (two-tailed) expressed above are those compared to control animals.
b
924
Antidepressant and Histamine Receptors
Vol. 30, No. ii, 1982
of i n h i b i t i o n was amitriptyline-phenelzine-desipramine. All of these drugs produced i n h i b i t i o n in the range of 35 to 55 percent of the control value. However, histamine-stimulated accumulation of 3H-cyclic AMP in the slices obtained from guinea pigs treated with chlorpromazine, which has been shown to be a potent blocker of histamine H9 receptors in v i t r o (2), was not s i g n i f i c a n t l y d i f f e r e n t from that in the contgol animals.
cO .I.O
'- -~ ":-
E
u~
u
u
a_
c~
1O0-
8oo8
-
Q_
.0.
<
.._
._~
g
--
v vv
~
VVV n
CL O_ O_
U
U
.
!i IIF;! ~ ]
I:1:
:::::r;* :I :~
If
50. Fi;ii!;I~ I~
L
• c-
13
.~ o ¢-
u
i!!i[i!i!fi!i~t I~
l~_
0 BASAL
HISTAMINE ( 10 -5 M)
STIMULATED ( 10-4 M)
FIG. 3 Effect of chronic treatment with antidepressants on 3H-cyclic AMP accumulation in c o r t i c a l slices obtained from guinea pigs s a c r i f i c e d 24 hours a f t e r last i n j e c t i o n . Another set of experiments was performed to determine i f the reduction in 3H-cyclic AMP accumulation in the guinea pigs treated with antidepressant drugs is related to the blockade or s u b s e n s i t i v i t y of histamine receptors. In this set of experiments groups of guinea pigs were treated for 15 days with the drugs ~nd were s a c r i f i c e d 24 hours a f t e r the last i n j e c t i o n . Histamine stimulated ~H-cyclic AMP accumulation was then determined in the c o r t i c a l slices in each animal. The r e s u l t s , which ~re shown in Fig. 3, indicated a s i g n i f i c a n t decrease in histamine-stimulated ~H-cyclic AMP accumulation in the slices obtained from animals treated with a m i t r i p t y l i n e , desipramine, and phenelzine as compared to the control animals. These results are thus similar to those obtained when animals were s a c r i f i c e d one hour a f t e r the last treatment, indicating that the effects persist at least up to 24 hours. I t has been shown that the e f f e c t of acute treatment (single i n j e c t i o n ) with antidepressants d i f f e r s from the e f f e c t of chronic treatment on betaadrenergic receptor s e n s i t i v i t y in the rat brain (9). We, therefore, also examined the e f f e c t s of acute treatment with antidepressants on accumulation of 3H-cyclic AMP in the guinea pig cortex. For acute studies, groups of guinea pigs (n=6 in each group) were injected once with a m i t r i p t y l i n e (8 mg/kg),
Vol. 30, No. ii, 1982
Antidepressant and Histamine Receptors
925
desipramine (I0 mg/kg), phenelzine (5 mg/kg), or saline and were k i l l e d one hour after injection for JH-cyclic AMP accumulation studies The basal accumulation of JH-cyclic AMP in the slices obtained from guinea pigs treated acutely with antidepressants was similar to that in control animals, as shown in Fig. 4.
°_
¢z °O _ O
0
E U U
<
0
.VV O_
0-
I00
(==
._u -~ ,~
• --
~5o ~
)
I U t-"
BASAL
HISTAMINE ( I0-5 M )
STIMULATED
(10-4M)
FIG. 4 Effect of 3acute treatment (single injection) with antidepressants on H-cyclic AMP accumulation in guinea pig cortical slices. Groups of guinea pigs (n=6 in each group) were injected once I.P. with amitriptyline (8 mg/kg), desipramine (I0 mg/kg), phenelzine (5 mg/kg), or normal saline. The animals were k i l l e d one hour after the injection, at which time the cortex was removed from the brain. The JH-cyclic AMP accumulation in the cortical slices was determined in the absence (basal) or presence of various concentrations of histamine in control and drug-treated animals. The figure shows comparisons of control and treated animals in the basal and histamine stimulated accumulation of 3H-cyclic AMP by the pro cedure indicated in Fig. 2. 4 The accumulation of 3H-cyclic AMP in the presence of histamine (IO-5M, I0- M) was s i g n i f i c a n t l y lower in the slices obtained from the animals acutely treated with amitriptyline and desipramine, but not in animals treated with phenelzine, indicating that the effect of acute treatment with phenelzine d i f fers from i t s effect under chronic conditions.
Discussion These results have some important implications. Since i t has been shown that in the guinea pig brain a histamine-stimulated increase in cyclic AMP production is related to the interaction of histamine with both histamine HI and
926
Antidepressant and Histamine Receptors
Vol. 30, No. ii, 1982
H~ receptors (10,11), i t is reasonable to assume that treatment with antidepressants causes s u b s e n s i t i v i t y of both HI and H2 receptors in the guinea pig brain although t h e i r r e l ~ t i v e e f f e c t s couId not be ascertained. The decrease in histamine-stimulated H-cyclic AMP accumulation in guinea pigs treated with a m i t r i p t y l i n e or desipramine under chronic and acute conditions is probably related at least in part to the blockade of histamine receptors by these drugs. I t has been shown that t r i c y c l i c antidepressants are potent blockers of histamine receptors (1,2), and the level of these drugs in the brain a f t e r a single dose is reported to be similar to the level observed a f t e r chronic treatment (12). This explanation appears to be consistent with the recent observation of i f f l e y et al. (13) that t r i c y c l i c antidepressants competed with the binding of H-mepyramine to histamine HI receptors in the mouse brain in vivo. However, the observation that t h i s decrease in histamine receptor responsiveness persists 24 hours a f t e r the last administration of drugs may suggest that mechanisms other than blockade of receptors are associated with reduced response of histamine receptors.
~
The antidepressant drug phenelzine, is a weak blocker of histamine receptors and reduces histamine receptor s e n s i t i v i t y a f t e r chronic treatment, but not a f t e r acute treatment. This observation f u r t h e r suggests that mechanisms other than blockade of histamine receptors may be associated with the observed reduction of histamine receptor responsiveness a f t e r chronic treatment with phenelzine. I n h i b i t i o n of methyl histamine metabolism by treatment with phenelzine probably results in increased postsynaptic concentrations of histamine receptor agonists (methyl histamine, histamine). Overexposure of histamine receptors to increased concentrations of agonists results in s u b s e n s i t i v i t y of histamine receptors. This explanation appears to be consistent with the reports of Taylor and Richelson (14) who observed desensitization of histamine HI receptors by agonists in mouse neuroblastoma c e l l s . This mechanism of desensitization of histamine receptors is also similar to those suggested for beta-adrenergic receptors (9). Whether or not a similar mechanism is associated with the decreased response to histamine in the animals treated with t r i c y c l i c antidepressants is unclear, since the effects of these drugs on histamine uptake, release or metabolism is not known. Two d i f f e r e n t mechanisms may thus be associated in decreasing histamine sensitive accumulation of ~H-cyclic AMP in the guinea pig cortex. Whereas under acute treatment, the decrease in histamine sensitive 3Hcyclic AMP f~rmation may be caused by the blockade of histamine receptors, the decrease in JH-cyclic AMP formation in chronically treated animals may be related to adaptive changes in the histamine receptor-adenylate cyclase system. The f a i l u r e of chlorpromazine to cause histamine receptor s u b s e n s i t i v i t y suggests that such effects may be specific to antidepressant drugs. However, the effects of several other phenothiazines, which have been shown to be morepetent blockers of histamine H2 receptors (2), should be studied before such a conclusion is drawn. I t is possible that the doses of chlorpromazine used in this study are low. The in v i t r o e f f e c t s of antidepressant drugs on histamine receptor sensit i v i t y has been studied by several investigators. Palmer et al. (15) observed that imipramine, desipramine and t h e i r metabolites i n h i b i t e d in v i t r o the histamine stimulated adenylate cyclase in the slices and homogenates obtained from rabbit cerebral cortex. Green and Mayaani ( I ) and Kanof and Greengard (2) reported that antidepressant drugs and neuroleptics were potent i n h i b i t o r s of histamine H2 receptor mediated cyclic AMP formation in the homogenates obtained from guinea pig hippocampus, whereas Richelson (16) found that these drugs were potent blockers of histamine HI receptors in neuroblastoma c e l l s . Althoygh D i f f l e y et al. (13) showed that t r i c y c l i c antidepressants competed with ~Hmepyramine for binding to HI receptors in vivo, to our knowledge the e f f e c t of treatment with antidepressant drugs on histamine receptor mediated c y c l i c AMP formation in the brain has not been reported before.
Vol. 30, No. ii, 1 9 8 2
~tidepressant and Histamine Receptors
927
Our observation that treatment with antidepressants but not with phenothiazines causes a reduction in histamine receptor response may suggest that certain therapeutic effects of antidepressant drugs may be related to t h e i r a b i l i t y to block histamine receptors in the brain. This assumption is also supported by the observations of Green and Mayaani ( I ) , and of Kanof and Greengard (2) that antidepressant drugs are potent blockers of histamine receptors and that they compete with JH-mepyramine for binding to the HI receptor sites in the brain under in vivo conditions (13). However, antidepressant treatment causes a reduction in the histamine receptor response a f t e r both acute (one administration) and chronic treatment, whereas the c l i n i c a l e f f e c t s of the antidepressant drugs are manifested only a f t e r prolonged treatment (at least I-3 weeks). Furthermore there is generally a poor correlation between the potency of antidepressant drugs as i n h i b i t o r s of histamine receptors in v i t r o and the average c l i n i c a l dose used in the treatment of depression (2). I t appears therefore that although histamine may play a role in the pathophysiology of a f f e c t i v e i l l n e s s and that some of the pharmacologic and side effects of the antidepressant drugs may result as a consequence of the blockade of histamine receptors, the results obtained thus far do not support the assumption that blockade of histamine receptors contribute to the c l i n i c a l e f f e c t s of the antidepressant drugs. Further work is therefore needed to elucidate the role of histaminergic mechanisms in a f f e c t i v e i l l n e s s .
References I. 2. 3. 4. 5. 6. 7. 8. 9. I0. II. 12. 13. 14. 15. 16.
J.P. GREEN and S. MAYAANI, Nature 269 163-169 (1977). P.D. KANOF and P. GREENGARD, Nature 272 329-333 (1978). D.C. U'PRICHARD, D.A. GREENBERGand S.H. SNYDER, Science 199 197-198 (1978). J.E. ROSENBLATT, C.B. PERT, J.F. TALLMAN, A. PERT and W.E. BUNNEY, Brain Res. 160 186-191 (1979). S. PSYCHOYOS, Life Sci. 23 2155-2162 (1978). A. FRAZER, G.N. PANDEY, J__MENDELS, A. NEELEY, M. KANE and M.E. HESS, Neuropharmacology 13 1131-1140 (1974). G. KRISHNA, B. WEISS and B.B. BRODIE, J. Pharmacol. Exp. Ther. 163 379-385 (1968). M. HUANG, H. SHIMIZU and J. DALY, Mol. Pharm. 7 155-162 (1971). G.N. PANDEY, W.J. HEINZE, B.W. BROWNand J.M. DAVIS, Nature 280 234-235 (1979). J.C. SCHWARTZ, Life Sci. 25 895-912 (1978). M. BAUDRY, M.P. MARTRESan~J.C. SCHWARTZ, Nature 253 362-364 (1975). K. SARAI, A. FRAZER, D. BRUNSWICKand J. MENDELS, Biochem. Pharmacol. 2_]_7 2179-2181 (1978). D. DIFFLEY, V.T. TRAN and S.H. SNYDER, Euro. J. Pharmacol. 64 177-181 (1980). J.E. TAYLOR and E. RICHELSON, Mol. Pharmacol. 15 462-471 (1979). G.C. PALMER, H.R. WAGNER, S.J. PALMERand A.A. M--ANIAN, Comm. Psychopharmacol. 1 61-69 (1977). E. RICHELSON, Nature 276 176-177 (1978).