Search PubMed⌕ Search

Biomedical subjects

D M Foster

Publications and source records attributed to D M Foster.

At least 73 records · Page 4Linked to original sources
PubMed1981

Hydrolysis of rat chylomicron acylglycerols: a kinetic model.

A quantitative model describing the kinetics of hydrolysis of rat chylomicron acylglycerols by bovine milk lipoprotein lipase has been developed using data from studies on rat lymph chylomicrons containing doubly labeled acylglycerols. The detailed analysis indicates that, in addition to hydrolysis from tri- to di-, di- to mono-, and monoacylglycerol to glycerol, and apparently direct hydrolysis pathway of tri- to monoacylglycerol is also present. This accounts for the transient accumulation of monoacylglycerol seen in some of the experiments. For most hydrolysis steps, a Michaelis-Menten mechanism adequately describes the rate of hydrolysis as a function of lipoprotein lipase concentration. A higher order, more complex mechanism, however, is necessary for the apparent tri- to monoacylglycerol hydrolysis pathway. A mathematical function that describes the way free fatty acid released can control the rates of hydrolysis, and how the presence of the binding sites for free fatty acid on albumin in the incubation medium can modulate this, in included. The model simultaneously satisfies the kinetics of hydrolysis for tri-, di-, and monoacylglycerol together with the kinetics of the glycerol and fatty acid moieties for a wide range of albumin and lipoprotein lipase concentrations.

Animals↗
PubMed1980

The stability of clinical chemistry specimens during refrigerated storage for 24 hours.

The authors investigated the stability of the tests comprising the SMA-6 and SMA-12 chemistry profiles during overnight refrigerated storage. Several constituents were found to undergo changes that were statistically significant when evaluated by a t test for paired comparisons. A recently published sequential method for judging sample stability was found to be somewhat less sensitive than the traditional statistical procedure. Only one determined value (CO2) underwent a change that was judged to be of medical significance. Two previously published criteria were used for this evaluation, one based on clinical judgment and the other on biologic variation. Variability of the results of repeat determination did not appear to be increased by overnight storage.

Blood Chemical Analysis↗
PubMed1980

A model for carbon kinetics among plasma alanine, lactate, and glucose.

To account for the exchange of carbon atoms among alanine, lactate, and glucose in vivo, [2,3-3H]- and [U-14C]alanine or [3-3H]- and [U-14C]glucose were injected simultaneously to nonanesthetized normal dogs. The concentrations in plasma of 14C-labeled alanine, lactate, and glucose, and the injected 3H-labeled substrate were followed for 160 min after injection of the tracers. An integrated kinetic model describing the exchange of carbon atoms among substrates was developed from these data. The analysis suggests that there is a very rapid exchange of the carboxyl carbon of alanine with lactate in contrast to carbons 2 and 3. The model was used to calculate the fluxes of carbon atoms among the substrates in a steady state. In normal dogs plasma alanine and lactate contribute 14% of the carbon atoms released into the circulation as glucose.

Alanine↗
PubMed1980

Transfer of carbon atoms among circulating glucose, alanine, and lactate in pancreatectomized dogs.

The rates of transfer of carbon atoms (mg C . kg body wt-1 . min-1) among plasma glucose, alanine, and lactate have been calculated in pancreatectomized dogs from the tracer concentration versus time curves in the plasma after an intravenous injection of either [2,3-3H]- and [U-14C]alanine or [3-3H]- and [U-14C]glucose. The calculations were based on an integrated kinetic model derived earlier from experimental data. In comparison to normal dogs, in insulin-deprived pancreatectomized dogs, the rate of turnover of glucose (mg C . kg-1 . min-1) is increased about twofold, but the turnover rates of lactate and alanine are not changed significantly. About twice as much carbon is transferred from lactate to glucose, whereas the transfer of carbon from alanine is increased by 47%. Carbon transfer to glucose from unidentified sources is also doubled. In conclusion, in the pancreatectomized dog, gluconeogenesis is increased not by an increased production of alanine and lactate but by an increased diversion of their carbon atoms to glucose at the expense of other pathways.

Alanine↗
PubMed1979

The composition and metabolism of high density lipoprotein subfractions.

The composition and metabolism of high density lipoprotein (HDL) subfractions were investigated in seven normal individuals. Mean HDL2 (d, 1.063-1.125 g/ml) composition (by weight) was 43% protein, 28% phospholipid, 23% cholesterol, and 6% triglyceride, and mean HDL3 (d, 1.125-1.21 g/ml) composition was 58% protein, 22% phospholipid, 14% cholesterol, and 5% triglyceride. The mean apoA-I; apoA-II weight ratio was 4.75 for HDL2 and 3.65 for HDL3. HDL2 protein was proportionally slightly richer in C apolipoproteins and higher molecular weight constituents (including apoE) than HDL3. Kinetic studies utilized radiolabeled HDLA (d, 1.09-1.21 g/ml), HDL2, and HDL3 demonstrated rapid exchange of apoA-I and apoA-II radioactivity among HDL subfractions, similar fractional rates of catabolism of apoA-I and apo A-II within HDL, and similar radioactivity decay within HDL subfractions. Mean plasma residence time was 5.74 days for radiolabeled HDL2 and 5.70 days for radiolabedled HDL3. Differences in HDL protein mass among individuals were largely due to alterations in catabolism, and in general both HDL2 and HDL3 were catabolized via a plasma and a nonplasma pathway. Data from simultaneous radiolabeled very low density lipoprotein and HDL studies in 2 individuals are consistent with the concept that apoC-II and apoC-III are catabolized at a different rate than are apo A-I and apo A-II within the HDL density range.

Adult↗
PubMed1979

Zinc metabolism in humans: a kinetic model.

A quantitative model is developed that describes the kinetics of the early phases of zinc metabolism in humans. The model is based on averaged data obtained over 5 days from 17 atients with smell and/or taste dysfunction who were given 69mZn in trace amounts orally and intravenously. A function describing the rate of entry of 69mZn into systemic plasma following ingestion of the isotope is derived showing that about 37% of the ingested zinc enters plasma. Gastrointestinal absorption is essentially completed by 4 h. Sixty-seven percent of the absorbed zinc in the portal circulation is extracted by the liver before being released into the systemic circulation and agrees with the calculated extraction efficiency from the systemic circulation. There are both rapid and slow exchnage phases between plasma and liver and between plasma and red cells. The calculated steady-state zinc values for plasma, red cells, and liver agree with previously reported measured values implying there are no additional zinc pools in these tissues. The tracer data, however, account for only 10% of total body zinc, the remaining 90% in tissues whose kinetics are too slow to be resolved from a 5-day study.

Adult↗
PubMed1978

Metabolism of high-density lipoprotein apolipoproteins in Tangier disease.

To define the metabolic defect in Tangier disease, we studied the kinetics of [125I]-high-density lipoprotein apolipoproteins (apolipoproteins A-I and A-II) in 11 normal subjects, two obligate heterozygotes, and two homozygotes. Mean synthesis of apolipoproteins A-1 and A-11 was 8.24 mg per kilogram per day in the normal group, 7.94 in heterozygotes and 3.66 in homozygotes. The mean plasma-residence time for both apolipoproteins was 5.21 days in the normal subjects, 3.41 days in heterozygotes, and 0.52 days in homozygotes. In normal subjects and heterozygotes the apolipoproteins were catabolized at similar rates, whereas in homozygotes apolipoprotein A-I was catabolized at a much greater fractional rate than apolipoprotein A-II. These findings indicate that the deficiency of these apolipoproteins in Tangier disease is largely due to rapid and altered catabolism.

Adult↗
PubMed1978

Comparison using central core model of renal medulla of the rabbit and rat.

The studies presented here use a central core model of the renal medulla, the details of which have been given elsewhere (Foster et al., Mathematical Biosci. 32: 307-335, 337-360, 1976). The central core model of the rabbit medulla predicts concentration gradients and volume flow rates in line with what is known for the rabbit. The handling of urea, however, is not consistent with the scheme proposed by Kokko and Rector (Kidney Intern. 2: 214-233, 1972). Moreover, the low concentration of urea predicted for the urine suggests an absence in the model of some form of mediated transport for urea in the inner medulla. The central core model of the rat medulla failed to predict results consistent with what is known about the rat. Substitution of the rabbit thermodynamic parameters into the model for the rat resulted in predictions that more closely resembled what one might expect, but were not entirely satisfactory. The implication is that there may be an interspecies difference in the concentration machinery between the rabbit and rat.

Animals↗
PubMed1976

An analysis of the adequacy of the asymmetric carrier model for sugar transport.

In 1972, Lieb, W. R. and Stein, W. D. (Biochim, Biophys. Acta 265, 187-207) in their review of sugar transport in human erythrocytes concluded that the conventional two-state carrier model was inconsistent with the experimental data available at that time. Since then, other papers have appeared which question the validity of the model. In this paper, we give a brief derivation of the equations describing the two-state carrier model, and analyze the predictions of the model in the classical experiments, i.e. zero-trans, infinite-cis, and equilibrium exchange. We show that the estimate of the half saturation constant of 2.8 mM for glucose at the inner face of the human red cell membrane for the infinite-cis procedure reported by Hankin, B.L., Liev, W.R. and Stein, W.D ((1972) Biochim. Biophys. Acta 288, 114-126) is unreliable. We note that all of the other experimental findings are consistent with the asymmetric carrier model.

Biological Transport, Active↗
PubMed1976

The action of a binary nonionic detergent on a kidney membrane fraction.

The disruption of a kidney cortex microsomal membrane preparation by a binary, nonionic detergent, was followed by using as markers, the changes in total protein content, and (Na+, K+)-ATPase in a supernatant fraction. Both markers responded similarly to changes in pH, microsome concentration and detergent concentration, but responded differently for time-dependent studies. The (Na+, K+)-ATPase activity was increased 2.2-fold (76.1 mumoles Pi/mg protein/h, 95% ouabain-sensitive) by a single detergent treatment and 3.5-fold (92% ouabain-sensitive) by a sequential detergent treatment. Changes in the critical micelle concentration (cmc) were observed for varying detergent and protein concentrations, which suggest interactions of monomeric detergent with the membrane. The peak of (Na+, K+)-ATPase activity occurred above the cmc which suggests the participation of micelles in releasing the enzyme from the membranes. Hill plots of the protein released as the detergent concentration was varied showed a change in the slope near the cmc indicating a four-fold increase in the binding of detergent to membranes as the detergent concentration is increased above the cmc. These results suggest that the disruption of membranes by detergent involves the binding of detergent monomers to the membrane followed by the formation of co-micelles of the detergent with segments of the membrane to complete the separation process.

Adenosine Triphosphatases↗