Document EdpKM1qZYLKjVN8xKoXdVLveN

Afl-I IH> VMARMArniOOV 28, 418-427 (1974) Effects of Chemically Pure Chlorobiphenyis on the Morphology of Rat Liver1 M. M. Hassell and D. I. EcomcHON Department* of Anatomy and Pharmacology, Dofhousle (JnivtrsHy, Halifax, Xat n Scotiu, Canaria Received September 4, 19T3; accepted Deiember 17, 1973 Effects of Chemically Pure Chlorobiphenyls on the Moiphology of Rot Liver. Hansill, M. M. ano Ecomchon, D. J. (1974). Toxical. Appl. TUarntacol. 28, 418-427. Pure biphenyl and a scries of isomerically pure mono-, di, tetra-, hexa* and octa-chlorobiphenyls of known chemical composition were injected ip (50 tng/kg) into young male Wi$tar rats for 3 consecutive days and the rats were killed 4 days after the last injection. In a second experi ment, rats were injected ip with 4-mono, 4,4'-di* and 2,5,2',5'-tcrachloro* biphenyl 000 mg/kg) for 7 days. The effects of the pure PCBs were com pared with those caused by o.p'- and p,p'-DDT and Aroclor 1254 and 1260 Samples of liver were examined by light and electron microscopy. The major alterations observed within the hepatocytes were marked proliferation of smooth endoplasmic reticulum and increased numbers of microbodies and lipid droplets. Diphenyl and 2.2'-dicMorohipheny> produced few morpho logic effects whereas 4,4'-di-. 2.5.2',5'* and 3,4,3',4 -tctrachlorobiphenyl caused more changes. The highly chlorinated hexa-and octachlorobiphcnyls produced morphological changes that were comparable to those produced by DDT, and Aroclon 1254 and 1260. The degree of ultrastructural altera tion appeared to be related directly to the number ofchlorine atoms and the presence of chlorine in the 4- or 4'-posilion. The structure of the liver of several species of animals treated with polychlorinated biphenyls (BCBs) has been examined using light and electron microscopy. With on-: exception (Vos and Notenboom-Ram, 1972), all these studies have employed com mercially available mixtures such as Arodors, Phenodors. and Kanedors (Bennett el al., 1938; von Wedel et at., 1943; Miller, 1944; Nishizumi, 1970; Kimbrough c! al, 1972; Norback and Allen, 1972; KollerandZinkl, 1973; Bruckner ft al., 1973). Some of these commercial mixtures were reported to be contaminated with impurities such <i> chlorinated dibenzofurans and dibenzoyi-dioxins (Vos cl al., 1970; Sissons and Welti, 1971; Zitlco and Choi, 1971; Greig, 1972; Hutzinger ei ai, 1972; Webb and McCall, 1972). Hammond (1972), in summarizing the relationship between toxicity and degree of chlorination of PCBs bosed on studies using commercial mixtures, found no consis tent relationship valid for different species and routes of exposure. Tucker and Crabtree (1970) suggested that sublethal effects w. : diiectly correlated with chlorine content, while lethal effects were inversely correlated. 1 Prevented in part at the Sixteenth Annual Meeting of the Canadian Federation of Biological Societies, Saskatoon, Saskatchewan, June 24-29, 1973 Coar'iihi f> IVJ4 hy Academic Inc. 418 Piinitd in lire*! tlriinift MQNS 081865 JPCJ* AND LIVLR MORPHOLOGY 419 To climinalc the eflccls of possible contaminants in commercial mixtures and to determine (lie tdationship between position and degree of chlorination, and effects on the liver, a sciics of isomcricHlIy pure chlorobiphenyl compounds of known position and degree of chlorination was administered ip to rats. The influence of these com pounds on functionally diverse hcpalic drug-metabolizing enzymes and hepatic mor phology were studied. The cfTccts on various drug-metabolizing enzymes arc reported elsewhere (Johnstone ct a!., 1974). METHODS The methods for the preparation of the pure chlorobiphenyl compounds and the doses administered were described in detail by Hutzinger ct at. (1971) and Johnstone ct hI, (1974), The compounds1 used arc listed in Table I. A group of7 young male Wistar rnts (Woodlyn strain) weighing 50-65 g was treated ip with each agent dissolved in peanut oil, tit a dosage of 50mg/kg daily for 3 days. The rats were killed with an overdose of CHCI, 4 days after the final injection following the determination of pentobarbital sleeping time. Control rats were treated with equivalent volumes of peanut oil and were killed by CHClj overdose after pentobarbital sleeping time was performed. In a second experiment, 3 compounds (4-mono-, 4,4'-di- and 2,5,2',5'-tetrachlorobiphcnyl) were injected ip at a dosage of 100 mg/kg/day for 7 days, the rats being killed 24 hr after the last injection by an overdose of CHCJ,. After euthanasia, the abdomen of the rats was quickly opened and samples of the liver were removed for fixation for light and electron microscopy. For light microscopy, samples were fixed in 10% buffered formalin and embedded in paraffin; sections were stained witli hematoxylin and eosin. For electron microscopy, I-mm cubes of liver were fixed in 1 % osmium leu oxide in sodium cacodylatc buffer at 0eC for 2 hr, dehydrated in u sciics of graded alcohol solutions and propylene oxide and embedded in Spurr low viscosity embedding medium. Ultrathin sections were cut on a Porter-Blum MT2B ultiamicrotomc stained with uranyl acetate and lead citrate and examined with a Philips 200 electron microscope. Thick plastic sections were cut from the same block and stained wilh methylene blue and azure A for light microscopy (Pease, 1964). RESULTS The results of ullraslruclural evaluation and the hepatic weights for the rats treated wilh the agents at 50 mg/kg for 3 days are presented in Tabic 1. Hepatic weights were significantly increased following treatment wiih/>,/'~DDT, Aroclor 1254, Aroclor 1260 and 2,3,5,2',3',5'-hexachlorobtphenyl. These compounds also induced major altera tions in hcpiitocyte ullrastructurc. Hcpatocylcs of treated rats were compared with hepatocyles from control, vehicletreated animats for the presence of these alterations. The grading syslem for alterations in amounts ol smooth endoplasmic reticulum (SBR), and numbers of lipid droplets and * Abbreviations used: o,/>'-DDT, l,l,l-lricliloro-2-(o-chlorophenyI)-2-(/*-chlorophcnyl)cth*nc; l.l.l-iiidiloro-2,2-his(/>-clili>rophenyl)elhanc. The nomenclature of the polychlorinated biphenyl (I'CH) compounds follows the accepted form, the position of chlorines on one phenyl being indicHied hy numbers from 2 to 6, while chlorine posii ions oil the second ring are designated by a num ber with a superscript prime, i.e., 2,2'-dichlorohiphenyl. IIW.: .'''A-?;*. `W'AV.:-*.`"'.yT- .*. \ :yx; '-A aV'-a; Y&'f*r:.vV ft y,'> v: ' >..? |pgl vf:: MONS 081866 420 I1AKSE1.L AND I.COUICHON microbodics is based on a comparison of the amounts present in any cell with the amount present in a control hcpatocytc (value 4) and a hcpatocytc having the maxi mum amount of change (value 4 4+H). The grading system reflects only relative numbers since morphometric techniques were not used for quantitation. The major ullraslructural alterations induced by the various pure chlorobiphenyls were prolifera tion of SER, alteration of the rough endoplasmic reticulum (RER) and increased num bers of lipid droplets and inicrobodics (Table 1). TABLE 1 Changes in Liver Weight, Hepatic Smooth Endoplasmic Ri mcuium, Lipin Droit+.ts and Microbodier, Following the Administration oi DDT, Aroclor 1254 and 1260 and Isomerically Puke Chlokobiphenyi s to Rais* Compound Liver weight* (8) - Smooth Lipid ER' droplets Micrubodies Vehicle.Treated o.p'-DDT p.p'-DDT Aroclor 1254 Aroclor 1260 Biphenyl (BP) 4-Chloro BP 2,2'-Dichloro BP 2.4'-Dichloro BP , 4,4'-Dichloro BP 2.5.2'.5'-Tctrachloro BP 2,4,2',4'-Tclrach!oro BP 3.4,3'.4'*Tctrachkro BP 2.4,5,2',4',5'-Hcxachk)ro BP 2,4,6.2\4',6'-Hexachloro BP 2,3f5,2',3't5'*Hcxad>loro BP 2,3,4,5,2',3,,4',5'-Octachloro BP 4.77 1.14 4.91 0.46 5.59 + 0.89* 6.23 + 0.30* 6.15 + 0.49* 4.87+0.N 4.76 0.69 4.85 0.96 4.69 0.34 4.21 0.44 4.68 0.69 5.03 + 0.48 4.73 + 0.47 4.JJH 0.91 3.82+ 1.29 5.80 + 0.78* 4.53 1.46 + 444+ ++++ +4+++ 4++ + 4+ + +++ 4+4 44 4+4 44 444-4-1-4 + 4 4444 44 + 4 444 4 441 4+44 444 44 444 4 44 4+ 4 44 44 1 44 44 44 44 4 4 f+4 444 4 44 !4 4 * 44 44 444 4 4 +4 44 4 44 +4 4 44 444 44 t 44 1 44 1 * Animals were injected ip with n peanut oil solution ai a dose of 50 mg/kg for 3 days and k illcd 4 days after the last injection. * Values presented are mean weights + SD of 14 (vehicle-treated) and 7 (agent-treated) animals per group. Values ate based on wet tissue weight. * Values are statistically significant from control weights at a probability level p< 0 05. * See text (Remit*) for grading system. Isomerically pure hexa- and ocln-chlorobiphenyls, administered at a concentration of 50 mg/kg for 3 consecutive days, caused alterations in hepatic morphology that were visible with the light microscope (Fig. 1). The changes included large numbers of hepatocytes with vacuolated cytoplasm and small foci of necrosis involving 5 or 6 cells. The necrotic foci were particularly numerous at the periphery of the lobule. Treatment with 4-mono-, 4, 4'-di and 2,5,2',5'-tctrachlorobiphenyl at 100 mg/kg for 7 days resulted in larger numbers of necrotic foci, ccntrolobular necrosis and proliferation of biliary ductules (Fig. 1), The lesions were most severe in rats given 4,4'-dichlorobiphenyl for 7 days. Hepatocytes of rats treated with o,p'-, orp,/>'-DDT (Fig, 2A) had increased amounts of SER in the form of vesicles (S) winch tended to accumulate at the periphery of the V/rA;,iV > :';*AV.'v VCj' .. MONS 081867 r-- 420 I1AKSE1.L AND I.COUICHON microbodics is based on a comparison of the amounts present in any cell with the amount present in a control hcpatocytc (value 4) and a hcpatocytc having the maxi mum amount of change (value 4 4+H). The grading system reflects only relative numbers since morphometric techniques were not used for quantitation. The major ullraslructural alterations induced by the various pure chlorobiphenyls were prolifera tion of SER, alteration of the rough endoplasmic reticulum (RER) and increased num bers of lipid droplets and inicrobodics (Table 1). TABLE 1 Changes in Liver Weight, Hepatic Smooth Endoplasmic Ri mcuium, Lipin Droit+.ts and Microbodier, Following the Administration oi DDT, Aroclor 1254 and 1260 and Isomerically Puke Chlokobiphenyi s to Rais* Compound Liver weight* (8) - Smooth Lipid ER' droplets Micrubodies Vehicle.Treated o.p'-DDT p.p'-DDT Aroclor 1254 Aroclor 1260 Biphenyl (BP) 4-Chloro BP 2,2'-Dichloro BP 2.4'-Dichloro BP , 4,4'-Dichloro BP 2.5.2'.5'-Tctrachloro BP 2,4,2',4'-Tclrach!oro BP 3.4,3'.4'*Tctrachkro BP 2.4,5,2',4',5'-Hcxachk)ro BP 2,4,6.2\4',6'-Hexachloro BP 2,3f5,2',3't5'*Hcxad>loro BP 2,3,4,5,2',3,,4',5'-Octachloro BP 4.77 1.14 4.91 0.46 5.59 + 0.89* 6.23 + 0.30* 6.15 + 0.49* 4.87+0.N 4.76 0.69 4.85 0.96 4.69 0.34 4.21 0.44 4.68 0.69 5.03 + 0.48 4.73 + 0.47 4.JJH 0.91 3.82+ 1.29 5.80 + 0.78* 4.53 1.46 + 444+ ++++ +4+++ 4++ + 4+ + +++ 4+4 44 4+4 44 444-4-1-4 + 4 4444 44 + 4 444 4 441 4+44 444 44 444 4 44 4+ 4 44 44 1 44 44 44 44 4 4 f+4 444 4 44 !4 4 * 44 44 444 4 4 +4 44 4 44 +4 4 44 444 44 t 44 1 44 1 * Animals were injected ip with n peanut oil solution ai a dose of 50 mg/kg for 3 days and k illcd 4 days after the last injection. * Values presented are mean weights + SD of 14 (vehicle-treated) and 7 (agent-treated) animals per group. Values ate based on wet tissue weight. * Values are statistically significant from control weights at a probability level p< 0 05. * See text (Remit*) for grading system. Isomerically pure hexa- and ocln-chlorobiphenyls, administered at a concentration of 50 mg/kg for 3 consecutive days, caused alterations in hepatic morphology that were visible with the light microscope (Fig. 1). The changes included large numbers of hepatocytes with vacuolated cytoplasm and small foci of necrosis involving 5 or 6 cells. The necrotic foci were particularly numerous at the periphery of the lobule. Treatment with 4-mono-, 4, 4'-di and 2,5,2',5'-tctrachlorobiphenyl at 100 mg/kg for 7 days resulted in larger numbers of necrotic foci, ccntrolobular necrosis and proliferation of biliary ductules (Fig. 1), The lesions were most severe in rats given 4,4'-dichlorobiphenyl for 7 days. Hepatocytes of rats treated with o,p'-, orp,/>'-DDT (Fig, 2A) had increased amounts of SER in the form of vesicles (S) winch tended to accumulate at the periphery of the V/rA;,iV > :';*AV.'v VCj' .. MONS 081867 r-- 420 I1AKSE1.L AND I.COUICHON microbodics is based on a comparison of the amounts present in any cell with the amount present in a control hcpatocytc (value 4) and a hcpatocytc having the maxi mum amount of change (value 4 4+H). The grading system reflects only relative numbers since morphometric techniques were not used for quantitation. The major ullraslructural alterations induced by the various pure chlorobiphenyls were prolifera tion of SER, alteration of the rough endoplasmic reticulum (RER) and increased num bers of lipid droplets and inicrobodics (Table 1). TABLE 1 Changes in Liver Weight, Hepatic Smooth Endoplasmic Ri mcuium, Lipin Droit+.ts and Microbodier, Following the Administration oi DDT, Aroclor 1254 and 1260 and Isomerically Puke Chlokobiphenyi s to Rais* Compound Liver weight* (8) - Smooth Lipid ER' droplets Micrubodies Vehicle.Treated o.p'-DDT p.p'-DDT Aroclor 1254 Aroclor 1260 Biphenyl (BP) 4-Chloro BP 2,2'-Dichloro BP 2.4'-Dichloro BP , 4,4'-Dichloro BP 2.5.2'.5'-Tctrachloro BP 2,4,2',4'-Tclrach!oro BP 3.4,3'.4'*Tctrachkro BP 2.4,5,2',4',5'-Hcxachk)ro BP 2,4,6.2\4',6'-Hexachloro BP 2,3f5,2',3't5'*Hcxad>loro BP 2,3,4,5,2',3,,4',5'-Octachloro BP 4.77 1.14 4.91 0.46 5.59 + 0.89* 6.23 + 0.30* 6.15 + 0.49* 4.87+0.N 4.76 0.69 4.85 0.96 4.69 0.34 4.21 0.44 4.68 0.69 5.03 + 0.48 4.73 + 0.47 4.JJH 0.91 3.82+ 1.29 5.80 + 0.78* 4.53 1.46 + 444+ ++++ +4+++ 4++ + 4+ + +++ 4+4 44 4+4 44 444-4-1-4 + 4 4444 44 + 4 444 4 441 4+44 444 44 444 4 44 4+ 4 44 44 1 44 44 44 44 4 4 f+4 444 4 44 !4 4 * 44 44 444 4 4 +4 44 4 44 +4 4 44 444 44 t 44 1 44 1 * Animals were injected ip with n peanut oil solution ai a dose of 50 mg/kg for 3 days and k illcd 4 days after the last injection. * Values presented are mean weights + SD of 14 (vehicle-treated) and 7 (agent-treated) animals per group. Values ate based on wet tissue weight. * Values are statistically significant from control weights at a probability level p< 0 05. * See text (Remit*) for grading system. Isomerically pure hexa- and ocln-chlorobiphenyls, administered at a concentration of 50 mg/kg for 3 consecutive days, caused alterations in hepatic morphology that were visible with the light microscope (Fig. 1). The changes included large numbers of hepatocytes with vacuolated cytoplasm and small foci of necrosis involving 5 or 6 cells. The necrotic foci were particularly numerous at the periphery of the lobule. Treatment with 4-mono-, 4, 4'-di and 2,5,2',5'-tctrachlorobiphenyl at 100 mg/kg for 7 days resulted in larger numbers of necrotic foci, ccntrolobular necrosis and proliferation of biliary ductules (Fig. 1), The lesions were most severe in rats given 4,4'-dichlorobiphenyl for 7 days. Hepatocytes of rats treated with o,p'-, orp,/>'-DDT (Fig, 2A) had increased amounts of SER in the form of vesicles (S) winch tended to accumulate at the periphery of the V/rA;,iV > :';*AV.'v VCj' .. MONS 081867 r-- 420 I1AKSE1.L AND I.COUICHON microbodics is based on a comparison of the amounts present in any cell with the amount present in a control hcpatocytc (value 4) and a hcpatocytc having the maxi mum amount of change (value 4 4+H). The grading system reflects only relative numbers since morphometric techniques were not used for quantitation. The major ullraslructural alterations induced by the various pure chlorobiphenyls were prolifera tion of SER, alteration of the rough endoplasmic reticulum (RER) and increased num bers of lipid droplets and inicrobodics (Table 1). TABLE 1 Changes in Liver Weight, Hepatic Smooth Endoplasmic Ri mcuium, Lipin Droit+.ts and Microbodier, Following the Administration oi DDT, Aroclor 1254 and 1260 and Isomerically Puke Chlokobiphenyi s to Rais* Compound Liver weight* (8) - Smooth Lipid ER' droplets Micrubodies Vehicle.Treated o.p'-DDT p.p'-DDT Aroclor 1254 Aroclor 1260 Biphenyl (BP) 4-Chloro BP 2,2'-Dichloro BP 2.4'-Dichloro BP , 4,4'-Dichloro BP 2.5.2'.5'-Tctrachloro BP 2,4,2',4'-Tclrach!oro BP 3.4,3'.4'*Tctrachkro BP 2.4,5,2',4',5'-Hcxachk)ro BP 2,4,6.2\4',6'-Hexachloro BP 2,3f5,2',3't5'*Hcxad>loro BP 2,3,4,5,2',3,,4',5'-Octachloro BP 4.77 1.14 4.91 0.46 5.59 + 0.89* 6.23 + 0.30* 6.15 + 0.49* 4.87+0.N 4.76 0.69 4.85 0.96 4.69 0.34 4.21 0.44 4.68 0.69 5.03 + 0.48 4.73 + 0.47 4.JJH 0.91 3.82+ 1.29 5.80 + 0.78* 4.53 1.46 + 444+ ++++ +4+++ 4++ + 4+ + +++ 4+4 44 4+4 44 444-4-1-4 + 4 4444 44 + 4 444 4 441 4+44 444 44 444 4 44 4+ 4 44 44 1 44 44 44 44 4 4 f+4 444 4 44 !4 4 * 44 44 444 4 4 +4 44 4 44 +4 4 44 444 44 t 44 1 44 1 * Animals were injected ip with n peanut oil solution ai a dose of 50 mg/kg for 3 days and k illcd 4 days after the last injection. * Values presented are mean weights + SD of 14 (vehicle-treated) and 7 (agent-treated) animals per group. Values ate based on wet tissue weight. * Values are statistically significant from control weights at a probability level p< 0 05. * See text (Remit*) for grading system. Isomerically pure hexa- and ocln-chlorobiphenyls, administered at a concentration of 50 mg/kg for 3 consecutive days, caused alterations in hepatic morphology that were visible with the light microscope (Fig. 1). The changes included large numbers of hepatocytes with vacuolated cytoplasm and small foci of necrosis involving 5 or 6 cells. The necrotic foci were particularly numerous at the periphery of the lobule. Treatment with 4-mono-, 4, 4'-di and 2,5,2',5'-tctrachlorobiphenyl at 100 mg/kg for 7 days resulted in larger numbers of necrotic foci, ccntrolobular necrosis and proliferation of biliary ductules (Fig. 1), The lesions were most severe in rats given 4,4'-dichlorobiphenyl for 7 days. Hepatocytes of rats treated with o,p'-, orp,/>'-DDT (Fig, 2A) had increased amounts of SER in the form of vesicles (S) winch tended to accumulate at the periphery of the V/rA;,iV > :';*AV.'v VCj' .. MONS 081867 r-- 420 I1AKSE1.L AND I.COUICHON microbodics is based on a comparison of the amounts present in any cell with the amount present in a control hcpatocytc (value 4) and a hcpatocytc having the maxi mum amount of change (value 4 4+H). The grading system reflects only relative numbers since morphometric techniques were not used for quantitation. The major ullraslructural alterations induced by the various pure chlorobiphenyls were prolifera tion of SER, alteration of the rough endoplasmic reticulum (RER) and increased num bers of lipid droplets and inicrobodics (Table 1). TABLE 1 Changes in Liver Weight, Hepatic Smooth Endoplasmic Ri mcuium, Lipin Droit+.ts and Microbodier, Following the Administration oi DDT, Aroclor 1254 and 1260 and Isomerically Puke Chlokobiphenyi s to Rais* Compound Liver weight* (8) - Smooth Lipid ER' droplets Micrubodies Vehicle.Treated o.p'-DDT p.p'-DDT Aroclor 1254 Aroclor 1260 Biphenyl (BP) 4-Chloro BP 2,2'-Dichloro BP 2.4'-Dichloro BP , 4,4'-Dichloro BP 2.5.2'.5'-Tctrachloro BP 2,4,2',4'-Tclrach!oro BP 3.4,3'.4'*Tctrachkro BP 2.4,5,2',4',5'-Hcxachk)ro BP 2,4,6.2\4',6'-Hexachloro BP 2,3f5,2',3't5'*Hcxad>loro BP 2,3,4,5,2',3,,4',5'-Octachloro BP 4.77 1.14 4.91 0.46 5.59 + 0.89* 6.23 + 0.30* 6.15 + 0.49* 4.87+0.N 4.76 0.69 4.85 0.96 4.69 0.34 4.21 0.44 4.68 0.69 5.03 + 0.48 4.73 + 0.47 4.JJH 0.91 3.82+ 1.29 5.80 + 0.78* 4.53 1.46 + 444+ ++++ +4+++ 4++ + 4+ + +++ 4+4 44 4+4 44 444-4-1-4 + 4 4444 44 + 4 444 4 441 4+44 444 44 444 4 44 4+ 4 44 44 1 44 44 44 44 4 4 f+4 444 4 44 !4 4 * 44 44 444 4 4 +4 44 4 44 +4 4 44 444 44 t 44 1 44 1 * Animals were injected ip with n peanut oil solution ai a dose of 50 mg/kg for 3 days and k illcd 4 days after the last injection. * Values presented are mean weights + SD of 14 (vehicle-treated) and 7 (agent-treated) animals per group. Values ate based on wet tissue weight. * Values are statistically significant from control weights at a probability level p< 0 05. * See text (Remit*) for grading system. Isomerically pure hexa- and ocln-chlorobiphenyls, administered at a concentration of 50 mg/kg for 3 consecutive days, caused alterations in hepatic morphology that were visible with the light microscope (Fig. 1). The changes included large numbers of hepatocytes with vacuolated cytoplasm and small foci of necrosis involving 5 or 6 cells. The necrotic foci were particularly numerous at the periphery of the lobule. Treatment with 4-mono-, 4, 4'-di and 2,5,2',5'-tctrachlorobiphenyl at 100 mg/kg for 7 days resulted in larger numbers of necrotic foci, ccntrolobular necrosis and proliferation of biliary ductules (Fig. 1), The lesions were most severe in rats given 4,4'-dichlorobiphenyl for 7 days. Hepatocytes of rats treated with o,p'-, orp,/>'-DDT (Fig, 2A) had increased amounts of SER in the form of vesicles (S) winch tended to accumulate at the periphery of the V/rA;,iV > :';*AV.'v VCj' .. MONS 081867 r-- rcil AND LIVLK MORPHOLOGY 425 alterations than 4-nionochlorobiphenyl or 2,5,2',5'-tetrach!orobii>Uenyl, the effects of the latter two agents being approximately the same. DISCUSSION Proliferation of SI;R is a response of the bepafocyte to a wide variety of drugs and poisons and is considered to be a structural reflection of the enhanced metabolism of foreign lipophilic compounds. The increase in SER can be related to increased amounts ofdrug metabolizing enzymes within the liver (Vos and Nolenboom-R&m, 1972). In all previous studies, administration of PCBs has resulted in increased amounts of SER in licpiilocytes (Nishizumi, 1970; Kimbrough ef al, 1972; Vos and Notenboom-Ram, 1972; Norback and Allen, 1972; Koiler and Zinkl, 1973). In this study, the proliferation of SfR was closely related to the structural characteristics of the compound used. Biphenyl and 2,2'-dichlorobiphcnyl appeared not to induce extensive proliferation of SIR. but with the other compounds, the proliferation appeared to be related to (he degree of chlorination and part icularly to (he presence ofa chlorine atom in the 4 and/or 4' position (Tnblc (). The morphological alterations correlated well with the activities of drug-metabolizing enzymes within the same rats (Johnstone r( a/., 1974). When commercial mixtures were employed, mixtures having a greater chlorine content (Aroclors 1254, 1260) lutd greater enzyme-inducing effects and caused more marked motplmlogicai changes than those having lower chlorine content (Villeneuve ei al, 1971; Bickm n al, 1972; Kollcr and Zinkl, 1973). The more highly chlorinated com pounds mny havegreater eHccf because metabolic studies showthat low chlorine analogs arc eliminated from tissues more rapidly than the more highly chlorinated compounds (Grant Ha!., 1971; Hailey ami Bunyan, 1972; Bickers ef at., 1972; Rehfeldeto/., 1972). In this stud)' and the report of Kimbrough e( al. (1972), administration of ArocJor 1254 resulted in more severe morphological alterations than Aroclor 1260 or any of the pure compounds used. It was also a more powerful inducer of drug-metabolizing enzymes than Aroclor 1260 (Johnstone ef al, 1974). Aroclor 1254 was not the most highly chlorinated compound used, and the response to its administration was inconMMcnt with the view that increased chlorine content caused greater alterations. The failure of Aroclor 1254 to follow the rule of increased (issue response with increased chlorination might be due to the particular combination of chlorobiphenyls present in the mixture or possibly to the presence of contaminants. Chlorinated dibenzofurans and dilcnzo-/;-djoxflns have been found in some commercial PCB mixtures and these compounds caused alterations in hepatocytc morphology that were similar to those caused by PCBs (Vos ei al., 1970; Zitko and Choi, 1971; Oreig, 1972; Hutzinger ef al, 1972; Webb and McCall, 1972; Norback and Allen, 1972). Such contuminants are not reported to be present in Aroclor 1260 (Vos et al, 1970). Kimbrough ef al. (1972) staled that preliminary analysis of the lot ofAroclor 1254 used in their study suggested pos sible contamination with a chlorinated dibenzofuran. It is likely, therefore, that increas ing chlorination of the biphenyl nucleus docs lead to proliferation of SER and to in creased activities of drug-metabolizing enzymes. The enhanced effect observed with Aroclor 1254 can be due to some other factor than chlorination. Treatment of rats wiih 4-chlovo-,4,4'-d>cbloro- and 2,5,2',5'-tctrachloro-biphcnyl at a dosage of 100 mg kg day for 7 days resulted in marked proliferation of SER. The rcil AND LIVLK MORPHOLOGY 425 alterations than 4-nionochlorobiphenyl or 2,5,2',5'-tetrach!orobii>Uenyl, the effects of the latter two agents being approximately the same. DISCUSSION Proliferation of SI;R is a response of the bepafocyte to a wide variety of drugs and poisons and is considered to be a structural reflection of the enhanced metabolism of foreign lipophilic compounds. The increase in SER can be related to increased amounts ofdrug metabolizing enzymes within the liver (Vos and Nolenboom-R&m, 1972). In all previous studies, administration of PCBs has resulted in increased amounts of SER in licpiilocytes (Nishizumi, 1970; Kimbrough ef al, 1972; Vos and Notenboom-Ram, 1972; Norback and Allen, 1972; Koiler and Zinkl, 1973). In this study, the proliferation of SfR was closely related to the structural characteristics of the compound used. Biphenyl and 2,2'-dichlorobiphcnyl appeared not to induce extensive proliferation of SIR. but with the other compounds, the proliferation appeared to be related to (he degree of chlorination and part icularly to (he presence ofa chlorine atom in the 4 and/or 4' position (Tnblc (). The morphological alterations correlated well with the activities of drug-metabolizing enzymes within the same rats (Johnstone r( a/., 1974). When commercial mixtures were employed, mixtures having a greater chlorine content (Aroclors 1254, 1260) lutd greater enzyme-inducing effects and caused more marked motplmlogicai changes than those having lower chlorine content (Villeneuve ei al, 1971; Bickm n al, 1972; Kollcr and Zinkl, 1973). The more highly chlorinated com pounds mny havegreater eHccf because metabolic studies showthat low chlorine analogs arc eliminated from tissues more rapidly than the more highly chlorinated compounds (Grant Ha!., 1971; Hailey ami Bunyan, 1972; Bickers ef at., 1972; Rehfeldeto/., 1972). In this stud)' and the report of Kimbrough e( al. (1972), administration of ArocJor 1254 resulted in more severe morphological alterations than Aroclor 1260 or any of the pure compounds used. It was also a more powerful inducer of drug-metabolizing enzymes than Aroclor 1260 (Johnstone ef al, 1974). Aroclor 1254 was not the most highly chlorinated compound used, and the response to its administration was inconMMcnt with the view that increased chlorine content caused greater alterations. The failure of Aroclor 1254 to follow the rule of increased (issue response with increased chlorination might be due to the particular combination of chlorobiphenyls present in the mixture or possibly to the presence of contaminants. Chlorinated dibenzofurans and dilcnzo-/;-djoxflns have been found in some commercial PCB mixtures and these compounds caused alterations in hepatocytc morphology that were similar to those caused by PCBs (Vos ei al., 1970; Zitko and Choi, 1971; Oreig, 1972; Hutzinger ef al, 1972; Webb and McCall, 1972; Norback and Allen, 1972). Such contuminants are not reported to be present in Aroclor 1260 (Vos et al, 1970). Kimbrough ef al. (1972) staled that preliminary analysis of the lot ofAroclor 1254 used in their study suggested pos sible contamination with a chlorinated dibenzofuran. It is likely, therefore, that increas ing chlorination of the biphenyl nucleus docs lead to proliferation of SER and to in creased activities of drug-metabolizing enzymes. The enhanced effect observed with Aroclor 1254 can be due to some other factor than chlorination. Treatment of rats wiih 4-chlovo-,4,4'-d>cbloro- and 2,5,2',5'-tctrachloro-biphcnyl at a dosage of 100 mg kg day for 7 days resulted in marked proliferation of SER. The '.^..v i -;-\-i ^j '<'^:xii':.'-iZf':.#h >*.JC^Vvnli*!.:.j2^<'3>.dciV.*? .*, -i*`y.<-* u*.V'.;i*.,;> pen AND LIVER MORPHOLOGY 427 Ml'i/inoir, 0., Saif, S. and Zuko, V. (1971). Polychlorinated biphenyls: synthesis of sonte individual chlorobiphcnyls. Bull. Environ, Contain. Toxicol. 6, 209-219. Hui/.ingih, 0., Nash, I). M., Sam-, S., Di:Fri;iio$, A. S. W., Nokstrom, R. J., Wildish, D. J. and Zuko, V. 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