Dehydroascorbic acid and cell division

Feeding Vitamin C during Neonatal and Juvenile Growth Improves Learning and Memory of Rats

We investigated the effects of feeding vitamin C (Vit C) during neonatal and juvenile growth on learning and memory of rats. Rats after delivery were randomly divided into four groups and treated. Group 1, control group, received normal drinking water. Groups 2-4 received Vit C 10, 100, and 500 mg/kg, respectively, from the first day. After 8 weeks, 10 male offspring of each group were randomly selected and tested in the Morris water maze (MWM) and passive avoidance (PA) tests. Finally, the brains were removed for biochemical measurement. In MWM, 10-500 mg/kg Vit C reduced the latency and traveled distance and increased time spent in the target quadrant. In PA, 10 and 100 mg/kg of Vit C increased the latency; 10-500 mg/kg of Vit C decreased the malondialdehyde (MDA) in the brain tissues and increased thiol and catalase (CAT) activity compared to the control group. We showed that feeding rats Vit C during neonatal and juvenile growth has positive effects on learning and memory.

Combined but not single administration of vitamin C and l-carnitine ameliorates cisplatin-induced gastric mucosa damage in male rats

Although cisplatin is a potent anticancer drug, it instigates oxidative and pro-inflammatory reactions that pose significant and distressing clinical symptoms. Therefore, this study investigated the effects of vitamin C and (or) l-carnitine on cisplatin-induced gastric mucosa damage in rat. The rats were allocated into 6 groups (n = 5). The control group received distilled water, while the treatment groups received cisplatin alone (CIP), or cisplatin with vitamin C, l-carnitine, or their combination. Cisplatin caused disruption of the gastric mucosa histoarchitecture and altered the mucus barrier function. Moreover, the stomach tissue of the CIP-treated group showed increased levels of oxidative stress markers (malondialdehyde and H₂O₂) and decreased activities of antioxidant (superoxide dismutase, glutathione peroxidase, catalase, glutathione S-transferase) and non-antioxidant (reduced glutathione) enzymes. These deleterious events were accompanied with significant increases in pro-inflammatory cytokines and inflammatory infiltration markers, myeloperoxidase and inducible nitric oxide synthase. However, the administration of both vitamin C and l-carnitine, and not either of the two showed additive effects in attenuating the adverse effects of cisplatin. The histological results agreed with the biochemical assays. The study concluded that the combined administration of vitamin C and l-carnitine, but not the single therapy, could prevent the adverse effects of cisplatin on gastric tissue.

Effect of Oral Coadministration of Ascorbic Acid with Ling Zhi Preparation on Pharmacokinetics of Ganoderic Acid A in Healthy Male Subjects: A Randomized Crossover Study

The objective of this randomized, open-label, single-dose, two-phase crossover study was to determine the effect of ascorbic acid on pharmacokinetics of ganoderic acid A, an important biologically active triterpenoid compound with anticancer activities, following oral administration of water extract of fruiting bodies of Ling Zhi in 12 healthy male subjects. Each subject was randomized to receive either one of the two regimens: (1) a single dose of 3,000 mg of the Ling Zhi preparation or (2) a single dose of 3,000 mg of the Ling Zhi preparation in combination with 2,500 mg of ascorbic acid. After a washout period of at least two weeks, subjects were switched to receive the alternate regimen. Blood samples were collected in each phase immediately before dosing and at specific time points for 8 hours after dosing. Plasma ganoderic acid A concentrations were quantified using liquid chromatography-mass spectrometry (LC-MS). The pharmacokinetic parameters analyzed were maximal plasma concentration (C_max), time to reach peak concentration (T_max), area under the plasma concentration-time curve (AUC), and half-life (t_1/2). An oral coadministration of ascorbic acid with Ling Zhi preparation did not significantly alter the pharmacokinetic parameters of ganoderic acid A in healthy male subjects.

Orthomolecular Oncology Review: Ascorbic Acid and Cancer 25 Years Later

The effect of ascorbic acid on cancer has been a subject of great controversy. This is a follow-up review of the 1979 article by Cameron, Pauling, and Leibovitz published in Cancer Research. In this updated version, the authors address general aspects of ascorbic acid and cancer that have been presented before, while reviewing, analyzing, and updating new existing literature on the subject. In addition, they present and discuss their own mechanistic hypothesis on the effect of ascorbic acid on the cancer cell. The objective of this review is to provide an updated scientific basis for the use of ascorbic acid, especially intravenously as adjuvant treatment in pharmacological nutritional oncology.

Feeding of Nigella sativa during neonatal and juvenile growth improves learning and memory of rats

The positive roles of antioxidants on brain development and learning and memory have been suggested. Nigella sativa (NS) has been suggested to have antioxidant and neuroprotective effects. This study was done to investigate the effects of feeding by the hydro-alcoholic extract of NS during neonatal and juvenile growth on learning and memory of rats. The pregnant rats were kept in separate cages. After delivery, they were randomly divided into four Groups including: (1) control; (2) NS 100 mg/kg (NS 100); (3) NS 200 mg/kg (NS 200); and (4) NS 400 mg/kg (NS 400). Rats in the control group (Group 1) received normal drinking water, whereas Groups 2, 3, and 4 received the same drinking water supplemented with the hydro-alcoholic extract of NS (100 mg/kg, 200 mg/kg, and 400 mg/kg, respectively) from the 1st day after birth through the first 8 weeks of life. After 8 weeks, 10 male offspring from each group were randomly selected and tested in the Morris water maze (MWM) and passive avoidance (PA) test. Finally, the brains were removed and total thiol groups and malondialdehyde (MDA) concentrations were determined. In the MWM, treatment by 400 mg/kg extract reduced both the time latency and the distance traveled to reach the platform compared to the control group (p < 0.05–p < 0.01). Both 200 mg/kg and 400 mg/kg of the extract increased the time spent in the target quadrant (p < 0.05–p < 0.01). In the PA test, the treatment of the animals by 200 mg/kg and 400 mg/kg of NS extract significantly increased the time latency for entering the dark compartment (p < 0.05–p < 0.001). Pretreatment of the animals with 400 mg/kg of NS extract decreased the MDA concentration in hippocampal tissues whereas it increased the thiol content compared to the control group (p < 0.001). These results allow us to propose that feeding of the rats by the hydro-alcoholic extract of NS during neonatal and juvenile growth has positive effects on learning and memory. The effects might be due to the antioxidant effects.

Carcinostatic effects of diverse ascorbate derivatives in comparison with aliphatic chain moiety structures: Promotion by combined hyperthermia and reduced cytotoxicity to normal cells

In this study, using human tongue squamous carcinoma cells (HSC-4) carcinostatic activity was compared for diverse L-ascorbic acid (Asc) derivatives, including the 'straight-C(16)-chain types', 6-O-palmitoyl-Asc (A6-P) and Asc-2-phosphate-6-O-palmitate sodium salt (APPS), as well as the 'branched-C(16)-chain types', Asc-2-phosphate-6-O-(2'-hexyl)decanoate (APHD), an isomer of APPS, and Asc-2,3,5,6-O-tetra-(2'-hexyl)decanoate (VCIP). The order of magnitude of the carcinostatic effects at 37°C was: APPS>A6-P = APHD>VCIP and at 42°C was APPS = A6-P>APHD>VCIP. Therefore, the two straight-C(16)-chain derivatives, APPS and A6-P, had a greater effect compared to the two branched-C(16)-chain Asc derivatives, which are considered to have more difficulty with 'orientation along cell-membrane-glycerolipid direction'. APPS-treated HCS-4 cells were observed for a decrease in cell number, cell shrinkage, pycnosis indicative of apoptosis and cell deformation. The order of cytotoxicity for the normal human dermal fibroblasts (OUMS-36) at 37°C was: A6-P (50% inhibitory concentration: 150-300 μM)>APHD (450-600 μM)>>Asc = APPS (800-1000 μM). Accordingly, APHD was more cytotoxic than APPS, since the straight-C(16)-chain type, which was eliminated after the enzymatic esterolysis of APPS, is metabolized via the 'fatty acid β-oxidation cycle' more efficiently in normal cells. Thus, APPS had a greater advantage over APHD, A6-P and VCIP in terms of carcinostatic effects at 37°C, carcinostasis promotion at 42°C and a decrease of cytotoxicity to normal cells. This observation suggests a marked potential for aliphatic chain-moiety structures as anticancer agents, due to their cancer-selective carcinostasis and combined efficacy with hyperthermia, without causing side effects.

Redox regulation of water stress responses in field-grown plants. Role of hydrogen peroxide and ascorbate

Abiotic stresses, such as drought, can increase the production of reactive oxygen species (ROS) in plants. An increase in ROS levels can provoke a partial or severe oxidation of cellular components inducing redox status changes, so continuous control of ROS and therefore of their metabolism is decisive under stress conditions. The present work focuses on the contribution of one pro-oxidant, hydrogen peroxide (H(2)O(2)) and one antioxidant, ascorbate (AA) and its redox status, in the control of plant responses to drought-oxidative stress in resistant plants growing in field conditions. After a general introduction to the concept of drought and oxidative stress and its relationship, we describe the role of H(2)O(2) in drought stress responses, emphasizing the importance of studies in H(2)O(2) subcellular localization, needed for a better understanding of its role in plant responses to stress. Although more studies are needed in the study of changes of redox status in plants subjected to stress, the AA pools and its redox status can be indicative of its involvement as a part of cellular mechanisms by which the plant respond to drought-induced oxidative stress. The mechanism of resistance and/or tolerance to drought-oxidative stress is complex, especially when studies are carried out in plants growing in field conditions, where an interaction of stresses occurs. This study sheds light on the mechanisms of plant responses to water-oxidative stress in plants growing in the field.

An overview of interactions between micronutrients and of micronutrients with drugs, genes and immune mechanisms

The objective of the present review is to examine critically the consequences of interactions that micronutrients undergo with nutrients and non-nutrients (mainly prescribed medicines) in diets and lifestyle factors (smoking, tea and alcohol consumption). In addition, the review describes recent work on interactions between nutrients and genes, the influence of gene polymorphisms on micronutrients, the impact of immune responses on micronutrients and specific interactions of antioxidant micronutrients in disease processes to minimise potential pro-oxidant damage.

Morphology and DNA degeneration during autoschizic cell death in bladder carcinoma T24 cells induced by ascorbate and menadione treatment

Feulgen and actin-phalloidin staining as well as gel electrophoresis have been employed in conjunction with cell ultrastructure to describe the effects of 1-, 2-, and 4-hr ascorbate (VC), menadione (VK(3)), and ascorbate:menadione (VC:VK(3)) treatments on the T24 human bladder carcinoma cell line. T24 cells exposed to VC alone display blebs and other superficial membrane defects related to membrane alterations and to superficial cytoskeleton changes. VK(3) treatment damages the cell nucleus and organelles, leads to the redistribution of the organelles in the perikaryon as a consequence of cytoskeletal damage, and results in cytoplasmic self-excisions. After VC:VK(3) treatment, the cells show exaggerated alterations characteristic of each vitamin treatment alone, including damaged mitochondria, self-excision of organelle-free pieces of cytoplasm, and extrusion of the perikaryon containing a nucleus surrounded by the damaged organelles. The nuclear envelope appears intact and contains chromatin that decondenses and dissipates. During the cellular demise that concludes with apparent karyolysis, the cells significantly decrease their size and alter their shape. However, the cisterns of rough endoplasmic reticulum are undamaged, but may become dilated. Since the cellular phenomena leading to cell death differ morphologically from apoptosis and necrosis, but entail self-cutting without nuclear bodies, this new form of cell death was called autoschizis. In addition, gel electrophoresis and Feulgen staining demonstrate that autoschizis is accompanied by random DNA degeneration.

Stimulation of matrix formation in rabbit chondrocyte cultures by ascorbate. 1. Effect of ascorbate analogs and beta-aminopropionitrile

The most consistent effects of 0.2 mM L-ascorbate on monolayer cultures of rabbit articular chondrocytes were a diversion of incorporated radiosulfate into a pericellular matrix and enhancement of cell proliferation. Only with certain batches of fetal bovine serum (FBS) was there a cell-for-cell increase of proteoglycan synthesis. These actions increased as the cell inoculum rose from 0.5 to 2 x 10(5) cells/T25 flask. Maximal effects of ascorbate and D-isoascorbate were found over a range of 0.05-0.2 mM. L-Dehydroascorbic acid was less effective than either, and no stimulatory action was exerted by L-cysteine, glutathione, dithiothreitol, methylene blue, or phenazine methosulfate. Ascorbate increased the hypro:pro ratio of newly synthesized proteins. beta-Aminopropionitrile (1 mM) reduced the proportion of [3H]hydroxyproline and [35S]O4-proteoglycans in the ascorbate-supplemented matrix 31 and 7%, respectively. In corresponding electronmicrographs, the number of pericellular filaments was reduced. We conclude: (a) Ascorbate has a general anabolic effect on chondrocytes in culture and enhances matrix assembly through mechanisms other than its redox function; (b) deposition of proteoglycans in the matrix is not simply the result of mechanical entrapment by allysine- or hydroxyallysine-derived cross-linking of collagen; and (c) contradictory reports on the subject result from variations in the serum employed, inoculum density, and concentration of ascorbate.

Ascorbic acid-dehydroascorbate induces cell cycle arrest at G2/M DNA damage checkpoint during oxidative stress

Reactive oxygen species induce cellular damage and have been implicated as mediators for cellular signaling pathways. However, a linkage between the cellular redox status and cell cycle progression has not been demonstrated. We previously demonstrated, using the Chinese hamster ovary cell line AS52, that the cytotoxic and mutagenic effects of oxidative stress is prevented by ascorbic acid (AA), but only when cells are treated with AA prior to treatment with the stressor. To elucidate the mechanism(s) responsible for this effect, we determined the effect of AA on cell cycle progression during oxidative stress. Flow cytometric analyses demonstrated that treatment of AS52 cells with AA (50 microM), prior to treatment with a radical generating system (RGS), enhanced cell cycle arrest at the G2/M DNA damage checkpoint when compared to cells treated with RGS. AA had no effect on cell cycle progression in the absence of oxidative stress. Furthermore, under conditions that prevent the reduction of dehydroascorbate (DHA), the oxidized form of AA, cell cycle arrest was also induced at the G2/M DNA damage checkpoint. These observations demonstrate that during periods of oxidative stress, AA functions as an antioxidant and DHA enhances transient arrest at the G2/M checkpoint by delaying the activation of cyclin B-cdc2. These results suggest the presence of a unique redox mechanism for the regulation of cell cycle progression and also demonstrate a novel mechanism by which AA protects cells from damage due to oxidative stress.

Ascorbate on cell growth and differentiation

Ascorbate, an essential nutrient in humans, primates, and guinea pig, is involved in many cellular functions. Ascorbate also modulates cell growth and differentiation. Ascorbate can reduce or stimulate the growth of tumor cells, depending on the cell type. The inhibitory effect is not specific for the biological active isomer L-ascorbate, and isoascorbate and D-ascorbate are more effective in reducing cell growth than L-ascorbate. These results indicate that ascorbate has a cytotoxic effect by killing cells directly, rather a cytostatic one. However, only L-ascorbate is able to stimulate cell growth, but the mechanism of this stimulation is still unknown. L-Ascorbate stimulates the in vitro differentiation of several mesenchyme-derived cell types by altering the expression of multiple genes as the cell progresses through specific differentiation programs. Stimulation of collagen matrix at gene transcription, mRNA stabilization, hydroxylation, and secretion is a key role for L-ascorbate. L-Ascorbate also prevents cell transformation by stabilization of the differentiated state and cooperates with other agents to induce differentiation in a leukemia cell line.

Enhanced inhibition of DNA synthesis and release of membrane phospholipids in tumour cells treated with a combination of acylated ascorbate and hyperthermia

Combined antitumour effects of mono- or diacyl ascorbates and heat treatment were studied in comparison with the parent compound, L-ascorbic acid (AsA). At 37 degrees C, 75 microM 6-O-palmitoyl (6P) and 6-O-stearoyl (6S) ascorbates appreciably inhibited DNA synthesis in Ehrlich ascites tumour cells. Hyperthermia at 42 degrees C for 1 h increased the inhibition. In contrast, AsA or 2,6-O-dipalmitoyl ascorbate (DP), even at concentrations as high as 100 microM, caused no inhibition at 37 degrees C or 42 degrees C. The results suggest that the inhibitory action is not caused by the fatty acid moiety itself; it is more likely to be caused by the balance in the hydrophobicity and hydrophilicity of the monoacylated AsA, a property not found in diacylated or intact AsA. Inhibition of DNA synthesis caused by exposure to 6P during hyperthermia of tumour cells was greater than before or after hyperthermia. 6P or 6S, but not AsA or DP, released phospholipids such as phosphatidylcholine and phosphatidylethanolamine from cells labelled with [14C]oleic acid, as shown by radiocurves taken from thin-layer chromatograms. Damage of the cell membrane seemed to be involved in the inhibition of DNA synthesis caused by monoacylated AsA, which is surface-active.

Ascorbic acid concentration of human fetal tissues in relation to fetal size and gestational age

1. Studies were carried out on the distribution of ascorbic acid in human fetal tissues with the progress of gestation. 2. Fetuses and stillborn babies varying in gestational age from 12 to 38 weeks were obtained from various Baroda hospitals. Ascorbic acid levels were determined in selected tissues: brain, adrenal, liver, kidney, lung, heart and placenta. 3. Ascorbic acid concentration in the brain was higher than that in the adrenal at all gestational ages, suggesting the importance of this vitamin in brain development. The concentrations of this vitamin in liver, kidney, lung and placenta were comparable, but that in the heart tended to be lower. In all the tissues, there was a fall in ascorbic acid during late gestation. However, the levels in tissues of stillborn babies were higher than those reported for adults.

Altered production of the active oxygen species is involved in enhanced cytotoxic action of acylated derivatives of ascorbate to tumor cells

Our previous study shows that 6-O-acyl derivatives of L-ascorbic acid inhibits more markedly cell growth of mouse Ehrlich carcinoma than ascorbic acid. The present study shows that 6-O-palmitoyl ascorbic acid but not ascorbic acid prolongs the lifespan of mice into which tumors such as Meth A fibrosarcoma, MM46 mammary carcinoma, Ehrlich carcinoma and sarcoma 180 are implanted. The potentiated cytotoxicity of 6-O-palmitoyl ascorbic acid is not due to an increase in duration time of the cytotoxic action, because 6-O-palmitoyl ascorbic acid is gradually inactivated during contact with tumor cells and exhibits a similar action time curve to that of ascorbic acid as shown by clonal growth assay. Cytotoxicity of 6-O-palmitoyl ascorbic acid is markedly diminished by combined addition of catalase and superoxide dismutase (SOD), as shown by dye exclusion assay, whereas the cytotoxicity was slightly reduced by either enzyme alone but not by the specifically inactivated or heat-denatured enzymes. In contrast, cytotoxicity of ascorbic acid is abolished by catalyse but not SOD. Autooxidation of 6-O-palmitoyl ascorbic acid was not inhibited by catalase plus SOD. The results indicate that cytotoxicity of 6-O-palmitoyl ascorbic acid is attributed at least partly to both hydrogen peroxide (H2O2) and superoxide (O2-.) generated at the early stage. Cytotoxicity of 6-O-palmitoyl ascorbic acid is also appreciably attenuated by singlet oxygen (1O2) scavengers such as hydroquinone, 1,4-diazobicyclo-2,2,2-octane or sodium azide, but not by hydroxyl radical scavengers including butylated hydroxytoluene, D-mannitol, benzoic acid and ethanol. Thus, in contrast to cytotoxicity of ascorbic acid mediated entirely by H2O2 initially generated, acylated ascorbic acid produces a diversity of active oxygen species including H2O2, O2-. and other species secondarily generated via disproportion, which may be additively involved in the enhanced cytotoxic action.

Non-toxic potentiation of cancer chemotherapy by combined C and K3 vitamin pre-treatment

The influence on the survival of ascitic liver tumor (TLT)-bearing mice of combined vitamins C and K3 administered before or after a single i.p. dose of 6 different cytotoxic drugs, all commonly used in human cancer therapy, was investigated. Combined i.p. administration of these vitamins produced a distinct chemotherapy-potentiating effect for all drugs examined, especially when injected before chemotherapy. This potentiating treatment did not increase the general and organ toxicity that accompanies cancer chemotherapy. The possible generation of peroxides followed by membrane lipid alteration, DNase activation and DNA destruction by combined vitamin C and K3 in catalase-deficient cancer cells might be involved in the mechanisms of this selective potentiation.

Effects of ascorbic and dehydroascorbic acid on the multiplication of tumor ascites cells in vitro

The effects of AA and DHA on ATP C+ cell multiplication in vitro were studied by measuring incorporation of 3H thymidine into DNA. The results obtained demonstrate that both AA and DHA have the same effects: they favor cell multiplication at low doses and inhibit it at high doses. Experiments carried out with serial doses of both these substances revealed that AA is more efficient in determining both stimulating and inhibiting effects. The lesser efficiency of DHA may be attributed to its limited stability in culture medium. Studies on the effect of high doses of AA and DHA added to the culture medium in single or fractionated doses revealed that fractionated administration is more efficient in inhibiting cell multiplication than single administration.

The antioxidant vitamins

This article is an attempt to study the metabolic functions of vitamin C and E together. Such a study must necessarily be imcomplete owing to the extreme richness of the literature. The increasing importance of the work on free radical reactions, their toxicity and carcinogenic action, and also their relation to the metabolism of metals, particularly iron, copper, selenium, and zinc, shows a number of metabolic pathways with which both vitamins interact. It is hoped that this article will indicate future research possibilities.

Differences in growth response to hydrocortisone and ascorbic acid by human diploid fibroblasts

The effects of hydrocortisone and ascorbic acid on growth parameters were measured in human diploid skin fibroblasts from fetal and adult donors. In the presence of culture medium containing 10% fetal bovine serum, 0.3 micrometer hydrocortisone produced a 20% increase in the population growth rate and a 50 to 70% increase in the confluent density of fibroblasts from adult donors. Daily addition of 28 micrometer ascorbic acid also stimulated the population growth rate and cell density at confluency. The effects of hydrocortisone and ascorbic acid on the final cell density were additive. The action of hydrocortisone was restricted to cells in log-phase growth, whereas ascorbic acid affected cells in both the log and the post-confluent phases of the growth cycle. In fibroblasts from fetal donors, ascorbic acid was stimulative but hydrocortisone was not. The data suggest that whereas both compounds stimulate cell growth in an additive manner, they do so by different cellular mechanisms.

Vitamin C metabolism and atopic allergy

The procedure for carrying out the Leucocyte Ascorbic Acid Uptake Direct Antigen Challenge Test (LAADACT) is described. Leucocytes from normal individuals, when incubated in a buffered medium containing ascorbic acid, increase their ascorbic acid concentration by about 80%. When leucocytes from atopic individuals are incubated in a medium containing the antigen to which they are sensitive, as shown by positive skin tests, the leucocyte uptake of ascorbic acid is significantly reduced. Addition of antigen, to which atopic or normal individuals are not sensitive, to the incubation mixture does not reduce leucocyte ascorbic acid uptake. Measurement of ascorbic acid uptake into leucocytes is a relatively simple, routine, laboratory procedure. The LAADACT, therefore, provides a quick and accurate blood test for diagnosing sensitivity to specific antigens, and measuring relative antigenic sensitivities. The underlying mechanism of the LAADACT is discussed.

Ascorbic acid in fetal human brain

Ascorbic acid concentrations in fetal human forebrain in the period 11 to 19 weeks' gestational age were 4 to 11 times higher than those of adults. Levels fell progressively with increasing gestational age but, in term babies dying within 4 weeks of birth, were still at least 3 times those of adults. It was confirmed that, in women delivering at term, ascorbic acid concentrations are approximately 4 times higher in cord blood plasma than in maternal blood plasma. The possible importance of ascorbic acid for normal human brain development is discussed.

Some EPR signals in tumour tissue

Normal and tumour tissues from rats, blood from normal and tumour bearing rats, and normal human blood were examined using the electron paramagnetic resonance (epr) technique. At low temperature a triplet epr signal, which is known to be produced by a NO-haemoprotein complex, was detected in some tumour samples and in decaying normal liver. At room temperature all of the tumour samples examined gave a doublet signal. This signal was also detected in blood but not in other normal tissues. The signal has a g value of 2·0054 ± 0·0002 and a hyperfine splitting of 1·80 ± 0·05 G and is assigned to the ascorbyl free radical. Model experiments suggest that the appearance of detectable concentrations of this radical result from a disturbance of the normal state of the ascorbic acid, dehydroascorbic acid redox system. It was verified that cell division is not responsible for the ascorbyl radical although autolysis may be involved. A possible relationship between the formation of ascorbyl radicals and other paramagnetic species in tumours is discussed.

Effect of oxygen on growth of cultured myocardial cells

The present study was designed to explore the effects of environmental oxygen as a possible regulator of cardiac cell division and growth. Trypsindispersed heart cells from the ventricles of chick embryos 8 to 12 days old were grown in culture at 37°C in a nutrient medium (NCI) with 10% fetal calf serum. They were exposed to constant 5% CO 2 gas environments in which the percent of O 2 was varied. Net protein synthesis increased progressively as O 2 was reduced from 80% to 2 to 5%. After the first 24 hours, little further protein synthesis occurred in plates grown in 80% O 2 . The rates of cellular incorporation of 14 C-amino acids and uridine-2- 14 C increased progressively as the fraction of O 2 was reduced. In cells grown at 80% O 2 , incorporation of uridine-2- 14 C into RNA was impaired before that of 14 C-amino acid into protein. After actinomycin-D (5 µg/ml) (which quickly halted uridine incorporation into the rapidly labeled fraction of RNA), the rate of incorporation of 14 C-amino acid into protein declined exponentially. This allowed for calculation of the half-life of messenger RNA (mRNA), which was the same for cells grown at 80% O 2 as for cells grown at 20% O 2 ; increased degradation of mRNA at higher P o 2 is thus ruled out. Decreased O 2 tension results in increased rates of cell division and protein synthesis in vitro. The molecular site of action appears to be at or before RNA readout from DNA.