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EFFECTS OF SINGLE AND REPEATED INJECTION OF METHAMPHETAMINE ON THE TISSUE CATECHOLAMINE OF RABBIT
EFFECTS
OF SINGLE
AND REPEATED
METHAMPHETAMINE CATECHOLAMINE
INJECTION
OF
ON THE TISSUE OF RABBIT
TAKASHI HONJO Department of Pharmacology, Facultyof Medicine, KyotoUniversity, Sakyo-ku, Kyoto Receivedfor publicationAugust27,1963
The main pharmacological effects of methamphetamine are the psychomotor stimula tion and the sympathomimetic effects on the peripheral adrenergic structures. There is evidence which indicates the facilitatory action of amphetamine on the synaptic trans mission (1). By increasing the dose of amphetamine the inhibitory action and the reversal of facilitation have been demonstrated in the synaptic transmission of severalparts of the central nervous system (2). It has been emphasized by many authors that the central actions of various sympathomimetic amines probably are not related to their peripheral sympathomimetic actions. It is possible that methamphetamine acts on the adrenergic system directly, and in directly through interference with the metabolism of endogenous catecholamine or through liberation of the latter from local sites of storage. Analyzing the dose-response curves of the normal, the denervated, the cocainized and the reserpinized nictitating membrane of cat, Burn and Rand (3) have classified the sympathomimetic amines into following two groups, i.e. the sympatomimetic amines with direct action, and those with indirect action. They have shown that amphetamine exerts its adrenergic effects in directly through liberation of noradrenaline from the target organs. The liberation of noradrenaline from the central nervous system as well as the peripheral adrenergic structures has been confirmed biochemically by several investigators. This experiment was designed to study whether the systemic administration of methamaphetamine depletes noradrenaline in the central nervous system of rabbits to the same extent that it does in the autonomic structures such as heart, adrenal glands. Further, the effects of the repetition of the injection on the level of noradrenaline or adrenaline in these structures were studied since the repetitive administration of the drug is known to produce tachyphylaxis in the autonomic structures. METHODS Unanesthetized albino rabbits, weighing 1.5 to 2.5 kg, were used in the experiment. The animals were injected 1.0 mg/kg of methamphetamine hydrochloride into the marginal ear vein. Five injections were made at the intervals of one hour. After each 本庄 俊
injection the animal was kept in a cage and the behavioral changes caused by the drug were observed. One hour after the last injection the animals were sacrificed through bleeding by cutting both common carotid arteries. Immediately thereafter, the brain, heart and adrenals were removed. The homogenates of the tissues were prepared for the chemical assay of adrenaline and noradrenaline according to the method described by Higuchi (4). RESULTS 1. Behavioraleffects The single injection of methamphetamine induced various degree of sympathetic, motor and psychomotor-like excitements. The sympathomimetic effects observed were mydriasis, piloerection of the tail and tachycardia, and these effects lasted usually for about 20 to 40 minutes. The most long-lasting sympathetic excitatory effect among them was the tachycardia. The coordinated, spontaneous movements were increased in quantity accompanying with the psychomotor-like excitement such as restlessness and hypersensitivity to nociceptive stimuli, and these effects lasted for about 30 to 40 minutes after the injection. However, the extent of the behavioral changes could not be cor related with the level of catecholamine in the tissues. The repetition of the injection of methamphetamine at the intervals of one hour did not diminish the behavioral response to methamphetamine and every injection produced almost same degree of the excitatory behaviors. 2. Effects of single and repeatedinjectionsof methamphetamineon the contentof catecholamine The mean control values of noradrenaline in the brain and heart and of adrena line in the adrenal glands were determined in 5 to 8 intact rabbits (Table 1). The TABLE
1. Normal content of catecholamine in the various tissues of rabbit.
values were somewhat lower in the brain, and slightly higher in the auricle and the adrenal glands than those in correspond ing tissues reported by Higuchi (4).
The single intravenous injec tion of 2.5 ing/kg of methamphe A : adrenaline, NA : noradrenaline tamine reduced considerably the content of catecholamine in tissues tested, the reduction being about 35%. But the repeated injection of methamphetamine in the dose of 2.5 mg/kg at the interval of one hour produced long-lasting motor and sympathomimetic excitements by which the animal was exhausted to death. The single injection of 5.0 mg/kg of methamphetamine caused marked central excitatory symptoms but the reduction of noradrenaline or adrenaline did not significantly exceed that produced by 2.5 mg/kg of the drug. Consequently, these dosage levels were abandoned for further experiments.
The single injection of 1.0mg/kg of methamphetamine produced the reduction of
the catecholamine in the range from 10 to 20% associated with the considerable degree of the central excitements. Therefore, the dose of 1.0mg/kg of methamphetamine was' used throughout the experiments. The heart rate was counted before, and 1'0and 30 minutes after the injection. The single injection of 1.0mg/kg of methamphetamine increased the heart rate by about 15to 20% and the repetition of the injection produced the same degree of increase in heart rate (Fig, 1). It is unlikely that the`'repeated in jection of methamphetamine does affect the chronotropic response to the drug.
FIG. 1. Percent changes of tissue catecholamine content and heart rate following repeated injections of methampheta mine in rabbit. heart rate • • adrenal glands x--x auricle o -o brain stem
1) Adrenals The injection of 1.0 mg/kg of methamphetamine reduced the content of adrenaline in the adrenal glands. Table 2 and Fig. 1 show the mean values of the content of ad renaline (,ug/g tissue) in the adrenals of rabbit which had been killed one hour after the last injection of 1.0 mg/kg of metham phetamine. The first injection of metham phetamine reduced the content of adrena line in the adrenals by about 17%, and the second injection resulted in a reduction of about 42%. However, further repetition of the injection of methamphetamine did not bring about the significant further decrease of adrenaline but the reduction reached a plateau at the level of about 40%, while every repetition of the injec
TABLE 2. Adrenaline content on rabbit adrenal glands after the repeated injections of meth amphetamine. 1.0 mg/kg i.v. at 1 hour interval.
tion caused the central excitatory symptoms. The significant reduction of adrenaline by the first and second injections and the plateau following further repetition of the injection are more clearly shown when the content of adrenaline is expressed in terms of pg/g tissue than when expressed in ,"g/glands. Although the reduction of adrenaline after the injection of methamphetamine were subjected to somewhat individual varia tions,
the
extent
generally
paralleled
with
TABLE 3. Noradrenaline content in rabbit atria after the repeated injections of metham phetamine. 1.0 mg/kg ix. at 1 hour interval.
TABLE 4. Noradrenaline content in rabbit brain stem after the repeated injections of meth amphetamine. 1.0 mg/kg i.v. at 1 hour interval.
the
behavioral
changes.
2) Atria The administration of methampheta mine also reduced that content of norad renaline in the atria. The reduction of the level of noradrenaline in the atria induced by the first and the second injections was slight but significant. After the injections above three times, there was no further decrease in atrial noradrenaline except fourth injection which produced a consi derable reduction of unknown origin. The decrease of noradrenaline in the atria also subjected to individual variations but the decrease was pronounced when the animal exhibited marked behavioral excitement. The results are shown in Table 3 and Fig. 1.
3) Brain stem The reduction of noradrenaline in the brain stem of rabbit which had received methamphetamine repeatedly is shown in Table 4 and Fig. 1. In response to the first injection of methamphetamine the content of noradrenaline was decreased by about 23%. The second and further injections of methamphetamine induced much less decrease of noradrenaline. Higuchi et al. (5) showed that the intravenous injection of 1.0 mg/kg of methamphetamine to the rabbit produced a reduction of about 40% of noradrenaline in the brain stem. In the present experiments such a profound depletion was not ob served after the single dose of methamphetamine. As described above (l. Behavioral effects)the excitement caused by the repetitive injections of methamphetamine was almost similar in degree, irrespective of the extent of the decrease in level of noradrenaline. Therefore, it is likely that the behavioral excitement does not correlate with the content of noradrenaline. However, the first injection of methamphetamine caused the marked depletion of noradrena]ine and therefore, only the excitement following the first injec tion was likely to relate with the reduction of noradrenaline.
4) Brain cortex The single injection of methampheta mine did not significantly affect the content of noradrenaline in the brain cortex. Further repetition of the injection resulted in slight and somewhat variable changes. The results are shown in Table 5.
TABLE5. Noradrenaline content in rabbit brain cortex after the repeated injections of methamphetamine. 1.0 mg/kg i.v. at 1 hour interval.
DISCUSSION The effects of the single and the repeated injections of methamphetamine on the content of tissue catecholamine in association with the behavioral changes of the intact rabbits were studied. The single injection of 1.0 mg/kg of methamphetamine reduced the level of the catecholamine in the brain, heart . and adrenals, but the level of reduction varied according to the tissues. The largest reduction was obtained in the brain stem and the smallest was in the heart. Although the reduction of the level of
catecholamine was subjected to individual variations, the sympathetic and the motor excitements produced by methamphetamine seemed to correlate with the reduction of catecholamine.. The depletion of the amine in response to methamphetamine varied with the dose administered, but the depletion caused by 2.5to 5.0 mg/kg did not usually exceed 50%. The similar depletion by amphetamine of the brain noradrenaline in the rat has been reported by McLean et al. (6). The first two injections produced progressive decreases in the atrial and adrenal catecholamines, but further injections did not result in more decrease. In the brain stem the decrease of noradrenaline was observed only in response to the first injection of methamphetamine. The most typical pattern of changes in the tissue amine was obtained in the adrenal glands. The similar depletion of the rat brain noradrenaline after the repetitive injection of amphetamine has been demonstrated by McLean et al. (6). Though the depletion of catecholamine was subjected to a tachyphylactic pheno menon after repetitive injections of methamphetamine, the behavioral excitements in cluding the increase in heart rate and'the spontaneous motor movements appeared as usual for every injection. This is clearly shown in Fig. 1. In the brain cortex the normal content of noradrenaline was much less than in other tissues. If the change of cortical noradrenaline is expressed as a per cent value, even small change of ,ug/g should be unexpectedly large in the per cent value. In this figure, therefore, the per cent change of noradrenaline in the brain cortex was not compared with that in other tissues. From the results described above, it is suggested that the sympathetic and motor excitements of the animal in response to the first injection derive from the direct effects of methamphetamine plus indirect effects which are exerted by noradrenaline released, while the large parts of the behavioral excitements including tachycardia after the second
injection of methamphetamine
drive mainly from the direct effects of the drug inde
pendent of the endogenous catecholamine. No development of tachyphylaxis in the positive chronotropic effect of methamphetamine is likely to drive from the direct action on the heart, or alternatively some `central effect apart from the peripheral autonomic action. The easy access of amphetamine in the brain with subsequent accumulation of it has been concluded by Young and Gordon (7). The question remained to be settled why the central excitement in response to every repetition of the injection of metham phetamine does not induce the further depletion of the tissue catecholamine. Davey and Farmer (8) have reported that the repetitive injection of tyramine to the isolated guinea-pig's heart depleted the content of heart noradrenaline until the posi tive inotropic effect disappeared. They also demonstrated that although in the case of tyramine the depletion of noradrenaline resulted in the absence of the positive inotropic effect, the decrease of the heart noradrenaline was not causally related to the absence of the inotropic effect of methamphetamine. From the results it is conceivable that tyramine exerts its effect by releasing the endogenous noradrenaline, while metham phetamine does so mainly by the direct effect on the receptive structures with the ad ditional effect through the mediation of the endogenous noradrenaline. Tne powerful antagonism of dexamphetamine against guanethidine demonstrated by Day and Rand (9) may support this thought. The fact that the tissue catecholamine consists of at least two fractions, one is easily released and depleted by the first and second injection of methamphetamine and the other is chemically extractable but difficult to deplete by the repetitive injections of methamphetamine may provide a clue to the elucidation of the physiological role of the endogenous catecholamine in free form and bound form. SUMMARY The effects of the single and repeated injections of methamphetamine on the content of tissue catecholamine in association with the behavioral changes of the intact rabbits were studied. 1. The first two injections of methamphetamine produced progressive decreases in the atrial and adrenal catecholamine, but further injections did not result in more decrease. 2. In the brain stem, the significant decrease of noradrenaline was observed only in response to the first injection of methamphetamine. The second and further injec tions of methamphetamine induced much less decrease of noradrenaline. 3. In the brain cortex, the single injection of methamphetamine did not signifi cantly affect the content of noradrenaline. Further repetition of the injection resulted in slight and somewhat variable changes. 4. Though the depletion of catecholamine was subjected to a tachyphylactic phe nomenon after repetitive injections of methamphetamine, the behavioral excitements including the increase in heart rate and spontaneous motor movements appeared as usual for every injection.
5. It is suggested that the behavioral excitements of the animal in response to the first injection of methamphetamine derive from the direct effects of it plus indirect effects which the noradrenaline released by methamphetamine exerts, while the large parts of the behavioral excitements including tachycardia in response to more than two injections of methamphetamine derive mainly from the direct effects of the drug, inde pendently the level of endogenous catecholamine. REFERENCES 1) TOMAN, J.E.P. AND DAVis, J.P.: Pharmacol. Rev. 1, 425 (1949) 2) MARRAZI,A.S.: Ann. N. Y. Acad. Sci. 66, 496 (1957) 3) BURN,J.H. AND RAND, M.J. : J. Physiol. 144, 314 (1958) 4) HIGUCHI, H. : THIS JOURNAL 12, 34 (1962) 5) HIGUCHI, H., MATSUO,T. AND SHIMAMOTO,K. : Ibid. 12, 48 (1962) 6) MCLEAN,J.R. AND MCCARTNEY,M.: Proc. Soc. exp. Biol., N. Y. 107, 77 (1961) 7) YOUNG, R.L. AND GORDON, M.W. : Biochem.Pharmacol. 6, 273 (1961) 8) DAVEY, M.J. AND FARMER,J.B. : J. Pharm. Pharmacol. 15, 178 (1963) 9) DAY, M.D. AND RAND, M.J.: Ibid. 14, 541 (1962)
OF SINGLE
AND REPEATED
METHAMPHETAMINE CATECHOLAMINE
INJECTION
OF
ON THE TISSUE OF RABBIT
TAKASHI HONJO Department of Pharmacology, Facultyof Medicine, KyotoUniversity, Sakyo-ku, Kyoto Receivedfor publicationAugust27,1963
The main pharmacological effects of methamphetamine are the psychomotor stimula tion and the sympathomimetic effects on the peripheral adrenergic structures. There is evidence which indicates the facilitatory action of amphetamine on the synaptic trans mission (1). By increasing the dose of amphetamine the inhibitory action and the reversal of facilitation have been demonstrated in the synaptic transmission of severalparts of the central nervous system (2). It has been emphasized by many authors that the central actions of various sympathomimetic amines probably are not related to their peripheral sympathomimetic actions. It is possible that methamphetamine acts on the adrenergic system directly, and in directly through interference with the metabolism of endogenous catecholamine or through liberation of the latter from local sites of storage. Analyzing the dose-response curves of the normal, the denervated, the cocainized and the reserpinized nictitating membrane of cat, Burn and Rand (3) have classified the sympathomimetic amines into following two groups, i.e. the sympatomimetic amines with direct action, and those with indirect action. They have shown that amphetamine exerts its adrenergic effects in directly through liberation of noradrenaline from the target organs. The liberation of noradrenaline from the central nervous system as well as the peripheral adrenergic structures has been confirmed biochemically by several investigators. This experiment was designed to study whether the systemic administration of methamaphetamine depletes noradrenaline in the central nervous system of rabbits to the same extent that it does in the autonomic structures such as heart, adrenal glands. Further, the effects of the repetition of the injection on the level of noradrenaline or adrenaline in these structures were studied since the repetitive administration of the drug is known to produce tachyphylaxis in the autonomic structures. METHODS Unanesthetized albino rabbits, weighing 1.5 to 2.5 kg, were used in the experiment. The animals were injected 1.0 mg/kg of methamphetamine hydrochloride into the marginal ear vein. Five injections were made at the intervals of one hour. After each 本庄 俊
injection the animal was kept in a cage and the behavioral changes caused by the drug were observed. One hour after the last injection the animals were sacrificed through bleeding by cutting both common carotid arteries. Immediately thereafter, the brain, heart and adrenals were removed. The homogenates of the tissues were prepared for the chemical assay of adrenaline and noradrenaline according to the method described by Higuchi (4). RESULTS 1. Behavioraleffects The single injection of methamphetamine induced various degree of sympathetic, motor and psychomotor-like excitements. The sympathomimetic effects observed were mydriasis, piloerection of the tail and tachycardia, and these effects lasted usually for about 20 to 40 minutes. The most long-lasting sympathetic excitatory effect among them was the tachycardia. The coordinated, spontaneous movements were increased in quantity accompanying with the psychomotor-like excitement such as restlessness and hypersensitivity to nociceptive stimuli, and these effects lasted for about 30 to 40 minutes after the injection. However, the extent of the behavioral changes could not be cor related with the level of catecholamine in the tissues. The repetition of the injection of methamphetamine at the intervals of one hour did not diminish the behavioral response to methamphetamine and every injection produced almost same degree of the excitatory behaviors. 2. Effects of single and repeatedinjectionsof methamphetamineon the contentof catecholamine The mean control values of noradrenaline in the brain and heart and of adrena line in the adrenal glands were determined in 5 to 8 intact rabbits (Table 1). The TABLE
1. Normal content of catecholamine in the various tissues of rabbit.
values were somewhat lower in the brain, and slightly higher in the auricle and the adrenal glands than those in correspond ing tissues reported by Higuchi (4).
The single intravenous injec tion of 2.5 ing/kg of methamphe A : adrenaline, NA : noradrenaline tamine reduced considerably the content of catecholamine in tissues tested, the reduction being about 35%. But the repeated injection of methamphetamine in the dose of 2.5 mg/kg at the interval of one hour produced long-lasting motor and sympathomimetic excitements by which the animal was exhausted to death. The single injection of 5.0 mg/kg of methamphetamine caused marked central excitatory symptoms but the reduction of noradrenaline or adrenaline did not significantly exceed that produced by 2.5 mg/kg of the drug. Consequently, these dosage levels were abandoned for further experiments.
The single injection of 1.0mg/kg of methamphetamine produced the reduction of
the catecholamine in the range from 10 to 20% associated with the considerable degree of the central excitements. Therefore, the dose of 1.0mg/kg of methamphetamine was' used throughout the experiments. The heart rate was counted before, and 1'0and 30 minutes after the injection. The single injection of 1.0mg/kg of methamphetamine increased the heart rate by about 15to 20% and the repetition of the injection produced the same degree of increase in heart rate (Fig, 1). It is unlikely that the`'repeated in jection of methamphetamine does affect the chronotropic response to the drug.
FIG. 1. Percent changes of tissue catecholamine content and heart rate following repeated injections of methampheta mine in rabbit. heart rate • • adrenal glands x--x auricle o -o brain stem
1) Adrenals The injection of 1.0 mg/kg of methamphetamine reduced the content of adrenaline in the adrenal glands. Table 2 and Fig. 1 show the mean values of the content of ad renaline (,ug/g tissue) in the adrenals of rabbit which had been killed one hour after the last injection of 1.0 mg/kg of metham phetamine. The first injection of metham phetamine reduced the content of adrena line in the adrenals by about 17%, and the second injection resulted in a reduction of about 42%. However, further repetition of the injection of methamphetamine did not bring about the significant further decrease of adrenaline but the reduction reached a plateau at the level of about 40%, while every repetition of the injec
TABLE 2. Adrenaline content on rabbit adrenal glands after the repeated injections of meth amphetamine. 1.0 mg/kg i.v. at 1 hour interval.
tion caused the central excitatory symptoms. The significant reduction of adrenaline by the first and second injections and the plateau following further repetition of the injection are more clearly shown when the content of adrenaline is expressed in terms of pg/g tissue than when expressed in ,"g/glands. Although the reduction of adrenaline after the injection of methamphetamine were subjected to somewhat individual varia tions,
the
extent
generally
paralleled
with
TABLE 3. Noradrenaline content in rabbit atria after the repeated injections of metham phetamine. 1.0 mg/kg ix. at 1 hour interval.
TABLE 4. Noradrenaline content in rabbit brain stem after the repeated injections of meth amphetamine. 1.0 mg/kg i.v. at 1 hour interval.
the
behavioral
changes.
2) Atria The administration of methampheta mine also reduced that content of norad renaline in the atria. The reduction of the level of noradrenaline in the atria induced by the first and the second injections was slight but significant. After the injections above three times, there was no further decrease in atrial noradrenaline except fourth injection which produced a consi derable reduction of unknown origin. The decrease of noradrenaline in the atria also subjected to individual variations but the decrease was pronounced when the animal exhibited marked behavioral excitement. The results are shown in Table 3 and Fig. 1.
3) Brain stem The reduction of noradrenaline in the brain stem of rabbit which had received methamphetamine repeatedly is shown in Table 4 and Fig. 1. In response to the first injection of methamphetamine the content of noradrenaline was decreased by about 23%. The second and further injections of methamphetamine induced much less decrease of noradrenaline. Higuchi et al. (5) showed that the intravenous injection of 1.0 mg/kg of methamphetamine to the rabbit produced a reduction of about 40% of noradrenaline in the brain stem. In the present experiments such a profound depletion was not ob served after the single dose of methamphetamine. As described above (l. Behavioral effects)the excitement caused by the repetitive injections of methamphetamine was almost similar in degree, irrespective of the extent of the decrease in level of noradrenaline. Therefore, it is likely that the behavioral excitement does not correlate with the content of noradrenaline. However, the first injection of methamphetamine caused the marked depletion of noradrena]ine and therefore, only the excitement following the first injec tion was likely to relate with the reduction of noradrenaline.
4) Brain cortex The single injection of methampheta mine did not significantly affect the content of noradrenaline in the brain cortex. Further repetition of the injection resulted in slight and somewhat variable changes. The results are shown in Table 5.
TABLE5. Noradrenaline content in rabbit brain cortex after the repeated injections of methamphetamine. 1.0 mg/kg i.v. at 1 hour interval.
DISCUSSION The effects of the single and the repeated injections of methamphetamine on the content of tissue catecholamine in association with the behavioral changes of the intact rabbits were studied. The single injection of 1.0 mg/kg of methamphetamine reduced the level of the catecholamine in the brain, heart . and adrenals, but the level of reduction varied according to the tissues. The largest reduction was obtained in the brain stem and the smallest was in the heart. Although the reduction of the level of
catecholamine was subjected to individual variations, the sympathetic and the motor excitements produced by methamphetamine seemed to correlate with the reduction of catecholamine.. The depletion of the amine in response to methamphetamine varied with the dose administered, but the depletion caused by 2.5to 5.0 mg/kg did not usually exceed 50%. The similar depletion by amphetamine of the brain noradrenaline in the rat has been reported by McLean et al. (6). The first two injections produced progressive decreases in the atrial and adrenal catecholamines, but further injections did not result in more decrease. In the brain stem the decrease of noradrenaline was observed only in response to the first injection of methamphetamine. The most typical pattern of changes in the tissue amine was obtained in the adrenal glands. The similar depletion of the rat brain noradrenaline after the repetitive injection of amphetamine has been demonstrated by McLean et al. (6). Though the depletion of catecholamine was subjected to a tachyphylactic pheno menon after repetitive injections of methamphetamine, the behavioral excitements in cluding the increase in heart rate and'the spontaneous motor movements appeared as usual for every injection. This is clearly shown in Fig. 1. In the brain cortex the normal content of noradrenaline was much less than in other tissues. If the change of cortical noradrenaline is expressed as a per cent value, even small change of ,ug/g should be unexpectedly large in the per cent value. In this figure, therefore, the per cent change of noradrenaline in the brain cortex was not compared with that in other tissues. From the results described above, it is suggested that the sympathetic and motor excitements of the animal in response to the first injection derive from the direct effects of methamphetamine plus indirect effects which are exerted by noradrenaline released, while the large parts of the behavioral excitements including tachycardia after the second
injection of methamphetamine
drive mainly from the direct effects of the drug inde
pendent of the endogenous catecholamine. No development of tachyphylaxis in the positive chronotropic effect of methamphetamine is likely to drive from the direct action on the heart, or alternatively some `central effect apart from the peripheral autonomic action. The easy access of amphetamine in the brain with subsequent accumulation of it has been concluded by Young and Gordon (7). The question remained to be settled why the central excitement in response to every repetition of the injection of metham phetamine does not induce the further depletion of the tissue catecholamine. Davey and Farmer (8) have reported that the repetitive injection of tyramine to the isolated guinea-pig's heart depleted the content of heart noradrenaline until the posi tive inotropic effect disappeared. They also demonstrated that although in the case of tyramine the depletion of noradrenaline resulted in the absence of the positive inotropic effect, the decrease of the heart noradrenaline was not causally related to the absence of the inotropic effect of methamphetamine. From the results it is conceivable that tyramine exerts its effect by releasing the endogenous noradrenaline, while metham phetamine does so mainly by the direct effect on the receptive structures with the ad ditional effect through the mediation of the endogenous noradrenaline. Tne powerful antagonism of dexamphetamine against guanethidine demonstrated by Day and Rand (9) may support this thought. The fact that the tissue catecholamine consists of at least two fractions, one is easily released and depleted by the first and second injection of methamphetamine and the other is chemically extractable but difficult to deplete by the repetitive injections of methamphetamine may provide a clue to the elucidation of the physiological role of the endogenous catecholamine in free form and bound form. SUMMARY The effects of the single and repeated injections of methamphetamine on the content of tissue catecholamine in association with the behavioral changes of the intact rabbits were studied. 1. The first two injections of methamphetamine produced progressive decreases in the atrial and adrenal catecholamine, but further injections did not result in more decrease. 2. In the brain stem, the significant decrease of noradrenaline was observed only in response to the first injection of methamphetamine. The second and further injec tions of methamphetamine induced much less decrease of noradrenaline. 3. In the brain cortex, the single injection of methamphetamine did not signifi cantly affect the content of noradrenaline. Further repetition of the injection resulted in slight and somewhat variable changes. 4. Though the depletion of catecholamine was subjected to a tachyphylactic phe nomenon after repetitive injections of methamphetamine, the behavioral excitements including the increase in heart rate and spontaneous motor movements appeared as usual for every injection.
5. It is suggested that the behavioral excitements of the animal in response to the first injection of methamphetamine derive from the direct effects of it plus indirect effects which the noradrenaline released by methamphetamine exerts, while the large parts of the behavioral excitements including tachycardia in response to more than two injections of methamphetamine derive mainly from the direct effects of the drug, inde pendently the level of endogenous catecholamine. REFERENCES 1) TOMAN, J.E.P. AND DAVis, J.P.: Pharmacol. Rev. 1, 425 (1949) 2) MARRAZI,A.S.: Ann. N. Y. Acad. Sci. 66, 496 (1957) 3) BURN,J.H. AND RAND, M.J. : J. Physiol. 144, 314 (1958) 4) HIGUCHI, H. : THIS JOURNAL 12, 34 (1962) 5) HIGUCHI, H., MATSUO,T. AND SHIMAMOTO,K. : Ibid. 12, 48 (1962) 6) MCLEAN,J.R. AND MCCARTNEY,M.: Proc. Soc. exp. Biol., N. Y. 107, 77 (1961) 7) YOUNG, R.L. AND GORDON, M.W. : Biochem.Pharmacol. 6, 273 (1961) 8) DAVEY, M.J. AND FARMER,J.B. : J. Pharm. Pharmacol. 15, 178 (1963) 9) DAY, M.D. AND RAND, M.J.: Ibid. 14, 541 (1962)