Catechins inhibit angiotensin II-induced vascular smooth muscle cell proliferation via mitogen-activated protein kinase pathway

Catechins, components of green tea, reduce the incidence of cardiovascular diseases such as atherosclerosis. Angiotensin II (Ang II) is highly implicated in the proliferation of vascular smooth muscle cells (VSMC), resulting in atherosclerosis. The acting mechanisms of the catechins remain to be defined in the proliferation of VSMC induced by Ang II. Here we report that catechin, epicatechin (EC), epicatechingallate (ECG) or epigallocatechingallate (EGCG) significantly inhibits the Ang II-induced [3H]thymidine incorporation into the primary cultured rat aortic VSMC. Ang II increases the phosphorylation of the extracellular signal-regulated protein kinase 1/2 (ERK 1/2), c-jun-N-terminal kinase 1/2 (JNK 1/2), or p38 mitogen-activated protein kinases (MAPKs) and mRNA expression of c-jun and c-fos. The EGCG pretreatment inhibits the Ang II-induced phosphorylation of ERK 1/2, JNK 1/2, or p38 MAPK, and the expression of c-jun or c-fos mRNA. U0126, a MEK inhibitor, SP600125, a JNK inhibitor, or SB203580, a p38 inhibitor, attenuates the Ang II-induced [3H]thymidine incorporation into the VSMC. In conclusion, catechins inhibit the Ang II-stimulated VSMC proliferation via the inhibition of the Ang II-stimulated activation of MAPK and activator protein-1 signaling pathways. The antiproliferative effect of catechins may be associated with the reduced risk of cardiovascular diseases by the intake of green tea. Catechins may be useful in the development of prevention and therapeutics of vascular diseases.

Inhibition of cutaneous oxidative stress and two-stage skin carcinogenesis by Hemidesmus indicus (L.) in Swiss albino mice.

Chemopreventive potential of H. indicus on 7,12-dimethyl-benz[a]anthracene (DMBA)-initiated and 12-O-tetradecanoyl 13-phorbol acetate (TPA) promoted murine skin carcinogenesis has been assessed. Topical application of H. indicus resulted in significant protection against cutaneous tumorigenesis. Topical application of plant extract prior to that of TPA resulted in significant inhibition against TPA-caused induction of epidermal ornithine decarboxylase (ODC) activity and DNA synthesis. Application of H. indicus at a dose level of 1.5 and 3.0 mg/kg body weight in acetone prior to that of TPA treatment resulted in significant inhibition of oxidative stress. The level of lipid peroxidation was significantly reduced. In addition, depleted levels of glutathione and reduced activities of antioxidant enzymes were restored respectively). The results indicate that H. indicus is a potent chemopreventive agent in skin carcinogenesis.

Macromolecular synthesis in wing discs of Spodoptera mauritia Boisd: effects of a juvenile hormone analogue.

Last instar larvae of S. mauritia treated topically on day 0, day 1, day 2 and day 3 with a daily (dose of 25 microg juvenile hormone analogue (JHA) moulted into supernumerary larvae. The imaginal discs of the supernumerary larvae especially those of mouthparts and thoracic appendages showed pupal characteristics. However the wing discs, which showed only partial differentiation, were uneverted and highly tanned. In an effort to provide an explanation to this anomaly the RNA, DNA and protein profile in the wing discs of supernumerary larvae were studied. Quantitative analysis of DNA, RNA and protein showed a considerable increase in the amount of DNA and protein and a decline in RNA level. SDS-PAGE analysis of wing disc proteins of JHA treated larvae showed a reduction in the expression of many major proteins that were predominant in the wing discs of control larvae. The results suggest that JHA induced inactivation of genes involved in the synthesis of proteins needed for evagination process may be responsible for the formation of uneverted, partially differentiated pupal wing discs in supernumerary larvae.

DNA synthesis in the imaginal wing discs of the American bollworm Helicoverpa armigera (Hübner).

The effect of two insect growth regulators of plant origin viz. plumbagin and azadirachtin and the ecdysteroids 20-hydroxyecdysone, makisterone A and a phytoecdysteroid on DNA synthesis in imaginal wing discs of day 4 final instar Helicoverpa armigera larvae was studied. DNA synthesis increased with increase in time of incubation up to 8 h and decreased later without the addition of moulting hormone. Addition of 20-hydroxyecdysone supported long term acquisition of competence for DNA synthesis in the wing discs. Both DNA synthesis and protein content were drastically reduced in plumbagin and azadirachtin-treated insects. Under in vitro conditions, plumbagin had a more pronounced inhibitory effect than azadirachtin. All the ecdysteroids tested, viz. makisterone A, 20-hydroxyecdysone and the ecdysteroidal fraction from the silver fern Cheilanthes farinosa enhanced DNA synthesis.

Peptídeos mitogênicos ou inibidores da atividade do Fator de Crescimento de Fibroblastos-1 humano baseados no complexo FGF/receptor/heparina / Mitogenic peptides or inhibitors of the human Fibroblast Growth Factor-1 activity based on the complex FGF/receptor/heparin

Os Fatores de Crescimento de Fibroblastos (®Fibroblast Growth Factors¼; FGFs) participam de fenômenos biológicos de grande importância, tais como migração, divisão e diferenciação celulares. O presente trabalho teve como objetivo central a busca de compostos biologicamente ativos através de um desenho racional de peptídeos derivados do FGF-1 e do seu receptor (FGFR-1). A partir da análise dos dados disponíveis na literatura, aliada a técnicas de modelagem molecular, foram desenhados, sintetizados e testados dois grupos de peptídeos. O primeiro conjunto (R1 - R3) é constituído por peptídeos lineares derivados do FGFR-1. Os ensaios de atividade mitogênica dos FGFs 1 e 2 em presença dos peptídeos mostram que R1 e R2 foram capazes de inibir a ação mitogênica do FGF-1...

TGF-betas Synthesized by RPE Cells Have Autocrine Activity on Mesenchymal Transformation and Cell Proliferation

The present study investigated the effects of transforming growth factor (TGF)-beta on retinal pigment epithelial (RPE) transformation in a simplified model and also whether or not TGF-beta exhibits similar proliferation effects on transformed RPE cells that it has on primary RPE cells. Furthermore, we examined the cell proliferation effects of RPE-conditioned medium (CM). A vertical wound measuring 2 mm in diameter was made on primary RPE monolayers. The expression of alpha- smooth muscle actin (SMA) by the cells located at the wound edges was observed using a confocal microscope under immunofluorescent staining. Cell proliferation was measured by incorporating 3H-thymidine into DNA. The presence of alpha- SMA was observed in the cells within the wound after treatment with TGF-beta2, while negative expression was observed in control cells. TGF-betas inhibited the proliferation of the primary cultures of RPE cells in a dose-dependent manner, but the spindle-shaped late-passaged RPE cells were not inhibited by these growth factors. The medium conditioned by RPE cells stimulated the proliferation of subconjunctival fibroblasts and inhibited the proliferation of primary RPE cells, in a manner similar to TGF-beta. These findings demonstrate that TGF-beta-stimulated RPE cells may evoke proliferative vitreoretinopathy through mesenchymal transformation and cell proliferation.

Effect of Centrifugal Force on Cellular Activity of Osteoblastic MC3T3-E1 Cells in vitro

The effects of centrifugal force on growth and differentiation of osteoblastic cells cultured in alpha-MEM containing 1% Fetal bovine serum were investigated by assays of DNA synthesis, alkaline phosphatase activity and osteocalcin- production in osteoblastic MC3T3-E1 cells. Centrifugation of the cells in low concentrations (1%) of fetal bovine serum caused a 1.9-fold increase of [3H] thymidine incorporation on day 3 from the start of centrifugation, and gradually decreased with culture up to day 9. Alkaline phosphatase activity was not affected by centrifugal force until day 5, and increased rapidly after day 7. Stimulation of DNA synthesis by centrifugation was abolished in the presence of H-7, an inhibitor of protein kinase C. These results suggest that centrifugal force stimulates the proliferation of osteoblastic cells through an autocrine secretion of some diffusable growth- promoting activity. Additional centrifugation of the cells also slightly stimulated alkaline phosphatase activity, although this did not directly influence the cell's osteocalcin-production activity.

The effective concentration and exposure time of mitomycin-C for the inhibition of lens epithelial cell proliferation in rabbit eyes

The proliferation of residual lens epithelial cells following cataract surgery is assumed to be a major cause of posterior capsular opacification. To assess the efficacy of mitomycin-C in preventing posterior capsular opacification, we determined the effective concentration and exposure time of mitomycin-C in inhibiting rabbit lens epithelial cell proliferation. The fourth-passaged rabbit lens epithelial cells were maintained for one day and then exposed to mitomycin-C for 1, 2, 3, and 5 minutes, respectively. There were 9 different plating concentrations of mitomycin-C with two-fold serial dilution. The maintenance of the phenotypic properties of lens epithelial cells was confirmed by continuous transcription of lambda-crystalline mRNA determined by reverse transcription-polymerase chain reaction and the polymorphism of the restriction fragment. Cell proliferation was assayed with 3H-thymidine incorporation into DNA. The fourth-passaged cells maintained the expression of lambda-crystalline mRNA, suggesting that they are phenotypically authentic lens epithelial cells. The effective concentrations and exposure time of mitomycin-C were 0.1 mg/ml for 1 minute and 2 minutes, and 0.025 mg/ml for 2 minutes. By these results, we postulated that mitomycin-C at relatively short incubation times could be clinically used for prevention of posterior capsular opacification after cataract surgery.

Angiotensin II stimulates proliferation of adventitial fibroblasts cultured from rat aortic explants

It has been proposed that the local renin-angiotensin system is activated in the adventitia after vascular injury. However, the physiological role of Angiotensin II (Ang II) in the adventitia has not been studied at a cellular level. This study was designed to assess the role of Ang II in the growth response of cultured adventitial fibroblasts (AFs). Adventitial explants of the rat thoracic aorta showed outgrowth of AFs within 5-7 days. Ang II caused hyperplastic response of AF cultures. The Ang II-induced mitogenic response of AFs was mediated primarily by the AT1 receptor. Ang II caused a rapid induction of immediate early genes (c-fos, c-myc and jun B). Induction of c-fos expression was fully blocked by an AT1 receptor antagonist but not by an AT2 receptor antagonist. Epidermal growth factor (EGF), platelet-derived growth factor-BB (PDGF-BB) and basic fibroblast growth factor (bFGF) induced DNA synthesis in AFs. Co-stimulation of AFs with the growth factors and Ang II potentiated the incorporation of 3H-thymidine into DNA. Results from this study indicate that Ang II causes mitogenesis of AFs via AT1 receptor stimulation and potentiates the responses to other mitogens. These data suggest that the Ang II may play an important role in regulating AF function during vascular remodeling following arterial injury.

La vitamina D induce la proliferación de células en cultivo del endometrio de rata / Vitamin D induces proliferation in rat endometrium cultured cells

Objetivo. Estudiar el efecto de 1,25-dihydroxycholecalciferol D(1,25-(OH)2D3 sobre la proliferación y muerte de las células de endometrio de la rata en cultivo. Material y métodos. Se usó la línea celular de endometrio de rata Rentro 1. El medio de incubación se suplementó con 1 por ciento de suero bovino fetal inactivado y previamente tratado con carbón para eliminar las hormonas esteroides. Las monocapas de células fueron mantenidas en presencia o ausencia de 1,25-(OH)2D3 o 17ß-estradiol o del vehículo. Posteriormente se evaluó la proliferación celular mediante conteo en un hemocitómetro, utilizando azul tripano 0.4 por ciento y se analizó la fase de síntesis de ADN por citofluorometría fe flujo. La muerte celular fue determinada por el análisis de la integridad del ADN genómico en geles de agarosa y tinción con bromuro de etidio. Resultados. Las células en presencia de 1 por ciento de suero bovina fetal sin hormonas esteroides en el medio de cultivo, estimuló su crecimiento de las mismas. Por otro lado, las células Rentro 1 no respondieron a la estimulación con 17ß-estradiol y sí al 1,25-(OH)2D3, lo que confirmó la ausencia del receptor de estrógenos en estas células y demostró la capacidad de esta línea celular para responder al 1,25-(OH)2D3. Por último, se encontró que a diferencia de otros tipos celulares, las células Rentro 1 no sufrieron daño a nivel del ADN (apoptosis) con el 1,25-(OH)2D3. Conclusiones. 1) El 1,25-(OH)2D3 promovió la proliferación de las células Rentro 1 de manera independiente de la dosis e independiente de la presencia del estímulo estrogénico; 2) el incremento en el número de células estuvo en relación con la activación de la fase de síntesis de ADN del ciclo celular; 3) la presencia de esta hormona en el cultivo celular no indujo la muerte celular no indujo la muerte celular por apoptosis

Effects of prostaglandins on ethanol damage in primary cultured rat hepatocytes

OBJECTIVES: Several reports demonstrated that ethanol administration impairs the DNA synthesis in rat hepatocytes. Also, it has been demonstrated that prostaglandin (PG) helps prevent membrane damage by hepatotoxic chemicals. In this study, the authors examined PG's effects on the toxicity of ethanol in the primary culture of rat regenerations. METHODS: We examined two kinds of parameters, i.e., DNA synthesis and lipid peroxidation in the primary culture of rat hepatocytes. Hepatocytes were isolated by the collagenase perfusion method. The rate of DNA synthesis was determined by pulse-labelling cultured cells with [3H]-thymidine. Incorporation of (3H)-thymidine was determined by liquid scintillation spectrophotometer. DNA content was measured by the fluorescence spectrophotometer. The lipid peroxidation was assayed with spectrophotometer. RESULTS: The results were as follows: 1) PG family (PGA1, PGD2, PGE1, PGE2, PGG2a, PGI2 & Thromboxane B2) stimulated the DNA synthesis of hepatocytes (especially PGD2 and PGE1), 2) ethanol decreased DNA synthesis by clear dose-dependent manner, 3) the combined treatment of PGD2 or PGE1, prevents the decreasing of DNA synthesis, which was induced by ethanol, 4) in ethanol treatment, lipid peroxidation was decreased significantly, but PGD2, PGE1 and PGA1 were not affected, and 5) PGD2, PGE1 and PGA1 decreased lipid peroxidation with ethanol, significantly. CONCLUSIONS: From these results, we concluded that PG could be useful for the treatment of degenerative liver disease and alcohol-induced liver disease in the assumption that further studies on the action mechanisms of PG will continue.

Hyperoxia influences mRNA expression of cytokines in cultured human umbilical vein endothelial cells

High concentrations of oxygen, indispensable for the treatment of severe hypoxemia from neonatal as well as adult respiratory distress syndrome, increase the risk of oxygen toxicity. Biochemical mechanisms are lipid peroxidation, protein sulfhydryl oxidation, enzyme inactivation, and DNA damage. Recent reports suggest that cytokines might be involved in free radical injury as well as in adaptive response to hyperoxic injury. However, actual signal transduction pathways involving cytokines have not yet been clarified. In this study we exposed cultured human umbilical vein endothelial cells (HUVECs) to either ambient air or 100% oxygen, and compared for the rate of DNA synthesis ([3H]thymidine uptake) at different time points up to 72 h. After exposing the cells to each treatment condition, we extracted RNA, constructed complementary DNA using reverse transcriptase, amplified the specific DNA segments of cytokines by polymerase chain reaction (PCR), and used the PCR products for gel electrophoresis to examine the bands which signified mRNA levels of corresponding cytokines. There was a significant decrease in the rate of DNA synthesis as early as 24 h. The mRNA expression of IL-1 beta and TNFa seemed less influenced by hyperoxia, while IL-8 and TGF beta showed marked increase in mRNA levels at 6 h of 100% oxygen exposure.

The effect of anti-hypertensive drugs on DNA synthesis and proliferation of ultured rat aortic smooth muscle cells

The aim of this study was to elucidate the effects of anti-hypertensive drugs, nifedipine, furosemide, hydrochlorothiazide, captopril, and atenolol on DNA synthesis and proliferation of cultured rat aortic smooth muscle cells induced by fetal calf serum. Aortic smooth muscle cells from Sprague-Dawley rats were isolated, cultured, and seeded in multi-well plates. When confluent, cells were cultured in a conditioned medium without fetal calf serum. After 72 hours, cells were cultured in the medium retaining 10% fetal calf serum with or without anti-hypertensive drugs by increasing the concentration between 10(-8) and 10(-4) M. DNA synthesis was assessed by [3H]-thymidine uptake and proliferation by cell numbers using a hemocytometer. Nifedipine at a concentration of 10(-5) M and 5 x 10(-5) M inhibited serum-induced DNA synthesis significantly by 50.8% and 86.6%, respectively (p < 0.05). The results of cell numbers paralleled those of 3H-thymidine incorporation. Serum-induced DNA synthesis was also reduced by 32.6% at the highest dose of furosemide (10(-4) M), but there was no statistical significance. Hydrochlorothiazide, captopril, and atenolol did not show anti-proliferative effect throughout any of the doses. In conclusion, among the various anti-hypertensive drugs, nifedipine seems to be most beneficial in view of its direct inhibitory effect on DNA synthesis and proliferation of smooth muscle cells, as well as for its anti-hypertensive effect.

Mechanisms of tetrahydroxy-1, 4-benzoquinone toxicity to V79 cells: involvement of free radicals produced by its autoxidation

The toxicity of a polyhydroxy derivative of p-benzoquinone, tetrahydroxy-l,4-benzoquinone (THQ), was investigated in Chinese hamster ribroblasts (V79-M8 line). The fast oxidative degradation of THQ, yielding reactive oxygen species, allowed its use as a suitable tool to study the mechanisms of cell injury under oxidative stress. Toxicity of THQ to V79 cells was evaluated by measuring its inhibitory effects on cell growth and upon DNA synthesis rate. Complete prevention of both effects by catalase implicated hydrogen peroxide as the central key in the mechanism of THQ cytotoxicity. The roles of the primary oxidative product of THQ, rhodizonic acid (RDZ), as well as that of calcium, were investigated. The dependence of THQ on hydrogen peroxide for cytotoxicity, together with the possibility of iron chelation by RDZ, led us to propose an intracellular Fenton-type reaction as the mediator of THQ toxicity toward V79 cells. The understanding of THQ toxicity mechanisms can help to gain insights into the way structurally related physiological compounds, such as catechol derivatives, produce their toxic effects on target cells.

Estudio de la regeneración hepática utilizando un nuevo modelo in vivo: "la hepatectomía total temporaria" / Study of liver regeneration with original model in vivo: \"temporary total hepatectomy\"

Luego de una hepatectomía parcial, se producen cambios metabólicos y expresión de protooncogenes en el hígado, con la aparición de substancias estimulantes en sangre periférica, que provienen de dentro (factores intrahepáticos) y fuera (factores extrahepáticos) del hígado. Si bien una señal para la regeneración está siempre presente, no es claro cómo estos factores interactúan para estimular la síntesis de ADN durante las primeras 24 horas. Es necesario conocer si estos factores están conectados entre sí, para poder interpretar correctamente el proceso regenerativo hepático y eventualmente estimular aún más la regeneración. Para responder a estos interrogantes hemos sometido a ratas machos tipo Wistar a una "Hepatectomía Total Temporaria", funcional, mediante la confección de un shunt-porto-cava con vena homóloga, hepatectomía parcial del 30 por ciento y exclusión de los lóbulos anteriores. Luego de 3 horas los lóbulos son reperfundidos y a las 22 horas se inyectan 50 µCi de 3H thymidina y el hígado es removido 2 horas después. Posterior a una "Hepatectomía Total Temporaria", la síntesis de ADN (10975 ñ 2599 DPM/mgr DNA) fue menor que en ratas sometidas a una hepatectomía del 30 por ciento (20150 ñ 2540 P<0,01) y marcadamente inferior que luego de una hepatectomía parcial del 70 por ciento (160315 ñ 22293 P<0,001). Mediante este original modelo queda demostrado que no existe una desconexión entre los factores intra y extra hepáticos que inician el impulso regenerativo por lo que la estimulación post hepatectomía debería hacerse teniendo en cuenta ambos factores

The effects of high glucose concentration on angiotensin II- or transforming growth factor-beta-induced DNA synthesis, hypertrophy and collagen synthesis in cultured rat mesangial cells

Hyperglycemia is a principal characteristic of diabetes, and has an influence on many cellular functions. In order to investigate whether the intracellular signaling pathways inducing proliferation, hypertrophy and matrix synthesis of mesangial cells are altered in a diabetic environment, we evaluated the effects of a high concentration of extracellular glucose(25 mM; 450 mg/dl) on [3H]thymidine uptake, hypertrophy, and [3H]proline incorporation into a collagenase-sensitive protein, induced by angiotensin II(Ang II) or transforming growth factor(TGF)-beta, in cultured rat mesangial cells. The exposure to a high glucose concentration for 7 days significantly inhibited Ang II(10(-6) M)-induced [3H]thymidine uptake, compared to normal glucose concentration (5 mM)(M +/- SD., 1050 +/- 100 cpm/well vs 550 +/- 97, p 0.05). In conclusion, although the signaling pathway for DNA synthesis by Ang II or TGF-beta are influenced, possibly mediated by PKC-independent mechanism(s), the pathway inducing hypertrophy or collagen synthesis by both agents appears to be unchanged under the high extracellular glucose concentration in cultured rat mesangial cells.

Preventive action of zinc against lead toxicity.

The study was aimed to assess the protective efficacy of zinc against hemo and hematotoxicity induced by lead. Two groups of 8 rats each, were administered lead acetate 20 mg/kg bw (ip) for 3 days. One group in addition was injected 5 mg/kg bw (ip) zinc acetate for next three days. A third group of 8 rats was given three injections of normal saline and served as control. All the animals were sacrificed on eighth day and assessed for hematological changes, heme synthesizing pathway enzymes, hepatic drug metabolizing status and sulfhydryl levels in blood and liver. Lead administration resulted in decreased hemoglobin, increased reticulocytosis, depression of delta aminolevulinic acid dehydratase (ALAD) and uroporphyrinogen I synthetase (UPS) activity in blood and liver. In vitro metabolism of drugs aminopyrine, aniline and p-nitroanisole by liver homogenate and in vivo metabolism of pentabarbitone was also reduced in lead exposed rate. Zinc treated rats showed improved hematological profile and activated ALAD and UPS activity, recovery of N-demethylation of aminopyrine and O-demethylation of p-nitroanisole and partial restoration of free thiol levels in blood and liver thereby indicating that zinc could confer protection against lead toxicity.

Stimulation of DNA synthesis in primary rat hepatocyte cultures by metanil yellow: a new liver tumour promoter.

In order to understand the possible mechanism(s) by which metanil yellow (MY) promotes liver tumour development, we have studied the effect of MY on DNA synthesis in primary cultures of normal rat hepatocytes, maintained under fully-defined conditions. MY alone was moderate, however, in combination with epidermal growth factor (EGF) showed synergism in markedly stimulating DNA synthesis which was dose-dependent. MY also showed stimulation of DNA synthesis either when added 16 h after the hepatocytes were primed with EGF or when first primed with MY for 16 h and then EGF was added. These observations suggest that the target site for MY action may be at the level of EGF-receptor of EGF-mediated early events. Further, MY induced DNA stimulation was found to be independent of insulin and dexamethasone. These results indicate that an important component of the tumour enhancement by MY may be its ability to cause an exaggerated version of the stimulation of DNA synthesis.

Murine splenic proliferative response to human recombinant erythropoietin along hypoxia

La hipoxia constituye el mejor stress fisiológico para la pertubación del estado estacionario eritropoyético. El present estudio tiende a analizar la respuesta proliferativa eritropoyética esplénica con diferentes dosis de eritropoyentina humana recombinante bajo condiciones hipóxicas a lo largo 18 días mediante el ensayo de síntesis del DNA. Los progenitores esplénicos normóxicos no sufren proliferación eritroide significativa al día 0. Una clara respuesta proliferativa a rh Epo se verificó entre los 2 y 8 días de hipoxia. La proliferación de los progenitores eritroides esplénicos hipóxicos retornó a un patrón basal desde los 10 días hasta el final de la experiencia. La mayor creatividad proliferativa, 25 veces sobre el control (p<0.001), se produjo a los 6 días de condicionamiento desde 62.5 hasta 250mU/ml de rh Epo. estos resultados son concordantes con el concepto que durante la daptación fisiológica a la hipoxia, las células progenitoras eritroides esplénicas modifican transitoriamente su tasa proliferativa observable por variaciones en la relación dosis-respueta a Epo

L-histidinol inhibition of the proliferation and DNA biosynthesis of Ehrlich ascites carcinoma in vivo

L-histidinol, a structural analogue of the essential amino acid L-histidine, has been demonstrated to improve the selectivity and efficacy of a variety of cancer drug in several transplantable tumors. L-histidinol causes a rapid decrease in the incorporation of labeled thymidine into Ehrlich ascites carcinoma [EAC] tumor cells. The effect is expressed during 24 hours after L-histidinol treatment [250 mg/kg, 5 doses i.p., 2 hours apart] of EAC-bearing mice. The observed reduced incorporation of labeled thymidine is due to an inhibition of DNA biosynthesis. DNA synthesis was measured by an isotope dilution assay after pulse-labeling with [3H] thymidine 1 muCi/mouse and by monitoring the increase in the total amount of DNA of cell population. The data demonstrated that L-histidinol inhibits DNA biosynthesis and cell proliferation of Ehrlich ascites carcinoma in vivo