Document vVwXDaQYBO2Z9epDO1m7yBjy9

Acta vet. scand. 1976, 17, 328--342. From the Section of Occupational Toxicology, National Board of Occupational Safety and Health, Stockholm, and the National Vete. rinarv Institute, Stockholm, Sweden. ; >> - THE PATHOLOGY OF VINYL CHLORIDE EXPOSED MICE* By B. Holmberg, T. Kronevi and 31. 3Vinell HOLMBERG, B., T. KRONEVI and M. WINELL: The pathology of vinyl chloride exposed mice. Acta vet. scand. 1976. 17, 328--342. _ Outhred albino laboratory mice were exposed to 50 p.p.m. and 500 p.p.m. vinyl chloride by inhalation 6 hrs./day, 5 days/week during o2 and 26 weeks, respectively. Pathologic examination showed the presence of histologically benign alveologenic lung adenomas, haemangiosarcomas in fat tissue as well as a few benign and malignant tumours at various sites. Only one liver haemangiosarcoma was noted. All animals exposed to 500 p.p.m. developed tumours; 71 9c of the animals given oO p.p.m. were tumour bearing. The frequency of all tumours, number of tumour foci and sire of foci in both groups sug gest a dose-dependent carcinogenic effect of vinyl chloride. Haeriiocoelia due to blood vessel rupture was a common cause of death. Telangiectasis of the liver was also observed in a few animals. The role of fat tissue as well as blood vessel involvement in the pathology of vinyl chloride is discussed. vinyl chloride; haemangiosarcoma; mouse; carci nogenicity; fat tissue; blood vessel. Vinyl chloride (VC, monochloroethylene) has been demon strated to possess mutagenic (Ducatman et al. 1975, Rannug et al. 1975, Loprieno et al. 1976, Funes-Cravioto et al. 1975, Bartsch <' Montesano 1975) and carcinogenic activities (Viola et al. 1971, Maltoni 1975) in experimental test systems and has also been established as an occupational hazard (Lloyd 1975, Tabershaw & Gaffey 1974) to workers in the VC production and polymeriza tion industries in several countries. In connection with a study reported elsewhere (Winell et al. 1976) on plasma enzyme variations associated with liver injury' ltd W.'.. i- in", 'mA-"M `*v-: jVTTi * This work was supported by the Swedish Work Environment Fund. 'Si4l fT..f r oard of naJ Vete-^ -Oil IDE rSKr lO/opy of -342. J. and 500 i during wed the aemJant , oted. of the y of all ups sug Haenif death. -Us. The ;tholosv " a r c i- lemonnug et 'artsch . 1971, > been rshai" leriza- ' ' et al. . -njury nnient Pathology of vinyl chloride exposed mice 329 and tumour occurrence in mice after chronic VC exposure some pathologic observations -were reported. Detailed results of the pathologic examination are reported here. MATERIALS AND METHODS Outbred albino NMRI mice were taken for experiment at 12 weeks of age. Twenty-four animals, 12 males and 12 females, were exposed in each group to 50 or 500 p.p.m. * 10 % VC, 6 hrs./ day, five days/week., One control series was run parallel to the 50 p.p.m. series, which was exposed for 52 weeks. Another control series was run parallel to the 500 p.p.m. series, which was exposed for 26 weeks. Those two series were started two months after the 50 p.p.m. and corresponding control series. In all series, four animals of each sex were sacrificed and subjected to pathological examina tion 26 weeks after start of exposure. Furthermore, four control animals were sacrificed one year after the start of experiment. The rest of the animals were subjected to pathological examina tion when moribund or spontaneously dead. All animals in the 50, 500 p.p.m. and one of the control series were kept in dark cylindric metal inhalation chambers (air volume 20 1) in which a constant flow of air was introduced. Air content of VC was analysed regularly by gas chromatography for control of the VC concentration. One control series, which was started at the same time as the 500 p.p.m. series, was kept in laboratory air outside the inhalation chamber. As no significant difference was observed between the two control series their data were treated together. Food and water were withdrawn during the daily exposure for all groups. Total body weight was registered every' two weeks. Spleen and liver of all animals were weighed. All mice were necropsied. Material for histological examination was fixed in 10 % neutral formalin. Eye and liver were fixed also in Bouin fluid. Spleen, lung, liver, kidney and brain as well as those organs and tissues where tumours were visible were histologically ex amined in all mice. In several mice of each group the following organs were also histologically examined: skeletal muscle, my ocardium, oesophagus, trachea, thyroid, brown fat, parotis, spinal cord, eye, lacrimal gland, eyelids, stomach, pancreas, small and large intestine, mesenteric lymph nodes, ovary, uterus, testicle, seminal vesicle, urinary bladder, bone marrow, and metatarsus. .2* '*1 3* sat >( VC5938 mm r *r V J* f IT1! T^lf fTTffr^f s 5~v vi"*s,v^ n.f.s i! efn1. > t`i-/ij'is,'is'>( \ **** mm*. v-.v. v v ' !-,;-: . u.v- . vj _____ ssf.VlV T it If I c .Summary of palliologlcut findings in tin; 50 p.p.ni. group. SlU. unit typo of himmirs X41 SirljpcrltoTimt - Siilicnltniemis 6c X? 1jj3j |) nni mini 'sO Tb3 *< 2 o purninlesllnnj In prlvlr nml/ or mmhil pin t Crf lllirfoinitlikf liruvvn Oil (idler sites ? rs ss 2- to CC cinrfly Lungs Skel. iinuclc Ollier jin Mini. rluiiiges ~------- 1258 r K 25 1270 f K 25 1271 r K 25 1272 in K 26 127-1 m K 25 1275 in K 26 1278 m K 25 210!) r I) 86 251(1 f I) 38 I [-sarcoma 266'1 2665 286!) 3297 8826 8028 `1059 '1305 <1701 `1791 '1816 '1863 5076 fvll 3 in f f f r r in in r tu in m in til H-sarcoma H-sarcoma ll-snrcnma H-sarcoma M-sarcnma 11-sarcnma M-sa ixfinta Il-siircnnin 11-sarconta ll-siircoiiist M-surro ma I [-sarcoma 11-sarconta ll-snrcnma H-sarcoma H-sarcoma I [-.sarcoma I (-sarcoma H-sarcoma 11-sarcoina Key oT aldtrcvalions 11-sarcoma Mam. care. Mv. ml, == Haernnngiosnrcoma. Muimnary enrcirumia. m MvvHlnitcnlc uilenimin. m hHOi mii v<i*Mirritmu, AIv. ad. Alv. ad. 11-sarconta Mam. care. H-sarcoma H-sarcoma H-sarcoma H-sarcoma Anaemia. II-cocli Ana out i a AIv. ad. Alv. ad. Alv. ad. Alv. ad. H-coclt Alv. ad. Anaemia. Il-cncli Anaemia. II-cocli Alv. ad. Hyp./ed. lungs Anaemia Anaemia. II-cocli Alv. ad. Alv. ad. Anaemia. [J-cocfi ri-niyn.siirc. Alv. ad. Alv. ml. AIv. ad. Anaemia. II-cocli Anaemia. II-cocli Hyp./ed. longs H-snrconin T able 2. Summary of palliological findings in Hie 506 p.p.m. group. Site unit lypr nf liiiinitir* B, Holmberg et at. U Pathology of vinyl chloride exposed mice 111 1) 56 * l *H i * H-sarcoma , ' ` fi."'V- ' ---- Ky of nWirevnlicms IKsnrcimid *=* HiinneciinttnnnngftiinnsMnrircroonniinn., ,!"" ';nrc`` ::.*&Mammary cnrclmmia. r \ . fi .a!**' * ilrniimt.J. ;i-r` _____ AW. iid. I-wircoma AW. :i<|. J f-snrcuma Anaemia. Il-cneli Hyp./ed. lungs innaiKiniiMI in--I Tn I> I tr 2. SimmiHry of pnlhnloftlonl S*i Hie MM) p.ji.iii. group. Mlo itml type nf fimtotirn Strlpcrt(ft>i<*i] Siihctiltincona rw-> tf ^ piirnrcttfll Co 5 >> JO 41 4| 2 2V. * V) Qa ai In prlvJc mid/ brown fnl or cnwlnl port of nbilumliml nivlly nlTirr allrs I^tniRs I.Lvcmt Uhlrn-y Other pii(fio). climiftci 2030 t K 20 2032 f K 20 2033 i K 26 2035 f K 26 2037 ni K 20 2038 in K 20 203!) m K 26 2010 m K 26 250!) r K 2!) 3052 IU 1) 32 3053 r I) 32 3102 in n 33 3020 r K 36 II-sarentnn '1000 r K 37 4401 r 1) 30 4407 f D 39 4408 111 I) 39 440*1 I) 39 44 {it n 351 4`iit i) 39 5130 in i) 45 H-sarcnnia 5131 in D 45 5752 r 1) 4!) H-sarcoma 0109 r 1) 52 IT-snrcomn Il-sarcoma H-sarcoma ll-surcmna H-sarcoma Il-sarcoma 11-sarcoma 11-sarcoma Mam. carc. Main. care. Mam. care. Mam. care. H-sarcoma Alv. ail. Alv. ad. Alv. ad. Alv. ad. Alv. ad. Alv. ad. AJv. ad. Alv, ad. Alv. ad. Alv. nd. Alv. ml. Alv. ad. Alv, ad. AW. ad. AW. ad. AW. ad. AW. ad. AW. ad. AW. ad. Alv. ad. AW. ad. Alv. ad. Alv. ad. Alv. ad. I Il-sarcoma Ilyp./cd. lungs Ityp./cd. lungs Telangiectasis 1I-coeti Tclnngicclasis Adenoma H-sarcoma Hyp./cd. lungs Ilyp./cd. lungs Ilyp./cd. lungs Ilyp./cd. lungs Ilyp./cd. lungs !l-coe!i Inanition Key of addtrcvalions Sec 'I'ahle 1 -I*~ r*.jyTjgg * wi a uiivMiuiiii i.s. i if in .......... . ******f 4 f la j j MT^-iji^V11***1: * -j*' *>'*)' * *r .%*!*' ' ix+ *, i * ^i-xr J " ' ' sm&*68i #1* ^-rfj%tKKJw.-ry 41y.V* irr;: itr" t II v,, ~ A.<m: '^nijsfW^L, .-* * ss- 8*F?V3^-"\.je;*--vT*,`*^*f.-*f-*l^.*iTli 1,1 -- 'L'~*>^,, 1 ywte* -"v %fcV-. 7/^t- : 37 - mm ' &: Ifti'CX&tvi?cl\ >i `: &>- Figure 1. Pararenal haemangiosarcoma (arrow). 50 p.p.m. series. Haemangiosarcoma is adherent to the kidney (K), but does not in filtrate normal kidney tissue. The tumour does, however, infiltrate the sublumbar muscle. Figure 2. Pararenal haemangiosarcoma (arrow). 50 p.p.m. series. Haemangiosarcoma is adherent to the kidney, but does not infiltrate normal kidney tissue. Note renal cysts. Figure 3. Paraintestinal haemangiosarcoma (arrow). 50 p.p.m. series. rp 't'.t' VC5941 >.m. senes. es not in- infiltrate .m. series.' . infiltrate .<.- 50 p.p.m. Figure 4. Lungs. Multiple alveologenic adenomas. 500 p.p.m. series. Lungs. Alveologenic adenoma. 500 p.p.m. series. H and E. x 32. i- f- e,-rt-re.r -- sfe-*"- VC5942 Figure 6. Haemangiosarcoma in brown fat tissue. (Arrow). 500 p.p.m. series. Note also pararenal haemangiosarcoma. (P). Figure 7. Liver. Telangiectasis. 500 p.p.m. series. VC5944 Pathology of vinyl chloride exposed mice 335 Frozen sections of skeletal muscle, myocardium, liver and kidney as -well as some tumour and lung tissue sections were stained with scarlet red. All embedded sections were stained with haematoxylin and eosin (HE). The tumours and some other organs were also stained with van Gieson, PAS and Pearl's method for ferric iron. RESULTS The total body weight of exposed animals did not increase at the same rate as non-exposed animals. Thus, from 24 weeks after start of exposure the total body weight curves of both exposed groups reached a plateau. After 40 weeks a decrease in body weight could generally be observed in exposed animals. Body fat was also reduced in VC-treated mice at the later half of the ex periment. Spleen and liver weights fell within the normal range throughout the observation time. No significant difference in tissue or total body weights between the two exposed animal series could be observed. Two control animals died two months after start of experi ment, one during anaesthesia and the other by unknown cause. In control series three animals out of a total of 48 animals were observed with tumours. One animal had a mammary adeno carcinoma on the left side of the chest with pulmonary' meta stasis occurring 38 weeks after exposure. The second animal was observed with a disgerminoma of the ovary at 46 weeks and the third animal died at 65 weeks with a reticulum cell sarcoma of the spleen and mesenteric lymph nodes. No other significant pathologic changes were observed in control animals. The main features of the histopathologic data in VC-exposed Figure 8. Haemangiosarcoma from pelvic/caudal part of the abdominal cavity. 50 p.p.m. series. Note that tumour tissue is em bedded in fat tissue. Scarlet red. Figure 9. Haemangiosarcoma from pelvic/caudal part of ab dominal cavity. 500 p.p.m. series. H and E. Figure 1 0. Haemangiosarcoma in the brown fat tissue. 500 p.p.m. series. H and E. Figure 11. Liver haemangiosarcoma. 500 p.p.m. series. H and E. Figure 1 2. Liver. Telangiectasis. 500 p.p.m. series. H and E. Figure 1 3. Haemangiosarcoma embedded in fat tissue is seen on each side of the uterus. 50 p.p.m. series. f*a*' it tm 336 B. Holmberg tt al. animals are displayed in Tables 1 and 2 and summarized as follows. A total of 18 animals out of 24 in those series exposed to 50 p.p.m. for 52 weeks were bearing a tumour. Two animals out of eight sacrificed at 26 weeks after start of exposure had lung adenomas (Table 1). AH animals necropsied thereafter were bearing tumours. Alveologenic adenomas were found in 13 ani mals out of 24. The lung tumours were often single or multiple with generally a few foci with approximate diameters up to 0.2 cm. One lung adenoma bearing animal also had a secondary haemangiosarcoma in the lung originating from a primary sub cutaneous tumour of the throat region (5413/75). Subperitoneal haemangiosarcomas were found in 14 animals distributed pararenally (Figs. 1 and 2) and paraintestinally (Fig. 3), and in the pelvic/caudal part (Figs. 8 and 13) of the abdomen. In cases of pararenal haemangiosarcomas, tumour tissue was microscopically well separated from normal kidney tissue. Subcutaneous tumours occurred in five animals, all bearing haemangiosarcomas in brown fat or other sites. One of those also had a mammary adenocarcinoma (2510/75). Rhabdomyo sarcoma of the left thigh was found in one case (4816/75). Among other pathologic changes rupture of haemangiosarcomas causing haemocoelia occurred in eight animals. In animals exposed to 500 p.p.m. dyspnoea was frequently noticed long before any other symptoms. The exposure to 500 p.p.m. was terminated at 26 weeks due to bad general condition of the majority of animals in these series. Inhalation of 500 p.p.m. for 26 weeks induced alveologenic adenomas in all mice (Table 2). The lung tumours in these series were multiple and were present in all lung lobes with 10 or more foci (Figs. 4 and 5). The approximate diameters of foci were up to 0.9 cm. Lung tumours were present also in all those mice which were killed at 26 weeks after start of exposure. Eight mice had subperitoneal haemangiosarcomas in the .. pelvic/caudal part of the abdomen (Fig. 9). Three of those also had pararenal haemangiosarcomas. Mammary adenocarcinomas appeared in four animals. Only one animal had haemangiosar coma of the liver (4408/75; Fig. 11) and one animal bore an adenoma of the kidney (4410/75). A haemangiosarcoma in brown fat (Figs. 6 and 1C) was seen in one case (5130/75). Among other pathological changes than neoplasia, telangi- cctasis (Figs. sarcomas can exposed to 5( All prima comas were p.p.m. series, was any pat animals. iF At 26 w( crificed. The 46 weeks fox series. In th weeks for fe no differenc The firs posure in tl series. VC is tumours in 1971, MalU hamsters ( a mutageni man et al. The fr< 100 % in c A tendenc The dosemultiplicil generally while onl; ir- one tumo resulted 2 sure to tl On th tendency suggested group we of 16 ar tumours VC5946 mnarized as iposed to 50 .mala out of ~e had lung eafter were i in 13 anior multiple ~s up to 0.2 . secondary imary sub.bperitoneal )Uted paraand in the In cases ot oscopically bearing those labdomyo4816/75). o sarcomas frequently re to 500 condition eologenic ese series or more were up ose mice in the lose also cinoroas ngiosarbore an :i brown telangi- Pathology of vinyl chloride exposed mice 337 ectasis (Figs. 7 and 12) of the liver and rupture of haemangiosarcomas causing haemocoelia were observed in a few animals exposed to 500 p.pjn. All primary subcutaneous and subperitoneal haemangiosarcomas were located in fat tissue both in the 50 p.p.m. and 500 p.p.m. series. No liver fibrosis was observed in any animal, nor was any pathological change observed in the spleen of exposed animals. At 26 weeks, eight animals were randomly chosen and sa crificed. The mean survival time of the remaining animals was 46 weeks for the 50 p.p.m. series and 35 weeks for the 500 p.p.m. series. In the 50 p.p.m. series the mean survival times were 42 weeks for females and 49 weeks for males. In the 500 p.p.m. series no difference in latency time was observed between the sexes. The first death due to tumour occurred at 36 weeks of ex posure in the 50 p.p.m. series and at 32 weeks in the 500 p.p.m. series. DISCUSSION VC is a potent multipotential carcinogen causing multiple tumours in experimental test systems, such as rats (Viola et al. 1971, Mattoni 1975), mice (Maltoni, Keplinger et al. 1975) and hamsters (Maltoni) irrespective of administration route, and also a mutagenic substance, at least after metabolic activation (Huberman et al. 1975, Rannug et al. 1976). The frequency of animals bearing any type of tumour was 100 % in our 500 p.p.m. series and 71 % in the 50 p.pjn. series. A tendency to a dose-response relationship may thus be seen. The dose-frequency relationship is more pronounced when the multiplicity of lung adenomas is concerned. Thus, 500 p.p.m. generally induces multiple lung tumours over the whole lung, while only a few animals exposed to 50 p.p.m. had more than one tumour in the lung. The exposure to the higher dose level resulted also in tumour foci of generally larger size than expo sure to the low dose level. On the other hand, when considering haemangiosarcomas, a tendency to an inverted dose-frequency relationship might be suggested by the fact that 14 out of 16 animals in the 50 p.p.m. group were found with this type of tumour but only eight out of 16 among the 500 p.p.m. animals. The mean number of tumours per animal (1.7) is the same for both dose groups cal- .{ H - :Y MM {I `UUi 'r VC5947 338 B. Holmberg et al. culated on the total number of animals used in each group. When ' the mean number of tumours is calculated on the number of 'r ' tumour bearing animals only, the mean number of tumour per animal in the 50 p.p.m. group, on the other hand, increases to 2.3. ~7 It is in this connection interesting that for other carcinogens, " such as pentacyclic hydrocarbons (Cramer Stowell 1943, Payne et al. 1960, Wynder et al. 1960), it has also been observed that a low exposure during a longer time may intensify the biological response, comparing to a high exposure during a short time period, or comparing to single exposure. - In animals exposed to 500 p.p.m. the first malignant tumour (mammary carcinoma) was observed already at 26 weeks, although the first tumour death occurred at 32 weeks. If mam mary carcinoma is accepted as a consequence of VC exposure, as suggested by other data (Maltoni), this might indicate that 500 p.p.m. for 26 weeks is sufficient to induce malignant tumours Thus, the "threshold time" -- or minimal true induc tion time -- for malignant tumours is shorter than 26 weeks for 500 p.p.m. It is to be noted that the exposure to 500 p.p.m. was terminated at 26 wTeeks. Exposure to 50 p.p.m. did, however, not induce other tumours than two lung adenomas during the first six months and no conclusion can be drawn about the true induction time for this dose level. The first death due to tumour among the 50 p.p.m. animals occurred after 36 weeks. A tendency to a dose-dependent latency time may thus be 1 suggested, when considering the time of the first death in malig- ( nant tumour. The higher dose level was thus associated with a de- f creased latency time at four weeks. The higher dose level was j also associated with a decrease in 11 weeks, when mean survival | time is considered. This is in accordance w7ith the inverted re- f lationship between dose and latency time, which is a well-known observation for other carcinogens (Bryan & Shimkin 1943). The difference in mean survival time between sexes exposed to 50 p.p.m. might also indicate that female mice are more sensitive to low dose levels of VC than male mice. The majority of tumours in mice exposed to 50 and 500 p.p.m. . of VC was lung adenomas. This was also observed by Maltoni, who noted a tendency to malignant transformation of lung tumours 61 weeks after exposure to 50 p.p.m. VC 4 hrs./day, five day-s/week for 30 weeks (30,000 p.p.m. hrs.). In spite of a total dose rate of 78,000 p.p.m. hrs. for 50 p.p.m. in our experi- | 1 ment we cou jn the lung t The term tumour. On tumours in capacity and a stress situ problem of Thus, it ha; tumours, sue does not inc there seems duces solely compound r or after a ] time. Furtht or 3-naftvla logically be nant tumor tion point c difference 1 mice expos as maligna, together wi A comr the propor dose level, lute minor carcinogen Haemai characters vessels plf This is fu servation angiosarcc dilation ir logical liv the patho7 (Thomas a more ge This i V, 1 group. When }, ae number of >i tumour per creases to 2.3. - carcinogens,-v U 1943, Payne r<" observed that the biologica] ^ a short time ~ mant tumour t 26 weeks, eks. If mamVC exposure, indicate that e malignant 1 true inducan 26 weeks `00 p.p.m. however, s during the )out the true ie to tumour ks. nay thus be sth in malig;d with a dese level was ean survival inverted rewell-known 1943). The posed to 50 re sensitive 1 500 p.p.m. by Maltoni, n of lung 4 hrs./day, . spite of a our experi- Pathology of vinyl chloride exposed mice 339 meat we could not find any sign on malignant transformation in the lung tissue. The term alveologenic adenoma implies a histologically benign tumour. On the other hand, the occurrence of multiple benign tumours in the lungs considerably decreases the respiratory capacity and may lead to immediate death of the animal during a stress situation, for instance during narcosis. This rises the problem of evaluation of chemically induced benign tumours. Thus, it has been argued that the induction of some benign tumours, such as hepatomas, in mice (Grasso & Crampton 1972) does not indicate chemical carcinogenicity. On the other hand, there seems to exist no situation where a chemical substance in duces solely benign tumours (Tomatis et al. 1973). The same compound may induce malignant tumours at higher dose levels or after a prolonged administration period and/or observation time. Furthermore, a compound, like henzidin (Prokofjeva 1971) or 3-naftviamine (Bonser et al. 1956), which induces histopathologically benign tumours in mice, may very well induce malig nant tumours in other species, including man. From an evalua tion point of view, as regards the carcinogenic risk to man, the difference between benign and malign tumours in the lungs of mice exposed to VC may thus not be very important, especially as malignant haemangiosarcomas occur in various other organs together with lung ademonas a few weeks later. A common feature in Maltoni's and our experiment is that the proportion of tumours of vascular origin is higher at a low dose level. The angiosarcomas of the liver are, however, in abso lute minority, a fact which is important in the evaluation of the carcinogenic risk to man after occupational exposure to VC. Haemangiosarcomas of various organs seem to be a notable characteristic of VC-exposed mice, implicating that the blood vessels play an important role in the biological activity of VC. This is furthermore corroborated by the presently reported ob servation that blood vessel rupture may easily occur in haemangiosarcoma-bearing mice and by the presence of blood vessel dilation in the liver (telangiectasis), without any other patho logical liver change. That the blood vessels may be involved in the pathogenesis of VC induced liver tumours has been suggested (Thomas & Popper 1975), but blood vessel disturbances are even a more general feature of VC toxicity than mere carcinogenesis. This is evident from the presence of Raynaud's phenomenon -* -11 jI wt S 4 9n VC5949 r-TfrT-'*'-*-*: !=' <t- ' c * ( .* ^ f * ' 0 tic. 340 B. Holmberg et at. and the acroosteolysis of VC-exposed -workmen (for further references, see Holmberg & Molina 1974) and is furthermore suggested by an overrepresentation in deaths of circulatory dis eases, as observed among Swedish VC/PVC-workers (Byren et al 1976). All subperitoneal and subcutaneous haemangiosarcomas pre sently observed were located in fat tissue. Histologically the para renal tumours, for instance, were distinctly separated from the kidney tissue. VC is, like other agents with anesthetic effects, lipophilic and the appearance of almost all haemangiosarcomas in fat tissue may reflect that physical characteristic. The VC con centration in fat might be comparatively very high, while the concentration of the shortlived possible ultimate carcinogen (Van Duuren 1975), the highly mutagenic (Rannug et al. 1976) chloroethylene epoxide is probably low. As white fat generally is a slowly metabolising tissue, one might speculate that the epoxidation is merely performed in the endothelial cells of the blood vessels at transport to and from fat tissue, thus subjecting these cells to genetic damage leading to neoplastic transformation. The presence of haemangiosarcomas in fat tissue would suggest that VC-induced tumours might be found also in the central nervous system. This was not the case in this experiment, nor in previous experimental studies. A tendency to an increased frequency of brain tumours was, however, observed in an epi demiological study on around 8,300 workers in PVC-polymerization industries in USA (Tabershaw & Gaffey 1974). ACKNOWLEDGEMENT The authors are indebted to Aina Ekner, Annika Eriksson, Ella Jensen, UHa Hammarstrom and Gun Lindkvist for technical assistance and to Inge Ericsson for preparing photographs. REFERENCES Bartsch, H. & B. Montesano: Mutagenic and carcinogenic effects of vinyl chloride. Mutation Res. 1975, 32, 93--114. Bonser, G. AL, D. B. Clayson, J. W. Jull & L. N. Pyrah: The carcino genic activity of 2-naphtylamine. Brit. J. Cancer 1956, 10, 533-- 538. Bryan, VV\ B. & M. B. Shimkin: Quantitative analysis of dose-response data obtained with three carcinogenic hydrocarbons in strain C3H male mice. J. nat. Cancer Inst. 1943, 3, 503--531. Byren, c v Cramer T c t Ducatn Van D i Funes- Grosso Holmt Hubei Jiepli- Lloyc Lopr Matt Payi Pro. Ban VC5950 V further lermore iry dis- -`-v in et al. ' ias preie paraom the effects, rcomas C con-ile the a (Van chlor:y is a Josida^k>od !0rese on. would in the intent, reased n epileriza- , Ella stance -ts of ionse train Pathology of vinyl chloride exposed mice 341 Byren, D., G. Engholm, A. England & P. Westerholm: Mortality and cancer morbidity in a group of Swedish VCM/PVC production workers. Environ. Hlth Persp. In press 1976. Cramer, TV. & P. E. Stowell: On the quantitative evaluation of experi mental skin carcinogenesis by methylcholanthrene. The factors of dosage, time, spacing of applications and the multiplicity of the carcinogenic response, Cancer Res. 1943, 3, 668--681. Ducatman, A., K. Hirschhorn A I. J. Selikoff: Vinyl chloride exposure and human chromosome aberrations. Mutation Res. 1975, 31, 163--168. Von Duuren, B. L.: On the possible mechanism of carcinogenic action of vinyl chloride. Ann. N. Y. Acad. Sci. 1975, 246, 258--267. Funes-Cravioto, F., B. Lambert, J. Lindsten, L. Ehrenberg, A. T. h'atarajan & S. Osterman-Golkar: Chromosome aberrations in wor kers exposed to vinyl chloride. Lancet 1975, 1 (Xo. 7904), 459. Grasso, P. & B. F. Crompton: The value of the mouse in carcinogeni city testing. Food Cosmet. Toxicol. 1972, 10, 418--426. Holmberg, B. & G. Molina: The industrial toxicology of vinyl chloride. A review. YY.-Environm.-Hlth. 1974, 11, 138--144. Htiberman, E., H. Bartsch A L. Sachs: Mutation induction in Chinese hamster V79 cells by two vinyl chloride metabolites, cbloroethylene oxide and 2-chloroacetaldehyde. Int. J. Cancer 1975, 16, '639--644. Keplinger, M. L., J. TV, Goode, D, E. Gordon A J. C. Catandra: Interim results of exposure of rats, hamsters and mice to vinyl chloride. Ann. N.Y. Acad. Sci. 1975, 246, 219--224. Lloyd, TV. J.: Angiosarcoma of the liver in vinyl chloride/polyvinyl chloride workers. J. occup. Med. 1975, 17, 333--334. Loprieno, A'., B. Barale, S. Baroncelli, C. Bauer, G. Bronzetti, A. Cammellini, G. Cercignani, C. Corsi, G. Gervasi, C. Leporini, B. Nieri, A. M, Bossi, G. Stretti A G. Tureni: Evaluation of the genetic effects induced by vinyl chloride monomer (VCM) under mammalian metabolic activation: studies in vitro and in vivo. Mutation Res. 1976, 40, 85--96. Maltoni, C.: The value of predictive experimental bioassays in occu pational and environmental carcinogenesis. Ambio 1975, 4, 18-- 23. Payne, TV. TV. A TV. C. Hueper: The carcinogenic effects of single and repeated doses of 3,4-benzpyrene. Amer. industr. Hyg. Ass. J. 1960, 21, 350--355. Prokofjeva, 0. G.: Induction of hepatic tumours in mice by benzidine. Vop. Onkol. 1971, 17, 61--64. Bannug, V., A. Johansson, C. Bamel A C. A. Wachtmeister: The muta genicity of vinyl chloride after metabolic activation. Ambio 1975, 3, 194--197. s* 7 *^ - 3 . rf: u 4 :* tl. r*- af * \% $ ' ^m VC5951 k:tt * * A' 5i? * *wi ,FV I he; i>prrt * Ck- % esc r^i" i>,v iiijpjsc: rjl^i **?'* f 91 342 5. Holmberg el al. Bannug, V., B. Gdthe & C. A. Wachtmeister: The mutagenicity 0f chloroethylene oxide, chloroacetaldehyde, 2-chloroethanol and chloroacetic acid, conceivable metabolites of vinyl chloride, Chem.-biol. Interactions 1976, 12, 251--263. Tabershaw, I. B. <fc TV. R. Gaffey: Mortally studies of workers in the manufacture of vinyl chloride and its polymers. J. occup. Med 1974, 16, 509--518. Thomas, L. B. & H. Popper: Pathology of angiosarcoma of the liver among vinyl chloride polyvinyl chloride -workers. Ann. N. Y. Acad. Sci. 1975, 246, 268--277. Tomatis, L,, C. Partensky & B. Montesano: The predictive value of mouse liver tumour induction in carcinogenicity testing -- a literature survey. Int. J. Cancer 1973, 12, 1--20. Viola, P. L., A. Bigotli & A. Caputo: Oncogenic response of rat skin, lungs and hones to vinvl chloride. Cancer Res. 1971, 31, 516-- 522. Winell, AL, B. Holmberg & T. Kronevi: Biological effects of vinyl chloride -- an experimental study. Environ. Hlth Persp. in press 1976. Wynder, E. L,, J. TV. Spranger & AL AL Park: Dose-response studies with benzo(a)pyrene. Cancer (Philad.) 1960, 13, 106--110. SAMMAXFATTXING Patologisk-anatomiska forandringar hos moss exponerade for vinyl- klorid. NMRI-albino-moss inhalerade 50 och 500 ppm vinylklorid 6 tim/ dag, 5 dagar/vecka under 52 respektive 26 vector. Histologiskt benigna alveolara lungadenom, hemangiosarkom i fettvavnaden och ett ffttal andra benigna och maligna tumorer pStraffades i olika lokalisationer. Endast ett djur hade leverhemangiosarkom. Samtliga djur exponerade for 500 ppm uppvisade tumorer; i 50 ppm-gruppen hade 71 9i av djuren tumorer. Tumorfrekvens, antalet tumorfoci och focusdiametrar i bkda grupperna antyder en dos-respons-relation. Hemocoeli, beroende p5 ruptur av hemangiosarkom, var en vanlig dfidsorsak. Telangiectasi i levern observerades hos nSgra djur. Fettvavnadens och blodkarlens roll i vinylkloridens patologi diskuteras. (Beceived July 13,1976). Reprints may be requested from: B. Holmberg, assoc, professor, National Board of Occupational Safety and Health, P. O. Box S-100 26, Stockholm, Sweden. Ada From i cone: 343-- lets f lied one . but t to re phos enha serol glucc regar pigl VC5952