1425 as having been caused by the neoplasm, presumably have been done for those occurring postoperatively.
certified but this would were
Ward 3, Woodend General Hospital, Aberdeen.
*** We showed this letter
C. D. NEEDHAM. to
Dr
Dyer, whose reply
follows.-ED. L.
SIR,-Dr Needham suggests that our findings in the Chicago Peoples Gas Company study of an association between high blood-pressure and an increased likelihood of death due to cancer might be due to an increase in operative mortality among hypertensives. An examination of our records shows that among those dying of cancer only 1 individual died either during or very shortly after surgery, and his 1958 blood-pressure was 118/70. Thus, this association cannot be accounted for by a modest increase in operative mortality among hypertensives. With regard to the question concerning an association between the occurrence of cancer and high blood-pressure, the data from this study are not really amenable to this type of analysis. Because the men in this study were originally 40-59 at entry, many retired during the course of the study and were eventually lost to follow-up for the determination of non-fatal events, such as cancer, although not for the purposes of determining mortality. Thus, any effort to sort out the data in this regard, in addition to being a herculean task, would be risky at best. Northwestern University Medical
School, 303 E. Chicago Avenue, Chicago, Illinois 60611, U.S.A.
ALAN R. DYER.
METABOLISM OF VINYL CHLORIDE SiR,—Recent reports1 of angiosarcoma of the liver due to occupational exposure to vinyl chloride (v.c.) prompted research on the metabolism of this substance. The microsomal mixed-function oxidase (M.F.o.) of the liver converts v.c. to polar metabolites such as chloroethanol and chloroacetic acid.2.3 In bacterial test systems, v.c. itself was not found to be mutagenic, but liver microsomes with N.A.D.P.H.
(reduced form of nicotinamide-adenine-dinucleotide-phosphate) as co-factor metabolise v.c. to mutagenic metabolites.4 Using microsomes from animals pretreated with phenobarbitone, which incudes the M.F.o. of liver micro4 somes, both the mutagenicity of v.c. in these test systems and also its liver toxicity was found to be enhanced.5 The reactive metabolite of v.c. has been considered to be the epoxide,3,5 which should be able to bind covalently to tissue macromolecules. It is commonly accepted that many chemical carcinogens exert their effects by binding covalently to cellular macromolecules. We incubated 1.4C-labelled v.c. in a closed all-glass system with liver microsomes from rat and human liver. The addition of N.A.D.P.H. regenerating system was necessary to metabolise v.c. Using rat-liver microsomes per mg. microsomal protein 10 nmol v.c. was transformed to 7-4:0-8 nmol (xs.D.; n=9) of more polar metabolites during 90 minutes’ incubation, and 0-14±0-07 nmol was bound covalently to 1 mg. microsomal protein. In addition, metabolites of v.c. were bound covalently to other SHcontaining proteins, and also to ribonucleic acid, if such macromolecular compounds were added to the incuba1. Lancet, 1974, i, 1323. 2. Hefner, R. E., Watanabe, P. G., Gehring, P. J. Ann. N. Y. Acad. Sci. 1975, 246, 135. 3. Van Duuren, B. L. ibid. p. 258. 4. Bartsch, H., Malaveille, C., Montesano, R. Int. J. Cancer, 1975, 15, 429. 5. Jaeger, R. J., Reynolds, E. S., Conolly, R. B., Moslen, M. T., Szabo, S., Murphy, S. D. Nature, 1974, 252, 724.
tions. If N.A.D.P.H. was omitted, no covalent binding occurred to proteins or ribonucleic acid. Similar results were obtained using microsomes from human liver. These results confirm the concept 3,5 that v.c. is metabolised in the liver to alkylating intermediates, which may chemically modify cellular macromolecules by covalent binding. Further studies are urgently needed to elucidate the possible relation of carcinogenicity of v.c. and the covalent binding of its metabolites in the liver. University Institute of Toxicology, D-74 Tübingen, Wilhelmstrasse 56, H. M. BOLT and University Institute of H. KAPPUS Occupational Medicine, A. BUCHTER D-5 Cologne, Josef-Stelzmann-Strasse 9, W. BOLT. German Federal Republic.
AMINES, ANTICONVULSANTS, AND EPILEPSY SIR,-Dr Green and Professor Grahame-Smith (March 15, p. 639) found that phenytoin, but not other anticonvulsants, potentiated locomotor hyperactivity in rats after the administration of tranylcypromine and L-tryptophan, although the administration of phenytoin alone had no effect on brain serotonin (5-H.T.) levels. However, they are mistaken in interpreting our own observation of raised cerebrospinal (C.S.F.) 5-hydroxyindoleacetic acid (5-H.i.A.A.) in anticonvulsant-treated epileptics (March 1, p. 473) as being entirely due to phenytoin administration. We pointed out that our patients were taking phenobarbitone, phenytoin, or primidone either alone or in various combinations. In fact, seven of our patients were not taking phenytoin, and in one of these, who presented with phenobarbitone toxicity, the c.s.F. 5-H.I.A.A. level fell from 53-2 to 33-6 ng. per ml. when the dose of phenobarbitone was reduced, and the signs of toxicity disappeared. Furthermore, several other reports indicate that many anticonvulsants are capable of influencing 5-H.T. metabolism experimentally. Thus, Bonnycastle et al. found that eleven different anticonvulsants were capable of increasing brain 5-H.T. levels in rats when injected daily for up to 16 days. Chase et al.7 demonstrated that phenytoin, phenobarbitone, and diazepam are all capable of increasing the retention of intraventricularly injected 14C-labelled 5-H.T. after a single intraperitoneal dose of each anticonvulsant. We have also demonstrated that diazepam, clonazepam, as well as phenytoin, will increase 5-H.T. levels in mice.8 Dr Green and Professor Grahame-Smith suggest that phenytoin increases the turnover of 5-H.T. Chase et al.,7 however, suggested that anticonvulsants both inhibit the metabolism of 5-H.T. and block the egress of the acid metabolite, 5-H.I.A.A., from the brain. Similarly, Lidbrink et a1.9 demonstrated that phenobarbitone and diazepam reduce the turnover of brain 5-H.T. in rats. The discrepancy between the findings of Dr Green and Professor Grahame-Smith and previous authors may have resulted in part from the differing dosage schedules used. Further studies to clarify the effects of various anticonvulsants on 5-H.T. metabolism would seem to be worth while. Dr Green and Professor Grahame-Smith suggest that the effects of lithium and phenytoin on 5-H.T. function and metabolism are similar and postulate a common mechanism of action. However, in contrast to our observation of increased c.s.F. 5-H.I.A.A. with phenytoin and phenobarbitone therapy, Goodwin and Post 10 reported that 6.
Bonnycastle, D. D., Giarman, N. J., Paasonen, M. K. Br. J. Pharmac. 1957, 12, 228. 7. Chase, T. N., Katz, R. I., Kopin, I. J. Trans. Am. neurol. Ass. 1969, 94, 236. 8. Jenner, P., Chadwick, D., Reynolds, E. H., Marsden, C. D. Unpublished. 9. Lidbrink, P., Corrodi, H., Fuxe, K. Eur. J. Pharmac. 1974, 26, 35. 10. Goodwin, F. K., Post, R. M. in Advances in Biochemical Psychopharmacology (edited by E. Costa, G. L. Gessa, and M. Sandler); vol. XI, p. 341. New York, 1974.
certified but this would were
Ward 3, Woodend General Hospital, Aberdeen.
*** We showed this letter
C. D. NEEDHAM. to
Dr
Dyer, whose reply
follows.-ED. L.
SIR,-Dr Needham suggests that our findings in the Chicago Peoples Gas Company study of an association between high blood-pressure and an increased likelihood of death due to cancer might be due to an increase in operative mortality among hypertensives. An examination of our records shows that among those dying of cancer only 1 individual died either during or very shortly after surgery, and his 1958 blood-pressure was 118/70. Thus, this association cannot be accounted for by a modest increase in operative mortality among hypertensives. With regard to the question concerning an association between the occurrence of cancer and high blood-pressure, the data from this study are not really amenable to this type of analysis. Because the men in this study were originally 40-59 at entry, many retired during the course of the study and were eventually lost to follow-up for the determination of non-fatal events, such as cancer, although not for the purposes of determining mortality. Thus, any effort to sort out the data in this regard, in addition to being a herculean task, would be risky at best. Northwestern University Medical
School, 303 E. Chicago Avenue, Chicago, Illinois 60611, U.S.A.
ALAN R. DYER.
METABOLISM OF VINYL CHLORIDE SiR,—Recent reports1 of angiosarcoma of the liver due to occupational exposure to vinyl chloride (v.c.) prompted research on the metabolism of this substance. The microsomal mixed-function oxidase (M.F.o.) of the liver converts v.c. to polar metabolites such as chloroethanol and chloroacetic acid.2.3 In bacterial test systems, v.c. itself was not found to be mutagenic, but liver microsomes with N.A.D.P.H.
(reduced form of nicotinamide-adenine-dinucleotide-phosphate) as co-factor metabolise v.c. to mutagenic metabolites.4 Using microsomes from animals pretreated with phenobarbitone, which incudes the M.F.o. of liver micro4 somes, both the mutagenicity of v.c. in these test systems and also its liver toxicity was found to be enhanced.5 The reactive metabolite of v.c. has been considered to be the epoxide,3,5 which should be able to bind covalently to tissue macromolecules. It is commonly accepted that many chemical carcinogens exert their effects by binding covalently to cellular macromolecules. We incubated 1.4C-labelled v.c. in a closed all-glass system with liver microsomes from rat and human liver. The addition of N.A.D.P.H. regenerating system was necessary to metabolise v.c. Using rat-liver microsomes per mg. microsomal protein 10 nmol v.c. was transformed to 7-4:0-8 nmol (xs.D.; n=9) of more polar metabolites during 90 minutes’ incubation, and 0-14±0-07 nmol was bound covalently to 1 mg. microsomal protein. In addition, metabolites of v.c. were bound covalently to other SHcontaining proteins, and also to ribonucleic acid, if such macromolecular compounds were added to the incuba1. Lancet, 1974, i, 1323. 2. Hefner, R. E., Watanabe, P. G., Gehring, P. J. Ann. N. Y. Acad. Sci. 1975, 246, 135. 3. Van Duuren, B. L. ibid. p. 258. 4. Bartsch, H., Malaveille, C., Montesano, R. Int. J. Cancer, 1975, 15, 429. 5. Jaeger, R. J., Reynolds, E. S., Conolly, R. B., Moslen, M. T., Szabo, S., Murphy, S. D. Nature, 1974, 252, 724.
tions. If N.A.D.P.H. was omitted, no covalent binding occurred to proteins or ribonucleic acid. Similar results were obtained using microsomes from human liver. These results confirm the concept 3,5 that v.c. is metabolised in the liver to alkylating intermediates, which may chemically modify cellular macromolecules by covalent binding. Further studies are urgently needed to elucidate the possible relation of carcinogenicity of v.c. and the covalent binding of its metabolites in the liver. University Institute of Toxicology, D-74 Tübingen, Wilhelmstrasse 56, H. M. BOLT and University Institute of H. KAPPUS Occupational Medicine, A. BUCHTER D-5 Cologne, Josef-Stelzmann-Strasse 9, W. BOLT. German Federal Republic.
AMINES, ANTICONVULSANTS, AND EPILEPSY SIR,-Dr Green and Professor Grahame-Smith (March 15, p. 639) found that phenytoin, but not other anticonvulsants, potentiated locomotor hyperactivity in rats after the administration of tranylcypromine and L-tryptophan, although the administration of phenytoin alone had no effect on brain serotonin (5-H.T.) levels. However, they are mistaken in interpreting our own observation of raised cerebrospinal (C.S.F.) 5-hydroxyindoleacetic acid (5-H.i.A.A.) in anticonvulsant-treated epileptics (March 1, p. 473) as being entirely due to phenytoin administration. We pointed out that our patients were taking phenobarbitone, phenytoin, or primidone either alone or in various combinations. In fact, seven of our patients were not taking phenytoin, and in one of these, who presented with phenobarbitone toxicity, the c.s.F. 5-H.I.A.A. level fell from 53-2 to 33-6 ng. per ml. when the dose of phenobarbitone was reduced, and the signs of toxicity disappeared. Furthermore, several other reports indicate that many anticonvulsants are capable of influencing 5-H.T. metabolism experimentally. Thus, Bonnycastle et al. found that eleven different anticonvulsants were capable of increasing brain 5-H.T. levels in rats when injected daily for up to 16 days. Chase et al.7 demonstrated that phenytoin, phenobarbitone, and diazepam are all capable of increasing the retention of intraventricularly injected 14C-labelled 5-H.T. after a single intraperitoneal dose of each anticonvulsant. We have also demonstrated that diazepam, clonazepam, as well as phenytoin, will increase 5-H.T. levels in mice.8 Dr Green and Professor Grahame-Smith suggest that phenytoin increases the turnover of 5-H.T. Chase et al.,7 however, suggested that anticonvulsants both inhibit the metabolism of 5-H.T. and block the egress of the acid metabolite, 5-H.I.A.A., from the brain. Similarly, Lidbrink et a1.9 demonstrated that phenobarbitone and diazepam reduce the turnover of brain 5-H.T. in rats. The discrepancy between the findings of Dr Green and Professor Grahame-Smith and previous authors may have resulted in part from the differing dosage schedules used. Further studies to clarify the effects of various anticonvulsants on 5-H.T. metabolism would seem to be worth while. Dr Green and Professor Grahame-Smith suggest that the effects of lithium and phenytoin on 5-H.T. function and metabolism are similar and postulate a common mechanism of action. However, in contrast to our observation of increased c.s.F. 5-H.I.A.A. with phenytoin and phenobarbitone therapy, Goodwin and Post 10 reported that 6.
Bonnycastle, D. D., Giarman, N. J., Paasonen, M. K. Br. J. Pharmac. 1957, 12, 228. 7. Chase, T. N., Katz, R. I., Kopin, I. J. Trans. Am. neurol. Ass. 1969, 94, 236. 8. Jenner, P., Chadwick, D., Reynolds, E. H., Marsden, C. D. Unpublished. 9. Lidbrink, P., Corrodi, H., Fuxe, K. Eur. J. Pharmac. 1974, 26, 35. 10. Goodwin, F. K., Post, R. M. in Advances in Biochemical Psychopharmacology (edited by E. Costa, G. L. Gessa, and M. Sandler); vol. XI, p. 341. New York, 1974.
