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Epinephrine accumulation in rat brain after chronic administration of pargyline and LY 51641 — comparison with other brain amines
342
B,mel t ewarc'~t.
!
BRE 20952
Epinephrine accumulation in rat brain after chronic administration of pargyline and LY 51641 - - comparison with other brain amines IVAN N. MEFFORD, KEV1N A. ROTH, SHEILA M. JURIK, VIGKI COLLMAN, STEVE MclNI'IRE. LORI TOLBERT and JACK D. BARCHAS Nancy Pritzker Laboratory of Behavioral Neurochemistry, Department of Psychiatry and Behavioral Sciences, Stan]~Jrd University School ~ (Medicine, Stan]brd, CA 94305 (U.S.A. )
(Accepted March 12th, 1985) Key words; monoamine oxidase inhibition - - epinephrine - - biogenic amines - - chronic administration - - LY 51641 ~ pargyline
Concentrations of biogenic amines and metabolites were measured in regions of rat brain following administration of monoamine oxidase (MAO) inhibitors for 21 days. Epinephrine concentrations were increased from 350 to 500% following chronic administration of LY 51641, a selective inhibitor of MAO type A. Norepinephrine, dopamine and serotonin showed much less relative accumulation. The marked relative accumulation of epinephrine may be related to the efficacy of inbibitors of MAO type A in the treatment of depression. The existence of multiple forms of monoamine oxidase ( M A O ) (EC 1.4.3.4) (ref. 10,19) and of selective inhibitors toward these multiple forms has been known for several yearsS.S,~0.Is. M A O inhibitors ( M A O I ) have been used effectively for many years in the treatment of depression 9A6. Most clinically approved M A O inhibitors, however, demonstrate little selectivity towards the two forms of M A O . Recent evidence from clinical trials suggests that selective inhibition of the A form of M A O may have more antidepressant efficacy than inhibition of M A O Type B14. It has been demonstrated in the rat that chronic regimens of selective M A O inhibitors can be chosen at dosages to maintain effective selectivity over several weeks I. In light of the possible clinical significance of selective M A O inhibition, a study was undertaken to determine the effects of chronic administration of selective inhibitors of both the A and B forms on regional rat brain catecholamines, serotonin and their metabolites. Selective inhibitors chosen for this work were pargyline (1 mg/kg i.p.), which has been shown to be a selective inhibitor of M A O Type B over a 3-week period I and Lilly (LY) 51641 (0.5 mg/kg i.p.), a potent selective M A O Type A inhibitorS.
Male S p r a g u e - D a w l e y rats, 200-220 g at the start of the study were used throughout. LY 51641, pargyline or saline were administered daily intraperitoneally in a volume of 1.0 ml. Drug regimens were based on both preliminary acute dose response studies and on clinically effective doses in man 14. The doses chosen were 1 mg/kg for pargyline and 0.5 mg/kg for LY 51641. Drugs were administered daily between 13.00 and 16.00 h for 21 days. Animals were sacrificed by decapitation 24 h following the last injection. Brains were removed and dissected over crushed ice. Raphe was dissected according to Deguchi et al.3. Brain parts were stored at --80 °C until analyzed. Catecholamines, serotonin, 5-hydroxyindole acetic acid ( 5 - H I A A ) , 3,4-dihydroxyphenyl acetic acid ( D O P A C ) and homovanillic acid ( H V A ) were analyzed by H P L C with electrochemical detection as previously described 15. Tissues were sonicated in 400 /~1 0.2 M HC104 plus 50/~1 10-6 M dihydroxybenzyiamine and 50 ktl 10-6 M 3-methoxy-4-hydroxyphenylethanol. A 100/zl aliquot was removed and centrifuged at 12,800 g for determination of serotonin, D O P A C , 5 - H I A A and H V A . Catechols in the remaining 400/~l of homogenate were extracted with
Correspondence. • I. N. Mefford, Department of Chemistry, Boston College, Chestnut Hill, MA 02167, U S.A.
0006-8993/85/$03.30 © 1985 Elsevier Science Publishers B.V. (Biomedical Division)
343 significantly d e c r e a s e d in all areas s t u d i e d f o l l o w i n g
A1203 as p r e v i o u s l y d e s c r i b e d 11. Chromatographic DOPAC,
resolution
of
serotonin,
5 - H I A A and H V A was a c c o m p l i s h e d on a
chronic administration
of L Y 51641 or p a r g y l i n e
w h i c h led to a lesser d e g r e e of d e p l e t i o n in e a c h re-
5 ktm u l t r a s p h e r e O D S r e v e r s e p h a s e c o l u m n ( B e c k -
gion. H V A was significantly d e p l e t e d o n l y in stria-
m a n ) , 4.6 m m i.d. x 25 cm length, using a s o l v e n t
t u m . D o p a m i n e was significantly e l e v a t e d only in
system of 0.1 M s o d i u m a c e t a t e , 0.1 M citric acid and
h i p p o c a m p u s . C o n c e n t r a t i o n s of 5 - H I A A w e r e n o t
2 0 % m e t h a n o l (v:v) at a flow rate of 1.0 m l / m i n . D e -
significantly c h a n g e d e x c e p t in h y p o t h a l a m u s w h e r e
t e c t i o n was a c c o m p l i s h e d with a c a r b o n p a s t e elec-
L Y 51641 a d m i n i s t r a t i o n led to a m o d e s t 2 5 % de-
t r o d e at an applied potential of + 0.75 V vs A g / A g C I .
c r e a s e ( P < 0.05).
R e s o l u t i o n of c a t e c h o l s was a c c o m p l i s h e d on a 25 cm
T h e effects of c h r o n i c a d m i n i s t r a t i o n of p a r g y l i n e
x 4.6 m m i.d., 5 ~ m u l t r a s p h e r e O D S c o l u m n ( B e c k -
and L Y 51641 w e r e m o s t a p p a r e n t with t h e o t h e r
m a n ) with a s o l v e n t system of 0.1 M s o d i u m a c e t a t e ,
amines measured,
0.02 M citric acid, 100 rag/1 s o d i u m octyl sulfate, 50
e p i n e p h r i n e . O n l y s t r i a t u m and c o r t e x failed to s h o w
serotonin,
norepinephrine,
and
mg/1 E D T A and 15% m e t h a n o l (v:v) at a flow rate of
significant a c c u m u l a t i o n of 5 - H T . In all cases, accu-
1.0 ml/min. D e t e c t i o n was a c c o m p l i s h e d at a c a r b o n
m u l a t i o n was g r e a t e r f o l l o w i n g c h r o n i c a d m i n i s t r a -
paste e l e c t r o d e at an a p p l i e d p o t e n t i a l of + 0.55 V vs
tion of L Y 51641. I n c r e a s e s in c o n c e n t r a t i o n of n e a r -
A g / A g C 1 . A m p e r o m e t r i c c o n t r o l was a c c o m p l i s h e d
ly 100% w e r e o b s e r v e d in r a p h e , h y p o t h a l a m u s and
by a m o d e l L C - 3 a m p e r o m e t r i c d e t e c t o r ( B i o A n a l y -
h i p p o c a m p u s (see Fig. 1). Significant a c c u m u l a t i o n of n o r e p i n e p h r i n e
tical Systems).
was
S h o w n in T a b l e I are the results o b t a i n e d for
not o b s e r v e d in striatum nor cortex. L Y 51641 admin-
D O P A C , H V A , 5 - H I A A and d o p a m i n e . D O P A C was
istration led to a m o r e m a r k e d a c c u m u l a t i o n than
TABLE I Effects of chronic M A 0 1 administration on rat brain dopamine, HVA, D O P A C and 5-HIAA
Pargyline, 1.0 mg/kg i.p. and LY 51641 0.5 mg/kg i.p. for 21 days. ND, not determined. Brain region
Striatum control pargyline LY 5164l Hypothalamus control pargyline LY 5164l Medulla control pargyline LY51641 Cortex control pargyline LY5164l Hippocampus control pargyline LY51641 Raphe control pargyline LY51641
Concentration (ng/g wet weight +_S. E. M.) Dopamine
HVA
D OPA C
5-HIA A
7565 ± 736 8297 ___309 9275 ± 597
726 + 60 538 + 34* 451 + 24***
1671 + 129 945 + 121"* 598 ± 50***
1056 _+ 124 910 _+ 44 893 _+ 68
109 + 6 64 + 2*** 49 + 5***
981 ± 107 862 +_ 51 709 + 37*
50 _+ 5 31 + 3* 15 + 1"**
813 _+ 52 711 ± 41 769 ± 74
296 ± 19 329 ± 28 325 ___17 105 ± 6 116 ± 3 112 ± 9
29 + 4 34 ± 6 27 ± 6 ND ND ND
79 ± 8 77 + 6 77 ± 10
32 _+4 23 ± 2 29_+ 9
38 + 4 21 + 2** 13 + 3***
444 _+ 62 456 + 60 310 + 28
16 ± 2 55 ± 13"* 36 ± 11
14 _+ 5 22 _+ 7 10 ± 1
24 + 7 17 _+ 6 12 + 2
591 +_ 82 638 + 46 638 _+ 86
62 ± 4 73 ± 3 76 ± 11
29 _+ 4 23 +_ 4 32 + 11
38 ± 8 21 + 2 13 ± 2*
1849 +_ 139 2154 + 118 1937 _+ 148
* P < 0.05; ** P < 0.01; ***P < 0.001 by Student's t-test.
344 line and clorgyline at the same doses chosen here for pargyline and LY 51641 had no effect on tyrosine hydroxylase or tryptophan hydroxylase while clorgylme produced 97% inhibition of MAO Type A and 28% inhibition of MAO Type B. Pargyline was somewhat less selective, causing 93% inhibition of MAO Type B and 44% inhibition of MAO Type A activity. We found only modest increases in dopamme following treatment with pargyline and LY 51641 m some areas. Norepinephrine was increased in several areas by 15-20% after pargyline treatment, in addition, epinephrine, which was not measured in the earlier study, proved to be the most labile of the amines measured. As with the earlier study of Campbell et al.t 5-HIAA was essentially unaffected by chronic MAO inhibition by either type inhibitor in any brain region. Only modest depletion was observed in hypothalamus. Serotonin, the precursor to 5-HIAA was, however, substantially elevated, suggesting that some alternative means of 5-HIAA synthesis has compensated in its formation. Others have proposed that perhaps transamination and decarboxylation may increase in conversion of serotonin to 5-HIAAI,~;. It also seems likely that 5-HT might be compensationally metabolized by uninhibited MAO type B. The novelty of the data presented in this report ties primarily in the demonstration of the lability of brain epinephrine to chronic administration of MAO inhibitors, particularly LY 51641. Zeller and Arora zil demonstrated in vitro that epinephrine was a nearly ideal substrate for MAO type A. Fuller and coworkers at Eli Lilly have demonstrated that epinephrine is metabolized by MAO type A in brain tissue ,'~,7. The data presented here demonstrate that the relative response of epinephrine is 5-1(}-fold greater to chronic administration of a selective inhibitor of MAO type A than other biogenic amines, notably norepinephrine and 5-HT, classically considered to be the primary substrates metabolized by this enzyme in brain. MAO inhibitors have been used clinically for many years in the treatment of depression. Recent work by Lipper et al. 14shows administration of an inhibitor of MAO type A to be more efficacious in the treatment of depression than either an inhibitor of MAO type B or a non-selective MAOI. Christensen et al. e have shown epinephrine concentrations in cerebrospinal fluid of depressed patients to be lower than in corK-
2ooo3° t °1iooot i SEROTOi ~ NtN
30002000i t NOREPINEPHRINE
I,-,ooo 16G 12( 3 8(3 40 It/
U) U)
1
re
\
Cc O Z ,,¢ Z
EPINEPHRINE ~u
Fig. 1. Effects of chronic M A O I on regional rat brain biogenic amines, D, control-saline; I , LY 51641, 0.5 mg/kg i.p.; [] pargyline I m g / k g i , p . * P < 0 . 0 5 , ** P < 0 . 0 1 , *** P < 0.001 vs controls by Student's t-test, n = 6 - 8 determinations.
pargyline in all other regions. Greatest relative accumulation was observed in hypothalamus and medulla. LY 51641 administration caused a marked accumulation of epinephrine in the three regions monitored. Hypothalamic epinephrine concentrations were elevated by ~ 350%. In the raphe area epinephrine concentrations were elevated by ~ 360% while in the medulla, which contains the Cj and C, cell body areas epinephrine concentrations were elevated by nearly 500%. These data confirm and extend an earlier studyl in which whole brain serotonin, 5-HIAA, norepinephrine and dopamine were measured. These authors also demonstrated that chronic treatment with pargy-
345 trois. F o l l o w i n g t h e r a p y e p i n e p h r i n e c o n c e n t r a t i o n s
M A O type A i n h i b i t o r ( L Y 51641) or pargyline, a B
w e r e i n c r e a s e d a p p r o x i m a t e l y 4-fold w h i l e n o r e p i -
type inhibitor. T h e possible r e l e v a n c e of this obser-
nephrine concentrations were unchanged.
Several
v a t i o n with respect to the efficacy of clorgyline or
a u t h o r s h a v e o b s e r v e d the lability of h y p o t h a l a m i c e p i n e p h r i n e to a c u t e 13,t7 and c h r o n i c stress 17.
L Y 51641 and o t h e r type A M A O inhibitors in the
A s with several e a r l i e r studies, the d a t a p r e s e n t e d
t r e a t m e n t of d e p r e s s i o n is as yet u n d e f i n e d and deserves f u r t h e r a t t e n t i o n .
in this r e p o r t are s u p p o r t i v e of two f u n c t i o n a l l y active f o r m s of m o n o a m i n e oxidase in vivo. W e h a v e
This w o r k was s u p p o r t e d by N I M H P r o g r a m - P r o -
r e p o r t e d a p p a r e n t r e g i o n a l substrate p r e f e r e n c e s for
ject G r a n t , M H 23861. L Y 51641 was g e n e r o u s l y
M A O T y p e A . E p i n e p h r i n e has b e e n d e m o n s t r a t e d
supplied by Dr. Ray Fuller, Eli Lilly R e s e a r c h Labs, Indianapolis, Indiana.
to be the m o s t r e s p o n s i v e M A O T y p e A substrate in vivo f o l l o w i n g c h r o n i c a d m i n i s t r a t i o n of e i t h e r an
1 Campbell, I. C., Robinson, D. S., Lovenberg, W. and Murphy, D. L., The effects of chronic regimens of clorgyline and pargyline on monoamine metabolism in the rat brain, J. Neurochem., 32 (1979) 49-55. 2 Christensen, N. J., Vestergaard, P., Sorensen, T. and Rafaelsen, O. J., Cerebrospinal fluid adrenaline and noradrenaline in depressed patients, Acta psychiat, scand., 61 (1980) 178-182. 3 Deguchi, T., Sinha, A. K. and Barchas, J. D., Biosynthesis of serotonin in raphe nuclei of rat brain: effect of p-chlorophenylalanine, J. Neurochem., 20 (1973) 1329-1336. 4 Dunlop, E., Antidepressant effects of MAO inhibitors, Ann. N.Y. Acad. Sci., 107 (1963) 1107-1116. 5 Fuller, R. W., Selective inhibition of monoamine oxidase. In E. Costa and M. Sandier (Eds.), Monoamine Oxidase - New Vistas, Adv. Biochem. Psychopharm., 5 (1972) 539-554. 6 Fuller, R. W., Hemrick-Luecke, S. K. and Midgley, J. M., Elevation of epinephrine concentration in rat brain by LY 51641, a selective inhibitor of type A monoamine oxidase, Res. Commun. C. P., 32 (1981) 207-221. 7 Fuller, R. W., Hemrick-Luecke, S. K. and Perry, K. W., Influence of harmaline on the ability of pargyline to alter catecholamine metabolism in rats, Biochern. Pharmacol.. 30 (1981) 1295-1298. 8 Hall, D. W. R., Logan, B. W. and Parsons, G. H., Further studies on the inhibition of monoamine oxidase by M and B 9302 I. Substrate specificity in various mammalian species, Biochem. Pharmacol., 18 (1969) 1447-1454. 9 Janecek, J., Schiele, B. C. and Vestre, N. D., Pargyline and tranylcypromine in the treatment of hospitalized depressed patients, J. New Drugs, 3 (1963) 309-316. 10 Johnston, J. P., Some observations upon a new inhibitor of monoamine oxidase in brain tissue, Biochem. Pharmacol., 17 (19681 1285-1297. 11 Keller, R. W., Oke, A. F., Mefford, I. and Adams, R. N., Liquid chromatographic analysis of catecholamines: rou-
tine assay for regional brain mapping, Lt~" Sci., 19 (19761 995-1004. 12 Kido, R., Noguchi, T. and Minatogawa, Y., Enzymic studies on the metabolism of 5-hydroxyindoles in the brain, Acta vitaminol, enzymol., 29 (1975) 344-345. 13 Kvetnansky, R., Kopin, I. J. and Saavedra, J. M., Changes in epinephrine in individual hypothalamic nuclei after immobilization stress, Brain Research, 155 (1978) 387-390. 14 Lipper, S., Murphy, D. L., Slater, S. and Buchsbaum, M. S., Comparative behavioral effects of clorgyline and pargyline in man: a preliminary evaluation, Psychopharmacology. 62 (1979) 123-128. 15 Mefford, I. N., HPLC with electrochemical detection in neurochemical analysis: assay for catecholamines, serotonin and their metabolites in rat brain, J. neurosci. Methods, 3 (19811 2117-224. 16 Ravaris. C. L., Robinson, D. S., Ivcs, J. O., Nies, A. and Bartlett, D., Phenelzine and amitriptylinc in the treatment of depression - - a comparison of present and past studies. Arch. gen. Psychiat., 37 (198111 1/175-1080. 17 Roth, K. A., Mefford, I. N. and Barchas, J. D., Epinephrine, norepinephrine, dopamine and serotonin: differential effects of acute and chronic stress on regional brain amines, Brain Research, 239 (1982) 417-424. 18 Yang, H.-Y. T. and Neff, N. H., The monoamine oxidases of brain: selective inhibition with drugs and the consequences for the metabolism of the biogenic amines. J. Pharmacol, exp. Ther., 189 (1974) 733-740. 19 Youdim, M. B. H., Collins, G. G. S. and Sandier, M., Multiple forms of rat brain monoamine oxidase, Nature (Lond.), 223 (19691 626-628. 20 Zeller, E. A, and Arora, K. L., On the role of hydroxylic and N-methyl groups in the interaction of phenylethylamines with monoamine oxidase types A and B, In E. Usdin, I. J. Kopin and J. D. Barchas (Eds.), Catecholamines: Basic and Clinical Frontiers, Vol. 1, Pergamon, New York, 1979, pp. 195-197.
B,mel t ewarc'~t.
!
BRE 20952
Epinephrine accumulation in rat brain after chronic administration of pargyline and LY 51641 - - comparison with other brain amines IVAN N. MEFFORD, KEV1N A. ROTH, SHEILA M. JURIK, VIGKI COLLMAN, STEVE MclNI'IRE. LORI TOLBERT and JACK D. BARCHAS Nancy Pritzker Laboratory of Behavioral Neurochemistry, Department of Psychiatry and Behavioral Sciences, Stan]~Jrd University School ~ (Medicine, Stan]brd, CA 94305 (U.S.A. )
(Accepted March 12th, 1985) Key words; monoamine oxidase inhibition - - epinephrine - - biogenic amines - - chronic administration - - LY 51641 ~ pargyline
Concentrations of biogenic amines and metabolites were measured in regions of rat brain following administration of monoamine oxidase (MAO) inhibitors for 21 days. Epinephrine concentrations were increased from 350 to 500% following chronic administration of LY 51641, a selective inhibitor of MAO type A. Norepinephrine, dopamine and serotonin showed much less relative accumulation. The marked relative accumulation of epinephrine may be related to the efficacy of inbibitors of MAO type A in the treatment of depression. The existence of multiple forms of monoamine oxidase ( M A O ) (EC 1.4.3.4) (ref. 10,19) and of selective inhibitors toward these multiple forms has been known for several yearsS.S,~0.Is. M A O inhibitors ( M A O I ) have been used effectively for many years in the treatment of depression 9A6. Most clinically approved M A O inhibitors, however, demonstrate little selectivity towards the two forms of M A O . Recent evidence from clinical trials suggests that selective inhibition of the A form of M A O may have more antidepressant efficacy than inhibition of M A O Type B14. It has been demonstrated in the rat that chronic regimens of selective M A O inhibitors can be chosen at dosages to maintain effective selectivity over several weeks I. In light of the possible clinical significance of selective M A O inhibition, a study was undertaken to determine the effects of chronic administration of selective inhibitors of both the A and B forms on regional rat brain catecholamines, serotonin and their metabolites. Selective inhibitors chosen for this work were pargyline (1 mg/kg i.p.), which has been shown to be a selective inhibitor of M A O Type B over a 3-week period I and Lilly (LY) 51641 (0.5 mg/kg i.p.), a potent selective M A O Type A inhibitorS.
Male S p r a g u e - D a w l e y rats, 200-220 g at the start of the study were used throughout. LY 51641, pargyline or saline were administered daily intraperitoneally in a volume of 1.0 ml. Drug regimens were based on both preliminary acute dose response studies and on clinically effective doses in man 14. The doses chosen were 1 mg/kg for pargyline and 0.5 mg/kg for LY 51641. Drugs were administered daily between 13.00 and 16.00 h for 21 days. Animals were sacrificed by decapitation 24 h following the last injection. Brains were removed and dissected over crushed ice. Raphe was dissected according to Deguchi et al.3. Brain parts were stored at --80 °C until analyzed. Catecholamines, serotonin, 5-hydroxyindole acetic acid ( 5 - H I A A ) , 3,4-dihydroxyphenyl acetic acid ( D O P A C ) and homovanillic acid ( H V A ) were analyzed by H P L C with electrochemical detection as previously described 15. Tissues were sonicated in 400 /~1 0.2 M HC104 plus 50/~1 10-6 M dihydroxybenzyiamine and 50 ktl 10-6 M 3-methoxy-4-hydroxyphenylethanol. A 100/zl aliquot was removed and centrifuged at 12,800 g for determination of serotonin, D O P A C , 5 - H I A A and H V A . Catechols in the remaining 400/~l of homogenate were extracted with
Correspondence. • I. N. Mefford, Department of Chemistry, Boston College, Chestnut Hill, MA 02167, U S.A.
0006-8993/85/$03.30 © 1985 Elsevier Science Publishers B.V. (Biomedical Division)
343 significantly d e c r e a s e d in all areas s t u d i e d f o l l o w i n g
A1203 as p r e v i o u s l y d e s c r i b e d 11. Chromatographic DOPAC,
resolution
of
serotonin,
5 - H I A A and H V A was a c c o m p l i s h e d on a
chronic administration
of L Y 51641 or p a r g y l i n e
w h i c h led to a lesser d e g r e e of d e p l e t i o n in e a c h re-
5 ktm u l t r a s p h e r e O D S r e v e r s e p h a s e c o l u m n ( B e c k -
gion. H V A was significantly d e p l e t e d o n l y in stria-
m a n ) , 4.6 m m i.d. x 25 cm length, using a s o l v e n t
t u m . D o p a m i n e was significantly e l e v a t e d only in
system of 0.1 M s o d i u m a c e t a t e , 0.1 M citric acid and
h i p p o c a m p u s . C o n c e n t r a t i o n s of 5 - H I A A w e r e n o t
2 0 % m e t h a n o l (v:v) at a flow rate of 1.0 m l / m i n . D e -
significantly c h a n g e d e x c e p t in h y p o t h a l a m u s w h e r e
t e c t i o n was a c c o m p l i s h e d with a c a r b o n p a s t e elec-
L Y 51641 a d m i n i s t r a t i o n led to a m o d e s t 2 5 % de-
t r o d e at an applied potential of + 0.75 V vs A g / A g C I .
c r e a s e ( P < 0.05).
R e s o l u t i o n of c a t e c h o l s was a c c o m p l i s h e d on a 25 cm
T h e effects of c h r o n i c a d m i n i s t r a t i o n of p a r g y l i n e
x 4.6 m m i.d., 5 ~ m u l t r a s p h e r e O D S c o l u m n ( B e c k -
and L Y 51641 w e r e m o s t a p p a r e n t with t h e o t h e r
m a n ) with a s o l v e n t system of 0.1 M s o d i u m a c e t a t e ,
amines measured,
0.02 M citric acid, 100 rag/1 s o d i u m octyl sulfate, 50
e p i n e p h r i n e . O n l y s t r i a t u m and c o r t e x failed to s h o w
serotonin,
norepinephrine,
and
mg/1 E D T A and 15% m e t h a n o l (v:v) at a flow rate of
significant a c c u m u l a t i o n of 5 - H T . In all cases, accu-
1.0 ml/min. D e t e c t i o n was a c c o m p l i s h e d at a c a r b o n
m u l a t i o n was g r e a t e r f o l l o w i n g c h r o n i c a d m i n i s t r a -
paste e l e c t r o d e at an a p p l i e d p o t e n t i a l of + 0.55 V vs
tion of L Y 51641. I n c r e a s e s in c o n c e n t r a t i o n of n e a r -
A g / A g C 1 . A m p e r o m e t r i c c o n t r o l was a c c o m p l i s h e d
ly 100% w e r e o b s e r v e d in r a p h e , h y p o t h a l a m u s and
by a m o d e l L C - 3 a m p e r o m e t r i c d e t e c t o r ( B i o A n a l y -
h i p p o c a m p u s (see Fig. 1). Significant a c c u m u l a t i o n of n o r e p i n e p h r i n e
tical Systems).
was
S h o w n in T a b l e I are the results o b t a i n e d for
not o b s e r v e d in striatum nor cortex. L Y 51641 admin-
D O P A C , H V A , 5 - H I A A and d o p a m i n e . D O P A C was
istration led to a m o r e m a r k e d a c c u m u l a t i o n than
TABLE I Effects of chronic M A 0 1 administration on rat brain dopamine, HVA, D O P A C and 5-HIAA
Pargyline, 1.0 mg/kg i.p. and LY 51641 0.5 mg/kg i.p. for 21 days. ND, not determined. Brain region
Striatum control pargyline LY 5164l Hypothalamus control pargyline LY 5164l Medulla control pargyline LY51641 Cortex control pargyline LY5164l Hippocampus control pargyline LY51641 Raphe control pargyline LY51641
Concentration (ng/g wet weight +_S. E. M.) Dopamine
HVA
D OPA C
5-HIA A
7565 ± 736 8297 ___309 9275 ± 597
726 + 60 538 + 34* 451 + 24***
1671 + 129 945 + 121"* 598 ± 50***
1056 _+ 124 910 _+ 44 893 _+ 68
109 + 6 64 + 2*** 49 + 5***
981 ± 107 862 +_ 51 709 + 37*
50 _+ 5 31 + 3* 15 + 1"**
813 _+ 52 711 ± 41 769 ± 74
296 ± 19 329 ± 28 325 ___17 105 ± 6 116 ± 3 112 ± 9
29 + 4 34 ± 6 27 ± 6 ND ND ND
79 ± 8 77 + 6 77 ± 10
32 _+4 23 ± 2 29_+ 9
38 + 4 21 + 2** 13 + 3***
444 _+ 62 456 + 60 310 + 28
16 ± 2 55 ± 13"* 36 ± 11
14 _+ 5 22 _+ 7 10 ± 1
24 + 7 17 _+ 6 12 + 2
591 +_ 82 638 + 46 638 _+ 86
62 ± 4 73 ± 3 76 ± 11
29 _+ 4 23 +_ 4 32 + 11
38 ± 8 21 + 2 13 ± 2*
1849 +_ 139 2154 + 118 1937 _+ 148
* P < 0.05; ** P < 0.01; ***P < 0.001 by Student's t-test.
344 line and clorgyline at the same doses chosen here for pargyline and LY 51641 had no effect on tyrosine hydroxylase or tryptophan hydroxylase while clorgylme produced 97% inhibition of MAO Type A and 28% inhibition of MAO Type B. Pargyline was somewhat less selective, causing 93% inhibition of MAO Type B and 44% inhibition of MAO Type A activity. We found only modest increases in dopamme following treatment with pargyline and LY 51641 m some areas. Norepinephrine was increased in several areas by 15-20% after pargyline treatment, in addition, epinephrine, which was not measured in the earlier study, proved to be the most labile of the amines measured. As with the earlier study of Campbell et al.t 5-HIAA was essentially unaffected by chronic MAO inhibition by either type inhibitor in any brain region. Only modest depletion was observed in hypothalamus. Serotonin, the precursor to 5-HIAA was, however, substantially elevated, suggesting that some alternative means of 5-HIAA synthesis has compensated in its formation. Others have proposed that perhaps transamination and decarboxylation may increase in conversion of serotonin to 5-HIAAI,~;. It also seems likely that 5-HT might be compensationally metabolized by uninhibited MAO type B. The novelty of the data presented in this report ties primarily in the demonstration of the lability of brain epinephrine to chronic administration of MAO inhibitors, particularly LY 51641. Zeller and Arora zil demonstrated in vitro that epinephrine was a nearly ideal substrate for MAO type A. Fuller and coworkers at Eli Lilly have demonstrated that epinephrine is metabolized by MAO type A in brain tissue ,'~,7. The data presented here demonstrate that the relative response of epinephrine is 5-1(}-fold greater to chronic administration of a selective inhibitor of MAO type A than other biogenic amines, notably norepinephrine and 5-HT, classically considered to be the primary substrates metabolized by this enzyme in brain. MAO inhibitors have been used clinically for many years in the treatment of depression. Recent work by Lipper et al. 14shows administration of an inhibitor of MAO type A to be more efficacious in the treatment of depression than either an inhibitor of MAO type B or a non-selective MAOI. Christensen et al. e have shown epinephrine concentrations in cerebrospinal fluid of depressed patients to be lower than in corK-
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30002000i t NOREPINEPHRINE
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EPINEPHRINE ~u
Fig. 1. Effects of chronic M A O I on regional rat brain biogenic amines, D, control-saline; I , LY 51641, 0.5 mg/kg i.p.; [] pargyline I m g / k g i , p . * P < 0 . 0 5 , ** P < 0 . 0 1 , *** P < 0.001 vs controls by Student's t-test, n = 6 - 8 determinations.
pargyline in all other regions. Greatest relative accumulation was observed in hypothalamus and medulla. LY 51641 administration caused a marked accumulation of epinephrine in the three regions monitored. Hypothalamic epinephrine concentrations were elevated by ~ 350%. In the raphe area epinephrine concentrations were elevated by ~ 360% while in the medulla, which contains the Cj and C, cell body areas epinephrine concentrations were elevated by nearly 500%. These data confirm and extend an earlier studyl in which whole brain serotonin, 5-HIAA, norepinephrine and dopamine were measured. These authors also demonstrated that chronic treatment with pargy-
345 trois. F o l l o w i n g t h e r a p y e p i n e p h r i n e c o n c e n t r a t i o n s
M A O type A i n h i b i t o r ( L Y 51641) or pargyline, a B
w e r e i n c r e a s e d a p p r o x i m a t e l y 4-fold w h i l e n o r e p i -
type inhibitor. T h e possible r e l e v a n c e of this obser-
nephrine concentrations were unchanged.
Several
v a t i o n with respect to the efficacy of clorgyline or
a u t h o r s h a v e o b s e r v e d the lability of h y p o t h a l a m i c e p i n e p h r i n e to a c u t e 13,t7 and c h r o n i c stress 17.
L Y 51641 and o t h e r type A M A O inhibitors in the
A s with several e a r l i e r studies, the d a t a p r e s e n t e d
t r e a t m e n t of d e p r e s s i o n is as yet u n d e f i n e d and deserves f u r t h e r a t t e n t i o n .
in this r e p o r t are s u p p o r t i v e of two f u n c t i o n a l l y active f o r m s of m o n o a m i n e oxidase in vivo. W e h a v e
This w o r k was s u p p o r t e d by N I M H P r o g r a m - P r o -
r e p o r t e d a p p a r e n t r e g i o n a l substrate p r e f e r e n c e s for
ject G r a n t , M H 23861. L Y 51641 was g e n e r o u s l y
M A O T y p e A . E p i n e p h r i n e has b e e n d e m o n s t r a t e d
supplied by Dr. Ray Fuller, Eli Lilly R e s e a r c h Labs, Indianapolis, Indiana.
to be the m o s t r e s p o n s i v e M A O T y p e A substrate in vivo f o l l o w i n g c h r o n i c a d m i n i s t r a t i o n of e i t h e r an
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