Effects of taurine on tolerance to [D-Ala2,Met5]enkephalinamide in rats

European Journal of Pharmacology, 82 (1982) 55-63

55

Elsevier Biomedical Press

E F F E C T S O F T A U R I N E O N T O L E R A N C E TO [D-ALA2,METS]ENKEPHALINAMIDE IN RATS KANJI IZUMI 1,., EISUKE MUNEKATA2, ANDRE BARBEAU3, TAKAO NAKANISHI4, MOTOAKIYOSH1DA4 HIROAKI YAMAMOTO5 and TAKEO FUKUDA 1 Department of Pharmacology, Faculty of Medicine, Kagoshima University, Kagoshima 890, Japan, 2 Institute of Applied Biochemistry, University of Tsukuba, lbaraki 305, Japan, 3 Department of Neurobiology, Clinical Research Institute of Montreal, Quebec, H2 W 1R7, Canada, 4 Institute of Clinical Medicine, University of Tsukuba, Japan, and 5 Institute of Community Medicine, University of Tsukuba, Japan

Received 4 January 1982, revised MS received 28 April 1982, accepted 13 May 1982

K. IZUMI, E. MUNEKATA, A. BARBEAU, T. NAKANISHI, M. YOSHIDA, H. YAMAMOTO and T. FUKUDA, Effects of taurine on tolerance to [ D-Ala2,MetS]enkephalinamide in rats, European J. Pharmacol. 82 (1982) 55-63.

Effects of taurine on tolerance to [D-Ala2,MetS]enkephalinamide (DAME) were investigated in rats. Tolerance was produced by five intraventricular administrations of DAME (50 ~g) during 3 consecutive days. The magnitude of developed tolerance to DAME was not uniform for each behavioral parameter; tolerance to analgesia effects developed more intensively and rapidly from the repeated injections of the peptide than that to akinesia effects. Pretreatment with taurine (9.5 × 10-2 M) which was injected in a volume of 10 #1 intraventricularly l0 rain prior to every administration of DAME suppressed the development of tolerance to both analgesia and akinesia effects of this peptide, whereas pretreatment with L-leucine at the same concentration did not. Spontaneous locomotor activity was measured for 1 h after the 90-rain behavioral observation period was completed. That activity increased with the number of the peptide injections. Taurine pretreatment inhibited the induction of 'hyper'-locomotor activity. These results support the view that taurine may possess an ability to inhibit development of tolerance to morphine-like peptides in rats. Enkephalinamide

Taurine

Tolerance

I. Introduction fl-Endorphin, a fragment of fl-lipotropin (flLPH) corresponding to fl-LPH61_91 , possesses morphine-like properties (Rossier and Bloom, 1979) and induces analgesia and akinesia when acutely administered intracerebrally in mammals (Bloom et al., 1976; Jacquet and Marks, 1976; Loh et al., 1976; Bradbury et al., 1977; Izumi et al., 1977; Meglio et al., 1977; Wei et al., 1977; Tseng et al., 1980). Repeated administrations or continuous infusion of the peptide resulted in the development of tolerance and physical dependence (Bl~isig and Herz, 1976; Van Ree et al., 1976; Wei and * Correspondence: Dr. Kanji Izumi, M.D., Department of Pharmacology, Faculty of Medicine, Kagoshima University, Kagoshima 890, Japan. 0014-2999/82/0000-0000/$02.75 © 1982 Elsevier Biomedical Press

Loh, 1976; Hosobuchi et al., 1977; Tseng et al., 1977). Implantation with morphine pellets in mice and rats has been shown to cause cross-tolerance to fl-endorphin, suggesting that the peptide and opioid alkaloid share common mechanisms of action (Tseng et al., 1976). [D-AlaZ,MetS]enkephalinamide (DAME) is an enkephalin analogue and causes pharmacological actions similar to fl-endolphin or morphine (Pert et al., 1976). D A M E also produces tolerance (Pert, 1976) but relatively less physical dependence after daily administrations in rats (Pert, 1976; Wei, 1981). To explore the mechanisms of the development of tolerance and physical dependence, the interaction of morphine or morphine-like peptides with certain amino acids has been investigated. For example, systemic administration of 5-hydroxytryptophan (5-HTP), a serotonin precursor, has

56 been shown to reverse tolerance to analgesia effects of /3-endorphin in cats (Hosobuchi et al., 1977). Similarly, 5-HTP suppressed the development of morphine tolerance in mice (Contreras et al., 1973). fl-Alanine induced a dose-dependent antagonism against the development of morphine tolerance in mice (Contreras and Tamayo, 1980). Elevation of brain levels of y-aminobutyric acid (GABA) by aminooxyacetic acid enhanced the development of tolerance to and physical dependence on morphine in mice (Ho et al., 1976). Glycine did not modify morphine tolerance in mice (Contreras and Tamayo, 1980). In previous studies we demonstrated the interaction between taurine and morphine-like peptides or morphine; acute administration of taurine promoted a recovery from akinesia and analgesia caused by D A M E in rats (Izumi et al., 1980) or increased the medium effective dose of morphine for analgesia in mice (Yamamoto et al., 1981). Taurine is a sulfur-containing amino acid and has an inhibitory action in the central nervous system (CNS) like GABA, /3-alanine and glycine. The present study aimed at investigating effects of taurine upon tolerance to D A M E in rats.

2. Materials and methods

2.1. General In male Wistar rats weighing 240-395 g, cannulation of the left lateral ventricle was carried out under anesthesia with pentobarbital (40 mg/kg, i.p.) as described previously (Izumi et al., 1982a). Rats fed standard food (Oriental Yeast Co.) and water ad libitum were kept in an air-conditioned room (24°C) and maintained under constant light-dark cycle. D A M E was dissolved in 0.85% saline solution. Taurine and L-leucine were dissolved in 5 mM phosphate buffer in NaC1 solution to obtain the desired osmolarity (280-290 mosM) and pH 7.2-7.4. All substances were administered in a volume of 10 /~1 through the cannula at an injection rate of 10/~1/30 sec.

2.2. Drug administration schedule 42 rats were divided into 7 groups of 6 animals. Rats were pretreated with 5 mM phosphate buffer in NaC1 solution (10 /~1: group A) or taurine (group B) or L-leucine (group C) at a concentration of 9.5 × 1 0 - 2 M and 10 min later injected with DAME (50 /~g: Enkephalinamide Group). Control animals were pretreated with 5 mM phosphate buffer in NaC1 solution (group D) or taurine (group E) or L-leucine (group F) at the identical concentration used for the Enkephalinamide Group and 10 min later received 0.85% saline solution (10 ~tl: Placebo Group). This set of injections was repeated twice daily (10 a.m. and 4 p.m.) for 2 days. On the 3rd day, the same dose (50/~g) of D A M E was administered to both Enkephalinamide (A, B, C) and Placebo (D, E, F) Groups 10 min after the pretreatment with each amino acid or 5 mM phosphate buffer in NaC1 solution. The dose of D A M E is equivalent to the ED99 for both akinesia and analgesia in rats. The dose of taurine was chosen from our previous data, in which acute administration of the sulfur amino acid at this concentration increased the EDs0 of D A M E for akinesia and analgesia determined at 60 min after the peptide administration in rats (Izumi et al., 1980). L-Leucine at the same molar concentration as that of taurine solution was taken as a monitor for the factors of osmolarity and injection volume. Those animals in the last group G which had received 5 mM phosphate buffer in NaC1 solution and 0.85% saline for 2 days were injected with also 0.85% saline 10 min after the pretreatment with a buffer-saline solution on the 3rd day.

2.3. Evaluation of behavior All animals were tested once a day at about 10 a.m. for the duration of akinesia and analgesia after the 1st, 3rd and 5th (the final) injection of D A M E or 0.85% saline solution had been carried out. Furthermore, spontaneous locomotor activity was recorded every day for 1 h using an Automex instrument following the 90-min observation period for akinesia and analgesia. Akinesia was evaluated by placing the forepaws

57 of the rat on a horizontal bar, 10 cm high. The duration of akinesia was individually recorded at 10, 30, 60 and 90 rain after the enkephalinamide or saline injection. The cut-off time was determined to be 300 sec at each estimation point. Akinesia was defined as positive when the animals sustained the position for at least 15 sec. Analgesia was assessed by a hot-plate procedure. The surface of the hot-plate was 40 × 40 cm in size and was maintained at 54-+0.1°C (mean -+S.D.) by a thermoregulated water-circulating pump. The time between placing the rat on the hot-plate and the first appearance of any reaction such as licking the paws, rearing or rapid movements was counted for estimation of the duration of analgesia. The duration of analgesia was individually recorded 1 rain before and 10, 30, 60 and 90 min after the enkephalinamide or saline injection. The cut-off time was determined to be 60 sec at each estimation point. Analgesia was defined as positive when the animal placed on the hot-plate showed no response for at least 10 sec. 2.4. Statistics

Analysis of variance was used when duration of akinesia, analgesia or locomotor activity induced by D A M E was compared between rats pretreated with amino acid and with 5 m M phosphate buffer in NaC1 solution. Daily alteration of the duration was also compared using analysis of variance among each group. 2.5. Materials

[D-Ala2,Met 5]enkephalinamide (Tyr-D-AlaGIy-Phe-Met-CONH2) was synthesized according to the classical solution method (Munekata et al., 1979). In a preliminary experiment, the biological activity of the peptide product intraventricularly injected was tested in rats and was found to be completely antagonized by naloxone, a specific opiate antagonist. Taurine and L-leucine were purchased from Sigma Chemical Company.

3. Results Figs. 1 and 2 demonstrate daily alterations of the duration of akinesia and analgesia, respectively, in rats treated with D A M E or 0.85% saline solution under various conditions. All 6 rats in group A which had been treated with 5 mM phosphate buffer in NaC1 solution 10 min prior to the administration of D A M E showed markedly prolonged duration of akinesia with muscle rigidity and analgesia on the 1st day. Such effects of the peptide lasted till the end of the 90-rain observation time (figs. 1 and 2). On the 2nd day, the duration of akinesia and analgesia became shorter and all animals recovered from the state of both akinesia and analgesia by 90 rain after the enkephalinamide injection. On the 3rd day, this tendency was more pronounced and the duration of akinesia was significantly reduced by the repeated administration of this peptide even at 10and 30-min observation times (as compared with those of the 1st day). The reduction of the duration of analgesia was prominent and analgesia completely disappeared in all cases on this day. Animals of group D naive to DAME, which had been treated with a buffer-saline solution and 0.85% saline solution for the first 2 days, responded well to the peptide on the 3rd day. The duration of akinesia and analgesia estimated at 10 and 30 min were comparable to those at these times on the 1st day in animals in group A. However, at later observation times (60 and 90 min), the durations of both akinesia and analgesia in group D tended to be shorter than those in group A. It should be emphasized that the magnitude of the reduction of the duration was found not to be equal between akinesia and analgesia; duration of analgesia was greatly decreased in rats in group A from the 2nd day and restored to the level with a normal latent period on the 3rd day. On the contrary, the reduction of the duration time of akinesia was mild and became significant for the first time on the 3rd day, although the duration seemed shorter at 60 and 90 min on the 2nd day. A similar tendency toward shortening the duration of akinesia and analgesia (as in group A) was obtained on the 2nd and the 3rd day by the

58

A

C

B

30E

200

b

•

b

b

100

< m

Z

o

t

i

<

~

1

t

I

I

D

I

I

E

&

I

F

0 Z

0

200

7 0

b

100

0

~

.2

g

=

,; 3b 8;

~'o

TIME

,'o 3'o AFTER

60

~o

INJECTION

,'o ~o ~o ~o (min)

Fig. 1. Effects of taurine on akinesia induced by single or repeated administration of [o-Ala2,Met 5]enkephalinamide (DAME) in rats. Rats were pretreated with 5 mM phosphate buffer in NaCI solution (group A) or taurine (B) or L-leucine (C) at a concentration of 9.5×10 2M and 10 min later injected with DAME (50 /~g: Enkephalinamide Group). Control animals were pretreated with buffer-saline solution (D) or taurine (E) or L-leucine (F) at the identical concentration used for the Enkephalinamide Group and 10 min later received 0.85% saline solution (Placebo Group). This set of injections was repeated twice daily for 2 days. On the 3rd day, the same dose of DAME was administered to both groups 10 min after the pretreatment with each amino acid or buffer-saline solution. All substances or solutions in a volume of 10/~1 were injected intraventricularly. The cut-off time was determined to be 300 sec at each estimation time. Data were obtained by testing following the 1st (on the 1st day: ©), 3rd (on the 2nd day: 0 ) and 5th (on the 3rd day: I I ) administration of D A M E or saline. Each point represents the mean of six animals. Vertical lines indicate S.E. In cases of points without vertical line, S.E. is within the symbol. The baseline values (mean ± S.E.) obtained at 10, 30, 60 and 90 min in six animals in the group G which had received buffer-saline solution and 0.85% saline for 3 days were as follow: 2.6m 1.1, 2.8 + 1.2, 2.6± 1.1 and 4.0±2.8 (sec) on the 1st day; 1.6--+0.6, 1.2±0.2, 1.4±0.4 and 2.2~ 1.2 on the 2nd day; and 2.2±0.8, 1.8+0.5, 4.6+2.5 and 1.0±0.0 on the 3rd day. a or b: Significantly different from the 1st day in the same group at P<0.05 or P<0.01, respectively, c: Significantly different from group A on corresponding day at P<0.05. d: Significantly different from group D on corresponding day at P < 0.05.

repeated injections of enkephalinamide in rats in group C which had been pretreated with L-leucine. In this group, duration times of analgesia were also greatly reduced even at 10 and 30 min estimation times on the 2nd day (fig. 2), whereas those of akinesia at these times on the same day were not significantly decreased yet (fig. 1). Animals of group F naive to D A M E responded well to this

peptide on the 3rd day, although the duration of analgesia tended to be shorter at later observation times in this group, like in group D, than that on the 1st day in group C. Neither akinesia nor analgesia was observed in group G rats which had received the repeated injections of 0.85% saline solution following the pretreatment with 5 m M phosphate buffer in NaC1 solution throughout 3

59

C

A 60

40 ~

a

b~bb

c

20

uJ

a

o

...i

b

L

J

I

b

i

Z .<

F

Z

o

40

~ 2o i

i

i

-I 10 30

i

J

60

90

TIME

i

i

i

i

i

60

90

I0

INJECTION

(rain)

I0 30 AFTER

,

,

,

30

I

60

T

90

Fig. 2. Effects of taurine on analgesia induced by single or repeated administration of [D-Ala2,MetS]enkephalinamide (DAME) in rats. Experimental conditions were the same as those described in the legend for fig. 1. The cut-off time was determined to be 60 s at each estimation time. Duration of analgesia was estimated also at 1 rain before the DAME or saline injection. Data were obtained by testing following the 1st (on the 1st day: ©), 3rd (on the 2nd day: Q) and 5th (on the 3rd day: m) administration of DAME or saline. Each point represents the mean of six animals. Vertical lines indicate S.E. In cases of points without vertical line, S.E. is within the symbol. The baseline values (mean -+ S.E.) obtained at - 1, 10, 30, 60 and 90 min in six animals in the group G which had received buffer-saline solution and 0.85% saline for 3 days were as follow: 4.8-+0.4, 5.0-+0.6, 4.6--+0.4, 3.8--+0.4 and 5.4-+0.2 (sec) on the 1st day; 5.0-+0.3, 5.0-+0.6, 4.2-+0.4, 4.4-+0.4 and 4.4-+0.4 on the 2nd day; and 4.2-+0.4; 4.4-+0.5, 4.4+0.5, 4.2--+0.4 and 3.8+0.2 on the 3rd day. a or b: Significantly different from the Ist day in the same group at P<0.05 or P<0.01, respectively, c: Significantly different from group A on corresponding day at P<0.05. d: Significantly different from group D on corresponding day at P<0.05.

days. A c t u a l d u r a t i o n o f a k i n e s i a o r a n a l g e s i a are s h o w n as b a s e l i n e v a l u e s in t h e l e g e n d f o r fig. 1 o r 2, r e s p e c t i v e l y . Taurine pretreatment exhibited some different e f f e c t s f r o m t h o s e o f b u f f e r - s a l i n e s o l u t i o n or L-leucine upon akinesia and analgesia induced by D A M E . O n the 1st d a y , the d u r a t i o n o f a k i n e s i a a n d a n a l g e s i a in rats in g r o u p B w e r e d e c r e a s e d at 60 a n d 90 m i n a f t e r the a d m i n i s t r a t i o n o f D A M E as c o m p a r e d w i t h t h o s e in a n i m a l s in g r o u p A o r C, w h i l e t h o s e at e a r l y p h a s e s (10 a n d 30 m i n ) w e r e n o t d e c r e a s e d . O n the 2 n d day, rats r e v e a l e d a l m o s t the s a m e d e g r e e in the d u r a t i o n o f a k i n e s i a at 10 a n d 30 m i n b e t w e e n g r o u p A, B a n d C. U n l i k e the effects o f b u f f e r - s a l i n e o r L - l e u c i n e in g r o u p A o r C, the d u r a t i o n s o f a n a l g e s i a at these

t i m e s w e r e n o t s h o r t e n e d by t a u r i n e p r e t r e a t m e n t ( g r o u p B) (fig. 2). O n t h e 3rd day, the d u r a t i o n o f a k i n e s i a in g r o u p B was n o t s i g n i f i c a n t l y r e d u c e d at 10 a n d 30 m i n , a l t h o u g h t h o s e at l a t e r e s t i m a t i o n t i m e s (60 a n d 90 m i n ) w e r e c l e a r l y d e c r e a s e d (fig. 1). F u r t h e r m o r e , the d u r a t i o n o f a k i n e s i a rem a i n e d r e l a t i v e l y l o n g e r at e i t h e r 10 or 30 m i n e s t i m a t i o n t i m e in c o m p a r i s o n w i t h t h a t in b u f f e r - s a l i n e - o r L - l e u c i n e - t r e a t e d a n i m a l s (fig. 1). T h e d u r a t i o n o f a n a l g e s i a o n the 3rd d a y o f the a d m i n i s t r a t i o n o f D A M E was s i g n i f i c a n t l y red u c e d at 10, 30 m i n as well as at 60 a n d 90 m i n f r o m the 1st d a y level in g r o u p B (fig. 2). H o w e v e r , t h e m a g n i t u d e o f the r e d u c t i o n was n o t so g r e a t as t h a t in rats p r e t r e a t e d w i t h b u f f e r - s a l i n e o r Ll e u c i n e (fig. 2). A n i m a l s n a i v e to D A M E in g r o u p

60 E, which had been pretreated with taurine 10 min prior to every injection of 0.85% saline solution for the first 2 days, responded well to the morphinelike peptide on the 3rd day, but the duration of both akinesia and analgesia were significantly reduced from the early estimation times (10 and 30 min) (figs. 1 and 2). Following the 1st (on the 1st day), 3rd (on the 2nd day) and 5th (on the 3rd day) injection of DAME, spontaneous locomotor activity was recorded for 1 h in each rat pretreated with taurine or 5 mM phosphate buffer in NaC1 solution after the 90-min observation was completed. As shown in fig. 3, spontaneous locomotor activity was increased in control rats with buffer-saline plus D A M E as the number of the peptide injection is increased. In contrast, the activity was not altered during 3 days in animals which had received taurine (9.5 × 1 0 - 2 M ) before the enkephalinamide injection.

100 o

50

o o

.A

0

90

100

110

120

130

140

TIME AFTER ENKEPHALINAMIDE(rain)

Fig. 3. Effects of taurine on spontaneous locomotor activity in rats with [D-Ala2,MetS]enkephalinamide (DAME). Following the 1st (on the 1st day), 3rd (on the 2nd day) and 5th (on the 3rd day) administration of DAME, spontaneous locomotor activity was recorded in rats with 10 ~tl of taurine (9.5 X 10-2 M) or 5 mM phosphate buffer in NaC1 solution (10 /tl) after the 90-min observation for akinesia and analgesia was completed. The average activity in taurine-treated rats is shown by solid symbols (O, 1st day; A, 2nd day; and II, 3rd day) and that in controls by open symbols(O, Ist day; A, 2nd day; and D, 3rd day). * Significantly different between buffer-saline and taurine pretreatment at P<0.05. n=6 for each point.

4. Discussion

In the present study, we demonstrated that the duration of akinesia and analgesia was decreased by the repeated administration of D A M E in rats. The response to D A M E observed on the 3rd day in naive animals (group D) was comparable to the initial effects of the peptide obtained on the 1st day in group A. The reduction of the duration is not due to the repeated manipulations per se, since no alteration of the duration time of either akinesia or analgesia was observed in group G rats. These results indicate that five intraventricular administrations of D A M E (50 #g) during 3 consecutive days can lead to tolerance to this morphine-like peptide in rats. This is in agreement with the data by Pert (1976) who showed that repetitive intraventricular administration of morphine (15 fig) and D A M E (30 ~g) over 2-10 days causes crosstolerance to their analgesia effects in rats, suggesting that both compounds act at the same receptor sites. In addition, it was observed in the present study that repeated administration of this peptide also resulted in the development of tolerance to akinesia effects. However, the magnitude of developed tolerance to D A M E appeared not to be identical for each behavioral parameter; development of tolerance to analgesia effects resulted more intensively and rapidly from the repeated injections of the peptide than tolerance to akinesia effects. This difference might be attributed to the selective stimulation of opiate receptors, since recent pharmacological evidence supports the concept that multiple types of opiate receptors exist in the CNS as well as in certain peripheral tissues (Lord et al., 1977; Chang and Cuatrecasas, 1979; Wtister et al, 1979). In this regard, analgesia has been suggested to be mediated by/~ receptors (Urca et al., 1978; Chang and Cuatrecasas, 1979; Kosterlitz et al., 1980) and other behavioral responses which may include catatonia or akinesia by 6 receptors (Stein and Belluzzi, 1978; Chang et al., 1980), although this view has been more recently challenged (Schulz et al., 1981). Schulz et al. (1981) demonstrated that chronic activation of 8 receptors by [D-Ala2,D-LeuS]enkephalin (DALE) resuited in tolerance to the action of this 8 receptor

61 agonist, whereas the/~ agonist sufentanyl did not exhibit cross-tolerance to D A L E in rats. On the other hand, animals which had tolerance to catatonia effects of sufentanyl failed to show crosstolerance to DALE. On the basis of this observation, they suggested that prolonged stimulation of specific opiate receptors in the CNS by highly selective agonist may produce the selective development of tolerance for particular receptors. D A M E has been described to possess higher affinity for /~ receptor than 8 receptor (Chang et al., 1980). This may be a factor responsible for the present finding that tolerance to analgesia effects of D A M E developed relatively rapidly and intensively as compared with the tolerance to akinesia. Pretreatment with taurine shortened the duration of both akinesia and analgesia at 60 and 90 min after D A M E injection on the 1st day. This is consistent with the previous results that taurine may promote a recovery from akinesia and analgesia caused by D A M E in rats (Izumi et al., 1980). For this reason, when effects of amino acids on tolerance to morphine-like peptides were investigated, i t w a s decided to compare the durations of akinesia and analgesia at the early estimation times (10 and 30 rain) which are not modified by acute administration of taurine. In addition, responses of animals in group D naive to DAME at 60 and 90 min on the 3rd day were found to be different from those of animals in group A at these times on the 1st day; the duration of both akinesia and analgesia in group D tended to be shorter than the durations of group A at the later observation times. However, durations at 10 and 30 rain were essentially identical between rats in group D on the 3rd day and group A on the 1st day. A similar pattern was observed in animals in group F (figs. 1 and 2). Pretreatment with taurine suppressed partly the development of tolerance to both akinesia and analgesia effects of D A M E in rats. The suppressive effects of taurine seem to be specific, since the same dose of L-leucine did not affect tolerance. Moreover, in contrast with buffer-saline-treated rats which exhibited the increased spontaneous locomotor activity following initial state of akinesia on the 2nd and 3rd day of the enkephalinamide injection, taurine-treated animals did not show

hyperlocomotor activity during the 3-day observation period. The increased locomotor activity has been regarded as one of the signs of morphine tolerance in rats (Hosoya et al., 1963). It has been also shown that in morphine-tolerant rats the initial depression of locomotor activity is reduced and the later increase in the activity is enhanced (Kaymakcalan and Woods, 1956; Kumar et al., 1971; Babbini and Davis, 1972; Vasko and Domino, 1978; Browne and Segal, 1980; Brady and Holtzman, 1981). Hence the finding presented in fig. 3 further supports the view that taurine suppresses the development of tolerance to D A M E in rats. The present study does not elucidate the mechanisms of the suppressive actions of taurine against development of tolerance to DAME. The possibility that taurine makes a complex with D A M E is unlikely, since our previous thin-layer chromatographic study did not exhibit any spot formation between two compounds (Izumi et al., 1982b). The most plausible speculation at present time concerning the interaction of taurine with morphinelike peptides comes from our previous data (Yamamoto et al., 1981); analgesia effects of morphine were antagonized in mice by intraventricular pretreatment with taurine and this suppressive action of the sulfur amino acid was considered to be due to its ability to normalize selective inhibition of 45Ca2+ uptake into synaptosomes caused by morphine. However, suppressive effects of taurine were not merely limited to analgesia but were also observed against akinesia as demonstrated in rats (group B on the 1st day and group E on the 3rd day) naive to D A M E in the present and previous behavioral studies (Izumi et al., 1980). Thus, it seems reasonable to assume that possible opioid peptide-induced alteration of calcium transport (Guerrero-Munoz et al., 1979) which may modulate neurotransmission in the CNS could be partially restored by pretreatment with taurine. This might be related to the observed suppressive actions of taurine against development of tolerance to akinesia and analgesia effects of D A M E in rats.

62

Acknowledgements This study was supported in part by grants from the Ministry of Health and Welfare of the Japanese Government and from Taisho Pharmaceutical Company. We are greatful to Miss M. Hirose for her technical assistance.

References Babbini, M. and W.M. Davis, 1972, Time-dose relationships for locomotor activity effects of morphine after acute or repeated treatment, Br. J. Pharmacol. 46, 213. Bl~isig, J. and A. Herz, 1976, Tolerance and dependence induced by morphine-like pituitary peptides in rats, NaunynSchmiedeb. Arch. Pharmacol. 294, 297. Bloom, F., D. Segal, N. Ling and R. Guillemin, 1976, Endorphins: profound behavioral effects in rats suggest new etiological factors in mental illness, Science 194, 630. Bradbury, A.F., D.G. Smyth, C.R. Snell, J.F.W. Deakin and S. Wendlandt, 1977, Comparison of the analgesic properties of lipotropin C-fragment and stabilized enkephalins in the rat, Biochem. Biophys. Res. Commun. 74, 748. Brady, L.S. and S.G. Holtzman, 1981, Effects of intraventricular morphine and enkephalins on locomotor activity in nondependent, morphine-dependent and postdependent rats, J. Pharmacol. Exp. Therap. 218, 613. Browne, R.G. and D.S. Segal, 1980, Alterations in /3-endorphin-induced locomotor activity in morphine-tolerant rats, Neuropharmacol. 19, 619. Contreras, E. and L. Tamayo, 1980, Effects of glycine,/3-alanine and diazepam upon morphine-tolerant-dependent mice, J. Pharm. Pharmacol. 32, 336. Contreras, E., L. Tamayo, L. Quijada and E. Silva, 1973, Decrease of tolerance development to morphine by 5-hydroxytryptophan and some related drugs, European J. Pharmacol. 22, 339. Chang, K.J. and P. Cuatrecasas, 1979, Multiple opiate receptors, J. Biol. Chem. 254, 2610. Chang, K.J., J.E. Hazum and P. Cuatrecasas, 1980, Multiple opiate receptors, Trends Neurosci., July, p. 160. Guerrero-Munoz, F., Marie de Lourdes Guerrero, E.L. Way and C.H. Li, 1979, Effect of/3-endorphin on calcium uptake in the brain, Science 206, 89. Ho, I.K., H.H. Loh and E.L. Way, 1976, Pharmacological manipulation of gamma-aminobutyric acid (GABA) in morphine analgesia, tolerance and physical dependence, Life Sci. 18, 1111. Hosobuchi, Y., M. Meglio, J.E. Adams and C.H. El, 1977, /3-Endorphin: development of tolerance and its reversal by 5-hydroxytryptophan in cats, Proc. Natl. Acad. Sci. USA 74, 4017. Hosoya, E., A. Oguli and H. Akita, 1963, Changes of the spontaneous activities of rats by the administration of morphine, Keio J. Med. 12, 83. Izumi, K., T. Motomatsu, M. Chr6tien, R.F. Butterworth, M.

Lis, N. Seidah and A. Barbeau, 1977,/3-Endorphin induced akinesia in rats: effect of apomorphine and a-methyl-otyrosine and related modifications of dopamine turnover in the basal ganglia, Life Sci. 20, 1149. Izumi, K., E. Munekata, H. Yamamoto, T. Nakanishi and A. Barbeau, 1980, Effects of taurine and "f-aminobutyric acid on akinesia and analgesia induced by D-Ala2-Met-enkepha linamide in rats, Peptides 1, 139. Izumi, K., E. Munekata, H. Yamamoto, T. Nakanishi and A. Barbeau, 1982a, Possible involvements of taurine and GABA in morphine-like peptide actions, Int. J. Neurol. (in press). lzumi, K., E. Munekata, H. Yamamoto, M. Yoshida, T. Nakanishi, P. Wong and A. Barbeau, 1982b, Central neuropharmacology of D-Ala2-Met-enkephalinamide and its interactions with taurine in rats, in: Taurine in Nutrition and Neurology, eds. R.J. Huxtable and H. Pasantes-Morales (Plenum Publishing Corporation, New York) p. 325. Jacquet, Y.F. and N. Marks, 1976, The C-fragment of fl-lipotropin: an endogenous neuroleptic or antipsychotogen? Science 194, 632. Kaymakcalan, S. and L.A. Woods, 1956, Nalorphine-induced 'abstinence syndrome' in morphine-tolerant albino rats, J. Pharmacol. Exp. Therap. 117, 112. Kosterlitz, H.W., J.A.H. Lord, S.J. Paterson and A.A. Waterfield, 1980, Effects of changes in the structure of enkephalins and of narcotic analgesic drugs on their interactions with p,- and 8-receptors, Br. J. Pharmacol. 68, 333. Kumar, R., E. Mitchell and P. Stolerman, 1971, Disturbed pattern of behaviour in morphine-tolerant and abstinent rats, Br. J. Pharmacol. 42, 473. Loh, H.H., L.F. Tseng, E. Wei and C.H. Li, 1976, fl-Endorphin is a potent analgesic agent, Proc. Natl. Acad. ~;ci. USA 73, 2895. Lord, J.A.H., A.A. Waterfield, J. Hughes and H.W. Kosterlitz, 1977, Endogenous opioid peptides: multiple agonists and receptors, Nature 267, 495. Meglio, M., Y. Hosobuchi, H.H, Loh, J.E. Adams and CH. Li, 1977, B-Endorphin: behavioral and analgesic activity in cats, Proc. Natl. Acad. Sci. USA 74, 774. Munekata, E., H. Ishiyama, F. Higa, T. Ohtaki and K. lzumi, 1979, Synthesis and pharmacological properties of enkephalinoligomers, Peptide Chemistry 17, 209. Pert, A., 1976, Behavioral pharmacology of D-alanine 2methionine-enkephalin amide and other long-acting opiate peptides, in: Opiates and Endogenous Opioid Peptides, eds. S. Archer, H.O.J. Collier, A. Goldstein, H.W. Kosterlitz, E.J. Simon, H. Takagi and L. Terenius (Elsevier/NorthHolland, Amsterdam) p. 87. Pert, C.B., A. Pert, J.-K. Chang and B.T.W. Fong, 1976, [D-Ala2]-Met-Enkephalinamide: a potent, long-lasting synthetic pentapeptide analgesic, Science 194, 330. Rossier, J. and F. Bloom, 1979, Central neuropharmacology of endorphins, in: Neurochemical Mechanisms of Opiates and Endorphins, eds. H.H. Loh and D.H. Ross (Raven Press, New York) p. 165. Stein, L. and J.D. Belluzzi, 1978, Brain endorphins and the sense of well-being: a psychobiological hypothesis, in: The

63 Endorphins, eds. E. Costa and M. Trabucchi (Raven Press, New York) p. 299. Schulz, R., M. Wtister and A. Herz, 1981, Differentiation of opiate receptors in the brain by the selective development of tolerance, Pharmacol. Biochem. Behav. 14, 75. Tseng, L.-F., H.H. Loh and C.H. Li, 1976, #-Endorphin: cross tolerance to and cross physical dependence on morphine, Proc. Natl. Acad. Sci. USA 73, 4187. Tseng, L.-F., H.H. Loh and C.H. Li, 1977, Human #-endorphin: development of tolerance and behavioral activity in rats, Biochem. Biophys. Res. Commun. 74, 390. Tseng, L.-F., E.T. Wei, H.H. Loh and C.H. Li, 1980, /3-Endorphin: central sites of analgesia, catalepsy and body temperature changes in rats, J. Pharmacol. Exp. Therap. 214, 328. Urca, G., H. Frenk and J.C. Liebeskind, 1978, Morphine and enkephalin: analgesic and epileptic properties, Science 197, 83. Van Ree, J.M., D. De Wied, A.F. Bradbury, E.C. Hulme, D.G. Smyth and C.R. Snell, 1976, Induction of tolerance to the analgesic action of lipotropin C-fragment, Nature 264, 792.

Vasko, M.R. and E.F. Domino, 1978, Tolerance development to the biphasic effects of morphine on locomotor activity and brain acetylcholine in the rat, J. Pharmacol. Exp. Therap. 207, 848. Wei, E.T., 1981, Enkephalin analogs and physical dependence, J. Pharmacol. Exp. Therap. 216, 12. Wei, E. and H. Loh, 1976, Physical dependence on opiate-like peptides, Science 193, 1262. Wei, E.T., L.F. Tseng, H.H. Loh and C.H. Li, 1977, Comparison of the behavioral effects of fl-endorphin and enkephalin analogs, Life Sci. 21,321. Wiister, M., R. Schulz and A. Herz, 1979, Specificity of opioids toward the #-, 8- and ~-opiate receptors, Neurosci. Lett. 15, 193. Yamamoto, H., H.W. McCain, K. Izumi, S. Misawa and E.L. Way, 1981, Effects of amino acids, especially taurine and -/-aminobutyric acid (GABA), on analgesia and calcium depletion induced by morphine in mice, European J. Pharmacol. 71, 177.