Comparative metabolic profiling of chloramphenicol by isolated hepatocytes from rat and trout (Oncorhynchus mykiss)

1. Isolated liver cells from rat and rainbow trout were used to study the biotransformation of labelled chloramphenicol (CP).2. The ³H-CP metabolic rates were 1.7 nmol/hr/10⁶ rat hepatocytes and 0.2nmol/hr/10⁶ trout hepatocytes.3. In rat, as in trout liver cells, the major metabolite was CP-glucuronide. In addition to this conjugate, CP-base, CP-alcohol and CP-oxamic acid were detected in significant amounts.4. These results are compared with in vivo data on CP metabolism previously obtained in our laboratory in fish and mammals.     

Maintenance of liver function in long term culture of hepatocytes following In Vitro or In Vivo Ha-ras EJ transfection

Collagenase isolated rat hepatocytes were transfected with liposome encapsulated pEJ (LE-pEJ), a plasmid carrying the human cellular activated Ha-ras^EJ oncogene. A proliferative cell line was cloned from these cells transfected in vitro. It secreted per day 0.87 µg albumin and 0.32 µg transferrin per 10⁶ cells, and 11.06 nmol free and conjugated bile acids (BA) per mg protein. Also, it metabolized 2-acetylaminoflourene (2-AFAF) into N- and ring-hydroxylated metabolites and 2-aminofluorene at rates of 1.50, 9.73, and 1.98 nmol/mg cell protein/24 hr, respectively. Rats were i.v. injected with both LE-pEJ and LE-p17hGHnneo carrying the hGH cDNA gene, and secreted hGH in the plasma which induced the synthesis of anti-hGH antibodies. A cell line was cloned from cultures of primary hepatocytes isolated from the liver of transfected rats. After 2 to 3 months in culture, this cell line secreted per day 18.9 µg albumin and 11.0 µg transferrin per 10⁶ cells, 38.75 nmol total BA per mg cell protein, and up to 31 ng hGHper 10⁶ cells without cloning hGH recombinant cells. A 24 hr control culture of primary hepatocytes isolated from non transfected rats secreted 25.5 µg albumin and 11.7 µg transferrin per 10⁶ cells, and produced 21.64 nmol total BA and 2.13 nmol N-OH-2-AFAF per mg cell protien. Hence, Ha-ras ^EJ transfection of either hepatocytes in vitro or liver cells in vivo, initiated cell cycles leading to presumptive proliferating hepatocytes which express liver function.Abbreviations BWE basal Williams' medium E - FBS fetal bovine serum - F10 or F12 basal Ham's F10 or F12 medium - Ha-ras ^EJ EJ allele of the human cellular ras oncogen of Harvey - hGH human growth hormone - hsp heat shock protein gene - LE-p liposome encapsulated plasmid - N-OH-2-AFAF N-hydroxy-2-acetylaminofluorene - RLECC rat liver epithelial cell - SF serum-free - SS serum-supplemented - UGG serum substitute UGltroser G® - 1-OH-, 3-OH-2-AFAFF 1-hydroxy-, 3-hydroxy-2-acetylaminofluorene - 2-AFAF 2-acetylaminofluorene - 2-AFF 2-aminofluorene     

The effect of EGF and the comitogen, norepinephrine, on the proliferative responses of fresh and cryopreserved rat and mouse hepatocytes

The effect of cryopreservation on the proliferative response of fresh and cryopreserved (CP) rat and mouse hepatocytes was studied. Of the parameters measured, incorporation of 3H-thymidine and bromodeoxyuridine (BdrU) incorporation were the most sensitive and LDH content was the least sensitive. The optimal seeding density for epidermal growth factor (EGF)-stimulated proliferative response in fresh rat and mouse hepatocytes was 1.8 x 10(4) cells/cm2 and 2.1 x 10(4) cells/cm2, respectively. 3H-thymidine incorporation by fresh rat and mouse hepatocytes was maximal in cultures treated with 10 and 5 ng/ml EGF, respectively. The cell attachment of fresh rat hepatocytes after 48 h was higher (68%) than CP (42%), therefore, the CP hepatocyte seeding density was increased to 7.1 x 10(4) cells/cm2 so that the cell number after 48 h was the same as fresh hepatocytes. Using the adjusted seeding density, the 3H-thymidine and BdrU incorporation into fresh and CP rat hepatocytes was equivalent. The attachment efficiencies of fresh and CP mouse hepatocytes were the same, therefore, no adjustment was needed. The proliferative response (3H-thymidine incorporation and DNA content) to EGF was the same in fresh and CP mouse hepatocytes. The comitogen, norepinephrine (NE), increased the proliferative response to EGF to the same extent in both fresh and CP rat hepatocytes. In summary, cryopreserved rat and mouse hepatocytes retain their ability to proliferate in culture. Adjustment and monitoring of the seeding density is of high importance, especially with rat hepatocytes, which lose some attachment capacity after cryopreservation. The secondary mitogenic effect of NE is also retained by cryopreserved rat hepatocytes, suggesting that these cells retain alpha1-receptor function.     

Differential regulation of insulin-like growth factor-II receptors in rat hepatocytes and hepatoma cells

This study compares the regulation of IGF-II receptors in three rat hepatoma lines, HTC, H-35 and 5123tc, and primary rat hepatocytes. In all cell types [125I]IGF-II bound solely to a species of approximately 250 kDa. Cell surface IGF-II receptors in hepatoma cells had slightly lower affinities (1-2 liters/nmol) than in hepatocytes (4 liters/nmol), but slightly higher IGF-I cross-reactivity (2-4% compared to 1% in hepatocytes). In confluent cultures, the three hepatoma lines expressed 5- to 15-fold more cell-surface receptors per cell than hepatocytes. However, while hepatocyte receptors showed marked inverse density-dependence, increasing over 6-fold between dense (3 x 10(5) cells/3.8 cm2) and sparse (0.16 x 10(5) cells/3.8 cm2) cultures, receptors in all hepatoma lines remained at a constant high level regardless of culture density. These distinct regulatory patterns resemble those described for growth-related functions in hepatocytes and hepatoma cells, and are thus consistent with a role for IGF-II receptors in liver cell proliferation.     

Respiratory activity of isolated rat hepatocytes following cold storage and subsequent rewarming: a comparison of sucrose-based and University of Wisconsin solutions

Investigations were carried out on the respiratory function of isolated rat hepatocytes after cold storage alone for periods up to 48 h in either sucrose-based solution (SBS) or University of Wisconsin (UW) solution and after subsequent normothermic preincubation. In both SBS and UW, cold storage for 24 h depressed respiratory function (to 21 +/- 3 and 23 +/- 3 nmol O(2)/min/10(6) cells, respectively) compared to control cell values (31 +/- 3 and 33 +/- 5 nmol O(2)/min/10(6) cells; P < 0.01 in each case). However, normothermic preincubation for 60 min returned respiratory activity to control values (for SBS and UW storage: 41 +/- 6 and 40 +/- 5 nmol O(2)/min/10(6) cells; for control cells: 43 +/- 5 and 46 +/- 6 nmol O(2)/min/10(6) cells). Storage for 48 h in both SBS and UW allowed further depression of respiratory activity, with no recovery after preincubation. Stimulation of respiration by succinate in hepatocytes stored for longer periods was suggestive of increased membrane permeability. Both SBS and UW are effective storage solutions for isolated hepatocytes for up to 24 h as judged by aerobic metabolism, but significant damage was expressed in both solutions when preservation was extended.     

Effects of coenzyme Q10 on changes in the membrane potential and rate of generation of reactive oxygen species in hydrazine- and chloramphenicol-treated rat liver mitochondria.

Effects of CoQ10 and cycloheximide (CHX) on hydrazine- and chloramphenicol (CP)-induced morphological and some functional changes of mitochondria using cultured rat hepatocytes and effects on the process of recovery from CP intoxication using mouse liver were examined. Results obtained are summarized as follows: (1) The formation of megamitochondria induced in the hepatocytes cultured for 22 h in the presence of 2 mM hydrazine or CP (300 microgram/ml) was suppressed by pretreatment of hepatocytes with CoQ10 (1 microM) or CHX (0.5 microgram/ml). This was proved by electron microscopic analysis of mitochondria. (2) Treatment of hepatocytes with hydrazine for 48 h or longer caused decreases in the membrane potential of mitochondria, which were suppressed by CoQ10. (3) Treatment of hepatocytes with hydrazine for 22 h or longer caused remarkable increases in intracellular levels of reactive oxygen species in hepatocytes, which were suppressed by CoQ10. (4) The process of recovery from the CP-induced changes of mitochondria in mouse liver was accelerated by CoQ10 and CHX.     

Cell and species differences in metabolic activation of chemical carcinogens

Metabolic activation and DNA binding of aflatoxin B1 (AFB1), N-nitrosodimethylamine (DMN) and benzo[a]pyrene (B[a]P) were compared in human, rat and mouse hepatocytes and human pulmonary alveolar macrophages (PAM). The degree of carcinogen activation by hepatocytes and PAM was measured by cell-mediated mutagenesis assays in which co-cultivated Chinese hamster V79 cells were used to monitor mutagenic metabolites. Hepatocytes from human, mouse and rat metabolized DMN and released the active metabolites to induce either ouabain- or 6-thioguanine-resistant mutation. The mutation frequencies mediated by hepatocytes of the 3 animal species were approximately 3-9 mutants/10(5) survivors at a concentration of 0.2 mM DMN. The variations of radioactivity bound to liver cell DNA were relatively small in cultured mouse, rat, and human hepatocytes exposed to 14C label DMN (0.5 mM) and the binding values were in a range of 6-12 X 10(3) pmoles/mg DNA. However, rat hepatocytes were at least 10-fold more effective than either human or mouse hepatocytes in generating mutagenic metabolites of AFB1 and also had a much higher AFB1 metabolite DNA-binding value. The AFB1 DNA-binding levels were 4.1, 12-27 (range), 120 pmoles/mg DNA respectively in mouse, human, and rat liver cells following AFB1 (3.3 microM) exposure for 20 h. Hepatocytes from the 3 animal species were unable to mediate mutation in the presence of 4 microM B[a]P; PAM activated B[a]P and effectively mediated mutation in the co-cultivated V79 cells. In contrast to results with hepatocytes, PAM failed to generate enough mutagenic metabolites of AFB1 (3.3 microM) and the mediation of mutations was seen only at very high concentration of DMN (80 mM). The genotoxic effects of the 3 carcinogens on hepatocytes from different species in vitro were in agreement with the in vivo animal experiments in that mice are relatively resistant to AFB1 carcinogenesis whereas rats are sensitive; B[a]P is not effective as a complete liver carcinogen in adult rat and mouse whereas DMN induces liver cancer.     

Decreased responsiveness of gluconeogenesis to the modulation by sulfonylureas in hepatocytes isolated from obese (fa/fa) Zucker rats

The influence of the hypoglycemic agent glipizide (0-100 microM) on the rate of gluconeogenesis from lactate, as well as on the levels of fructose 2,6-bisphosphate, has been investigated in hepatocytes isolated from genetically obese (fa/fa) Zucker rats and from their corresponding lean (Fa/-) littermates. As compared to lean rat hepatocytes, liver cells isolated from obese animals showed a lower rate of basal gluconeogenesis (0.9 +/- 0.2 vs 5.4 +/- 0.5 micromol of lactate converted to glucose/g cell x 30 min, n=4) and higher levels of fructose 2,6-bisphosphate (11.5 +/- 1.0 vs 5.9 +/- 0.4 nmol/g cell, n=8-9). In lean rat hepatocytes, the presence of glipizide in the incubation medium caused a dose-dependent inhibition of the rate of lactate conversion to glucose (maximal inhibition=46%; EC50 value=26 microM), and simultaneously raised the cellular content of fructose-2,6-bisphosphate (maximal increment=40%; EC50 value=10 microM). In contrast, in hepatocytes isolated from obese rats, the inhibition of gluconeogenesis and the increment in fructose-2,6-bisphosphate levels elicited by glipizide were significantly reduced (maximal effects of 22 and 13%, respectively). Similarly, the activation of glycogen phosphorylase and the increase in hexose 6-phosphate levels in response to glipizide were less marked in obese rat hepatocytes than in liver cells isolated from lean animals. These results demonstrate that the efficacy of sulfonylureas as inhibitors of hepatic gluconeogenesis is reduced in the genetically obese (fa/fa) Zucker rat.     

Lymphocyte ecto-5'-nucleotidase activity in infancy: increasing activity in peripheral blood B cells precedes their ability to synthesize IgG in vitro

Ecto-5'-nucleotidase activity was measured in peripheral blood lymphocytes isolated from serial specimens from nine healthy full-term infants and two premature infants at 0, 2, 4, and 6 mo of age. The postnatal nadir in activity was 7.1 +/- 2.0 nmol/hr/10(6) cells, which is the same as the activity in cord blood lymphocytes (7.0 +/- 2 nmol/hr/10(6) cells). The activity rose twofold to 13.2 +/- 3.8 nmol/hr/10(6) cells at 6 mo of age (p less than 0.001, paired t-test), which is similar to the activity in adult peripheral blood lymphocytes (14.1 +/- 6.3 nmol/hr/10(6) cells). This increased activity in total lymphocytes reflects increased activity in the B cell population. B cell ecto-5'-nucleotidase activity in two infants at 12 to 13 mo of age was 19.3 and 25.2 nmol/hr/10(6) cells, values that are four-to fivefold higher than for cord blood B cells (5.6 +/- 2.8 nmol/hr/10(6) cells) and within the normal range for adult B cells (27.9 +/- 12 nmol/hr/10(6) cells). In spite of a greatly expanded peripheral blood B cell population, studies of immunoglobulin biosynthesis in vitro demonstrated that infant peripheral blood B cells are functionally immature with no synthesis of IgG in response to Epstein Barr virus. Thus, the increase in peripheral blood B lymphocyte ecto-5'-nucleotidase activity in infants precedes their acquisition of a capacity for IgG synthesis in vitro. Data from a hypogammaglobulinemic infant revealed a persistently low ecto-5'-nucleotidase activity over a 10-mo period until at 14 mo of age the activity was 8.8 nmol/hr/10(6) cells in total lymphocytes and 13.0 nmol/hr/10(6) cells in B cells, which correlated with in vivo and in vitro evidence of delayed B cell maturation. Thus, ecto-5'-nucleotidase activity may be a useful cell surface marker in studies of human postnatal B cell maturation.     

Respiration rates, ATP content and ionic regulation in hepatocytes of starving lamprey during the pre-spawning period of their life cycle

During the winter pre-spawning migration, lampreys Lampetra fluviatilis stop feeding, and their liver metabolism is reduced substantially. Aerobic ATP production in hepatocytes decreased to one third and ATP content decreased by 50% as compared with the values in autumn. In spite of the decrease of endogenous and phosphorylating (oligomycin-sensitive) respiration in winter, the oxygen consumption used to drive sodium and potassium pumping through Na,K-ATPase activity (ouabain-sensitive respiration) remained virtually constant. Consequently its share in phosphorylating respiration increased from 16·3% in November to 54·2% in February. Potassium influx was similar within the range of ATP content between 2·5 and 1 nmol 10⁻⁶ cells and decreases only in hepatocytes which contained <0·8 nmol ATP 10⁻⁶ cells.     

Difference in glucose sensitivity of liver glycolysis and glycogen synthesis. Relationship between lactate production and fructose 2,6-bisphosphate concentration.

Incubation of isolated rat hepatocytes from fasted rats with 0-6 mM-glucose caused an increase in [fructose 2,6-bisphosphate] (0.2 to about 5 nmol/g) without net lactate production. A release of 3H2O from [3-3H]glucose was, however, detectable, indicating that phosphofructokinase was active and that cycling occurred between fructose 6-phosphate and fructose 1,6-bisphosphate. A relationship between [fructose 2,6-bisphosphate] and lactate production was observed when hepatocytes were incubated with [glucose] greater than 6 mM. Incubation with glucose caused a dose-dependent increase in [hexose 6-phosphates]. The maximal capacity of liver cytosolic proteins to bind fructose 2,6-bisphosphate was 15 nmol/g, with affinity constants of 5 X 10(6) and 0.5 X 10(6) M-1. One can calculate that, at 5 microM, more than 90% of fructose 2,6-bisphosphate is bound to cytosolic proteins. In livers of non-anaesthetized fasted mice, the activation of glycogen synthase was more sensitive to glucose injection than was the increase in [fructose 2,6-bisphosphate], whereas the opposite situation was observed in livers of fed mice. Glucose injection caused no change in the activity of liver phosphofructokinase-2 and decreased the [hexose 6-phosphates] in livers of fed mice.     

Effect of selenium deficiency and vitamin E deficiency on glutathione metabolism in isolated rat hepatocytes

Selenium deficiency and vitamin E deficiency both affect xenobiotic metabolism and toxicity. In addition, selenium deficiency causes changes in the activity of some glutathione-requiring enzymes. We have studied glutathione metabolism in isolated hepatocytes from selenium-deficient, vitamin E-deficient, and control rats. Cell viability, as measured by trypan blue exclusion, was comparable for all groups during the 5-h incubation. Freshly isolated hepatocytes had the same glutathione concentration regardless of diet group. During the incubation, however, the glutathione concentration in selenium-deficient hepatocytes rose to 1.4 times that in control hepatocytes. The selenium-deficient cells also released twice as much glutathione into the incubation medium as did the control cells. Total glutathione (intracellular plus extracellular) in the incubation flask increased from 47.7 +/- 8.9 to 152 +/- 16.5 nmol/10(6) selenium-deficient cells over 5 h compared with an increase from 46.7 +/- 7.1 to 92.0 +/- 17.4 nmol/10(6) control cells and from 47.7 +/- 11.7 to 79.5 +/- 24.9 nmol/10(6) vitamin E-deficient cells. This overall increase in glutathione concentration suggested that glutathione synthesis was accelerated by selenium deficiency. The activity of gamma-glutamylcysteine synthetase was twice as great in selenium-deficient liver supernatant (105,000 X g) as in vitamin E-deficient or control liver supernatant (105,000 X g). Hemoglobin-free perfused livers were used to determine the form of glutathione released and its route. Selenium-deficient livers released 4 times as much GSH into the caval perfusate as did control livers. Plasma glutathione concentration in selenium-deficient rats was found to be 2-fold that in control rats, suggesting that increased GSH synthesis and release is an in vivo phenomenon associated with selenium deficiency.     

Degradation of extracellular thymidine by cultured hepatocytes from rainbow trout (Salmo gairdneri)

1. Trout hepatocytes cultured as attached monolayers had low rates of [3H]-thymidine ([3H]-TdR) incorporation during replicative or repair synthesis of DNA. 2. Within 2 hr, most [3H]-TdR was metabolized by trout hepatocytes to a major product that eluted in advance of intact [3H]-TdR on Sephacryl S-200 columns. 3. Metabolism of [3H]-TdR by trout hepatocytes rapidly destroyed its ability to label replicating indicator cultures of proliferating rat hepatocytes. 4. These studies demonstrate that [3H]-TdR tracer assays for DNA synthesis cannot be reliably used in cultured trout hepatocytes which catabolize thymidine much more rapidly than do rat hepatocytes.     

Microcarrier-attached rat hepatocytes as a xenobiotic-metabolizing system in cocultures

A method for the primary culture of rat liver cells on collagen-coated dextran microcarriers is described. Ethoxycoumarin deethylase (EOD) activity 24 hr after inoculation was comparable for liver cells cultured on microcarriers and on collagen-coated dishes. Cells were cultured on microcarriers for up to 48 hr and retained 25% of the initial EOD-activity that was seen in freshly isolated liver cells. Microcarrier-attached hepatocytes were cocultured with BALB/c 3T3 cells to study the metabolism-mediated cytotoxicity of cyclophosphamide (CPA). In the absence of hepatocytes, growth of 3T3 cells was not affected by CPA at concentrations up to 3600 M. In coculture with hepatocytes, cytotoxicity of CPA was expressed in a time- and concentration-dependent manner. At high concentrations, CPA slightly depressed the EOD-activity of hepatocytes. Our results indicate that cocultivation of microcarrier-attached rat liver cells with target cells represents a valuable approach to the study of the metabolism-mediated toxicity of xenobiotics in vitro.Abbreviations CPA cyclophosphamide - EOD Ethoxycoumarin deethylase - FBS fetal bovine serum - HBSS Hanks' balanced salt solution - HEPES N-2-Hydroxyethylpiperazine-N-2-ethanesulfonic acid - PASA Na-pyruvate, asparagine, serine, alanine - 7-HC 7-hydroxycoumarin This work was presented in part at the VIIIth Scandinavian Workshop on In Vitro Toxicology, Kongsvoll, Norway (1990).     

Time course changes in glycogen accretion, 6-phosphogluconate, fructose-2,6-bisphosphate, and lipogenesis upon refeeding a high sucrose diet to starved rats

1. Starved rats refed 60% sucrose diets were used to determine in vivo lipogenesis and levels of hepatic metabolites. 2. Fatty acid synthesis increased 11-fold 4 hr after refeeding. 3. Glycogen rose from 3 to 100 mg/g liver after 8 hr. 4. Fructose-2,6-bisphosphate rose to 6 nmol/g at 1 hr and remained constant. 5. 6-Phosphogluconate increased from 10 to 45 nmol/g liver after 2 hr and remained constant.     

Isolation and characterization of biliary epithelial cells from rainbow trout liver

Summary Lectin binding and density gradient centrifugation were explored for isolating epithelial cells from trout liver. Hepatocytes exhibited preferential attachment to coverslips coated withPhaseolus vulgaris erythroagglutinin. Biliary epithelial cells attached with glycine max agglutinin; however, significant attachment of cellular debris limited the use of glycine max agglutinin. Percoll-density gradient centrifugation separated liver cells into two distinct populations with biliary cells and hepatocytes banding at densities of 1.04 and 1.09, respectively. A discontinuous gradient composed of 13% Ficoll (wt/wt) separated biliary cells from hepatocytes. The recovery of highly enriched biliary epithelial cells from trout liver using Ficoll gradients yielded approximately 8 million cells (0.1 ml packed cells) from 10 g liver. Western blot analysis demonstrated that the cytokeratin profile for extracts from biliary epithelial cell-enriched populations differ significantly from those seen with whole liver extracts or with extracts from hepatocyte-enriched populations. Ficoll-gradient purified biliary cells and hepatocytes attached to culture plates coated with trout skin extract and carried out linear incorporation of leucine into protein and thymidine into DNA for 24 h. A mixture of growth hormones (insulin, epidermal growth factor, and dexamethasone) stimulated thymidine incorporation into DNA; however, long-term culture of dividing biliary epithelial cells was not achieved. Chemical analysis of neutral and acidic glycolipids indicated that hepatocytes and biliary cells have similar glycolipid profiles with an exception in the region of GM3 mobility, which is attributable to differences in the ceramide moiety. These studies provide a starting point for further characterization of unique cell types of the trout liver that may be important in their response to toxic and carcinogenic agents.     

Oxygen toxicity: unique cytoprotective properties of vitamin E succinate in hepatocytes

Freshly isolated rat hepatocytes suspensions were incubated under an atmosphere of 95% O2/5% CO2 or 95% air/5% CO2 for 10 h. Cell injury and death were observed between the 6th and 10th hour of incubation, only in 95% O2-treated hepatocytes. Oxygen-induced injury was preceded by marked lipid peroxidation and rapid depletion of cellular alpha tocopherol content. The exogenous administration of unesterified alpha tocopherol (T, 25 microM) resulted in a 20-fold increase in cellular T levels (4.2 nmol/10(6) cells) but failed to protect these hepatocytes from the toxic effects of oxygen. In contrast, hepatocytes incubated with 25 microM of the succinate ester of alpha tocopherol (TS) contained both TS (3.0 nmol/10(6) cells) and T (1.4 nmol/10(6) cells) and were completely protected from the toxic effects of oxygen, including the induction of lipid peroxidation. These findings suggest that TS cytoprotection results not from the cellular accumulation of T but rather, from cellular TS accumulation. The data also indicate that the depletion of cellular T is not the critical cellular event that is responsible for hyperoxia (reactive oxygen intermediate)-induced injury. Instead, it appears that TS possesses unique cytoprotective properties that intervene in the critical cellular events that lead to oxygen toxicity. Thus, vitamin E succinate and our hyperoxic hepatocyte preparation provide a promising new model system for the study and prevention of tissue damage resulting from the toxic effects of hyperoxia and reactive oxygen intermediates.     

Distribution of terminal deoxynucleotidyl transferase and purine degradative and synthetic enzymes in subpopulations of human thymocytes

Terminal deoxynucleotidyl transferase (TdT) and purine metabolic enzymes were examined in subsets of human infant thymocytes (defined by surface cell antigens) and normal peripheral T lymphocytes. Putative prothymocytes (RFB-1+, HTA-1+/- large blast-like cells), medium and high density cortical thymocytes (RFB-1+, HTA-1+), and medullary thymocytes (RFB-1-, HTA-1-, OKT3+) were isolated by density gradient centrifugation, monoclonal antibody and complement-mediated cytolysis, and cell-antibody affinity chromatography. Peripheral T lymphocytes were isolated from normal adult mononuclear cells using nylon fiber technique. Adenosine deaminase (ADA) and TdT were highest in prothymocytes 48.8 +/- 14.7 mumol/hr/10(8) cells (mean +/- SE) and 22.9 +/- 1.4 U/10(8) cells, respectively. Both enzymes decreased progressively down the maturation pathway. In peripheral T lymphocytes, ADA was 3.9 +/- 1.5 mumol/hr/10(8) cells, and TdT was undetectable. Purine nucleoside phosphorylase (PNP) and ecto-5'nucleotidase (5'NT) were lowest in cortical thymocytes (27.5 +/- 11.0 nmol/hr/10(6) cells and 2.8 +/- 1.3 nmol/hr/10(6) cells, respectively) and increased with T cell maturation. The PNP level was 124.9 +/- 17.2 nmol/hr/10(6) cells and 5'NT was 30.1 +/- 3.9 nmol/hr/10(6) cells in peripheral T lymphocytes. The deoxynucleoside kinases (deoxyguanosine, deoxyadenosine, and deoxycytidine kinases) paralleled the changes in ADA and TdT activity among the different T subsets. The proliferative activity (labeling index) was highest in the prothymocyte fraction and lowest in peripheral T cells. Variation in the distribution of these enzymes in T cell subsets may explain their different sensitivities to deoxyadenosine and deoxyguanosine toxicity and the different effects on T cell development of ADA or PNP deficiency.     

Phorbol ester induction of rat hepatic metallothionein in vivo and in vitro.

1. The induction of metallothionein (MT) protein by TPA (O-tetradecanoyl phorbol acetate), a protein kinase C activator, was demonstrated in vivo in rat liver and in vitro in rat hepatocytes in primary culture. In vivo half maximal induction at 25 hr was seen at 26 nmol TPA/kg body wt. Five- to seven-fold inductions were seen in vivo. De novo protein synthesis was required for this induction as demonstrated by cycloheximide inhibition of [35S]cysteine incorporation into MT protein. 2. TPA induction of MT protein in primary cultures of rat hepatocytes reached levels of 2.6-4.1-fold, as assessed by [35S]cysteine incorporation, 1.34-2.20-fold, as assessed by 109Cd binding in a metal displacement/HPLC assay, and 2.5-5-fold, as assessed by 109Cd binding in a metal displacement/Sephadex G-75 Superfine assay. 3. The induction of MT mRNA by TPA was demonstrated in vivo in rat liver and in vitro in 2 rat hepatoma cell lines, EC3 and 2M. MT mRNA was quantitated using dot blot and Northern gel assays. In vivo TPA induced hepatic MT mRNA 2.36-5.88-fold (dot blot) and 7.4-22-fold (Northern gels). In vitro TPA induced MT mRNA 1.71-15.26-fold in EC3 cells and 2.23-8.43-fold in 2M cells. MT mRNA was 0.54 kb, and alpha-tubulin mRNA was 1.62 kb in size on Northern gels. 4. TPA induction of MT protein and mRNA in vivo and in vitro is rapid and persistent and occurs at low concentrations. The 2 rat hepatoma cell lines provide a useful system in which to study MT induction in vitro without confounding secondary effects which can occur in vivo.     

Prostaglandin synthesizing enzyme activities of hepatocytes and non-hepatocytes in rat liver as a function of age

The developmental profile of prostaglandin (PG)-synthesizing enzymes in liver was investigated in rats from the fetus to 2 years old. In the neonatal period, the activities of PGD2-(2.7 nmol/min/mg protein) and PGE2-(2.2 nmol/min/mg protein) synthesizing enzymes were predominant, whereas PGE2-synthesizing enzyme alone further increased in activity during adult to old ages (5.2-6.1 nmol/min/mg protein). In order to determine the sites of PGs production in rat liver, we prepared hepatocytes and non-hepatocytes by a collagenase digestion method. Regardless of the ages we examined, the major PG produced in the hepatocytes was proved to be PGE2, on the other hand, PGD2 was almost exclusively produced in the non-hepatocytes. These results suggest that each PG may have individual roles in the development of rat liver.