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Biomedical subjects

S Bottomley

Publications and source records attributed to S Bottomley.

10 recordsLinked to original sources
PubMed1990

Absence of insulin-receptor downregulation in hepatocytes from hyperinsulinemic rats.

Insulin-induced downregulation of the insulin receptor occurs in conditions associated with high extracellular concentrations of insulin. This paper describes the effect of experimental hyperinsulinemia on insulin binding to isolated hepatocytes. In vivo experimental hyperinsulinemia was produced in rats by subcutaneous injection of long-acting insulin at low (10 mU.g-1.day-1), medium (up to 25 mU.g-1.day-1), and high (up to 50 mU.g-1.day-1) doses over 1 or 2 wk. Insulin-stimulated lipogenesis was measured to determine the efficacy of the experimentally produced hyperinsulinemia. The results showed that 1) insulin-induced downregulation, determined by insulin binding, was not present in hepatocytes from any of the hyperinsulinemic rats; 2) insulin binding was increased in hepatocytes from 1- and 2-wk high-dose hyperinsulinemic rats compared with 1-wk sucrose-control (P less than 0.05), 2-wk sucrose-control (P less than 0.01), and normal rats (P less than 0.01); 3) increased binding may have been due to an increase in the number of low-affinity receptors; 4) insulin's effect on lipogenesis (i.e., insulin-stimulated lipogenesis minus the basal value) was increased in either 1-wk (P less than 0.001) or 2-wk (P less than 0.001) high-dose insulin-treated rats compared with either normal or 2-wk sucrose-control rats; 5) insulin's effect on hepatocyte lipogenesis in sucrose-control (P less than 0.025) and in all other insulin-treated (P less than 0.008 or P less than 0.05 for 2-wk medium dose) rats was greater than insulin's effect in normal hepatocytes. The reasons for the absence of downregulation are not clear, but rapid receptor recycling, rapid degradation, and upregulation are listed as possibilities.

Animals↗
PubMed1988

HPLC separation of corticosterone metabolites and its use in following corticosterone metabolism and transport in the isolated rat hepatocyte.

Incubating isolated rat hepatocytes with tritium labelled and unlabelled corticosterone at 37 degrees C resulted in the rapid appearance of at least nine corticosterone metabolites. A quick, relatively easy, and quantitative high performance liquid chromatographic (HPLC) method was used to separate these metabolites and follow their rate of appearance both intra- and extracellularly. We found different intra- and extracellular amounts of each metabolite at a particular time and this suggested that some metabolites were more available for transport than others.

Animals↗
PubMed1987

Rat hepatocyte lipogenesis and insulin-stimulated lipogenesis: comparison of metabolite effects and methods of measurement.

This study compared the effects of certain metabolites (either singly or in various combinations) and the methods of measuring lipogenesis (using either 14C-acetate or 3H2O incorporation into lipids) on total lipid synthesis and insulin-stimulated total lipid synthesis in the isolated rat hepatocyte. There were quantitative and qualitative differences between 14C-acetate and 3H2O incorporation into lipids; metabolites acutely affected both lipogenesis and insulin-stimulated lipogenesis with either isotope; and insulin's effect on lipogenesis was greater when measured by 14C-acetate incorporation. It is suggested that a particular choice of incubation media and isotope may inadvertently bias a study of insulin-stimulated lipogenesis and that metabolite supply plays a major role in regulating insulin-stimulated lipogenesis.

Amino Acids↗
PubMed1984

Factors affecting fasting serum C-peptide levels in Micronesians: comparison with a Caucasoid population.

Fasting serum C-peptide immunoreactivity was determined on Nauruans, a Micronesian population with a high prevalence of diabetes. In Micronesian subjects neither age nor gender had a significant effect on fasting serum C-peptide. In non-diabetic subjects, as has been shown previously for Caucasiod subjects, both obesity and fasting plasma glucose levels were determinants of fasting serum C-peptide. Obesity was the major determinant. Taken overall, mean fasting serum C-peptide increased then possibly fell in subjects grouped by increasing 2-h post-glucose plasma glucose levels. Mean fasting serum C-peptide in newly-diagnosed diabetic subjects was greater than that in non-diabetic subjects with a similar degree of obesity, supporting the concept that the transition to diabetes may be associated with an increase in insulin resistance. The data for non-diabetic subjects were compared with serum C-peptide measured in the same laboratory on samples from a Caucasoid population in Busselton, Western Australia. There was no difference in fasting serum C-peptide level between Micronesian and Caucasoid subjects approximately matched for obesity and fasting plasma glucose levels.

Adult↗