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At least 19 recordsLinked to original sources
PubMed1990

Thymidine uptake, thymidine incorporation, and thymidine kinase activity in marine bacterium isolates.

One assumption made in bacterial production estimates from [3H]thymidine incorporation is that all heterotrophic bacteria can incorporate exogenous thymidine into DNA. Heterotrophic marine bacterium isolates from Tampa Bay, Fla., Chesapeake Bay, Md., and a coral surface microlayer were examined for thymidine uptake (transport), thymidine incorporation, the presence of thymidine kinase genes, and thymidine kinase enzyme activity. Of the 41 isolates tested, 37 were capable of thymidine incorporation into DNA. The four organisms that could not incorporate thymidine also transported thymidine poorly and lacked thymidine kinase activity. Attempts to detect thymidine kinase genes in the marine isolates by molecular probing with gene probes made from Escherichia coli and herpes simplex virus thymidine kinase genes proved unsuccessful. To determine if the inability to incorporate thymidine was due to the lack of thymidine kinase, one organism, Vibrio sp. strain D19, was transformed with a plasmid (pGQ3) that contained an E. coli thymidine kinase gene. Although enzyme assays indicated high levels of thymidine kinase activity in transformants, these cells still failed to incorporate exogenous thymidine into DNA or to transport thymidine into the cells. These results indicate that the inability of certain marine bacteria to incorporate thymidine may not be solely due to the lack of thymidine kinase activity but may also be due to the absence of thymidine transport systems.

Autoradiography↗
PubMed1979

Design of species- or isozyme-specific enzyme inhibitors. 1. Effect of thymidine substituents on affinity for the thymidine site of hamster cytoplasmic thymidine kinase.

5-(Ethylamino)- and 5-acetamido-2'-deoxyuridine 5'-triphosphates were synthesized; the extent and concentration dependence of their inhibitory action on the title enzyme resembled that of the feedback inhibitor TTP. This and other findings provide a tentative indication that bulk tolerance near C-5 of the thymine ring may be more extensive at the TTP site than at the thymidine site. Enzyme-inhibitor dissociation constants (Ki values) were determined for thymidine derivatives monosubstituted at various positions. Competitive inhibition with respect to thymidine (indicative of substituent tolerance in the enzyme-thymidine complex) was produced by 3-amylthymidine (Ki = 65 muM), trans-5-bromo-6-ethoxy-5,6-dihydrothymidine diastereoisomers (Ki = 180 and 310 muM), 5'-C-(acetamidomethyl)- and 5-C-(propionamidomethyl)thymidine epimers (Ki range 65--1100 muM), 3'-acetamido- and 3'-(ethylthio)-3'-deoxythymidines (Ki = 2.5 mM and 12 muM, respectively), and certain 5'-(alkylamino)- and 5'-(alkylthio)-5'-deoxythymidines (Ki range 180--1200 muM). Evidence indicates that bulk tolerance at some, if not most, of the above atoms of thymidine is found in the enzyme-thymidine complexes of human and other mammalian thymidine kinases; attachment of suitable substituents to such atoms could, in principle, lead to thymidine site directed isozyme-specific inhibitors of human cytoplasmic thymidine kinase, which is a candidate target in the design of antineoplastic drugs.

Animals↗
PubMed1989

Enzyme regulatory site-directed drugs: study of the interactions of 5'-amino-2', 5'-dideoxythymidine (5'-AdThd) and thymidine triphosphate with thymidine kinase and the relationship to the stimulation of thymidine uptake by 5'-AdThd in 647V cells.

5'-Amino-2',5'-dideoxythymidine (5'-AdThd) is a nontoxic thymidine (dThd) analogue capable of antagonizing the feedback inhibition exerted by thymidine triphosphate (dTTP) on thymidine kinase (EC 2.7.1.21). In intact cells, this results in stimulation of thymidine uptake by 5'-AdThd. We have studied the interaction between 5'-AdThd and thymidine kinase purified from 647V cells. We found that 5'-AdThd inhibited competitively thymidine kinase activity (Ki of 0.5 microM) in the absence of dTTP whereas dTTP inhibited thymidine kinase activity in a noncompetitive manner. However, in the presence of dTTP, 5'-AdThd was able to stimulate enzyme activity in a mode that suggests competition with dTTP for the regulatory site. Altered interactions were observed at high substrate (dThd) concentrations, with dThd showing competitive kinetics with dTTP. In intact cells, we evaluated the hypothesis that antagonism of feedback inhibition could account for stimulation of dThd uptake by 5'-AdThd. If inhibition of thymidine kinase activity by dTTP is critical, then depletion of cellular dTTP by methotrexate should reduce the ability of 5'-AdThd to stimulate dThd uptake. Indeed, this was the case. If the dTTP pools were repleted by the addition of higher concentrations of dThd, the ability of 5'-AdThd to stimulate dThd uptake was restored. Furthermore, effects of 5'-AdThd on nucleoside phosphorylase or cytoplasmic 5'-nucleotidase activity (dTMP breakdown) could not account for the stimulation of dThd uptake in 647V cells. In summary, our results indicate that 5'-AdThd interacts with thymidine kinase at the dTTP-binding site, resulting in stimulation of enzyme activity and stimulation of dThd uptake in intact cells.

5'-Nucleotidase↗
PubMed1976

Utilization of exogenous thymidine by Chlamydia psittaci growing in the thymidine kinase-containing and thymidine kinase-deficient L cells.

The incorporation of [3H]thymidine into the deoxyribonucleic acid (DNA) of Chlamydia psittaci (strain 6BC) growing in thymidine kinase (adenosine 5'-triphosphate-thymidine 5'-phosphotransferase, EC 1.7.1.21)-containing L cells, L(TK+), and thymidine kinase-deficient L cells, LM(TK-), was examined by autoradiography. Label was detected over C. psittaci inclusions in L(TK+) but not LM(TK-) cells. No evidence for a chlamydia-specific thymidine kinase activity in either L(TK+) or LM(TK-) cells was obtained. Entry of [3H]thymidine into the DNA of C. psittaci growing in L(TK+) cells was quantitated by measuring label in purified C. psittaci. It was 265 times less efficient than entry into infected host cell DNA. It is concluded that low levels of exogenous thymidine are incorporated into the DNA of C. psittaci and that this incorporation is dependent on a fully competent host thymidine kinase activity. Evidence also is presented that L cells possess at least two thymidine kinase activities, both of which are capable of supplying thymidylate precursors for nuclear DNA synthesis.

Animals↗
PubMed1980

Effect of thymidine auxotrophy, thymidine starvation and nalidixic acid inhibition on the properties of DNA labelled by a pulse of [3H]thymidine in Staphylococcus aureus.

The labelling of DNA by pulse/chase experiments in Staphylococcus aureus has been investigated, analysing the products by alkaline sucrose velocity centrifugation. In S. aureus NCTC 8325 a short (60 s) pulse of [3H]thymidine labels both small (10 to 20 S) fragments and DNA that co-sediments with long-term label. In a thymidine-requiring derivative, 8325thy, most pulse label is incorporated into small fragments. In both bacterial strains small fragments can be chased into high molecular weight DNA. Thymidine starvation of 8325thy prior to pulse labelling results in smaller fragments (4 to 10S) being labelled. In a subsequent chase with unlabelled thymidine this label is incorporated into high molecular weight DNA, although more slowly than in the absence of thymidine starvation. The fact that nalidixic acid, an antibiotic which specifically inhibits DNA replication in S. aureus, does not inhibit the [3H]thymidine incorporation immediately after thymidine starvation and that nalidixic acid shows down the increase in size of pulse-labelled fragments through inhibition of DNA synthesis suggests that thymidine starvation results in changes at the replication fork. The possible nature of these changes is discussed. It is proposed that one of the results of thymidine starvation is to cause a long-lived gap between DNA synthesized before starvation and DNA synthesized after starvation.

Centrifugation, Density Gradient↗
PubMed1983

Nucleotide sequence of the herpes simplex virus type 2 (HSV-2) thymidine kinase gene and predicted amino acid sequence of thymidine kinase polypeptide and its comparison with the HSV-1 thymidine kinase gene.

To analyze the boundaries of the functional coding region of the HSV-2(333) thymidine kinase gene (TK gene), deletion mutants of hybrid plasmid pMAR401 H2G, which contains the 17.5 kbp BglII-G fragment of HSV-2 DNA, were prepared and tested for capacity to transform LM(TK-) cells to the thymidine kinase-positive phenotype. These studies showed that hybrid plasmids containing 2.2-2.4 kbp subfragments of HSV-2 BglII-G DNA transformed LM(TK-) cells to the thymidine kinase-positive phenotype and suggested that the region critical for transformation might be less than 2 kbp. That the activity expressed in the transformants was HSV-2 thymidine kinase was shown by experiments with type-specific enzyme-inhibiting rabbit antisera and by disc-polyacrylamide gel electrophoresis analyses. DNA fragments of the HSV-2 TK gene were subcloned in phage M13mp9 and M13mp8. A sequence of 1656 bp containing the entire coding region of the TK gene and the flanking sequences was determined by the dideoxynucleotide chain termination method. Comparisons with the HSV-1(Cl 101) TK gene revealed that PstI, PvuII, and EcoRI cleavage sites had homologous locations as did promoter, translational start and stop, and polyadenylation signals. Extensive homology was observed in the nucleotide sequence preceding the ATG translational start signal and in portions of the coding region of the genes. Comparisons of the predicted amino acid sequences of the HSV-1 and HSV-2 thymidine kinase polypeptides revealed that both were enriched in alanine, arginine, glycine, leucine, and proline residues and that clear, but interrupted homology existed within several regions of the polypeptide chains. Stretches of 15-30 amino acid residues were identical in conserved regions. The possibility is suggested that domains containing some of the conserved amino acid sequences might have a role in substrate binding and as major antigenic determinants.

Amino Acid Sequence↗
PubMed1983

Thymidine plaque autoradiography of thymidine kinase-positive and thymidine kinase-negative herpesviruses.

Plaques formed by herpes simplex virus (HSV), pseudorabies virus, and varicella-zoster virus were studied by plaque autoradiography after [14C]thymidine labeling. Standard thymidine kinase-positive (TK+) viruses and TK- mutants of HSV types 1 and 2 and pseudorabies virus were studied, including cell cultured viruses and viruses isolated from animals. Autoradiography was performed with X-ray film with an exposure time of 5 days. After development of films, TK+ plaques showed dark rims due to isotope incorporation, whereas TK- plaques were minimally labeled. Plaque autoradiography of stock TK- viruses showed reversion frequencies to the TK+ phenotype of less than 10(-3). Autoradiography indicated that TK- virus retained the TK- phenotype after replication in vivo. In addition, it was shown that TK- HSV could be isolated from mouse trigeminal ganglion tissue after corneal inoculation of TK- HSV together with TK+ HSV. The plaque autoradiographic procedure was very useful to evaluate proportions of TK+ and TK- virus present in TK+-TK- virus mixtures.

Animals↗
PubMed2001

Altered thymidine metabolism due to defects of thymidine phosphorylase.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive human disease due to mutations in the thymidine phosphorylase (TP) gene. TP enzyme catalyzes the reversible phosphorolysis of thymidine to thymine and 2-deoxy-D-ribose 1-phosphate. We present evidence that thymidine metabolism is altered in MNGIE. TP activities in buffy coats were reduced drastically in all 27 MNGIE patients compared with 19 controls. All MNGIE patients had much higher plasma levels of thymidine than normal individuals and asymptomatic TP mutation carriers. In two patients, the renal clearance of thymidine was approximately 20% that of creatinine, and because hemodialysis demonstrated that thymidine is ultrafiltratable, most of the filtered thymidine is likely to be reabsorbed by the kidney. In vitro, fibroblasts from controls catabolized thymidine in medium; by contrast, MNGIE fibroblasts released thymidine. In MNGIE, severe impairment of TP enzyme activity leads to increased plasma thymidine. In patients who are suspected of having MNGIE, determination of TP activity in buffy coats and thymidine levels in plasma are diagnostic. We hypothesize that excess thymidine alters mitochondrial nucleoside and nucleotide pools leading to impaired mitochondrial DNA replication, repair, or both. Therapies to reduce thymidine levels may be beneficial to MNGIE patients.

Cells, Cultured↗
PubMed1967

Thymidine and thymine incorporation into deoxyribonucleic acid: inhibition and repression by uridine of thymidine phosphorylase of Escherichia coli.

Thymidine is poorly incorporated into deoxyribonucleic acid (DNA) of Escherichia coli. Its incorporation is greatly increased by uridine, which acts in two ways. Primarily, uridine competitively inhibits thymidine phosphorylase (E.C.2.4.4), and thereby prevents the degradation of thymidine to thymine which is not incorporated into normally growing E. coli. Uridine also inhibits induction of the enzyme by thymidine. It prevents the actual inducer, probably a deoxyribose phosphate, from being formed rather than competing for a site on the repressor. The inhibition of thymidine phosphorylase by uridine also accounts for inhibition by uracil compounds of thymine incorporation into thymine-requiring mutants. Deoxyadenosine also increases the incorporation of thymidine, by competitively inhibiting thymidine phosphorylase. Deoxyadenosine induces the enzyme, in contrast to uridine. But this is offset by a transfer of deoxyribose from deoxyadenosine to thymine. Thus, deoxyadenosine permits incorporation of thymine into DNA, even in cells induced for thymidine phosphorylase. This incorporation of thymine in the presence of deoxyadenosine did not occur in a thymidine phosphorylase-negative mutant; thus, the utilization of thymine seems to proceed by way of thymidine phosphorylase, followed by thymidine kinase. These results are consistent with the data of others in suggesting that wild-type E. coli cells fail to utilize thymine because they lack a pool of deoxyribose phosphates, the latter being necessary for conversion of thymine to thymidine by thymidine phosphorylase.

DNA, Bacterial↗
PubMed1977

[Incorporation of thymidine into the DNA of actinomycetes. I. Incorporation of exogenous thymidine into the DNA of Thermoactinomyces vulgaris].

The incorporation of exogenous thymidine and thymine into acid-insoluble material of Thermoactinomyces vulgaris has been studied during germination and subsequent growth. Thymine is not incorporated. The incorporation of thymidine stops after a short time due to the rapid breakdown of thymidine to thymine and deoxyribose-1-phosphate by the inducible thymidine phosphorylase. Deoxyadenosine enhances the incorporation of thymidine as well as of thymine and prolongs the tine of uptake. Uridine stimulates only the incorporation of thymidine but not of thymine. These effects can be explained by the function of these substances within the salvage pathway. Deoxyadenosine acts as donor of deoxyribosyl groups being necessary for the conversion of thymine to thymidine by thymidine phosphorylase and uridine inhibits thymidine phosphorylase, and thereby it prevents the degradation of thymidine to thymine. Thymidine is incorporated into alkali-, RNase-and protease-stable, hot TCA-soluble and DNase-sensitive material. That means that the cellular DNA of T. vulgaris can be specifically labelled by radioactive thymidine in the presence of deoxyadenosine and uridine, respectively.

DNA, Bacterial↗
PubMed1985

Thymidine salvage in Pseudomonas stutzeri and Pseudomonas aeruginosa provided by heterologous expression of Escherichia coli thymidine kinase gene.

Unlike enteric bacteria, Pseudomonas spp. generally lack thymidine phosphorylase and thymidine kinase activities, thus preventing their utilization of exogenous thymine or thymidine and precluding specific radioactive labeling of their DNA in vivo. To overcome this limitation, a DNA fragment encoding thymidine kinase (EC 2.7.1.21) from Escherichia coli was cloned into pKT230, a small, broad-host-range plasmid derived from plasmid RSF1010. From transformed E. coli colonies, the recombinant plasmid bearing the thymidine kinase gene was conjugally transferred to Pseudomonas stutzeri, Pseudomonas aeruginosa, Pseudomonas mendocina, Pseudomonas alcaligenes, and Pseudomonas pseudoalcaligenes. Thymidine kinase activity was expressed in all of these species, and all gained the ability to incorporate exogenous [2-14C]thymidine into their DNA. Thymidine incorporation into P. stutzeri was enhanced 12-fold more in mutants lacking thymidylate synthetase activity. These mutants produced higher levels of thymidine kinase and were thymidine auxotrophs; thymineless death resulted from removal of thymidine from a growing culture.

DNA Replication↗
PubMed1977

Recovery of Pisum root meristems after mitotic-inhibitory treatments with 3H-thymidine. Inhibition of cell-cycle progression by unincorporated 3H-thymidine.

Primary root meristems of Pisum sativum recover form a 3H-thymidine-induced reduction in mitotic activity once the roots are no longer exposed to exogenous 3H-thymidine. Cells arrested in G2 during 3H-thymidine treatment apparently do not divide for at least 16 hours after treatment, whereas cells remaining in G1 and S do divide and thereby account for recovery. Recovery occurs only when meristems are no longer exposed to exogenous (i.e. unincorporated) 3H-thymidine, suggesting that cytoplasmic irradiation from unincorporated 3H-thymidine prevents cellular recovery from 3H-thymidine-induced inhibition of cell progression through the mitotic cycle. Concentrations of 14C-thymidine which result in cytoplasmic irradiation nearly equivalent to that achieved with 3H-thymidine, but much lower levels of nuclear irradiation, also prevent recovery from 3H-thymidine-induced inhibition of mitotic activity, but do not alone produced such inhibition. These results support the contention that cytoplasmic irradiation prevents recovery from the effects of nuclear irradiation. Unincorporated 3H-thymidine also prevents recovery from sucrose deprivation in stationary phase G2 cells which have not incorporated 3H-thymidine into nuclear DNA.

Mitosis↗
PubMed1991

Independent characterization of thymidine transport and subsequent metabolism in Hymenolepis diminuta--II. Purification and preliminary analysis of thymidine kinase.

1. An affinity column for the purification of thymidine kinase (TK) from the cestode Hymenolepis diminuta is described. Using an epoxy-activated Sepharose 6B affinity column containing thymidine as a ligand, a 698-fold purification of thymidine kinase was obtained. 2. Thymidine kinase eluted from this affinity column was partially characterized as having an apparent Km value of 3.94 microM thymidine. This value is very similar to those observed in mammalian systems. 3. Thymidine kinase appears to be an extremely active and ubiquitous enzyme, whose primary function is to rapidly phosphorylate incoming thymidine and thus "trap" it for the cell's use, reducing efflux to a minimum. 4. The apparent Km for TK is two orders of magnitude lower than the Kt for thymidine transport. Thus, theories postulating that long-term (2 min) uptake kinetics for thymidine actually represent subsequent metabolism must look further along the thymidine phosphorylating pathway, beyond TK and its very active role.

Ammonium Sulfate↗
PubMed2002

Synthesis of a small library of 3-(carboranylalkyl)thymidines and their biological evaluation as substrates for human thymidine kinases 1 and 2.

A small library consisting of two series of thymidine derivatives containing o-carboranylalkyl groups at the N-3 position was prepared. In both series, alkyl spacers of 2-7 methylene units were placed between the o-carborane cage and the thymidine scaffold. In one series, an additional dihydroxypropyl substituent was introduced at the second carbon atom of the carborane cage. In the series of N-3-substituted carboranyl thymidines without additional dihydroxypropyl substituent, three steps were required to obtain the target compounds in overall yields as high as 75%, while in the series of N-3-substituted carboranyl thymidines with additional dihydroxypropyl substituent, 9-10 steps were necessary with significantly lower overall yield. All target compounds were good substrates of human cytosolic thymidine kinase 1 while they were, if at all, poor substrates of the mitochondrial thymidine kinase 2. There was only a minor difference in phosphorylation rates between N-3-substituted carboranyl thymidines with additional dihydroxypropyl substituents with thymidine kinase 1 (range: 13-49% relative to thymidine) and their counterparts lacking this group (range: 11-57% relative to thymidine). Tether lengths of two and five methylene groups in both series gave the highest enzyme activities in the present study. A hypothesis for this result is presented.

Boron Compounds↗
PubMed1975

Purification of thymidine phosphorylase from Escherichia coli and its photoinactivation in the presence of thymine, thymidine, and some halogenated analogs.

Isoelectric focusing was used as the final step in the isolation of thymidine phosphorylase which was found to have an isoelectric point of 4.1. Analytical acrylamide gel electrophoresis showed the purified enzyme preparation contained one major protein band which stained for thymidine phosphorylase activity and usually a minor, faster migrating band devoid of activity. Inactivation of thymidine phosphorylase alone or in the presence of sensitizers by ultraviolet light, primarily at 253.7 nm, followed first order inactivation kinetics. The rate of inactivation of the enzyme was the same at pH 5 and 7.4 and the addition of various pyrimidine bases and nucleosides enhanced the inactivation rate at both pH values, but to a greater extent at pH 5. Linear plots of inactivation rates versus concentrations of thymidine or thymine were the same. At 7.8 mM thymidine or thymine, 11- and 4.4-fold increases in photoinactivation of thymidine phosphorylase were observed at pH 5 AND 7.4 RESPECTIVELY. Parabolic curves were obtained with increasing concentrations of either 5-iodo-2'-deoxyuridine or 5-iodouracil. 5-Iodouracil at 5.2 mM caused 212- (pH 5) and 100- (pH 7.4) FOLD INCREASES IN THE RATES OF PHOTOINACTIVATION OF THYMIDINE PHOSPHORYLASE. However, 5-iodo-2'-deoxyuridine at 5.0mM only enhanced the photoinactivation of enzyme by factors of 83 (pH 5) and 21 (pH 7.4). Neither 5-bromo-2'-deoxyuridine or 5-bromo-uracil was as potent in sensitizing the enzyme as the iodo analogs. Combinations of 5-iodouracil or 5-iodo-2'-deoxyuridine with thymine resulted in higher inactivation rates than the additive inactivation rates of individual compounds, whereas combinations of either iodo analog with thymidine resulted in lower inactivation rates. Increasing concentrations of phosphate or NaCl lessened the photoinactivation rate of thymidine phosphorylase alone and protected the enzyme from the sensitization caused by the different bases and nucleosides. No quantitative changes in the number of primary amino groups in thymidine phosphorylase was evident as a result of irradiation in the presence or absence of 5-iodouracil or 5-iodo-2'-deoxyuridine. Examination of the irradiated enzyme on Sephadex G-150 indicated that a larger protein species is formed and that 5-iodouracil promotes this process.

Bromodeoxyuridine↗
PubMed1984

Interferon inhibition of thymidine incorporation into DNA through effects on thymidine transport and uptake.

Replenishment of medium after 72 hr of growth of HeLa-S3 cells in dense suspension cultures increased [3H]-thymidine uptake into cells and incorporation into DNA, with the levels reaching a peak approximately 12 hr following medium change; beta interferon inhibits the enhanced uptake of [3H]-thymidine and labeling of DNA in a dose-dependent manner. Some reduction in these processes is observed at a concentration as low as 1 u/ml, and approximately 75% inhibition at 640 u/ml. Kinetic analysis has revealed that the rate of labeling of the acid-soluble pool with [3H]-thymidine, measured either at 22 degrees C or 37 degrees C, is reduced in interferon-treated (640 u/ml, 24 hr) HeLa-S3 cells. At 22 degrees C, the initial rate of thymidine transport at a high (500 microM) thymidine concentration, determined within the first 30 sec of [3H]-thymidine addition was depressed by 44% in interferon-treated HeLa cells. At 37 degrees C, labeled precursors accumulate in acid-soluble material for approximately 8 min after the addition of [3H]-thymidine, after which an apparent equilibrium level is attained. At this temperature, the rate of thymidine uptake and the apparent equilibrium level attained were depressed by 70% in interferon-treated HeLa cells. The reduced incorporation of [3H]-thymidine into DNA in interferon-treated HeLa-S3 cells can be largely explained by interferon inhibition of thymidine transport and phosphorylation.

Biological Transport↗
PubMed1999

[3H]thymidine incorporation into whole liver as an alternative to [3H]thymidine incorporation into DNA as a parameter of cell proliferation in regenerating liver tissue in rats.

OBJECTIVE: To monitor liver regeneration following partial hepatectomy, liver cell proliferation can be measured by assaying in vivo [3H]thymidine incorporation into liver cell DNA. We hypothesized that [3H]thymidine incorporation into whole liver tissue parallels [3H]thymidine incorporation into liver cell DNA, both in high proliferating and low proliferating liver. STUDY DESIGN: Liver cell proliferation in rats after partial hepatectomy or a sham operation was studied by measuring incorporation of [3H]thymidine into various fractions of liver tissue on days 1, 2, 3, 4 and 10 after surgery. RESULTS: [3H]thymidine incorporation into whole liver tissue and in the protein fraction correlated well with DNA-specific [3H]thymidine incorporation into regenerating (r > .80, P < .0001) and nonregenerating liver (r > .69, P < .005). [3H]thymidine incorporation into DNA was < 5% of the total amount of administered [3H]thymidine in both sham-operated and hepatectomized rats. Significant differences in [3H]thymidine incorporation into partially hepatectomized livers as compared to sham-operated rat livers were found on days 1 and 2 (whole liver tissue and protein fraction) or day 1 (DNA) after surgery. CONCLUSION: [3H]thymidine incorporation into whole liver tissue is a simple technique that can be used for the study of liver cell proliferation after partial hepatectomy in rats.

Animals↗