Br. J. exp. Path. (1979) 60, 389
THE TOXIC EFFECTS OF LONG-TERM, ORAL ADMINISTRATION OF L-TRYPTOPHAN IN RATS WITH PORTACAVAL SHUNT L. BUCCI AND R. CHIAV-ARELLI
Fronb the Laboratorio di Farmacologia, Istituto Superiore della SanitM, Rome, Italy Received for ptublication February 19, 1979
Summary.-The oral, long-term administration of 200 mg/kg of L-tryptophan to rats previously submitted to a portacaval shunt causes significant loss of body weight, muscular hypertonicity and aggressivity, as well as marked alterations of the liver structure. Conversely, the same treatment is well tolerated by control animals. It is postulated that the derangement of tryptophan metabolism normally occurring in rats with portacaval shunt is by itself insufficient to induce behavioural changes and liver damage which, on the contrary, develop when tryptophan metabolism is further altered by the administration of the amino acid to the animals for a long period of time.
A DERANGEMENT of the metabolism of tryptophan (Try) is known to occur in rats submitted to a portacaval shunt (PCS). Baldessarini and Fisher (1973) have, in fact, reported increased brain Try concentration along with an increase of 5hydroxytryptamine (5HT) and 5hydroxyindolacetil acid (5HIAA) in rats 2 months after an end-to-side portacaval shunt, while Curzon et al. (1975) found higher levels of Try, 5HT and 5HIAA in different regions of the brain of rats submitted to a PCS 3 weeks previously. Comparable results have been obtained in our laboratory in rats 40 days after an end-to-side PCS (Bucci et al., unpublished). These biochemical derangements, however, are not followed by significant or detectable behavioural changes. Several investigators have, in fact, reported that behaviourally it is not possible to distinguish rats with PCS from their controls, even several months after surgery (Masland, 1964; Assal et al., 1971; Wasterlain, Lockwood and Conn, 1978). Bloxan et al. (1977), however, have noticed that a dose of 20 mg/kg of L-Try injected i.p. into rats previously subjected to PCS caused
a decrease of ambulation, together with an increase in brain Try concentration, much higher than in normally behaving controls. To evaluate further the effects of L-Try in rats with a PCS we have administered large doses of L-Try by mouth daily for several weeks to a group of rats previously subjected to a portacaval anastomosis. In this paper we report our results.
METHOD AND MATERIAL
Eighteen male Wistar rats, weighing initially 280-325 g each were used. They were divided into 3 groups of 6 each labelled Groups A, B and C. Groups A and B were subjected to an end-toside portacaval anastomosis under pentobarbital anaesthesia (Lee et al., 1974). The patency of the shunt was confirmed at necropsy. Grouip C rats were sham-operated as follows: the portal vein and the vena cava were isolated and clamped for 30 min. Blood circulation was then re-established and the abdomen
suitured.
Following surgery the rats were housed 2 per cage, receiving standard chow food (Morini Lab.) and water ad libitum, while their body weight was checked weekly for 30 days. From the 31st day oni, the food remained the same for
Address for correspondence: Luigi Buicci, Via Veneto, 116, Rome, Italy.
390
L. BUCCI AND R. CHIAVARELLI
3 groups of rats, while their drinking was varied. Group A rats drank daily a 2% solution of L-tryptophan (AMerk Lab.) dissolved in water; Group B rats drank only water, and those of Grouip C again drank a 2% solution of L-Try, like Grouip A. Hence, apart from a group of PCS rats which drank L-Try (Group A), we had two gr'oulps of controls: one with PCS which drank only water (Group B) and another, shamoperated group which drank L-Try (Grouip C). As we have previously calculated that a 300-g rat drinks approximately 30 ml of water per day, and that its water intake increases or decreases roughly in proportion to its body weight, we estimate that in the present experiment each rat received by iyouth approximately 200 mg/kg of L-Try per day. Once a week the rats were removed from their cages, weighed and then placed in a plastic box (40 x 50 cm) where they could move around freely, and observed for 30 min. Since the animals with PCS which drank L-Try approximately 2 weeks later started to show a marked loss of body weight and signs of physical deterioration, all .3 groups of animals were killed 60 days after treatment (90 days after sturgery). The liver of each animial was carefully remnoved, weighed and its gross appearances noted. Samples of each liver w ere fixed in 70% ethyl alcohol and Bouiin's fluid and stained with haematox-ylini eosin for histological examinaall
Days after surg.
15
Days of treat
Finc.
Variations in body weight of the 3 of rats: (A) Portacaval-shunte(d rats treate(d with L-tryptophan. (B) Untreated portacaval-shunted rats. (C) Sham-operated r'ats treated with L-tryptophan. 1.
groups
physical condition and behaviour. Rats of Groups A and C appeared always to be in good health and reacting normally to handling and changes of environment, tionl. their fur remaining soft and white throughout the time of the experiment (Fig. 2). RESULTS By contrast PCS animals treated with Body weight L-Try, in addition to weight loss, showed As shown in Fig. 1, all 3 groups of rats muscular hypertonicity, pilo-erection, yelshowed a loss of body weight during the lowish fur, ataxic gait, somewhat infirst 2 weeks after surgery amounting to creased spontaneous motor activity (as about 2% in those subjected to sham assessed by simple observation), increased operation, and 8-12% in those which sensitivity to external stimuli, and agunderwent PCS. By the end of the 30th gressivity: in fact, they frequently attempday after surgery, all 3 groups of animals ted to bite when handled or touched by a showed a gain in body weight, slightly stick (Fig. 3). less in those subjected to PCS. By contrast marked differences in body weight occurred Liver examination in the 3 groups of animals during the The sham-operated rats had a liver following 2 months of treatment. While which on gross examination appeared norrats of Groups B and C showed respec- mal in size, shape and colour. PCS tively an average gain of 53.3% (s.d. + animals which drank water had a shrunken 7.07) and 64.5% (s.d. + 13.9) of their and wrinkled liver, slightly flabby, with initial weight, those of Group A lost 24.5% sharp edges. Their mean weight averaged 15-20% less than those of the previous (s.d. + 5.6). groups. The same kind of changes, but Phy8ical condition and behaviour much more pronounced, were evident in Marked differences could also be ob- livers of Group A rats. The capsules were served among the 3 groups of rats in thicker and adherent to the parenchyma,
TOXIC EFFECTS OF LONG-TERM L-TRYPTOPHAN
391
FIG. 2.-Right, a sham-operated rat treated with 200 mg/kg L-tryptophan daily by mouth for 60 days, weighing 505 g. Left, an untreated, portacaval-shunted rat weighing 455 g at the 60th day of the experiment. FIG. 3.-A portacaval-shunted rat treated with 200 mg/kg L-tryptophan daily by mouth for 60 days, weighing 245 g.
392
L. BUCCI AND R. CHIAVARELLI
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TOXIC EFFECTS OF LONG-TERM L-TRYPTOPHAN
which was somewhat flabby. Their mean weight averaged 35-40% less than those of Group C. Histological examination carried out by a neutral examiner also demonstrated marked differences among the 3 groups of rats. The sham-operated animals revealed no pathology of the organ (Fig. 4a). The PCS water-drinking animals showed changes in liver structure characterized by mild congestion and dilatation of the centrilobular vein and of the sinusoids, and some cloudy swelling of the hepatocytes (Fig. 4b). Markedly altered were the livers of the PCS rats treated with Try. Numerous sinusoids were dilated and anastomosed among themselves, enclosing small portions of liver parenchyma which appeared atrophic. The centrilobular appeared atrophic. The centrilobular veins were dilated and congested. Hepatocytes showed nuclear and cytoplasmic polymorphism with dispersion of cytoplasmic granules as seen in cloudy swelling. A few cells were necrotic. Pyknosis was common, but binucleated cells rare and mitoses even rarer. Kupffer cells were slightly hypertrophic and increased in number. No signs of inflammation were detectable. The histological diagnosis was that of a toxic hepatitis (Fig. 4c, d). DISCUSSION
The results of this pilot study show that an approximate daily dose of 200 mg/kg administered by mouth and for a sufficiently long period of time is quite toxic to rats previously submitted to PCS, whereas it is quite well tolerated by sham-operated controls. In this latter group, in fact, none of the 3 parameters taken into consideration-body weight, behaviour and liver structure has been adversely affected. Their body weight increased normally and progressively up to 64.4% (s.d. + 13.9) of their initial value, their appearance and behaviour were normal throughout the time of the experiment, and gross and histological examination of their liver showed no structural alteration whatsoever. By
393
contrast, the PCS rats treated with L-Try underwent a constant and progressive loss of weight (24.5%, s.d. + 5.6) and developed pilo-erection, yellowish fur, ataxic gait, restlessness and aggressive behaviour. Furthermore, their livers showed marked structural changes. The results obtained with untreated PCS animals are in many ways comparable to those reported by other investigators. Their body weight increased regularly although by a slightly lower percentage than in the sham-operated (53.3%, s.d. + 7.07), confirming the observations of Assal et at. (1971) and Wasterlain et al. (1978). In agreement with the reports of Masland (1964), Assal et al. and Wasterlain et al., no significant change could be detected in their behaviour. However, in agreement with Henzel, Turcotte and Child (1963) Masland, and Kyu and Cavanagh (1970), but not with Assal et al., some changes in liver structure were observed. Several investigators have noted that a portacaval anastomosis induces in rats a derangement of the metabolism of several amino acids characterized, among other things, by an increase in plasma and brain levels of tyrosine, phenylalanine and Try, and they have inferred that the changes in Try metabolism may play an important role in the pathogenesis of hepatic encephalopathy (Cummings et al., 1976; Curzon et al., 1975). Such an hypothesis, however, does not seem to find support in behavioural studies, since our results, as well as those reported by other investigators (Masland, 1964; Assal et al., 1971; Wasterlain et al., 1978) clearly show that no relationship can be detected between biochemical derangement and behaviour, for there is a lack of significant changes of the latter. However, Bloxan et al. (1977) observed, and our results also show, that behavioural changes and/or toxic effects occur in PCS rats given additional Try. Hence we may claim that the derangement of Try metabolism which takes place in PCS rats is by itself not sufficient to induce behavioural and/or toxic effects, but that such effects occur when the Try metabol-
394
L. BUCCI AND R. CHIAVARELLI
ism is further altered by additional ad- plasma Try were always accompanied by ministration of this amino acid. By con- neurological symptoms and signs. trast, the daily administration of fairly We thank Professor A. Bigotti and large doses of L-Try is well tolerated by B. Nicohetti for their technical assistance normal (sham-operated) rats. The main in preparing histological and photograquestion raised by these results is why relatively large doses of L-Try are well phic material. tolerated by normal rats but are so toxic REFERENCES to PCS animals. ASSAL, J. PH., LEVRAT, R., CAHN, T. & RENOLD, A. E. (1971) Metabolic Consequences of Portacaval At the moment we are unable to give a Shunting in the Rat. Z. ges exp. Med., 154, 87. satisfactory explanation. As a simple BALDESSARINI, R. J. & FISHER, E. J. (1973) Seroworking hypothesis, however, we may tonin Metabolism in Rat Brain after Surgical Diversion of the Portal Venous Circulation. Nature assume the following. Individual free (New Biol.), 245, 25. essential amino acids in the body are BLOXAN, D. L., CU-RZON, G., KANTAMANEMI, B. D. & TRICKLEBANK, M. D. (1977) Effects of Tryptonormally present in relatively constant phan and Portacaval Anastomosis on Activity fixed proportions (Job et al., 1970). If this and Brain Tryptophan Metabolism. Proc. of the concentration is altered, untoward effects BPS 30th, Mlarch 31, 277P. may develop as a result of any of a number CI-MMINGS, M. J., SOLIERS, P. B., JAMES, J. H., KEANE, J. M. & FISHER, E. J. (1976) Regional of mechanisms, inncluding direct toxicity Brain Indoleamines Metabolism Following Chronic resulting from an abnormally high conPortacaval Anastomosis in the Rat. J. Neurodern., 27, 501. centration of one of them (Job et al., 1970). G., KANTAMANEMI, B. D., FERNANDO, In the sham-operated rats the higher CITRZON, J. C., WOODS, AM. S. & CAVANAGH, J. B. (1975) quantities of L-Try which reach the liver Effects of Chronic Portacaval Anastomosi on Brain Tryptophan, Tyrosine and 5-Hydroxyfrom the gut are mostly metabolized tryptamine. J. Neurochem., 24, 1065. through the kynurenine pathway (Knox HENZEL, J., TuRCOTTE, J. G. & CHILD, C. G. (1963) The Response of Normal Rat to Portacaval Shunt. and Greengard, 1964); therefore the plasma Arch. Surg., 86, 342. Try levels, although higher than normal, HYRAYAMA, C. (1970) Tryptophan Metabolism in remain within limits which can be tolerLiver Disease. Clin. Acta, 32, 190. ated by the animals. Conversely, in the IOB,WV. V., MATTSON, W. J., Jr, SLOAN, M., COON, W., TURCOTTE, J. G. & CHILD, C. G. (1970) PCS rats, owing to the presence of the Alteration in Plasma Free Amino Acids in Dogs with Hepat.ic Insufficiency. Surg. Gyn. & Obstr., by-pass, the Try plasma (and brain) con130, 794. centrations reach and remain at values so KNOX, W. E. & GREENGARD, 0. (1964) The Regulahigh that in due time they cause changes tion of Some Enzymes of Nitrogen Metabolism. An Introduction to Enzyme Physiology. In in liver structure and, directly or indirectly, Advances in Enzyme Regulation, Vol. 3, G. Weber, in the central nervous system. This hypoEd. New York: Pergamon. p. 247. thesis (which obviously requires further KyI-, M. H. & CAVANAGH, J. B. (1970) Some Effects of Portacaval Anastomosis in the MIale Rat. investigation) finds some indirect support Br. J. exp. Path., 51, 217. in the findings of Hyrayama (1970), who LEE, S., CHANLER, J. G., BROELSH, C. E., FLAMANT, in fact reported that the tryptophan G. M. & ORLOFF, M. J. (1974) Portal-Systemic Anastomosis in Rats. J. Surg. Res., 17, 53. loading test in patients with liver cirrhosis MIASLAND, W. S. (1964) Interrelationship between (that is, with a natural vascuilar portol)iet and Weight Gain in Rats with Portacaval Shunt. Am. J. Physiol., 206, 304. systemic shunt) was characterized by C. G., LoCKWOOD, A. H. & CONN, AM. higher plasma Try levels owing to delayed WA'ASTERLAIN, (1978) Chronic Inhibition of Brain Protein Synremoval, and that such high levels of thesis after Portacaval Shunt. Neurology, 28, 233.
THE TOXIC EFFECTS OF LONG-TERM, ORAL ADMINISTRATION OF L-TRYPTOPHAN IN RATS WITH PORTACAVAL SHUNT L. BUCCI AND R. CHIAV-ARELLI
Fronb the Laboratorio di Farmacologia, Istituto Superiore della SanitM, Rome, Italy Received for ptublication February 19, 1979
Summary.-The oral, long-term administration of 200 mg/kg of L-tryptophan to rats previously submitted to a portacaval shunt causes significant loss of body weight, muscular hypertonicity and aggressivity, as well as marked alterations of the liver structure. Conversely, the same treatment is well tolerated by control animals. It is postulated that the derangement of tryptophan metabolism normally occurring in rats with portacaval shunt is by itself insufficient to induce behavioural changes and liver damage which, on the contrary, develop when tryptophan metabolism is further altered by the administration of the amino acid to the animals for a long period of time.
A DERANGEMENT of the metabolism of tryptophan (Try) is known to occur in rats submitted to a portacaval shunt (PCS). Baldessarini and Fisher (1973) have, in fact, reported increased brain Try concentration along with an increase of 5hydroxytryptamine (5HT) and 5hydroxyindolacetil acid (5HIAA) in rats 2 months after an end-to-side portacaval shunt, while Curzon et al. (1975) found higher levels of Try, 5HT and 5HIAA in different regions of the brain of rats submitted to a PCS 3 weeks previously. Comparable results have been obtained in our laboratory in rats 40 days after an end-to-side PCS (Bucci et al., unpublished). These biochemical derangements, however, are not followed by significant or detectable behavioural changes. Several investigators have, in fact, reported that behaviourally it is not possible to distinguish rats with PCS from their controls, even several months after surgery (Masland, 1964; Assal et al., 1971; Wasterlain, Lockwood and Conn, 1978). Bloxan et al. (1977), however, have noticed that a dose of 20 mg/kg of L-Try injected i.p. into rats previously subjected to PCS caused
a decrease of ambulation, together with an increase in brain Try concentration, much higher than in normally behaving controls. To evaluate further the effects of L-Try in rats with a PCS we have administered large doses of L-Try by mouth daily for several weeks to a group of rats previously subjected to a portacaval anastomosis. In this paper we report our results.
METHOD AND MATERIAL
Eighteen male Wistar rats, weighing initially 280-325 g each were used. They were divided into 3 groups of 6 each labelled Groups A, B and C. Groups A and B were subjected to an end-toside portacaval anastomosis under pentobarbital anaesthesia (Lee et al., 1974). The patency of the shunt was confirmed at necropsy. Grouip C rats were sham-operated as follows: the portal vein and the vena cava were isolated and clamped for 30 min. Blood circulation was then re-established and the abdomen
suitured.
Following surgery the rats were housed 2 per cage, receiving standard chow food (Morini Lab.) and water ad libitum, while their body weight was checked weekly for 30 days. From the 31st day oni, the food remained the same for
Address for correspondence: Luigi Buicci, Via Veneto, 116, Rome, Italy.
390
L. BUCCI AND R. CHIAVARELLI
3 groups of rats, while their drinking was varied. Group A rats drank daily a 2% solution of L-tryptophan (AMerk Lab.) dissolved in water; Group B rats drank only water, and those of Grouip C again drank a 2% solution of L-Try, like Grouip A. Hence, apart from a group of PCS rats which drank L-Try (Group A), we had two gr'oulps of controls: one with PCS which drank only water (Group B) and another, shamoperated group which drank L-Try (Grouip C). As we have previously calculated that a 300-g rat drinks approximately 30 ml of water per day, and that its water intake increases or decreases roughly in proportion to its body weight, we estimate that in the present experiment each rat received by iyouth approximately 200 mg/kg of L-Try per day. Once a week the rats were removed from their cages, weighed and then placed in a plastic box (40 x 50 cm) where they could move around freely, and observed for 30 min. Since the animals with PCS which drank L-Try approximately 2 weeks later started to show a marked loss of body weight and signs of physical deterioration, all .3 groups of animals were killed 60 days after treatment (90 days after sturgery). The liver of each animial was carefully remnoved, weighed and its gross appearances noted. Samples of each liver w ere fixed in 70% ethyl alcohol and Bouiin's fluid and stained with haematox-ylini eosin for histological examinaall
Days after surg.
15
Days of treat
Finc.
Variations in body weight of the 3 of rats: (A) Portacaval-shunte(d rats treate(d with L-tryptophan. (B) Untreated portacaval-shunted rats. (C) Sham-operated r'ats treated with L-tryptophan. 1.
groups
physical condition and behaviour. Rats of Groups A and C appeared always to be in good health and reacting normally to handling and changes of environment, tionl. their fur remaining soft and white throughout the time of the experiment (Fig. 2). RESULTS By contrast PCS animals treated with Body weight L-Try, in addition to weight loss, showed As shown in Fig. 1, all 3 groups of rats muscular hypertonicity, pilo-erection, yelshowed a loss of body weight during the lowish fur, ataxic gait, somewhat infirst 2 weeks after surgery amounting to creased spontaneous motor activity (as about 2% in those subjected to sham assessed by simple observation), increased operation, and 8-12% in those which sensitivity to external stimuli, and agunderwent PCS. By the end of the 30th gressivity: in fact, they frequently attempday after surgery, all 3 groups of animals ted to bite when handled or touched by a showed a gain in body weight, slightly stick (Fig. 3). less in those subjected to PCS. By contrast marked differences in body weight occurred Liver examination in the 3 groups of animals during the The sham-operated rats had a liver following 2 months of treatment. While which on gross examination appeared norrats of Groups B and C showed respec- mal in size, shape and colour. PCS tively an average gain of 53.3% (s.d. + animals which drank water had a shrunken 7.07) and 64.5% (s.d. + 13.9) of their and wrinkled liver, slightly flabby, with initial weight, those of Group A lost 24.5% sharp edges. Their mean weight averaged 15-20% less than those of the previous (s.d. + 5.6). groups. The same kind of changes, but Phy8ical condition and behaviour much more pronounced, were evident in Marked differences could also be ob- livers of Group A rats. The capsules were served among the 3 groups of rats in thicker and adherent to the parenchyma,
TOXIC EFFECTS OF LONG-TERM L-TRYPTOPHAN
391
FIG. 2.-Right, a sham-operated rat treated with 200 mg/kg L-tryptophan daily by mouth for 60 days, weighing 505 g. Left, an untreated, portacaval-shunted rat weighing 455 g at the 60th day of the experiment. FIG. 3.-A portacaval-shunted rat treated with 200 mg/kg L-tryptophan daily by mouth for 60 days, weighing 245 g.
392
L. BUCCI AND R. CHIAVARELLI
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.
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=$
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TOXIC EFFECTS OF LONG-TERM L-TRYPTOPHAN
which was somewhat flabby. Their mean weight averaged 35-40% less than those of Group C. Histological examination carried out by a neutral examiner also demonstrated marked differences among the 3 groups of rats. The sham-operated animals revealed no pathology of the organ (Fig. 4a). The PCS water-drinking animals showed changes in liver structure characterized by mild congestion and dilatation of the centrilobular vein and of the sinusoids, and some cloudy swelling of the hepatocytes (Fig. 4b). Markedly altered were the livers of the PCS rats treated with Try. Numerous sinusoids were dilated and anastomosed among themselves, enclosing small portions of liver parenchyma which appeared atrophic. The centrilobular appeared atrophic. The centrilobular veins were dilated and congested. Hepatocytes showed nuclear and cytoplasmic polymorphism with dispersion of cytoplasmic granules as seen in cloudy swelling. A few cells were necrotic. Pyknosis was common, but binucleated cells rare and mitoses even rarer. Kupffer cells were slightly hypertrophic and increased in number. No signs of inflammation were detectable. The histological diagnosis was that of a toxic hepatitis (Fig. 4c, d). DISCUSSION
The results of this pilot study show that an approximate daily dose of 200 mg/kg administered by mouth and for a sufficiently long period of time is quite toxic to rats previously submitted to PCS, whereas it is quite well tolerated by sham-operated controls. In this latter group, in fact, none of the 3 parameters taken into consideration-body weight, behaviour and liver structure has been adversely affected. Their body weight increased normally and progressively up to 64.4% (s.d. + 13.9) of their initial value, their appearance and behaviour were normal throughout the time of the experiment, and gross and histological examination of their liver showed no structural alteration whatsoever. By
393
contrast, the PCS rats treated with L-Try underwent a constant and progressive loss of weight (24.5%, s.d. + 5.6) and developed pilo-erection, yellowish fur, ataxic gait, restlessness and aggressive behaviour. Furthermore, their livers showed marked structural changes. The results obtained with untreated PCS animals are in many ways comparable to those reported by other investigators. Their body weight increased regularly although by a slightly lower percentage than in the sham-operated (53.3%, s.d. + 7.07), confirming the observations of Assal et at. (1971) and Wasterlain et al. (1978). In agreement with the reports of Masland (1964), Assal et al. and Wasterlain et al., no significant change could be detected in their behaviour. However, in agreement with Henzel, Turcotte and Child (1963) Masland, and Kyu and Cavanagh (1970), but not with Assal et al., some changes in liver structure were observed. Several investigators have noted that a portacaval anastomosis induces in rats a derangement of the metabolism of several amino acids characterized, among other things, by an increase in plasma and brain levels of tyrosine, phenylalanine and Try, and they have inferred that the changes in Try metabolism may play an important role in the pathogenesis of hepatic encephalopathy (Cummings et al., 1976; Curzon et al., 1975). Such an hypothesis, however, does not seem to find support in behavioural studies, since our results, as well as those reported by other investigators (Masland, 1964; Assal et al., 1971; Wasterlain et al., 1978) clearly show that no relationship can be detected between biochemical derangement and behaviour, for there is a lack of significant changes of the latter. However, Bloxan et al. (1977) observed, and our results also show, that behavioural changes and/or toxic effects occur in PCS rats given additional Try. Hence we may claim that the derangement of Try metabolism which takes place in PCS rats is by itself not sufficient to induce behavioural and/or toxic effects, but that such effects occur when the Try metabol-
394
L. BUCCI AND R. CHIAVARELLI
ism is further altered by additional ad- plasma Try were always accompanied by ministration of this amino acid. By con- neurological symptoms and signs. trast, the daily administration of fairly We thank Professor A. Bigotti and large doses of L-Try is well tolerated by B. Nicohetti for their technical assistance normal (sham-operated) rats. The main in preparing histological and photograquestion raised by these results is why relatively large doses of L-Try are well phic material. tolerated by normal rats but are so toxic REFERENCES to PCS animals. ASSAL, J. PH., LEVRAT, R., CAHN, T. & RENOLD, A. E. (1971) Metabolic Consequences of Portacaval At the moment we are unable to give a Shunting in the Rat. Z. ges exp. Med., 154, 87. satisfactory explanation. As a simple BALDESSARINI, R. J. & FISHER, E. J. (1973) Seroworking hypothesis, however, we may tonin Metabolism in Rat Brain after Surgical Diversion of the Portal Venous Circulation. Nature assume the following. Individual free (New Biol.), 245, 25. essential amino acids in the body are BLOXAN, D. L., CU-RZON, G., KANTAMANEMI, B. D. & TRICKLEBANK, M. D. (1977) Effects of Tryptonormally present in relatively constant phan and Portacaval Anastomosis on Activity fixed proportions (Job et al., 1970). If this and Brain Tryptophan Metabolism. Proc. of the concentration is altered, untoward effects BPS 30th, Mlarch 31, 277P. may develop as a result of any of a number CI-MMINGS, M. J., SOLIERS, P. B., JAMES, J. H., KEANE, J. M. & FISHER, E. J. (1976) Regional of mechanisms, inncluding direct toxicity Brain Indoleamines Metabolism Following Chronic resulting from an abnormally high conPortacaval Anastomosis in the Rat. J. Neurodern., 27, 501. centration of one of them (Job et al., 1970). G., KANTAMANEMI, B. D., FERNANDO, In the sham-operated rats the higher CITRZON, J. C., WOODS, AM. S. & CAVANAGH, J. B. (1975) quantities of L-Try which reach the liver Effects of Chronic Portacaval Anastomosi on Brain Tryptophan, Tyrosine and 5-Hydroxyfrom the gut are mostly metabolized tryptamine. J. Neurochem., 24, 1065. through the kynurenine pathway (Knox HENZEL, J., TuRCOTTE, J. G. & CHILD, C. G. (1963) The Response of Normal Rat to Portacaval Shunt. and Greengard, 1964); therefore the plasma Arch. Surg., 86, 342. Try levels, although higher than normal, HYRAYAMA, C. (1970) Tryptophan Metabolism in remain within limits which can be tolerLiver Disease. Clin. Acta, 32, 190. ated by the animals. Conversely, in the IOB,WV. V., MATTSON, W. J., Jr, SLOAN, M., COON, W., TURCOTTE, J. G. & CHILD, C. G. (1970) PCS rats, owing to the presence of the Alteration in Plasma Free Amino Acids in Dogs with Hepat.ic Insufficiency. Surg. Gyn. & Obstr., by-pass, the Try plasma (and brain) con130, 794. centrations reach and remain at values so KNOX, W. E. & GREENGARD, 0. (1964) The Regulahigh that in due time they cause changes tion of Some Enzymes of Nitrogen Metabolism. An Introduction to Enzyme Physiology. In in liver structure and, directly or indirectly, Advances in Enzyme Regulation, Vol. 3, G. Weber, in the central nervous system. This hypoEd. New York: Pergamon. p. 247. thesis (which obviously requires further KyI-, M. H. & CAVANAGH, J. B. (1970) Some Effects of Portacaval Anastomosis in the MIale Rat. investigation) finds some indirect support Br. J. exp. Path., 51, 217. in the findings of Hyrayama (1970), who LEE, S., CHANLER, J. G., BROELSH, C. E., FLAMANT, in fact reported that the tryptophan G. M. & ORLOFF, M. J. (1974) Portal-Systemic Anastomosis in Rats. J. Surg. Res., 17, 53. loading test in patients with liver cirrhosis MIASLAND, W. S. (1964) Interrelationship between (that is, with a natural vascuilar portol)iet and Weight Gain in Rats with Portacaval Shunt. Am. J. Physiol., 206, 304. systemic shunt) was characterized by C. G., LoCKWOOD, A. H. & CONN, AM. higher plasma Try levels owing to delayed WA'ASTERLAIN, (1978) Chronic Inhibition of Brain Protein Synremoval, and that such high levels of thesis after Portacaval Shunt. Neurology, 28, 233.
