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), phenobarbital (PB) and dexamethasone (DEX) on the expression of three cytochrome P450 (P450) isoforms, 1A1, 2B1 and 3A2, and on glycogen storage was investigated in intrasplenic liver cell explants in comparison to adult liver. Fetal liver tissue suspensions were transplanted into the spleens of adult male syngenic Fisher inbred rats. Four months after surgery, transplant recipients and age matched controls were orally treated 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 solvent 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 hepatocytes around the central veins (zone III, according to Rappaport). After BNF administration a P450 1A1 expression was induced in the hepatocytes of the peripheral regions of the liver lobules (zone I, according to Rappaport), whereas the staining of the hepatocytes around the central veins disappeared. Also the staining for P450 2B1 in the hepatocytes of zone III became slightly more pronounced. Following PB treatment the P450 1A1 expression in the hepatocytes of the central regions (zone III), as seen in few lobules after solvent treatment only, was reduced, whereas the staining for P450 2B1 and 3A2 was more pronounced in the hepatocytes of the intermedial and central regions of the liver lobules (zone II and III). DEX treatment diminished P450 1A1 and 2B1 expression within the livers of both transplant recipients and control rats. In contrast, the staining for P450 3A2 was enhanced in all regions of the liver lobules. Transplantation of fetal liver tissue suspensions into the spleens did not influence the inducibility of P450 isoforms expression within the respective livers of the animals. Spleens of control rats displayed no P450 isoforms expression without as well as with induction. In the explant containing spleens, however, similar to normal liver, the transplanted hepatocytes displayed nearly no P450 1A1, but a strong P450 2B1 and 3A2 expression. After BNF treatment a staining for P450 1A1 was induced and also the P450 2B1 expression was slightly more pronounced. PB treatment caused an increase in the staining for P450 2B1 and 3A2 and DEX administration for P450 3A2 within the transplanted hepatocytes. Additionally, after DEX treatment some bile ducts of the explants displayed a slight staining for P450 1A1, 2B1 and 3A2. All hepatocytes within the livers of both solvent treated transplant recipients and control rats displayed a slightly PAS-positive cytoplasma and, in most cases, homogeneously distributed, fine-grained, strongly PAS-stained granules indicating glycogen storage. No regional variance in the glycogen content of the hepatocytes was seen within the liver lobules, but there was a marked difference between the individual hepatocytes of the same lobular region in the extent of glycogen accumulation. The hepatocytes within the explants displayed the same type of glycogen storage as did the adult liver cells. BNF treatment did not display any effect on the glycogen accumulation in livers and intrasplenic liver cell explants. After PB administration, only in livers, but not in the transplants, the glycogen content in the hepatocytes around the central veins was slightly reduced. DEX treatment lead to an excessive storage of fat within the hepatocytes of both livers and spleens. 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 seemed to be stored and the granules appeared to be more coarse-grained. (ABSTRACT