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Biomedical subjects

B V Howard

Publications and source records attributed to B V Howard.

At least 199 records · Page 11Linked to original sources
PubMed1980

Insulin stimulation of glycogen synthase in cultured human diploid fibroblasts.

The effect of insulin on glycogen synthase activity in human diploid fibroblasts has been studied. As little as 2 X 10(-10) M insulin increased the glycogen synthase / activity without changing the total activity. Stimulation occurred within 5 min and became maximal in 30 min. A half-maximal increase of / activity was achieved at 3 X 10(-9) M insulin. Glucose starvation increased the magnitude of response of glycogen synthase to insulin but did not change the insulin concentration necessary to give a half-maximal stimulation. Glucose increased the basal level of / activity in human diploid fibroblasts; the effect of insulin was additive. During in vitro senescence the total glycogen synthase activity declined, but the concentration of insulin that produced a half-maximal stimulation remained unchanged. These data indicate that regulation of glycogen synthase activity in human diploid fibroblasts is responsive to physiologic insulin levels and that the system provides a useful model for the in vitro study of insulin sensitivity.

Cells, Cultured↗
PubMed1980

Studied of very low density lipoprotein triglyceride metabolism in an obese population with low plasma lipids: lack of influence of body weight or plasma insulin.

Pima Indians have a high prevalence of hyperinsulinemia, obesity, and diabetes, but they have low plasma cholesterol levels, reduced low density lipoprotein synthesis, and little arteriosclerotic heart disease. To investigate lipoprotein metabolism further in this group, very low density lipoprotein (VLDL) metabolism was studied, using [3H]glycerol as an endogenous precursor of triglyceride (TG) synthesis, in 15 obese Pima nondiabetic males and compared to that of 10 obese and 13 normal weight, normolipidemic, nondiabetic Caucasian males. The resultant kinetic data were analyzed using a multicompartmental model which includes two pathways for VLDL-TG synthesis and a process of stepwise delipidation for VLDL catabolism. As compared to obese Caucasians, the obese Pimas had a lower rate of VLDL-TG synthesis, and a lower proportion of slow pathway for synthesis. The fractional catabolic rate in the Pimas was higher than in either Caucasian group, a larger proportion of VLDL-TG was delipidized at each step, and particle residence time was shorter. When the relation between VLDL-TG metabolism and plasma insulin was examined, plasma insulin levels in the Pima were not correlated with VLDL-TG synthetic rates, catabolic rates, or plasma pools. On the other hand VLDL-TG synthetic rates were correlated with plasma free fatty acid levels. Thus, in this population with low plasma lipids and reduced arteriosclerotic heart disease, VLDL-TG synthesis is low, VLDL-TG catabolism is accelerated, and VLDL pools appear to be insensitive to the influence of body weight and hyperinsulinemia.

Adolescent↗
PubMed1979

Cell triacylglycerol accumulation from very low density lipoproteins isolated from normal and hypertriglyceridemic human sera.

Human fibroblast cells in culture increased their intracellular triacylglycerol levels when exposed to very low density lipoproteins (VLDL) isolated from human plasma. This response was dependent on the amount of VLDL added. VLDL from normal, type IV or type V sera gave similar results. Lipoprotein lipase enhanced this intracellular triacylglycerol accumulation. It was concluded that human fibroblast cells in culture have at least two mechanisms for triacylglycerol uptake from VLDL: (1) uptake from intact lipoprotein either by surface transfer of lipoprotein lipid or internalization of the entire lipoprotein particle, and (2) re-esterification of lower glyceride and fatty acids released by lipoprotein lipase degradation of VLDL.

Fibroblasts↗
PubMed1979

Insulin stimulation of glucose entry in cultured human fibroblasts.

The effect of insulin on glucose entry has been studied in monolayer cultures of human diploid fibroblastic cells. Influence of insulin on total cell glucose incorporation was evaluated using [14C] glucose. Glucose incorporation was increased up to two-fold in the presence of insulin. Insulin action occurred within 30 minutes and could be observed with insulin concentrations as low as 10(-10) M (10 microU)ml). The action of insulin was enhanced by preincubation in glucose-free medium. After glucose starvation the cells converted glucose primarily to glycogen and nucleotides, and the stimulation by insulin was observed equally in both fractions. Influence of insulin on the kinetics of hexose transport was studied using 2-deoxyglucose and 3-0-methyl glucose. A large diffusion component was corrected using rho-chloromercuribenzoic acid or phloridzin. Km for facilitated diffusion averaged 1.9 mM for 2-deoxyglucose and 5.3 mM for 3-O-methyl glucose, and Vmax ranged from 10-24 nmoles/min/mg cell protein. Insulin resulted in a 150% increase in Vmax with no significant change in Km. The data suggest that human diploid fibroblasts can be a useful system for the study of insulin's glucoregulatory action.

Biological Transport, Active↗
PubMed1979

Comparison of the intracellular lipids of cultured vascular endothelial cells and fibroblasts.

The lipids of human umbilical vein endothelial cells, calf aortic endothelial cells and foreskin fibroblasts have been compared. Cell cultures were established, and, upon confluency, the lipids were extracted and analyzed with respect to total lipid content, classes of lipids and total lipid fatty acid composition. The total quantity of lipid per milligram protein found in both human umbilical vein endothelium and calf aorta endothelium was similar to that found in fibroblasts grown in similar medium. Both types of endothelium contained the same major neutral lipid classes as fibroblasts, although they contained more phospholipid than did fibroblasts. The fatty acid composition of the three cells examined was influenced by cell type as well as the type of serum in the culture medium.

Animals↗
PubMed1979

Changes in plasma lipoproteins accompanying diet therapy in obese diabetics.

Plasma lipoprotein cholesterol and triglyceride levels were measured in 24 obese not-insulin dependent Pima Indian diabetics and 9 obese nondiabetic controls before and after 1-8 months on a 500 calorie diet. The diabetics were divided into 3 groups--severe, recent onset (n = 10), severe long-term (n = 6), and borderline (n = 8). The diet regimen resulted in weight loss and improved glucose tolerance in all of the diabetics, and insulin secretion increased in the 2 groups of severe diabetics. After the period of weight loss, total plasma cholesterol had declined greater than 20%, and LDL cholesterol decreased 25% in all diabetic groups and in the controls. In all diabetic groups, HDL cholesterol did not decline; therefore the ratio of HDL/LDL cholesterol after diet therapy was significantly increased. In the controls HDL cholesterol declined with weight loss, and the distribution of HDL/LDL cholesterol remained constant. Plasma and VLDL triglyceride levels decreased in all groups in those with initial triglyceride levels greater than 150 mg/dl. The results indicate that weight loss in not-insulin dependent diabetics not only improves glucose tolerance, but also lowerss plasma lipids and reverses the dyslipoproteinemia often associated with this disorder. This may influence the risk of arteriosclerotic heart disease in these individuals.

Adult↗
PubMed1979

Bimodality of glycosylated hemoglobin distribution in Pima Indians: relationship to fasting hyperglycemia.

Glycosylated hemoglobin (HbA1) concentrations were determined in 300 Pima Indians aged 15 yr and older. Frequency distributions of HbA1 were unimodal in the 15--24-yr-old age group, but were bimodal in those aged 25 yr and over. The bimodality indicated that the subpopulation with diabetes could be identified by the presence of elevated HbA1 levels. This group was comprised primarily of subjects who also had fasting plasma glucose levels of less than or equal to 140 mg/dl, but subjects with impaired glucose tolerance without fasting hyperglycemia had HbA1 levels that were not significantly higher than those with normal glucose tolerance. The prevalence of diabetic retinopathy was much higher in the subgroup with elevated HbA1 levels and increased with increasing HbA1 level. HbA1 levels and triglyceride concentrations showed only a modest association. HbA1 determinations provided no advantage over fasting or post challenge glucose levels in the diagnosis of diabetes.

Adolescent↗
PubMed1978

Lipoprotein composition in diabetes mellitus.

Lipoprotein cholesterol and triglyceride levels have been determined in normal and diabetic Pima Indian women aged 20-35, HDL cholesterol levels were lower, LDL cholesterol levels were higher, and the ratio of HDL cholesterol/LDL cholesterol, a reflection of lipoprotein cholesterol distribution, was lower in the diabetics compared to the normals. VLDL triglyceride levels were also elevated in the diabetics. An analysis of lipoprotein composition suggested that these changes primarily reflect changes in numbers of particles, since lipid composition and lipid/protein ratios were similar in lipoproteins isolated from normals and diabetics. The ratio of ester/free cholesterol in LDL and HDL was lower in normal Pima Indians than in a comparable group of Caucasians, although plasma LCAT activity was not significantly different. The data indicate that diabetes may be associated with shifts in distribution of LDL and HDL, as well as with increases in VLDL.

Adult↗
PubMed1977

Acetate as a carbon source for lipid synthesis in cultured cells.

Lipid synthesis from acetate and glucose has been studied in fibroblast cultures grown in lipid free medium containing various concentrations of acetate and glucose. Their role in lipid synthesis was evaluated by comparing the specific activities of total cell lipid, and sterol and fatty acid subfractions, to that of the carbon source in the medium. When glucose was present at 1000 microgram/ml (5.6 mM) and acetate at 100 microgram/ml (1.2 mM), the majority of the total cell lipid and subfractions were derived from glucose. As acetate concentrations increased, lipid synthesis from acetate increased, and glucose declined as a carbon source; in cells grown in the presence of 1000 microgram/ml (12 mM) acetate more of the lipid was derived from acetate than from glucose. When acetate was present at 1000 microgram/ml (12 mM) and glucose was varied from 1000 to 200 microgram/ml (5.6 to 1.1 mM), the relative amount of lipid synthesis from acetate was further increased. The data indicate that acetate can serve as a significant carbon source for lipid synthesis in cultured fibroblasts when it is presented to the cells at high extracellular concentrations relative to glucose.

Acetates↗
PubMed1977

Properties of calf endothelial cells in culture.

Calf aorta endothelial cells, obtained by collagenase treatment of vessels from freshly killed animals, were cultured in medium 199 supplemented with fetal bovine serum, amino acids, and vitamins. The material released from the vessel wall after collagenase treatment consists of clumps of cells which quickly attach to the dish and spread to form confluent islands of cells. These islands of cells coalesce to form a confluent monolayer in 6 to 8 days. Cultures labeled with [3H]thymidine show an increase in labeling commencing 3 days after initial culture. Cells within monolayers do not overgrow one another and retain their epithelioid appearance after subculture. Identification of endothelial cells was based on culture morphology and by the presence of factor VIII antigen as localized by indirect immunofluorescence microscopy. These data indicate that large numbers of endothelial cells (5 to 7 x 10(6) cells per aorta) can be obtained and maintained in culture.

Animals↗
PubMed1977

Uptake of very low density lipoprotein triglyceride by bovine aortic endothelial cells in culture.

Primary monolayers of calf aortic endothelial cells were presented with isolated human very low density lipoproteins that had been labeled with radioactive triglyceride. The cells were observed to take up triglyceride over a 24 hr period; incorporation increased with exogenous lipoprotein concentrations, and up to 60% of the triglyceride taken up was converted to other cell lipids within 24 hr. When [2-3H]glyceryl tri[1-14C]oleate-labeled very low density lipoprotein was used, the 3H/14C ratio in the cell triglyceride was always similar to that of the exogenous lipoprotein triglyceride. Moreover, no significant hydrolysis of the exogenous very low density lipoprotein triglyceride was observed during the time of exposure to the cells. Similar experiments using doubly-labeled triglyceride exposed to endothelial cells in triglyceride-phospholipid liposome preparations also resulted in incorporation of the exogenous triglyceride without evidence of extracellular hydrolysis. The results indicate that primary monolayers of endothelial cells in culture are able to incorporate and metabolize very low density lipoprotein triglyceride. However, triglyceride does not appear to be significantly hydrolyzed during uptake, suggesting an absence of lipoprotein lipase activity in these cells.

Adipose Tissue↗
PubMed1976

Regulation of lipid synthesis from acetate in diploid fibroblast cultures -- variation with passage level and stage of cell growth.

Regulation of lipid synthesis from acetate in human diploid fibroblast cultures has been studied at various passage levels and at different stages of cell growth. When cultures were transferred to lipid free medium, a stimulation of [14C]acetate incorporation into lipid occurred within three to six hours after removal of exogenous lipid. In early passage cultures, this stimulation was observed whether cells were transferred to protein-free medium or medium supplemented with delipidized serum protein. However, in late passage cultures the presence of delipidized serum protein was required for the stimulation of lipid synthesis. When logarithmically dividing and stationary phase cultures were compared, the cultures in log phase showed stimulation of acetate incorporation into lipid in the presence or absence of delipidized serum protein, whereas in the stationary cultures the delipidized serum protein was required. When cultures were partially synchronized by a thymidine block, stimulation of acetate incorporation into lipid in the blocked cells only occurred in the presence of delipidized serum protein; in released cells stimulation occurred in protein free medium. When inhibition of lipid synthesis from acetate was compared in young vs. old or dividing vs. stationary cultures, however, no differences were observed. The data indicate the response of diploid fibroblast cultres to change in exogenous lipid is dependent on passage level and state of growth.

Acetates↗
PubMed1976

Preparation of delipidized serum protein for use in cell culture systems.

A rapid procedure for the preparation of delipidized serum protein is described. The delipidized protein can be used for the maintenance and growth of tissue culture cells in a lipid-free environment. The extraction procedure greatly reduces all serum lipid classes and the delipidized protein supports the growth of a variety of cells in culture.

Blood Proteins↗
PubMed1976

Characterization of the collagen synthesized by endothelial cells in culture.

[14C]Proline and [14C]lysine were incorporated into collagen by cultures of endothelial cells derived from calf aortae. The isomer 3-hydroxy[14C]proline accounted for 10% of the total hydroxy[14C]proline in the collagen isolated from the medium. Approximately 81% of the hydroxy[14C]lysine isolated from the medium was glycosylated, and 91% of the glycosylated hydroxy[14C]lysine was in the form of the disaccharide glucosylgalactose. Gel filtration chromatography or acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate indicated that the initially synthesized peptide chain of [14C]collagen had a molecular weight of about 135,000; after pepsin digestion this was converted to 115,000. The ratio of hydroxy[14C]proline to total [14C]proline x 100 in the pesin-resistant fraction was 59. When examined by immunofluorescence microscopy, the endothelial cultures stained positively with antiserum to (Type IV) collagen from basement membrane of bovine anterior lens capsule. The data indicate that cultured endothelial cells derived from calf aortae synthesize collagen that resembles that of basement membrane collagen.

Aorta↗