Developmental expression of cytochrome P450s within intrasplenically transplanted fetal hepatocytes from spontaneously hypertensive rats

Expression and Inducibility of Cytochrome P450 Iiia Family within Intrasplenically Transplanted Fetal Hepatocytes

With the development of transplantation of hepatocytes into the spleen, interest has focused on the metabolic changes associated with hepatocyte proliferation. As these changes are important for drug metabolism in hepatocytes, we examined the expression and inducibility of the cytochrome P450 IIIA family within transplanted hepatocytes. Fetal hepatocytes were harvested at 20 days of gestation from spontaneously hypertensive rats (SHRs) and transplanted into recipient adult SHR spleens. Microscopic examination of the recipient spleens 4 and 10 wk after transplantation revealed masses of hepatocytes with cordlike structures in the red pulp. Proliferating hepatocytes were detected with a bromodeoxyuridine (BrdU) immunohistochemical stain. Immunochemical studies detected cytochromes (cytos) P450 p and P450 HLp in fetal hepatocytes before transplantation without prior induction. And although these cytos were not detected by 10 wk after transplantation, they were induced with dexamethasone. These results demonstrated that fetal hepatocytes can be transplanted successfully into recipient spleens and suggested that fetal hepatocytes grow in the spleen, similar to the adult hepatocyte response.

Intrasplenic transplantation of isolated adult rat hepatocytes: sex-reversal and/or suppression of the major constituent isoforms of cytochrome P450

Adult male and female rat hepatocytes were individually transplanted into the spleens of adult male and female rats. The recipients were euthanized at either eight, sixteen, thirty, or forty-five weeks following transplantation, at which time hepatic and splenic levels of liver-specific rat albumin mRNA as well as sex-dependent transcript levels of CYP2C11, -2C12, -2C7, -2A1, and -3A2-which accounts for > 60% of the total concentration of hepatic constituent cytochrome P450-were determined. Whereas the pre-infused hepatocytes expressed their expected cytochrome P450 sexual dimorphisms (female-specific CYP2C12, male-specific CYP3A2, and female-predominant CYP2A1), their post-transplantational competence now reflected the sexual dimorphisms of the recipient (as observed in the host's liver), which supports the concept that the sex-dependent growth hormone circulating profiles are the determinants regulating the expression levels of hepatic cytochrome P450. Also expressed at normal concentrations in the pre-infused hepatocytes, male-specific CYP2C11 and female-predominant CYP2C7 were inexplicably undetectable in the spleens of both recipient males and females, regardless of the sex of the donor hepatocytes, almost one year after transplantation.

Developmental changes in glutathione S-transferase isoforms expression and activity in intrasplenic fetal liver tissue transplants in rats

The aim of the present study was to characterise developmental changes in glutathione S-transferase (GST) isoforms expression and in glutathione conjugation capacity in intrasplenic liver tissue transplants. For this purpose, syngenic fetal liver tissue suspensions were transplanted into the spleens of adult male Fischer 344 rats. Three days, 1, 2, 4 weeks, 2, 4, 6 months and 1 year later, transplant-recipients and control animals were sacrificed and class alpha, mu and pi GST isoforms expression and GST activities using the substrates o-dinitrobenzene and 1-chloro-2,4-dinitrobenzene were assessed in livers and spleens. In the hepatocytes of the adult livers no class pi, but a distinct class alpha and mu GST expression was seen. The bile duct epithelia were class pi GST positive. Fetal livers displayed almost no class alpha and mu, but a slight class pi GST expression. The same pattern was seen in 3-day-old intrasplenic liver tissue transplants. Up to 2 weeks after surgery the class alpha and mu GST expression increased in the hepatocytes of the transplants, whereas the immunostaining for class pi GST disappeared. No remarkable changes were seen thereafter. Normal conjugation capacities were observed with the livers of both groups of rats. Control spleens displayed only low GST activities. From 2 months after transplantation on activities were significantly higher in transplant-containing spleens than in respective control organs with a further increase up to one year after grafting. These results show that intrasplenically transplanted fetal liver cells proliferate and differentiate into mature cells displaying a GST expression pattern with respective enzyme activities similar to adult liver.

Influence of recipient gender on intrasplenic fetal liver tissue transplants in rats: cytochrome P450-mediated monooxygenase functions

Rat livers display a sex-specific cytochrome P450 (P450) isoforms expression pattern with consecutive differences in P450-mediated monooxygenase activities, which have been shown to be due to a differential profile of growth hormone (GH) secretion. Parallel to previous investigations on P450 isoforms expression, the aim of the present study was to elucidate the influence of recipient gender on P450-mediated monooxygenase activities in intrasplenic liver tissue transplants in comparison to orthotopic liver. Fetal liver tissue suspensions of mixed gender were transplanted into the spleen of adult male or female syngenic recipients. Four months after grafting transplant-recipients and age-matched controls were treated with beta-naphthoflavone (BNF), phenobarbital (PB), dexamethasone (DEX) or the vehicles and sacrificed 24 or 48 h thereafter. P450-dependent monooxygenase activities were assessed by a series of model reactions for different P450 subtypes in liver and spleen 9000 g supernatants. In spleens of male and female control rats only very low monooxygenase activities were detectable, whereas with most model reactions distinct activities were observed in transplant-containing organs. Livers and transplant-containing spleens from male rats displayed higher basal ethoxycoumarin O-deethylase and testosterone 2alpha-, 2beta-, 6beta-, 14alpha-, 15alpha-, 15beta-, 16alpha-, 16beta- and 17-hydroxylase activities than those from females. On the other hand, like the respective livers, spleens from female transplant-recipients demonstrated more pronounced p-nitrophenol- and testosterone 6alpha- and 7alpha-hydroxylase activities than those from male hosts. With nearly all model reactions gender-specific differences in inducibility by BNF, PB or DEX could be demonstrated in livers as well as in transplant-containing spleens. These results further confirm that the P450 system of intrasplenic liver tissue transplants and the respective orthotopic livers is similarly influenced by recipient gender.

Evaluation of 2-year-old intrasplenic fetal liver tissue transplants in rats

Liver cell transplantation into host organs like the spleen may possibly provide a temporary relief after extensive liver resection or severe liver disease or may enable treatment of an enzyme deficiency. With time, however, dedifferentiation or malignant transformation of the ectopically transplanted cells may be possible. Thus, in the present study syngenic fetal liver tissue suspensions were transplanted into the spleen of adult male rats and evaluated 2 years thereafter in comparison to orthotopic livers for histopathological changes and (as markers for preneoplastic transformation) for cytochrome P450 (P450) and glutathione S-transferase (GST) isoform expression. Because inducibility of P450 and GST isoforms may be changed in preneoplastic foci, prior to sacrifice animals were additionally treated either with beta-naphthoflavone, phenobarbital, dexamethasone, or the respective solvent. In the 2-year-old grafts more than 70% of the spleen mass was occupied by the transplant. The transplanted hepatocytes were arranged in cord-like structures. Also few bile ducts were present. Morphologically, no signs of malignancy were visible. With all rats, transplant recipients as well as controls, however, discrete nodular structures were seen in the livers. Due to age, both livers and transplants displayed only a low P450 2B1 and 3A2 and GST class alpha and mu isoform expression. No immunostaining for P450 1A1 was visible. At both sites, beta-naphthoflavone, phenobarbital, or dexamethasone treatment enhanced P450 1A1, P450 2B1 and 3A2, or P450 3A2 expression, respectively. No immunostaining for GST class pi isoforms was seen in the transplants. The livers of both transplant recipients and control rats, however, displayed GST pi-positive foci, corresponding to the nodular structures seen histomorphologically. Compared to the surrounding tissue, these foci also exhibited a more pronounced staining for GST class alpha and mu isoforms and a stronger inducibility of the P450 1A1 expression due to beta-naphthoflavone. In conclusion, in contrast to the livers, no preneoplastic foci seem to appear in the intrasplenic transplants even 2 years after transplantation. This may be due either to the protection of these transplants by the orthotopic livers or to the different humoral and nerval influences at the ectopic site.

Influence of recipient gender on cytochrome P450 isoforms expression in intrasplenic fetal liver tissue transplants in rats

Rat livers display a sex-specific cytochrome P450 (P450) isoforms expression pattern which is regulated by a differential profile of growth hormone (GH) secretion. The aim of the present study was to elucidate whether liver cell transplants at an ectopic site are also subject to this influence. Fetal liver tissue suspensions of mixed gender were transplanted into the spleen of adult male or female syngenic recipients. Four months after grafting transplant recipients and age-matched controls were treated with beta-naphthoflavone (BNF), phenobarbital (PB), dexamethasone (DEX) or the solvents and sacrificed 24 or 48 h thereafter. Livers and intrasplenic transplants were evaluated for the expression of the P450 subtypes 1A1, 2B1, 2E1, 3A2 and 4A1 by means of immunohistochemistry. The livers of both male and female rats displayed nearly no P450 1A1, but a distinct P450 2B1, 2E1, 3A2 and 4A1 expression. Whereas no sex differences were seen in the P450 1A1 expression, the immunostaining for P450 2B1, 3A2 and 4A1 was stronger in males and that for P450 2E1 in females. Similarly, in the intrasplenic liver cell transplants almost no P450 1A1, but a noticeable P450 2B1, 2E1, 3A2 and 4A1 expression was observed. Like in the respective livers, the immunostaining for P450 2B1, 3A2 and 4A1 was stronger in the transplants hosted by male than by female rats, whereas the opposite was the case for the P450 2E1 expression. Both in livers and transplants with some sex-specific differences P450 1A1 and 2E1 expression was induced by BNF, that of P450 2B1 by BNF and PB, and that of P450 3A2 by PB and DEX. These results indicate that the P450 system of ectopically transplanted liver cells is influenced by the gender of the recipient organism like that of the orthotopic livers.

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

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.

Developmental changes of cytochrome P450 dependent monooxygenase functions after transplantation of fetal liver tissue suspension into spleens of adult syngenic rats

Fetal liver tissue suspensions were transplanted into the spleens of adult male syngenic Fisher 344 inbred rats. Animals were sacrificed at 3 days, 1, 2, 4 weeks, and 2, 4 and 6 months after transplantation and cytochrome P450 (P450) dependent monooxygenase functions in spleen and liver 9000 g supernatants were assessed by measuring three model reactions for different P450 subtypes: ethoxyresorufin O-deethylation (EROD; mainly 1A), ethoxycoumarin O-deethylation (ECOD; predominantly 1A, 2A, 2B) and ethylmorphine N-demethylation (END; mainly 3A). Values of transplant recipients were compared to those of sham operated and age matched control rats. Spleen weights were significantly higher in transplanted rats, compared to controls or sham operated animals, but there was no influence of the transplants within the spleens on liver weights. With fetal livers at the 21st day of gestation, the day of transplantation, a weak EROD and ECOD, but no END activity was seen. Spleens of controls or sham operated animals displayed nearly no P450 mediated monooxygenase functions. In the explant containing spleens a significant and increasing EROD activity was found from 4 weeks after surgery on and an ECOD activity already 2 weeks after transplantation. END was only slightly enhanced at 6 months after surgery. The livers of all three groups of rats displayed normal EROD, ECOD and END activities. Transplantation of fetal liver tissue suspensions into the spleens did not influence the P450 dependent monooxygenase functions within the livers of the animals. From these results it can be concluded that intrasplenically transplanted liver cells originating from syngenic fetal liver tissue suspensions proliferate and differentiate within the host organs. They display P450 dependent monooxygenase functions with some developmental changes during the observed time period of 6 months.

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

Influence of different transplantation methods on liver cell survival in spleens of rats

Isolated hepatocytes, liver tissue suspensions, or liver tissue cylinders from biopsies were transplanted into the spleens of adult male rats. Donors were syngenic fetuses, syngenic or allogenic adult rats, or autologous material was obtained from the rat's own liver. The outcome of the different transplantation procedures was evaluated at 1 and 6 months after surgery. Additionally the influence of a 30% hepatectomy (HX) on the result of the transplantation was investigated. When fetal material was transplanted, the best results in sequence with respect to the number of viable hepatocytes within the spleens were obtained (1) after transplantation of syngenic fetal liver tissue suspensions, (2) syngenic fetal liver tissue cylinders and (3) syngenic fetal isolated hepatocytes. HX only improved the results with transplantation of syngenic fetal isolated hepatocytes. After transplantation of syngenic fetal liver tissue suspensions and isolated hepatocytes, but not after transplantation of syngenic fetal liver tissue cylinders, the number of hepatocytes was higher at 6 months than at 1 month after surgery. Concerning syngenic adult liver material, only transplantation of isolated hepatocytes lead to a remarkable and increasing number of surviving hepatocytes at both 1 and 6 months after surgery. These results were further improved by HX. With syngenic adult liver, the other transplantation methods yielded no or nearly no viable hepatocytes in the spleens. In comparison to the results after transplantation of syngenic fetal liver tissue suspensions, transplantation of syngenic adult isolated hepatocytes was less efficient, but still yielded more viable hepatocytes than the transplantation of syngenic fetal isolated hepatocytes. After transplantation of autologous liver tissue suspensions, autologous liver tissue cylinders or allogenic adult liver material only few surviving hepatocytes were observed. At 1 month after transplantation of syngenic fetal liver material, syngenic adult isolated hepatocytes or autologous liver tissue cylinders into the spleens 40-80% of the explants consisted of bile ducts independent from the transplantation method. At 6 months after surgery the bile ducts were much less and in some cases no longer visible. After transplantation of autologous liver tissue suspensions or allogenic adult liver material only very few bile ducts were seen, but anyhow in those cases only poor results were obtained. Thus, with respect to transplantation outcome and long-term liver cell survival, intrasplenic transplantation of both syngenic fetal liver tissue suspensions and syngenic adult isolated hepatocytes seem to be the most suitable methods and should be chosen for further investigations on explant morphology and function.

Developmental expression of cytochrome P450 isoforms after transplantation of fetal liver tissue suspension into the spleens of adult syngenic rats

In the present study, the developmental expression of three cytochrome P450 (P450) isoforms, 1A1, 2B1 and 3A2, and the ability to store glycogen was investigated in intrasplenic liver cell explants in comparison to adult and fetal liver. Fetal liver tissue suspensions were transplanted into the spleens of adult male syngenic Fisher inbred rats. Animals were sacrificed at 3 days, 1, 2, 4 weeks, 2, 4, 6 months and 1 year after transplantation. Spleens and livers of transplant recipients were compared to those of sham operated and control rats. Three days after transplantation little bulks of hepatocytes and only few bile ducts were seen in the red pulp of the transplant containing spleens. A massive hypertrophy and proliferation of bile ducts and also an augmentation in the number of hepatocytes were observed 4 weeks after transplantation. One month later, however, the bile ducts had become more and more atrophic, while instead the number of hepatocytes continuously increased. One year after surgery large masses of hepatocytes with apparent cord structure and only few but well preserved bile ducts were seen. Within the livers of adult rats, P450 1A1 was only slightly expressed by some hepatocytes around the central veins. P450 2B1 and 3A2 isoforms expression was much stronger, but also predominantly located in the hepatocytes of the central zone of the liver lobule. Hepatocytes of fetal livers displayed a moderate P450 1A1 expression. In some cells also a very mild staining for P450 2B1 and 3A2 was observed. Within the hepatocytes of the intrasplenic liver cell explants P450 1A1 was still expressed 3 days after transplantation, disappeared at 1 week after surgery, but reappeared at 4 weeks after transplantation. After 2, 4 and 6 months no staining for P450 1A1 was detectable any more. One year after transplantation again a slight P450 1A1 expression appeared. With P450 2B1 and 3A2 a mild to moderate expression was seen already at 3 days after transplantation. Four weeks after surgery nearly all of the hepatocytes were stained for P450 2B1 and 3A2, but there were marked differences between the individual cells in the extent of the expression of these two P450 subtypes, like it was also the case with normal adult liver. Within hepatocytes of the fetal livers strongly stained glycogen granules were seen, which, in comparison to adult livers, were rather coarse-grained. Three days after transplantation the glycogen granules in the transplanted hepatocytes were still coarse-grained, but from 1 week after transplantation on, they became more and more fine-grained. As it was also the case with normal adult liver cells, there were marked differences between the individual transplanted hepatocytes in their glycogen content. These results demonstrate that transplanted liver cells originating from syngenic fetal liver tissue suspensions can survive in host organs like the spleen for at least 1 year. They proliferate, differentiate, are able to store glycogen, and express different P450 isoforms, like normal adult liver cells.

Enzymatic activity and expression of cytochrome P450 LA omega within intrasplenically transplanted fetal hepatocytes in spontaneously hypertensive rats

We examined the expression and enzymatic activity of cytochrome P450 LA omega within transplanted hepatocytes. Fetal hepatocytes were harvested at day 20 of gestation from spontaneously hypertensive rats (SHRs) and transplanted into recipient adult SHR spleens. Microscopic examination of the recipient spleens at 4 and 10 wk after transplantation revealed masses of hepatocytes with cord-like structures in the red pulp. Immunochemical studies detected cytochrome (cyto) P450 LA omega in the fetal hepatocytes before transplantation without prior induction. Although the cyto P450 LA omega was not detected by the second week after transplantation, by the 6th and 10th wk after transplantation, it was. Cyto P450-arachidonic acid omega/omega-1 hydroxylase activity (formation of 20- and 19-hydroxyeicosatetraenoic acid) was detected at 10 wk after transplantation, but not 2 or 6 wk after transplantation. These results demonstrated that fetal hepatocytes can be transplanted successfully into recipient spleens and then grow in the spleens, as in the case of the adult hepatocyte response.

Enzymatic Activity and Expression of Cytochrome P450 LAω within Intrasplenically Transplanted Fetal Hepatocytes in Spontaneously Hypertensive Rats

We examined the expression and enzymatic activity of the cytochrome P450 LAω within transplanted hepatocytes. Fetal hepatocytes were harvested at day 20 of gestation from spontaneously hypertensive rats (SHRs) and transplanted into recipient adult SHR spleens. Microscopic examination of the recipient spleens 4 and 10 wk after transplantation revealed masses of hepatocytes with cordlike structures in the red pulp. Immunochemical studies detected cytochrome (cyto) P450 LAω in the fetal hepatocytes before transplantation without prior induction. Although the cyto P450 LAω was not detected by the second week after transplantation, by the 6th and 10th wk after transplantation, it was. Cyto P450-arachidonic acid ω/4oM-1 hydroxylase activity (formation of 20- and 19-hydroxyeico-satetraenoic acid) was detected at 10 wk after transplantation, but not 2 or 6 wk after transplantation. These results demonstrated that fetal hepatocytes can be transplanted successfully into recipient spleens and then grow in the spleens, as in the case of the adult hepatocyte response.

Developmental expression of cytochrome P450S within intrasplenically transplanted fetal hepatocytes

Fetal hepatocytes were harvested at day 20 of gestation from spontaneously hypertensive rats (SHR) and then transplanted into recipient adult SHR spleens. Morphological examination of the recipient spleens revealed that, after 4 and 10 wk, large masses of hepatocytes were present in the red pulp with apparent cord-like structures. Larger batches of hepatocytes were observed in the spleens at 10 wk after than at 4 wk after transplantation. Of major significance was the fact that hepatocyte transplanted spleens were able to express several families of cytochrome P450 (cyto P450) proteins 2-10 wk after transplantation. Immunochemical determinations revealed that cytos P450 IA1, P450 IIB1, P450 p, P450 HLp, and P450 LA omega could be detected without any prior induction. All were intensely expressed 6 wk after transplantation; however, P450 IA1 and P450 IIB1 did not appear to be expressed by 2 wk after transplantation. Although cytos P450 p and P450 HLp did not appear to be expressed by 10 wk after transplantation, they were induced with dexamethasone at that time. Cyto P450 LA omega and peroxisomal acyl CoA oxidase were expressed 6 wk after transplantation in a 70% hepatectomized host. These results demonstrate that fetal hepatocytes can be successfully transplanted into the spleens of recipients and that the fetal hepatocytes appear to grow and develop cyto P450 metabolizing systems.