- Email: [email protected]
The mechanism of the inhibitory effect of dithiocarbamates and carbon disulfide on the lipid-peroxidation of the rat liver microsomes
145
I N D U C T I O N OF Z O N A L H E P A T O C Y T E H E T E R O G E N E I T Y K. J u n g e r m a n n , H.J. Balks, K. B e c k h , I. P r o b s t and D. W ~ I f l e Y-nstltut ~Qr B i o c - - - ~ m l e , ~ - 3 ~ - ~ O ~ n ~ e n - The periportal (pp) to p e r i v e n o u s (pv) g r a d i e n t s of h o r m o n e and o x y g e n are believed to cause the h e t e r o g e n e o u s expression of the hepatocyte genome leading to a p r e d o m i n a n c e e.g. of g l u c o g e n i c e n z y m e s in the pp zone and of g l y c o l y t i c e n z y m e s in the pv zone (i). It was the p u r p o s e of the p r e s e n t s t u d y to q u a n t i t a t e these g r a d i e n t s and to i n v e s t i g a t e h o w the different zonal milieu c o u l d c o n t r i b u t e to the i n d u c t i o n of liver cell h e t e r o g e n e i t y . Insulin and g l u c a g o n w e r e m e a s u r e d in a r t e r i a l , portovenous and hepatovenous blood in the rat; catecholamines w e r e d e t e r m i n e d in the portal and hepatic vein d u r i n g n o n - r e c i r c u l a t i n g liver p e r f u s i o n . In the h e p a t i c vein (~ pv c o n d i t i o n s ) as c o m p a r e d to the p o r t a l vein (~ pp c o n d i t i o n s ) i n s u l i n levels were l o w e r e d to 85% d u r i n g m e a l s and to 55% d u r i n g a fast; the c o r r e s p o n d i n g values for g l u c a g o n w e r e a b o u t 70%, for a d r e n a l i n e 15% and for noradrenaline 50%. Thus the r a t i o of i n s u l i n to its a n t a g o n i s t s g l u c a g o n plus c a t e c h o l a m i n e s appears to be h i g h e r in the pv than in the pp zone, e s p e c l a l l y after a meal. The insulin predominance in the pv zone is in line with the postulated prevalence of g l y c o l y s i s in this area; c o n v e r s e l y , the g l u c a g o n and c a t e c h o l a m i n e predominance in the pp zone is in accord w i t h the p r e v a l e n c e of g l u c o n e o g e n e sis in that area. In 48 h c u l t u r e d h e p a t o c y t e s an e n z y m e p a t t e r n could be induced which resembled, w i t h r e s p e c t to c a r b o h y d r a t e m e t a b o l i s m , that of pp or pv cells in vivo if e i t h e r g l u c a g o n or i n s u l i n was s u p p l i e d as the major hormone. Th--e ~Tl-l:erences were further accentuated if " g l u c a g o n - c e l l s " w e r e kept under high pp 0 2 - t e n s i o n s and "insulin-cells" under low pv 02-concentrations. The glucagon-insulin a n t a g o n i s m was s t u d i e d in m o r e d e t a i l with the i n d u c t i o n of phosphoenolpyruvate carboxykinase in c u l t u r e d h e p a t o c y t e s . It is c o n c l u d e d that, in a c c o r d w i t h the w o r k i n g h y p o t h e s i s , the c h a n g i n g i n s u l i n / g l u c a g o n r a t i o and the d e c r e a s i n g 0 2 - t e n s i o n d u r i n g liver p a s s a g e are involved in the i n d u c t i o n of h e p a t o c y t e h e t e r o g e n e i t y . (i) J u n g e r m a n n , K., Katz, N. (1982) H e p a t o l o g y 2, 385-395.
146
THE MECHANISM O F T HE INHIBITORY ~'wF~CT OF DITHIOCARBAMATES AND CARBON DISULFIDE ON THE LIPID-P~O×IDATION OF THE RAT L I V ~ MICROSOMES . A.M.KAMAL,K.G.FREUNDT*,A.A.MASSOUD. Department of Ccmlnunity,Enviror~nental and Occupational Medicine ,Eaculty of Medicine Aim ~hams University ,Abbassia,Cairo,Egypt. and *Institut fur Pharmakologie und Toxikologie,Mannheim,F.R.G.
The effect of the dithiocarbamates:TMTD(tetramethylthiuram disulfide~TETD(tetraethylthiuram disulfide), DMDTC (dimethyldithiocarbamate), DEDTC (diethyldithiocarbamate), ~[I%1(tetramethylthiuram monosulfide ) and CS 2 (carbon disulfide) on the L P O (lipid peroxidation )of the rat liver microsomes were in vitro investigated . L P 0 was measured in terms of Malondialdehyde formation and cytochrcme P-450 destruction.TMTD, TETD,DMDYC and D~IYfC inhibited in relatively low concentrations the enzymatically and non-enzymatically induced L P 0 in the rat liver microscmes as well as the 9000xg suDernatent of rat liver homogenate.TMTM and CS 2 exhibited also a similar effect but in much higher concentrations . Interestingly, it was found that the inhibitory effect of TETD and TMTD are double that for DEIYlX~ and DMDTC respectively. Moreover ,the dithiocarbamates inhibited the L P O process not only when added at the beginning of the incubation reaction but also when added at a later time after initiation of the reaction . However,the concentrations needed increased with delaying the time of their addition. Analysis of the results and proposal of the site and mechanism of the inhibitery action of these compounds on L P O process were given .
$73
I N D U C T I O N OF Z O N A L H E P A T O C Y T E H E T E R O G E N E I T Y K. J u n g e r m a n n , H.J. Balks, K. B e c k h , I. P r o b s t and D. W ~ I f l e Y-nstltut ~Qr B i o c - - - ~ m l e , ~ - 3 ~ - ~ O ~ n ~ e n - The periportal (pp) to p e r i v e n o u s (pv) g r a d i e n t s of h o r m o n e and o x y g e n are believed to cause the h e t e r o g e n e o u s expression of the hepatocyte genome leading to a p r e d o m i n a n c e e.g. of g l u c o g e n i c e n z y m e s in the pp zone and of g l y c o l y t i c e n z y m e s in the pv zone (i). It was the p u r p o s e of the p r e s e n t s t u d y to q u a n t i t a t e these g r a d i e n t s and to i n v e s t i g a t e h o w the different zonal milieu c o u l d c o n t r i b u t e to the i n d u c t i o n of liver cell h e t e r o g e n e i t y . Insulin and g l u c a g o n w e r e m e a s u r e d in a r t e r i a l , portovenous and hepatovenous blood in the rat; catecholamines w e r e d e t e r m i n e d in the portal and hepatic vein d u r i n g n o n - r e c i r c u l a t i n g liver p e r f u s i o n . In the h e p a t i c vein (~ pv c o n d i t i o n s ) as c o m p a r e d to the p o r t a l vein (~ pp c o n d i t i o n s ) i n s u l i n levels were l o w e r e d to 85% d u r i n g m e a l s and to 55% d u r i n g a fast; the c o r r e s p o n d i n g values for g l u c a g o n w e r e a b o u t 70%, for a d r e n a l i n e 15% and for noradrenaline 50%. Thus the r a t i o of i n s u l i n to its a n t a g o n i s t s g l u c a g o n plus c a t e c h o l a m i n e s appears to be h i g h e r in the pv than in the pp zone, e s p e c l a l l y after a meal. The insulin predominance in the pv zone is in line with the postulated prevalence of g l y c o l y s i s in this area; c o n v e r s e l y , the g l u c a g o n and c a t e c h o l a m i n e predominance in the pp zone is in accord w i t h the p r e v a l e n c e of g l u c o n e o g e n e sis in that area. In 48 h c u l t u r e d h e p a t o c y t e s an e n z y m e p a t t e r n could be induced which resembled, w i t h r e s p e c t to c a r b o h y d r a t e m e t a b o l i s m , that of pp or pv cells in vivo if e i t h e r g l u c a g o n or i n s u l i n was s u p p l i e d as the major hormone. Th--e ~Tl-l:erences were further accentuated if " g l u c a g o n - c e l l s " w e r e kept under high pp 0 2 - t e n s i o n s and "insulin-cells" under low pv 02-concentrations. The glucagon-insulin a n t a g o n i s m was s t u d i e d in m o r e d e t a i l with the i n d u c t i o n of phosphoenolpyruvate carboxykinase in c u l t u r e d h e p a t o c y t e s . It is c o n c l u d e d that, in a c c o r d w i t h the w o r k i n g h y p o t h e s i s , the c h a n g i n g i n s u l i n / g l u c a g o n r a t i o and the d e c r e a s i n g 0 2 - t e n s i o n d u r i n g liver p a s s a g e are involved in the i n d u c t i o n of h e p a t o c y t e h e t e r o g e n e i t y . (i) J u n g e r m a n n , K., Katz, N. (1982) H e p a t o l o g y 2, 385-395.
146
THE MECHANISM O F T HE INHIBITORY ~'wF~CT OF DITHIOCARBAMATES AND CARBON DISULFIDE ON THE LIPID-P~O×IDATION OF THE RAT L I V ~ MICROSOMES . A.M.KAMAL,K.G.FREUNDT*,A.A.MASSOUD. Department of Ccmlnunity,Enviror~nental and Occupational Medicine ,Eaculty of Medicine Aim ~hams University ,Abbassia,Cairo,Egypt. and *Institut fur Pharmakologie und Toxikologie,Mannheim,F.R.G.
The effect of the dithiocarbamates:TMTD(tetramethylthiuram disulfide~TETD(tetraethylthiuram disulfide), DMDTC (dimethyldithiocarbamate), DEDTC (diethyldithiocarbamate), ~[I%1(tetramethylthiuram monosulfide ) and CS 2 (carbon disulfide) on the L P O (lipid peroxidation )of the rat liver microsomes were in vitro investigated . L P 0 was measured in terms of Malondialdehyde formation and cytochrcme P-450 destruction.TMTD, TETD,DMDYC and D~IYfC inhibited in relatively low concentrations the enzymatically and non-enzymatically induced L P 0 in the rat liver microscmes as well as the 9000xg suDernatent of rat liver homogenate.TMTM and CS 2 exhibited also a similar effect but in much higher concentrations . Interestingly, it was found that the inhibitory effect of TETD and TMTD are double that for DEIYlX~ and DMDTC respectively. Moreover ,the dithiocarbamates inhibited the L P O process not only when added at the beginning of the incubation reaction but also when added at a later time after initiation of the reaction . However,the concentrations needed increased with delaying the time of their addition. Analysis of the results and proposal of the site and mechanism of the inhibitery action of these compounds on L P O process were given .
$73