Biomedical subjects

G Warnecke

Publications and source records attributed to G Warnecke.

At least 19 recordsLinked to original sources

PubMed2001

Combined exogenous surfactant and inhaled nitric oxide therapy for lung ischemia-reperfusion injury in minipigs.

BACKGROUND: The combined application of exogenous surfactant and inhaled nitric oxide was evaluated for prevention of ischemia-reperfusion injury of the lung. METHODS: Left lungs were selectively perfused in 18 minipigs in situ with cold preservation solution. After 90 min of warm ischemia, the lungs were reperfused and the right pulmonary artery and bronchus were ligated (control group, n=6). Exogenous surfactant was instilled via bronchoscopy during ischemia (surfactant group, n=6). In a third group, surfactant was applied, followed by administration of inhaled nitric oxide (surfactant+NO group, n=6). Hemodynamic and respiratory parameters were recorded for 7 hr, and bronchoalveolar lavage fluid (BALF) was obtained before and after reperfusion for measurement of surface tension, small aggregate/large aggregate ratio, protein and phospholipid contents, and a differential cell count. RESULTS: Control group animals survived for 3.7+/-1.4 hr. In both surfactant-treated groups, five out of six animals survived the observation period (P<0.001). Dynamic compliance of the lung was decreased in control animals (P<0.001). In the surfactant+NO group, arterial PO2 was higher than in both other groups (P<0.001). BALF cell count and histology showed reduced neutrophil infiltration in surfactant+NO-treated lungs. Surface tension assessed in BALF with a pulsating bubble surfactometer was severely impaired in control animals (gammamin, 14.82+/-9.95 mN/m), but maintained in surfactant-treated (gammamin, 1.11+/-0.56 mN/m) and surfactant+NO-treated animals (gammamin, 3.90+/-2.35 mN/m, P=0.02). CONCLUSIONS: Administration of exogenous surfactant in lung reperfusion injury results in improved lung compliance. The addition of inhaled NO improves arterial oxygenation and reduces neutrophil extravasation compared with surfactant treatment alone.

Administration, Inhalation↗

PubMed2001

Simian virus 40 large-T-antigen-specific rejection of mKSA tumor cells in BALB/c mice is critically dependent on both strictly tumor-associated, tumor-specific CD8(+) cytotoxic T lymphocytes and CD4(+) T helper cells.

Protective immunity of BALB/c mice immunized with simian virus 40 (SV40) large T antigen (TAg) against SV40-transformed, TAg-expressing mKSA tumor cells is critically dependent on both CD8(+) and CD4(+) T lymphocytes. By depleting mice of T-cell subsets at different times before and after tumor challenge, we found that at all times, CD4(+) and CD8(+) cells both were equally important in establishing and maintaining a protective immune response. CD4(+) cells do not contribute to tumor eradication by directly lysing mKSA cells. However, CD4(+) lymphocytes provide help to CD8(+) cells to proliferate and to mature into fully active cytotoxic T lymphocytes (CTL). Depletion of CD4(+) cells by a single injection of CD4-specific monoclonal antibody at any time from directly before injection of the vaccinating antigen to up to 7 days after tumor challenge inhibited the generation of cytolytic CD8(+) lymphocytes. T helper cells in this system secrete the typical Th-1 cytokines interleukin 2 (IL-2) and gamma interferon. Because in this system TAg-specific CD8(+) cells secrete only minute amounts of IL-2, it appears that T helper cells provide these cytokines for CD8(+) T cells. Moreover, this helper effect of CD4(+) T cells in mKSA tumor rejection in BALB/c mice does not simply improve the activity of TAg-specific CD8(+) CTL but actually enables them to mature into cytolytic effector cells. Beyond this activity, the presence of T helper cells is necessary even in the late phase of tumor cell rejection in order to maintain protective immunity. However, despite the support of CD4(+) T helper cells, the tumor-specific CTL response is so weak that only at the site of tumor cell inoculation and not in the spleen or in the regional lymph nodes can TAg-specific CTL be detected.

Animals↗

PubMed2000

Improved right ventricular function after intracoronary administration of a C1 esterase inhibitor in a right heart transplantation model.

OBJECTIVE: Myocardial injury from ischemia can be augmented after reperfusion due to proinflammatory events including complement activation, leukocyte adhesion, and release of various chemical mediators. It has been shown that intracoronary administration of a C1 esterase inhibitor (C1 INH) significantly reduces myocardial necrosis in an experimental model of ischemia. Our study addresses the question whether the most susceptible region of the heart for ischemic injury, the right ventricle (RV), can benefit from the protective effects of C1 esterase inhibition after transplantation. METHODS: To precisely control RV volume in vivo an isovolumic model was used in which the RV volume was regulated using an intracavity high compliance balloon inserted into donor hearts of domestic pigs (34+/-4 kg). After 4 h of ischemia, donor hearts were transplanted into recipient pigs (44+/-4 kg). Treatment groups, each with six animals, consisted of C1 INH treatment or control. After opening the cross clamp, the C1 INH group animals received 20 IU/kg body weight of C1 INH intracoronary over a 5 min period. The control animals received no drug therapy. The hearts were reperfused for 60 min, and thereafter the RV balloon volume was increased in 10 ml increments until RV failure occurred. These measurements were repeated after 120 min of reperfusion. RESULTS: There was no significant difference in maximal RV developed pressure between the two groups (after 1 h, 35.7+/-5.9 vs. 40.6+/-12.7 mm Hg; after 2 h, 41.5+/-10.7 vs. 46.3+/-15.2 mm Hg; for C1 INH and control animals, respectively). However, the RV could be loaded with a significantly higher volume after both 1 h (60.0+/-20.0 ml (C1 INH) vs. 46.7+/-13.7 ml (control) balloon volume, P<0.05), and 2 h of reperfusion (70.0+/-8.9 ml vs. 60.0+/-6.3 ml; C1 INH and control animals, respectively; P<0.05). CONCLUSIONS: Intracoronary administration of a C1 INH significantly improves right ventricular function in an experimental transplant model. Thus, inhibition of the classic complement cascade may be a promising therapeutic approach for effective protection of myocardium from reperfusion injury after transplantation.

Animals↗

PubMed2000

Low-potassium dextran solution ameliorates reperfusion injury of the lung and protects surfactant function.

OBJECTIVE: This study was designed to compare the effect of lung preservation with low-potassium dextran solution and Euro-Collins solution on reperfusion injury and surfactant function by using an in situ model of warm ischemia. METHODS: The left lungs of 6 minipigs were selectively perfused with Euro-Collins solution. In an additional 6 animals low-potassium dextran solution was used for flush perfusion. After 90 minutes of warm ischemia, the lungs were reperfused, and the contralateral pulmonary artery and bronchus were clamped. Hemodynamic and respiratory measurements were obtained for 7 hours of reperfusion. Surface tension of bronchoalveolar lavage and surfactant small and large aggregates were determined before perfusion (right lung) and after 2 hours of reperfusion (left lung). RESULTS: In the group receiving Euro-Collins solution, right heart failure developed within 215 +/- 39 minutes of reperfusion. An increase in minimal surface tension (P =.03), surfactant small aggregates/large aggregates ratio (P =.003), and bronchoalveolar lavage protein content (P =.012) were found after 2 hours of reperfusion. In the group receiving low-potassium dextran solution, all minipigs survived (P =.0001). Dynamic lung compliance (P =.034) and oxygen tension/inspired oxygen fraction ratios were higher (P =. 0001). Lung water content was lower (P =.049). The increase of minimal surface tension (P =.02) and bronchoalveolar lavage protein concentration (P =.015) were significantly less. CONCLUSION: Preservation of the lung with Euro-Collins solution leads to a reduction of physical surfactant function during reperfusion. Low-potassium dextran solution protects surfactant function and metabolism, thereby reducing reperfusion injury of the lung.

Animals↗

PubMed1999

Exogenous surfactant improves survival and surfactant function in ischaemia-reperfusion injury in minipigs.

Reperfusion injury is the major cause of early morbidity and mortality after lung transplantation. This complication has been experimentally linked to dysfunction of pulmonary surfactant. Therefore, the hypothesis that reperfusion injury might be preventable by exogenous surfactant treatment was tested. Left lungs of minipigs were exposed to 120 min of ischaemia, and the lungs were then reperfused for up to 7 h. Animals were divided into a control group and a surfactant group (n=5 each). The surfactant group received 50 mg x kg(-1) Alveofact intrabronchially via a bronchoscope at the beginning of the ischaemic period. Bronchoalveolar lavage was performed at baseline before ischaemia and 90 min after reperfusion. Surfactant treatment significantly improved short-term survival. Pulmonary vascular resistance increased markedly in control animals leading to right heart failure and death within 3 h after reperfusion whereas the surfactant-treated animals survived the 7 h observation period. After reperfusion, alveolar accumulation of neutrophils and exuded proteins was present in both groups to the same extent. Surfactant activity after reperfusion deteriorated markedly in the control group but was preserved in the surfactant group. In conclusion, early surfactant treatment alleviates the deterioration of surfactant function and improves survival in this minipig model of ischaemia-reperfusion injury.

Animals↗

PubMed1998

Specific interaction of mutant p53 with regions of matrix attachment region DNA elements (MARs) with a high potential for base-unpairing.

Mutant, but not wild-type p53 binds with high affinity to a variety of MAR-DNA elements (MARs), suggesting that MAR-binding of mutant p53 relates to the dominant-oncogenic activities proposed for mutant p53. MARs recognized by mutant p53 share AT richness and contain variations of an AATATATTT "DNA-unwinding motif," which enhances the structural dynamics of chromatin and promotes regional DNA base-unpairing. Mutant p53 specifically interacted with MAR-derived oligonucleotides carrying such unwinding motifs, catalyzing DNA strand separation when this motif was located within a structurally labile sequence environment. Addition of GC-clamps to the respective MAR-oligonucleotides or introducing mutations into the unwinding motif strongly reduced DNA strand separation, but supported the formation of tight complexes between mutant p53 and such oligonucleotides. We conclude that the specific interaction of mutant p53 with regions of MAR-DNA with a high potential for base-unpairing provides the basis for the high-affinity binding of mutant p53 to MAR-DNA.

Animals↗

PubMed1998

High affinity MAR-DNA binding is a common property of murine and human mutant p53.

We recently reported that murine MethA mutant but not wild-type p53 specifically binds to MAR-DNA elements (MARs) with high affinity. Here we show that this DNA binding activity is exerted not only by MethA mutant p53 but also by other murine mutant p53 proteins isolated from the transformed murine BALB/c cell lines 3T3tx and T3T3 and differing in their conformational status. High affinity MAR-DNA binding was not restricted to the Xbal-IgE-MAR-DNA fragment from the murine immunoglobulin heavy chain gene enhancer locus [Cockerill et al. (1987): J Biol Chem 262:5394-5397] used in previous studies, as MethA p53 also specifically interacted with other A/T-rich bona fide MARs. Not only murine but also human mutant p53 proteins carrying the mutational hot spot amino acid exchanges 175Arg-->His, 273Arg-->Pro, or 273Arg-->His bound to the Xbal-IgE-MAR-DNA fragment. We therefore conclude that high affinity MAR-DNA binding is a property common to a variety of mutant p53 proteins.

3T3 Cells↗

PubMed1996

Protective immunity in BALB/c mice against the simian virus 40-induced mKSA tumor resulting from injection of recombinant large T antigen. Requirement of CD8+ T lymphocytes.

BALB/c mice are often considered "low responders" or even "nonresponders" with regard to cytolytic CD8+ T lymphocytes and SV40 large T Ag (TAg). Large TAg and fragments thereof were produced by recombinant technology and injected into BALB/c mice that were subsequently challenged by i.p. injection of syngeneic TAg-expressing mKSA tumor cells. Two portions of the TAg were found to induce protective immunity, one stretching from amino acid residues 1-272 and the other from amino acid residues 683-708. In mice thus protected, the spleens were virtually free of cytotoxic T cells but CD8+ T lymphocytes obtained from the peritoneal cavity during rejection of the mKSA cells were directly lytic for TAg-expressing target cells. Depleting immune mice of CD4+ or CD8+ T lymphocytes by treatment with mAb abolished their ability to resist tumor development. We conclude that immunity against SV40 TAg-expressing tumor cells in BALB/c mice is dependent on both CD4+ and CD8+ T lymphocytes.

Animals↗

PubMed1995

Species- and tissue-specific expression of the C-terminal alternatively spliced form of the tumor suppressor p53.

Alternative splicing of the p53 transcript which so far has been demonstrated only in the murine system has been proposed as a general regulatory mechanism for the generation of functionally different p53 proteins. We analyzed by RT-PCR the pattern of p53 mRNAs within the region spanning exons 10 and 11 of the p53 gene in 13 different tissues from two independent mouse strains, in 10 different rat tissues and in six different human tissues. PCR products of the expected sizes, corresponding to the normally spliced and the alternatively spliced p53 mRNAs, were detected in mice. Alternatively spliced mRNA was found at approximately 25-20% the level of the normally spliced p53 mRNA in most tissues analyzed. In spleen and kidney the proportion of alternatively spliced p53 mRNA was much lower. Surprisingly, examination of p53 mRNAs isolated from 10 different rat tissues and six human tissues within the same region of the p53 gene showed only products of normal size. Although a potential homologous alternative 3' splice site within intron 10 of the human p53 gene is present in the genomic sequence of human p53, the expected corresponding alternatively spliced p53 mRNA was undetectable. These findings imply that the generation of functionally different forms of p53 by alternative splicing of p53 transcripts is a species-specific event, possibly indicating species-specific mechanisms for regulating p53 activities.

Alternative Splicing↗

PubMed1995

Aluminum levels and stores in patients with total hip endoprostheses from TiAIV or TiAINb alloys.

Aluminum ranks as a potentially hazardous agent. Pathologic findings in different organs show that it can accumulate in brain, muscle, liver and bone. Therefore, we investigated whether patients with cementless total hip endoprostheses made out of titanium alloys containing aluminum are at risk. In order to determine the complete aluminum body loading in patients who have had their hip replacement for a long period of time (mean 58 months), we mobilized possible stores of aluminum with desferoxamine (DFO). Electrothermal atomic absorption spectroscopy was used to quantify the level of aluminum in serum and urine before and after DFO treatment. A serum aluminum value of 10 micrograms/l or less is internationally accepted as safe. The average serum aluminum level in this study was 14.2 micrograms/l, which is slightly above the limit, but clearly below those levels which can lead to disease (> 50 micrograms/l). No relevant storage of aluminum was found. This latter finding is more important since chronically elevated aluminum levels lead to cellular deposits, which affect the cellular biochemistry. The values before and after DFO mobilization did not differ substantially, indicating that aluminum in alloys for biomaterials can be regarded as safe as far as the risk of aluminum release in vivo is concerned. Histologic studies of bone from the bone-metal interface also showed no deposits of local aluminum release.

Adult↗

PubMed1992

[The magnesium and calcium content of pre- and postmenopausal myometrium].

Magnesium and calcium, as well as sodium and potassium, have an important influence on the physiology of contraction of the uterus. The ionic concentrations in the pre- and postmenopausal myometrium were examined. We assumed, that there are differences in the electrolytic contents because of the different functions of the corpus, isthmic part and cervix uteri during pregnancy and throughout labour. Small tissue samples from 37 premenopausal and 20 postmenopausal patients, who underwent an operation with different indications, were dissected after hysterectomy. Magnesium and calcium levels were determined by atomic absorption spectrophotometry and potassium and sodium by emission spectrometry in the wet tissue. In both groups, we found significant differences of the electrolytic contents of the myometrium. In the premenopausal uteri, the magnesium levels decrease significantly (p < 0.001) from the corpus (mean = 4.14 mmol/kg) to the cervix (mean = 2.14 mmol/kg). The same scenario can be observed for the potassium levels (Corpus mean = 56.2 mmol/kg and cervix mean = 25.4 mmol/kg). In contrary, the calcium levels (Corpus mean = 1.60 mmol/kg and cervix mean = 2.26 mmol/kg) and sodium levels (Corpus mean = 69.3 mmol/kg and cervix mean = 93.0 mmol/kg) increase significantly (p < 0.001). In the postmenopausal group, we found slightly elevated concentrations of magnesium, sodium and potassium. Only the calcium content of the corpus uteri rises up to three times about 20 years after the menopause (from mean = 1.60 mmol/kg) (p < 0.001). The electrolytic contents in the myometrium were shown to be different in the corpus, isthmus and cervix uteri.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

[Is the lithium chloride-coated heat and moisture exchanger a danger for patients?].

Such hygroscopic compounds as LiCl, CaCl2, and MgCl2 are used to improve water retention capacity and, as a consequence, the effectiveness of heat and moisture exchangers (HME). Resorption of these substances via the bronchopulmonary tract and a resulting systemic action cannot be excluded, especially if additional active moisturizing devices are used. The narrow therapeutic range of lithium is known, as are its unwanted side effects, such as nausea, vomiting, somnolence and even cardiac arrhythmia. These are symptoms that also frequently occur during anaesthesia and intensive care, so that differentiation against effects of lithium is nearly impossible. We investigated whether, in theory and in practice, LiCl-coated HME could result in effective Li plasma concentrations. We measured (1) total LiCl content of HMEs, (2) release of this content, simulating the worst-case situation with a breathing model, and (3) lithium plasma concentrations of adult patients being ventilated during anaesthesia with a rebreathing circuit and LiCl-coated HME, but with no additional active moisturizing system incorporated. RESULTS. The results show striking differences with LiCl content ranging from 3 to 251 mg varying not only between different types of HME but also within the same lots. After 20 min of ventilation more than 90% of the LiCl coating was rinsed into the test lung of the breathing model. In practical use, we observed an increase in lithium plasma concentration in 3 of 20 investigated patients. The plasma values of maximum 49.5 micrograms/l (= 0.007 mmol/l) do not amount to potentially toxic concentrations. Nevertheless, clinically relevant concentrations might occur in patients with small distribution volumes, e.g. newborns or infants with frequent exposition within short intervals such as in intensive care units. The differences in lithium content also indicate qualitative differences in water retention capacity. Because of the potential side effects of lithium, we prefer qualitatively equivalent HMEs, e.g., with MgCl2 or CaCl2 as hygroscopic substance.

Adult↗

PubMed1992

Sodium fluoride-induced gastric mucosal lesions: comparison with sodium monofluorophosphate.

In a randomized double-blind study with two parallel groups of 10 male healthy volunteers each the response of gastric mucosa after a 7 days ingestion of sodium fluoride tablets (NaF) or sodium monofluorophosphate tablets (MFP) was compared. Gastroscopic evaluations were performed before treatment, day 1 and day 7. Simultaneously blood samples were collected for determination of laboratory data and serum fluoride values. In the MFP-group no severe gastric lesions were observed, whereas in the NaF-group in 7 of the 10 subjects significant gastric mucosal lesions including acute hemorrhages and free blood in the gastric lumen were found. The differences of the lesions scores in both groups were statistically significant (p = 0.0015). The serum fluoride content was comparable in both treatment groups. Possible adverse drug reactions were reported in 4 subjects with NaF and in 1 subject with MFP. In summary, under the experimental conditions used MFP is well tolerated by the stomach while NaF produces significant gastric mucosal lesions.

Adult↗

PubMed1991

[Psychosomatic dysfunctions in the female climacteric. Clinical effectiveness and tolerance of Kava Extract WS 1490].

Within the framework of a randomized, placebo-controlled double-blind study, two groups each containing 20 patients with climacteric-related symptomatology were treated for a period of 8 weeks with kava WS 1490 extract 3 X 100 mg/day or a placebo preparation. The target variable - the HAMA overall score of anxiety symptomatology - revealed a significant difference in the drug-receiving group vis-à-vis the placebo group already after only 1 week of treatment. The course of such further parameters as depressive mood (DSI), subjective well-being (patient diary), severity of the disease (CGI), and the climacteric symptomatology (Kuppermann Index and Schneider scale) over the overall period of treatment demonstrate a high level of efficacy of kava extract WS 1490 in neurovegetative and psychosomatic dysfunctions in the climacteric, associated with very good tolerance of the preparation.

Climacteric↗

PubMed1987

Detection and localization of a cytoplasmic domain on the beta-subunit of Na+,K+-ATPase. A monoclonal antibody study.

A monoclonal antibody directed against the beta-subunit of dog kidney Na+,K+-ATPase was generated. Immunoblots demonstrate that monoclonal antibody III 18A binds exclusively to the denaturated beta-subunit. Binding experiments with membranes and whole cells reveal that III 18A binds to membranes but not to whole cells, indicating that the antibody binds to a cytoplasmic domain on the native beta-subunit. To localize the antibody-binding epitope, purified membrane-bound enzyme was fragmented by protease treatment. Tryptic digestion yields a 30-kDa fragment of the beta-subunit, which still retains the binding capacity for the antibody. Thus III 18A probably does not bind to the NH2-terminal segment of the protein. On the other hand, fragmentation of the beta-subunit with low concentrations of papain, which is known to yield a 40-kDa NH2-terminal and a 16-kDa COOH-terminal fragment, results in a complete loss of III 18A binding. These results suggest that the antibody-binding epitope is localized at or near a papain cleavage site on the COOH-terminal part of the beta-subunit. This is inconsistent with a structure model of the beta-subunit containing only a single transmembrane hydrophobic segment with a cytoplasmic NH2-terminal portion, but agrees quite well with a hypothetical structure with four intramembrane segments.

Animals↗

PubMed1985

Production of a monoclonal antibody against an epitope on HeLa cells that is the functional poliovirus binding site.

Cell lines of primate origin carry receptors on their plasma membrane which are responsible for the specific binding of poliovirus. This paper describes the isolation and characterization of a monoclonal antibody reacting with the plasma membrane of HeLa cells. The antibody (D171) was selected for its protection of HeLa cells against the cytopathic effect of poliovirus type 1. This protection was found to extend to all three viral serotypes, while the replication of five other viruses in HeLa cells was not affected. The 125I-labelled purified antibody did not react with cell lines derived from pig, dog or rodents but bound specifically to all lines of human or primate origin. Immunoglobulin or Fab fragments of D171 prevented the binding of 35S-labelled poliovirus to HeLa cells. Conversely, nearly all binding sites of 125I-labelled D171 immunoglobulins or Fab fragments could be blocked after preincubation of HeLa cells with poliovirus. These results indicate that D171 recognizes the poliovirus receptor site on different susceptible cells and that practically all D171 binding sites are involved in the specific attachment of poliovirus to the plasma membrane. To determine whether the epitope recognized by D171 could be separated from the receptor for poliovirus, human-mouse cell hybrids were prepared and analysed. In all 40 clones tested, the susceptibility to poliovirus correlated with the binding of D171.

Animals↗

PubMed1984

Lack of retrovirus gene expression in somatic cell hybrids of friend cells and teratocarcinoma cells with a teratocarcinoma phenotype.

Two types of hybrids between cells with erythroid phenotype (Friend cells) and teratocarcinoma cells can be distinguished: cell hybrids with an erythroid phenotype, which release or can be induced to release large amounts of Friend spleen focus-forming virus (F-SFFV) on exposure to bromodeoxyuridine and cell hybrids with a teratocarcinoma phenotype, which do not release Friend virus and are not inducible for F-SFFV release. In this paper, we attempted to relate these differences to the expression of F-SFFV and Friend murine leukemia virus (F-MuLV) functions. Teratocarcinoma phenotype hybrids retained F-SFFV-and F-MuLV-related provirus sequences. They did not express F-SFFV- or F-MuLV-related RNA or proteins. The hybrids differentiated to endoderm-like cells on exposure to retinoic acid or hexamethylene-bis -acetamide. These cells, in contrast to the teratocarcinoma phenotype (uninduced) cells expressing SSEA-1-like antigens, did not express SSEA-1-like antigens; they formed typical, prekeratin-staining cytoskeletal structures and could be induced to release mouse interferon. The differentiating cells, but not the uninduced teratocarcinoma hybrids, were infected productively with F-MuLV or the F-MuLV--F-SFFV complex. They, however, did not express endogenous F-SFFV. Endogenous F-SFFV functions could not be rescued by infection with F-MuLV. Induction of teratocarcinoma hybrids with retinoic acid did not activate endogenous F-MuLV or F-SFFV transcription or protein synthesis. These data demonstrated two control mechanisms of Friend virus repression: one which acted trans during formation of the cell hybrids and was maintained only in teratocarcinoma phenotype cells and the other which acted cis and was still operative during induction of endodermal differentiation.

Animals↗

PubMed1982

Induction and inhibition of Friend erythroleukemia cell differentiation by pyrimidine analogs: analysis of the requirement for intracellular accumulation and incorporation into DNA.

Alkyldeoxyuridines which differ from thymidine by a C5 substitution of straight or branched alkyl chains of two to six carbon atoms have been tested for their ability to be taken up, phosphorylated, and incorporated into DNA. Analysis of the uptake of 5-ethyl-2'-deoxyuridine and 5-propyl-2'-deoxyuridine (n-PrdU)--similar to both thymidine and 5-bromo-2'-deoxyuridine--indicates that transport is dependent upon a functional cellular thymidine kinase. All of the aforementioned pyrimidines with the exception of n-PrdU are phosphorylated to the triphosphate and incorporated into DNA. The homologs 5-iso-propyl-2'-deoxyuridine (iso-PrdU) and 5-hexyl-2'-deoxyuridine are neither transported into the cell, phosphorylated, nor incorporated into DNA. These analogs were tested (i) for their ability to induce in the absence of dimethyl sulfoxide and (ii) to determine whether they enhance or inhibit dimethyl sulfoxide-induced differentiation of Friend erythroleukemia cells. Inhibition of erythroid differentiation appears to require the incorporation of thymidine analogs into DNA, and thus only 5-ethyl-2'-deoxyuridine and 5-bromo-2'-deoxyuridine were effective in inhibiting dimethyl sulfoxide-induced differentiation. The observation that iso-PrdU, and to a lesser extent n-PrdU and 5-propyldeoxyuridine monophosphate, induce differentiation under conditions in which they are not detectable intracellularly is strong evidence that this class of inducer acts at the cell membrane.

Animals↗