TRANSPLANTATION OF FETAL LIVER-TISSUE SUSPENSION INTO THE SPLEENS OF ADULT SYNGENIC RATS - EFFECTS OF BETA-NAPHTHOFLAVONE, PHENOBARBITAL AND DEXAMETHASONE ON CYTOCHROME-P450 ISOFORMS EXPRESSION AND ON GLYCOGEN-STORAGE

In the present study, the effect of beta-naphthoflavone (BNF), phenoba rbital (PB) and dexamethasone (DEX) on the expression of three cytochr ome P450 (P450) isoforms, 1A1, 2B1 and 3A2, and on glycogen storage wa s investigated in intrasplenic liver cell explants in comparison to ad ult liver. Fetal liver tissue suspensions were transplanted into the s pleens of adult male syngenic Fisher inbred rats. Four months after su rgery, transplant recipients and age matched controls were orally trea ted with BNF(1 x 50 mg/kg body weight (b.wt.)), PB (1 x 50 mg/kg b.wt. ), DEX (for 3 days 4 mg/kg b.wt. per day), or the respective solvents (dimethylsulfoxide or 0.9% NaCl). The animals were sacrificed 24 (BNF, DEX) or 48 (PB) hours after the last treatment. The livers of both so lvent treated transplant recipients and control rats displayed only in few liver lobules a slight P450 1A1, but in all lobules a strong P450 2B1 and 3A2 expression, which was all mainly located in the hepatocyt es around the central veins (zone III, according to Rappaport). After BNF administration a P450 1A1 expression was induced in the hepatocyte s of the peripheral regions of the liver lobules (zone I, according to Rappaport), whereas the staining of the hepatocytes around the centra l veins disappeared. Also the staining for P450 2B1 in the hepatocytes of zone III became slightly more pronounced. Following PB treatment t he P450 1A1 expression in the hepatocytes of the central regions (zone III), as seen in few lobules after solvent treatment only, was reduce d, whereas the staining for P450 2B1 and 3A2 was more pronounced in th e hepatocytes of the intermedi al and central regions of the liver lob ules (zone II and III). DEX treatment diminished P450 1A1 and 2B1 expr ession within the livers of both transplant recipients and control rat s. In contrast, the staining for P450 3A2 was enhanced in all regions of the liver lobules. Transplantation of fetal liver tissue suspension s into the spleens did not influence the inducibility of P450 isoforms expression within the respective livers of the animals. Spleens of co ntrol rats displayed no P450 isoforms expression without as well as wi th induction. In the explant containing spleens, however, similar to n ormal liver, the transplanted hepatocytes displayed nearly no P450 1A1 , but a strong P450 2B1 and 3A2 expression. After BNF treatment a stai ning for P450 1A1 was induced and also the P450 2B1 expression was sli ghtly more pronounced. PB treatment caused an increase in the staining for P450 2B1 and 3A2 and DEX administration for P450 3A2 within the t ransplanted hepatocytes. Additionally, after DEX treatment some bile d ucts of the explants displayed a slight staining for P450 1A1, 2B1 and 3A2. All hepatocytes within the livers of both solvent treated transp lant recipients and control rats displayed a slightly PAS-positive cyt oplasma and, in most cases, homogeneously distributed, fine-grained, s trongly PAS-stained granules indicating glycogen storage. No regional variance in the glycogen content of the hepatocytes was seen within th e liver lobules, but then was a marked difference between the individu al hepatocytes of the same lobular region in the extent of glycogen ac cumulation. The hepatocytes within the explants displayed the same typ e of glycogen storage as did the adult liver cells. BNF treatment did not display any effect on the glycogen accumulation in livers and intr asplenic liver cell explants. After PB administration, only in livers, but not in the transplants, the glycogen content in the hepatocytes a round the central veins was slightly reduced. DEX treatment lead to an excessive storage of fat within the hepatocytes of both livers and sp leens. Thus, the glycogen was displaced, leading to a ''spoke-wheel'' like pattern of glycogen storage. Additionally, within the hepatocytes of both livers and liver cell explants a higher amount of glycogen se emed to be stored and the granules appeared to be more coarse-grained. These results demonstrate that transplanted liver cells originating f rom syngenic fetal liver tissue suspensions are able to survive in hos t organs like the spleen at least for 4 months. Similar to normal adul t liver cells, the transplanted hepatocytes display a P450 isoforms ex pression, which can be induced by treatment with BNF, PB or DEX. Addit ionally, they are able to store glycogen.