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Biomedical subjects

B J Barnhart

Publications and source records attributed to B J Barnhart.

At least 19 recordsLinked to original sources
PubMed1986

Feto-placental steroid metabolism in growth retarded human fetuses.

The goal of the study was the determination of the relative roles of the placenta and the fetus in causing low serum estriol (E3) levels in women bearing fetuses with intrauterine growth retardation (IUGR). Umbilical venous levels of E3 and dehydroepiandrosterone sulfate (DHAS) were measured in 31 samples from fetuses with IUGR, 21 of whom were vaginally delivered and 10 who were delivered by cesarean section. In addition, estrone (E1) and estradiol (E2) were measured in 11 of the samples. The results were compared with 11 samples from cesarean section delivered control term infants and 54 samples from vaginally delivered control infants. The vaginally delivered IUGR group had a significantly lower mean umbilical venous DHAS level than did their control group (2128 +/- 158 ng/ml SEM versus 2645 +/- 130, p less than 0.05). Both the vaginally delivered and cesarean section delivered IUGR infants had umbilical venous E3 levels significantly lower than in their control groups (70 +/- 10 ng/ml SEM versus 144 +/- 10, p less than 0.001, and 46 +/- 11 ng/ml SEM versus 136 +/- 23, p less than .01, respectively). Umbilical venous E1 and E2 levels were not different from the control values. E1, E2, E3, and DHAS were measured in eight maternal venous samples obtained from mothers bearing fetuses with IUGR. In comparison with 11 control mothers, only E3 was significantly different (10.7 +/- 3.0 ng/ml SEM in mothers with IUGR fetuses versus 25.0 +/- 4.9 in control mothers p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗
PubMed1982

Induction of 6-thioguanine-resistant mutations by rat-liver homogenate (S9)-activated promutagens in human embryonic skin fibroblasts.

Most normal human fibroblasts grown in culture do not metabolize promutagens/procarcinogens. Thus screening assays employing normal human fibroblasts have only been successful for direct-acting chemical mutagens and various radiations. In this report we describe a mutation assay (HGPRT locus) employing a normal human embryonic skin fibroblast and a rat-liver homogenate (S9) mixture. 3 model promutagens, benzo[a]pyrene (B[a]P), 3-methylcholanthrene (3MC), and dimethylnitrosamine (DMN) have been utilized in these studies. In addition to discussing conditions for optimizing the response of this assay, our results indicate that at constant amount of S9 protein concentration, there exists a linear correlation between mutagenicity and dose. At 50% survival, the mutant frequencies induced by B[a]P and 3MC (5 micrograms/ml) are 60 and 30 times the background mutant frequency, respectively. Similarly, at 50% survival, DMN (5 mg/ml) induced 6-TGr mutant frequencies are 25-fold over the background frequency. The increase in cytotoxicity resulting from exposure of cells to these 'activated' chemicals is also a linear dose response. At high S9 concentrations a deactivation or detoxification phenomenon occurs. However, the mutagenic efficiency of S9-activated chemicals when plotted as the number of induced mutations versus log survival is unaffected by the deactivating capacity of S9 proteins. This study demonstrates a quantitative mutation assay using an early passage human culture with an exogenous rat-liver microsomal preparation providing activating enzymes.

Animals↗
PubMed1980

Mutation of Chinese hamster cells by near-UV activation of promutagens.

A tissue-culture assay for mutagenesis and cytotoxicity incorporating near ultraviolet (NUV) light activation of polyaromatic hydrocarbons (PAH) has been developed. Cultures of Chinese hamster cells (line CHO) growing in suspension culture were inoculated with benzo[a]pyrene (B[a]P), 7,12-dimethylbenzanthracene (DMBA) of shale-oil retort-water and exposed to light from a high-pressure mercury lamp fitted with a Corning NUV bandpass filter. This light source both permitted activation of PAH and the shale-oil water and preculded detectable damage to DNA. Neither the PAH nor the NUV alone had any effect on cell survival or mutation frequencies but the chemicals plus NUV were extremely effective in producing mutations to 6-thioguanine resistance (hgprt gene).

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1980

Adrenal cortical function in the postmature fetus and newborn infant.

The umbilical venous blood concentrations of cortisol, dehydroepiandrosterone sulfate (DHAS), and unconjugated estriol were compared in 54 normal, 37 postterm, and 22 postmature newborns. Pre- and postadrenocorticotropic hormone (ACTH) stimulation levels of serum cortisol and DHAS were compared in the first 2 to 4 days of life in 19 postterm and 15 postmature infants. Comparison was also made between vaginally an cesarean section delivered postterm and postmature newborns. There were significantly greater cord blood cortisol levels in th postmature [260 +/- 22 ng/ml (+/- S.E.)], than in the normal (193 +/- 11 ng/ml) (P less than 0.01) or postterm (193 +/- 18 ng/ml) (0.01 less than P less than 0.05) vaginally delivered infants. There were no significant differences in the mean cord blood DHAS levels in the three groups (normal, 2645 +/- 130 ng/ml; postterm 2323 +/- 188 ng/ml; postmature, 2310 +/- 224 ng/ml). Cortisol and DHAS responses to ACTH stimulation were the same in the postterm and postmature groups. There was a significantly lower mean umbilical venous unconjugated estriol level in the vaginally delivered postmature group (75 +/- 11 ng/ml) as compared to values in vaginally delivered postterm [120 +/- 14 ng/ml (P = 0.01)] and normal [144 +/- 10 ng/ml (P less than 0.002)] newborns. Stressed postmature infants delivered by cesarean section had higher unconjugated estriol levels (83 +/- 12 ng/ml) than their unstressed, postterm cesarean section controls [40 +/- 9 ng/ml (P less than 0.01)], but levels were still below those from vaginally delivered postterm infants. These findings substantiate normal adrenal function in the postmature fetus and newborn. Lowered umbilical venous unconjugated estriol levels in the postmature infants at birth appear to be a function of limited aromatizing activity of the placenta rather than due to the low levels of fetal adrenal-derived neutral steroid substrate.

Adrenal Cortex↗
PubMed1977

Growth and biochemical characteristics of a detachment variant of CHO cells.

A variant subline of Chinese hamster cells (line CHO) was isolated that had increased resistance to detachment from the substratum. Comparisons between parental and variant cells of the complex carbohydrates liberated during trypsin detachment showed that the variant cells synthesized little or no hyaluronic acid. These cells also had reduced amounts of other complex carbohydrates in the cell periphery. However, parental and variant cells did not differ in morphology, growth control, or cyclic AMP concentration. Profound changes in the physical nature of the cell periphery, in themselves, evidently are insufficient to cause changes in many aspects of cell behavior.

Animals↗
PubMed1976

Prophage induction and inactivation by UV light.

Analysis of the induction curves for UV light-irradiated Haemophilus influenzae lysogens and the distribution of pyrimidine dimers in a repair-deficient lysogen suggests that one dimer per prophage-size segment of the host bacterial chromosome is necessary as a preinduction event. The close correlations obtained prompted a renewed consideration of the possibility that direct prophage induction occurs when one dimer is stabilized within the prophage genome. The host excision-repair system apparently functions to reduce the probability of "stabilizing" within the prophage those dimers that are necessary for induction and inactivation. The presence of the inducible defective prophage in strain Rd depresses the inducibility of prophage HP1c1.

Bacteriophages↗
PubMed1973

Repair of single-strand deoxyribonucleic acid breaks in ultraviolet light-irradiated Haemophilus influenzae.

The wild-type strain and mutants of Haemophilus influenzae, sensitive or resistant to ultraviolet light (UV) as defined by colony-forming ability, were examined for their ability to perform the incision and rejoining steps of the deoxyribonucleic acid (DNA) dark repair process. Although UV-induced pyrimidine dimers are excised by the wild-type Rd and a resistant mutant BC200, the expected single-strand DNA breaks could not be detected on alkaline sucrose gradients. Repair of the gap resulting from excision must be rapid when experimental conditions described by us are employed. Single-strand DNA breaks were not detected in a UV-irradiated sensitive mutant (BC100) incapable of excising pyrimidine dimers, indicating that this mutant may be defective in a dimer-recognizing endonuclease. No single-strand DNA breaks were detected in a lysogen BC100(HP1c1) irradiated with a UV dose large enough to induce phage development in 80% of the cells.

Bacteriophages↗
PubMed1973

DNA replication of induced prophage in Haemophilus influenzae.

DNA synthesis during transition from the lysogenic state to the lytic cycle and throughout the latter has been studied in Haemophilus influenzae BC200 (HP1c1). Following exposure to ultraviolet light, there is a 30-min delay in DNA synthesis after which there is a rapidly increasing rate of phage DNA synthesis. The phage genome is replicated without extensive utilization of segments or of breakdown products of the bacterial chromosome. The mode of phage DNA replication was investigated by zonal sedimentation of labeled DNA in 5 to 20% neutral and alkaline sucrose gradients. Tritiated thymidine, incorporated during a 2-min pulse given at 38 min, chases rapidly into DNA, sedimenting like linear DNA of approximately 2 x 10(8) daltons, and then, at the expense of label in this peak, chases into slower-sedimenting phage DNA (2 x 10(7) daltons). The fast-sedimenting, rapidly labeled DNA satisfies certain criteria for being a concatenated replicative intermediate. Observations in the electron microscope revealed linear concatemers in the faster-sedimenting material and circular phage-sized DNA in the slower-sedimenting DNA. When induced cells are gently lysed with lysozyme and Brij 58 to maintain DNA-membrane associations and sedimented in neutral sucrose over a cesium chloride shelf, the concatemer is found with the cell-membrane-wall complex. Membrane-associated label chases to membrane-free material sedimenting like deproteinized HP1c1 DNA. When membrane-associated DNA from the cesium chloride shelf is deproteinized and resedimented in neutral sucrose, the sedimentation profile reveals that sedimentation rates of labeled DNA from this complex are indicative of sizes ranging from 2 x 10(8) daltons down to phage-sized pieces of 2 to 3 x 10(7) daltons. A model is presented which places HP1c1-DNA replication on the cell membrane where a concatemer of phage DNA is synthesized and subsequently degraded to phage-equivalent DNA. Phage-equivalent DNA is then either released from the membrane for packaging or is packaged while still membrane associated. Thus, the cell membrane is not only the site of DNA replication during which phage DNA is synthesized in multiple phage-equivalent concatemers but it is also the site at which these concatemers are selectively reduced to phage-sized pieces.

Bacteriophages↗
PubMed1970

Effect of ultraviolet light on division and deoxyribonucleic acid synthesis in Haemophilus influenzae.

The effects of ultraviolet (UV) light on cell morphology, deoxyribonucleic acid (DNA) synthesis, and protein synthesis in UV-sensitive and UV-resistant strains of Haemophilus influenzae were examined. Relatively low doses of UV induce lyses in the sensitive strains but not in the resistant mutant; however, UV temporarily blocks cell division of the resistant mutant, and elongated cells are formed after a period of incubation. Low doses of UV do not stop DNA synthesis in any of the strains examined; however, they do slow the rate of DNA synthesis in a manner consistent with the model correlating the kinetics of postirradiation DNA synthesis with the cell's ability to repair UV-induced DNA lesions. The data are not consistent with a model in which UV causes all DNA synthesis to stop for a time linearly dependent on dose.

Bacterial Proteins↗