Biomedical subjects

M A Lea

Publications and source records attributed to M A Lea.

97 records · Page 6Linked to original sources

PubMedDate not supplied

Heart rate, swimming speed, and estimated oxygen consumption of a free-ranging southern elephant seal.

Heart rate, swimming speed, and diving behaviour were recorded simultaneously for an adult female southern elephant seal during her postbreeding period at sea with a Wildlife Computers heart-rate time depth recorder and a velocity time depth recorder. The errors associated with data storage versus real-time data collection of these data were analysed and indicated that for events of short duration (i.e., less than 10 min or 20 sampling intervals) serious biases occur. A simple model for estimating oxygen consumption based on the estimated oxygen stores of the seal and the assumption that most, if not all, dives were aerobic produced a mean diving metabolic rate of 3.64 mL O2 kg-1, which is only 47% of the field metabolic rate estimated from allometric models. Mechanisms for reducing oxygen consumption while diving include cardiac adjustments, indicated by reductions in heart rate on all dives, and the maintenance of swimming speed at near the minimum cost of transport for most of the submerged time. Heart rate during diving was below the resting heart rate while ashore in all dives, and there was a negative relationship between the duration of a dive and the mean heart rate during that dive for dives longer than 13 min. Mean heart rates declined from 40 beats min-1 for dives of 13 min to 14 beats min-1 for dives of 37 min. Mean swimming speed per dive was 2.1 m s-1, but this also varied with dive duration. There were slight but significant increases in mean swimming speeds with increasing dive depth and duration. Both ascent and descent speeds were also higher on longer dives.

Animals↗

PubMedDate not supplied

Induction of histone acetylation and growth regulation in eryrthroleukemia cells by 4-phenylbutyrate and structural analogs.

The objective of this investigation was to study the relationship between histone acetylation and growth inhibition by 4-phenylbutyrate and structural analogs. Inhibition of growth of DS19 mouse erythroleukemia cells and K562 human leukemic cells by 4-phenylbutyrate did not appear to be mediated by glutamine depletion. Vanadate blocked differentiation of DS19 cells but did not affect the hyperacetylation of histones. 2-phenylbutyrate was a more effective inhibitor of cell proliferation than 3-phenylbutyrate but was less effective as an inducer of histone acetylation. 4-Phenylbutyrate was a more effective inhibitor of histone deacetylase and inducer of histone acetylation than the structural analogs examined including 2- and 3-phenylbutyrate, cinnamate, methoxycinnamate, 2-phenoxybutyrate and phenoxyacetate.

Acetamides↗

PubMedDate not supplied

Induction of histone acetylation in rat liver and hepatoma by organosulfur compounds including diallyl disulfide.

In previous studies, diallyl disulfide induced histone acetylation and differentiation in DS19 mouse erythroleukemic cells. In the present work the potential induction of histone acetylation in tumor-bearing rats was examined. Increased acetylation of histones in liver and Morris hepatoma 7777 was induced by treatment of rats with diallyl disulfide (200 mg/kg body weight), allyl mercaptan (100 mg/kg body weight) and butanethiol (100 mg/kg body weight). The level of histone acetylation was greater in liver than in the hepatoma and the response to the organosulfur compounds tended to be less in the tumor. The data suggested that compounds in garlic or their metabolites may increase the acetylation of core nucleosomal histones and thereby favor cell differentiation.

Acetylation↗

PubMedDate not supplied

Discordant effects of butyrate analogues on erythroleukemia cell proliferation, differentiation and histone deacetylase.

Actions of butyrate and structural analogues on histone deacetylase activity were compared with effects on proliferation and differentiation of erythroleukemia cells. Proliferation was inhibited by 5 mM tert- butylacetate, phenylacetate, phenylbutyrate, 3-bromopropionate and ethyl butyrate without induction of hemoglobin synthesis. n - Butyramide was a stronger inhibitor of cell proliferation and a more effective inducer of hemoglobin synthesis than isobutyramide. The data from combination studies were compatible with butyramide and isobutyramide being weaker agonists that competed for a common site with butyrate. Butyramide and isobutyramide were weaker inhibitors of histone deacetylase than 4-phenylbutyrate and phenylacetate, which in turn were less effective than 3-bromopropionate and butyrate. Butyrate and analogues had similar inhibitory effects on histone deacetylase activity in nuclei from mouse DS19 cells and human K562 cells. Effects on histone deacetylase did not show a consistent correlation with inhibition of cell proliferation or induction of hemoglobin synthesis.

Amides↗

PubMedDate not supplied

Butyramide and monobutyrin: growth inhibitory and differentiating agents.

Butyramide and monobutyrin were chosen for study as neutral compounds that might exhibit some of the growth inhibitory and differentiating effects of butyrate. Inhibitory effects on DNA synthesis in hepatoma cells and on cellular proliferation in mouse erythroleukemia cells were observed. Induction of differentiation by butyramide and monobutyrin was seen in mouse erythroleukemia cells as monitored by increased synthesis of hemoglobin and H1 zero histone. Butyramide and monobutyrin were less effective inducers of hemoglobin synthesis than butyrate but their neutral character may offer an advantage in the induction of tumor cell differentiation.

Amides↗

PubMedDate not supplied

Effects of C18 fatty acid isomers on DNA synthesis in hepatoma and breast cancer cells.

The influence of geometrical isomerism on the growth regulatory effects of 18 carbon unsaturated fatty acids on the incorporation of [3H]thymidine into DNA was studied in 7800NJ rat hepatoma and T47D human breast cancer cells. 9 cis, 12 cis linoleic acid was more inhibitory than the trans 9, trans 12 isomer (linolelaidic acid). The monounsaturated cis isomer, oleic acid, was also more inhibitory than the trans isomer. In contrast to published studies on the proliferation of breast cancer cells, we observed conditions in which linoleic acid was more inhibitory than conjugated linoleic acid for thymidine incorporation into DNA. Increasing the concentration of bovine serum albumin from 1 mg/ml to a physiological concentration of 38 mg/ml greatly diminished inhibitory effects and favored stimulatory effects on hepatoma and breast cancer cells. The results suggested that the growth inhibitory and stimulatory effects of C18 unsaturated fatty acids on cancer cells are influenced by geometrical isomerism and the ratio of the albumin to fatty acid concentrations.

Animals↗

PubMedDate not supplied

Induction of reporter gene expression by inhibitors of histone deacetylase.

The relationship between histone acetylation and induction of gene expression was studied in Ros 17/2.8 rat osteosarcoma cells transfected with the pCH110 plasmid. This plasmid is commonly used in cotransfections as a measure of transfection efficiency. Cells were incubated for 48 hours with sodium butyrate, phenylbutyrate, 3-bromopropionate or trichostatin A. There was an approximate relationship between the extent of beta-galactosidase induction and the degree of histone hyperacetylation. Trichostatin A was the most effective agent followed by sodium butyrate and then phenylbutyrate. The toxicity of 3-bromopropionate made it difficult to compare its action with the other agents. Phenylbutyrate was less effective than sodium butyrate in causing induction of gene expression and histone hyperacetylation but this action may be a factor in the growth-inhibitory and differentiating activity of phenylbutyrate which has also been attributed to glutamine depletion.

Animals↗