Transplantation of fetal liver tissue suspension into the spleens of adult syngenic rats: Inducibility of cytochrome P450 dependent monooxygenase functions by β-naphthoflavone, phenobarbital and dexamethasone

Abstract

In the present study the effects of beta-naphthoflavone (BNF), phenobarbital (PB) and dexamethasone (DEX) on cytochrome P450 (P450) dependent monooxygenase functions were investigated in intrasplenic liver cell explants in comparison to adult liver. Fetal liver tissue suspensions were transplanted into the spleens of 60-90 days old adult male syngenic Fisher 344 inbred rats. 2, 4 or 6 months after surgery, transplant recipients and age matched controls were orally treated with BNF (1x50 mg/kg body weight (b.wt.)), PB (1x50 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. P450 mediated monooxygenase functions were measured in spleen and liver 9000 g supernatants by three model reactions for different P450 subtypes: ethoxyresorufin O-deethylation (EROD; 1A), ethoxycoumarin O-deethylation (ECOD; 1A, 2A, 2B), and ethylmorphine N-demethylation (END; 3A). Spleen weights were significantly higher in transplanted rats, compared to controls, at all three time points after surgery. Induction with PB or DEX, and in some cases also with BNF, lead to a significant increase in liver weights of transplant recipients and control rats independent of the time after transplantation. In contrast, there was no influence on spleen weights due to BNF or PB. At all time points after surgery, with DEX a marked decrease in body weights, weights of adrenal glands and of lymphatic organs like thymus glands and spleens was observed, with the weights of the transplant containing spleens being still higher in comparison to control organs. Spleens of control animals displayed nearly no P450 mediated monooxygenase functions neither without nor with induction. After transplantation, however, significant EROD and ECOD, but hardly any END activities were seen in the host organs at all three time points after surgery. In transplant containing spleens EROD and ECOD were significantly increased after BNF or PB treatment at all three time points after surgery, and ECOD after DEX administration, but at 4 and 6 months after transplantation only. END was only induced after DEX treatment at 6 months after transplantation. With the livers of both transplant recipients and control rats EROD and ECOD were increased after BNF induction and EROD, ECOD, and END after PB treatment at all three time points after transplantation. After DEX administration END was significantly enhanced only at 2 and 4 months after transplantation, ECOD was decreased at 2 and 4 months, and EROD was diminished at all three time points after surgery. Transplantation of fetal liver tissue suspensions into the spleens did not influence monooxygenase functions and their inducibility within the respective livers of the animals. These results demonstrate that transplanted liver cells originating from syngenic fetal liver tissue suspensions display P450 dependent monooxygenase functions which are, simi lar to normal adult liver, inducible by BNF, PB and DEX. Both monooxygenase functions and their inducibility within the transplant containing spleens display quantitative and qualitative developmental changes.