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Biomedical subjects

A Stern

Publications and source records attributed to A Stern.

At least 217 records · Page 12Linked to original sources
PubMed1983

Pancreatic polypeptide secretion. A marker for disturbed pancreatic function in cystic fibrosis.

Pancreatic polypeptide, a 36-amino peptide, is released from the pancreas by a variety of stimuli, including intravenous Boots secretin. Studies in a generalized destructive and inflammatory process such as chronic pancreatitis have revealed a markedly diminished response to stimulation. To assess whether pancreatic polypeptide release in response to Boots secretin provides a useful measure of pancreatic destruction in cystic fibrosis, 41 patients with proven cystic fibrosis, aged 14 months-23 years, and seven control subjects, aged 18-24 years were studied. Serum pancreatic polypeptide, measured by radioimmunoassay, rose from a basal of 18.5 +/- 2.7 pmol/liter to a peak of 35.6 +/- 4.3 pmol/liter at 5 min in cystic fibrosis, and from a basal of 10.8 +/- 2.8 pmol/liter to a 5-min peak of 109 +/- 27.7 pmol/liter in control subjects. The basal levels of both groups were similar but the cystic fibrosis patients had a significantly lower peak response than controls (P less than 0.05). The peak over basal pancreatic polypeptide ratio was calculated and was less than five in 93% of cystic fibrosis patients, whereas all control subjects had a ratio greater than five. Pancreatic polypeptide measurements in response to secretin may be a convenient and useful means of following the course of pancreatic disease in a chronic illness such as cystic fibrosis.

Adolescent↗
PubMed1983

Stimulation of ATP hydrolysis by chloroquine and primaquine in human red blood cells.

Primaquine, an 8-aminoquinoline, and chloroquine, a 4-aminoquinoline, both stimulate ATP hydrolysis in human red blood cells incubated in the absence of glucose. In the presence of glucose, ATP levels are partially maintained by increased flux of glucose through glycolysis. Glucose dependence of chloroquine uptake and the activity of primaquine as a redox reagent explain quantitative differences in ATP hydrolysis and accumulation of specific glycolytic products.

Adenosine Triphosphate↗
PubMed1983

Insulin hypoglycaemia and cholinergic blockade: response of plasma immunoreactive beta-endorphin.

Six normal subjects were studied to investigate the mechanisms involved in the release of immunoreactive beta-endorphin (ir-beta EP) in response to insulin hypoglycaemia. Insulin alone (0.2 U/kg body weight) was followed after a 30 min lag period by a congruent to 2.5 fold elevation of plasma ir-beta EP, with a return to basal levels by 90 min. Concurrent infusion of 10% dextrose at 250 ml/h for 2 h prevented the increase in plasma ir-beta EP levels, suggesting an effect of hypoglycaemia rather than a direct effect of insulin. Premedication with atropine 0.6 mg at -30 min was followed by hypoglycaemia equivalent to that seen with insulin alone, but no increase in plasma ir-beta EP, suggesting the involvement of cholinergic mechanisms in the neural mediation of ir-beta EP release in response to hypoglycaemia.

Adult↗
PubMed1982

Primaquine-mediated oxidative metabolism in the human red cell. Lack of dependence on oxyhemoglobin, H2O2 formation, or glutathione turnover.

Stimulation of the hexose monophosphate shunt by primaquine results from the oxidation of NADPH by primaquine. This conclusion was based on the observations that primaquine lowered cellular NADPH but not GSH and that, in red cells in which the GSH was unavailable for reaction, primaquine still stimulated the rate of the hexose monophosphate shunt. In a non-cellular system, primaquine interacted with NADPH, but not GSH, to produce H2O2. Stimulation of the hexose monophosphate shunt by primaquine does not primarily involve H2O2 accumulation since stimulation of the pathway by primaquine was also observed in red cells containing methemoglobin, a red cell preparation in which no H2O2 accumulates. Methemoglobin prevented the formation and/or accumulation of H2O2 in intact red cells incubated with primaquine as well as in a non-cellular system containing primaquine plus Fe2+-EDTA as an H2O2 source. Methemoglobin probably acts by scavenging reactive intermediates since oxyhemoglobin was formed from methemoglobin in the non-cellular experiments. In the red cell, primaquine stimulated glucose-dependent conversion of methemoglobin to oxyhemoglobin.

Blood Glucose↗
PubMed1982

Lipid peroxidation and haemoglobin degradation in red blood cells exposed to t-butyl hydroperoxide. Effects of the hexose monophosphate shunt as mediated by glutathione and ascorbate.

Lipid peroxidation and haemoglobin degradation were the two extremes of a spectrum of oxidative damage in red cells exposed to t-butyl hydroperoxide. The exact position in this spectrum depended on the availability of glucose and the ligand state of haemoglobin. In red cells containing oxy- or carbonmono-oxy-haemoglobin, hexose monophosphate-shunt activity was mainly responsible for metabolism of t-butyl hydroperoxide; haem groups were the main scavengers in red cells containing methaemoglobin. Glutathione, via glutathione peroxidase, accounted for nearly all of the hydroperoxide metabolizing activity of the hexose monophosphate shunt. Glucose protection against lipid peroxidation was almost entirely mediated by glutathione, whereas glucose protection of haemoglobin was only partly mediated by glutathione. Physiological concentrations of intracellular or extracellular ascorbate had no effect on consumption of t-butyl hydroperoxide or oxidation of haemoglobin. Ascorbate was mainly involved in scavenging chain-propagating species involved in lipid peroxidation. The protective effect of intracellular ascorbate against lipid peroxidation was about 100% glucose-dependent and about 50% glutathione-dependent. Extracellular ascorbate functioned largely without a requirement for glucose metabolism, although some synergistic effects between extracellular ascorbate and glutathione were observed. Lipid peroxidation was not dependent on the rate or completion of t-butyl hydroperoxide consumption but rather on the route of consumption. Lipid peroxidation appears to depend on the balance between the presence of initiators of lipid peroxidation (oxyhaemoglobin and low concentrations of methaemoglobin) and terminators of lipid peroxidation (glutathione, ascorbate, high concentrations of methaemoglobin).

Ascorbic Acid↗
PubMed1982

The free coenzyme A requirement of animal fatty acid synthetase. Participation in the continuous exchange of acetyl and malonyl moieties between coenzyme a thioester and enzyme.

A hypothesis that the existence of common binding sites for acetyl and malonyl moieties on the animal fatty acid synthetase necessitates that free CoA be available continuously to facilitate unloading of inappropriately bound acetyl or malonyl moieties, allowing initial access of an acetyl moiety and subsequent access by malonyl moieties to the site of chain elongation, was formulated and tested. The unloading of acetyl or malonyl moieties from the enzyme was blocked by a CoA-scavenging system and the enzyme was unable to reload with the other substrate; the inhibition was relieved by the addition of CoA or pantetheine. The freely reversible nature of the loading/unloading reaction was established as follows. CoA or pantetheine, but not S-acetyl-N-acetylcysteamine, could act as donor or acceptor for acetyl moieties in the loading or unloading reactions; incubation of fatty acid synthetase, acetyl-CoA, and [G-3H]CoA resulted in the formation of acetyl-[G-3H]CoA in an amount consistent with the predicted equilibrium; and addition of a high concentration of CoA shifted the equilibrium toward unloading, leaving most of the substrate-binding sites vacant. These results support our hypothesis and provide a plausible explanation both for the requirement of free CoA by the fatty acid synthetase and for the observed inhibition of fatty acid synthesis by high concentrations of CoA.

Acetyl Coenzyme A↗
PubMed1981

Lipid peroxidation and hemoglobin degradation in red blood cells exposed to t-butyl hydroperoxide. Dependence on glucose metabolism and hemoglobin status.

Changes in hemoglobin status and lipid peroxidation were followed in red cells containing either oxy-met-, or carbonmonoxyhemoglobin, incubated with t-butyl hydroperoxide in a medium with or without glucose. Loss of intact hemoglobin (the sum of oxyhemoglobin and methemoglobin) was inversely proportional to the degree of lipid peroxidation in red cells containing either oxy- or methemoglobin. When glucose was added to the medium, lipid peroxidation increased while there was a decreased loss of intact hemoglobin in red cells containing either oxy- or methemoglobin, while both lipid peroxidation and changes in hemoglobin decreased in red cells containing carbonmonoxyhemoglobin. Methemoglobin formation and loss of intact hemoglobin were directly proportional to the degree of lipid peroxidation in red cells containing carbonmonoxyhemoglobin. The greatest amount of lipid peroxidation occurred in red cells containing carbonmonoxyhemoglobin, incubated without glucose. These results indicate that methemoglobin and non-intact hemoglobin may protect the membrane against lipid peroxidation. We propose that, depending on the availability of glucose and the liganded state of hemoglobin, lipid peroxidation and hemoglobin alterations represent extremes of a spectrum of oxidative damage.

Adult↗
PubMed1981

Purification and properties of fatty acid synthetase from a human breast cell line.

A human mammary epithelial cell line (SKBr3) has been identified in which fatty acid synthetase constitutes up to 28%, by weight of the cytosolic proteins. The enzymes has been purified to near homogeneity from this cell line and some of its properties studied. In common with fatty acid synthetases from other animal tissues, the enzyme is a 480 000 dalton dimer of similar molecular weight subunits, it synthesizes predominantly palmitic acid and is inactive in the absence of free coenzyme A. The kinetic properties and amino acid composition of the enzyme are also similar to those of fatty acid synthetases from various tissues of other animals. Appreciable structural resemblance between human and rodent fatty acid synthetases is indicated by studies on the immunological cross-reactivities of these enzymes.

Amino Acids↗
PubMed1981

Development of the capacity of mouse mammary glands for medium chain fatty acid synthesis during pregnancy and lactation.

The time-course for appearance of fatty acid synthetase and thioesterase II, enzymes required for the synthesis of medium chain (C8--C12) fatty acids by the mammary gland, has been studied in the mouse and compared with that in the rat. The development of high levels of fatty acid synthetase in the mouse mammary gland during the early days of lactation coincided with an observed increase in the overall lipogenic capacity of the gland, assessed by measuring the incorporation of radioactive acetate into fat in tissue slices. Both the level of thioesterase II in the gland and the proportion of medium chain fatty acids synthesized from acetate by tissue slices began to increase in late gestation but did not reach a maximum until lactation was well established. In this regard the mouse is distinctly different from the rat, which establishes maximum levels of thioesterase II in the mammary gland prior to parturition. The significance of this difference as it relates to mammary gland development is discussed.

Acetates↗
PubMed1980

Studies with [35S]methionine indicate that the 22,000-dalton [Met]enkephalin-containing protein in chromaffin cells is a precursor of [Met]enkephalin.

It has been shown that [35S]methionine is incorporated into the [Met]enkephalin sequences of a 22,000-dalton enkephalin-containing protein in the adrenal medulla. Pulse-chase experiments indicate that label is incorporated into the large polypeptide before it appears in free [Met]enkephalin and a smaller [Met]enkephalin-containing peptide. These findings provide direct evidence of a precursor-product relationship of these structurally related polypeptides.

Adrenal Medulla↗