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Biomedical subjects

O H Lowry

Publications and source records attributed to O H Lowry.

At least 109 records · Page 6Linked to original sources
PubMed1978

Localization of glutamine accumulation and tubular reabsorption in rat nephron.

Glutamine accumulation in rat kidney was investigated by giving large loads of gluta, mate and aspartate and measuring glutamine changes in seven completely defined portions of the nephron and in small patches from the thin limb area and from the papilla. Both glutamate and aspartate (which is partly coverted to glutamate) caused increases up to sixfold in glutamine which were mainly confined to the proximal straight tubule. Plasma glutamine is minimally affected. In contrast, large glutamine loads doubled plasma glutamine and caused about a doubling of glutamine concentrations in all parts of the nephron, but resulted in no greater change in the proximal straight tubule than elsewhere. Simultaneous inulin and glutamine measurements make it seem likely that the proximal convoluted tubule is a major site of glutamine reabsorption. The low glutamine concentrations in these cells (only 40% higher than that in plasma) indicate a very small gradient at the antiluminal surface. We suggest that the proximal straight tubule is the major site of glutamine synthesis but that it may not be an important site of glutamine breakdown.

Animals↗
PubMed1978

Distribution along the rat nephron of three enzymes of gluconeogenesis in acidosis and starvation.

Methods were devised or modified which made it possible to measure phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase in seven defined parts of single nephrons and in patches from thin limb and papilla areas dissected from freeze-dried microtome sections of rat kidney. All three enzymes were essentially confined to the proximal tubule. In normal kidneys, the levels were highest in the proximal convoluted tubule. Glucose-6-phosphatase was 20 times higher in the early part of the convoluted segment than in the late part of the straight segment. With one exception, in acidosis, only phosphoenolpyruvate carboxykinase increased (fourfold in the proximal convoluted segment but much less in the straight portion). In starvation, phosphoenolpyruvate carboxykinase increased about as much as in acidosis in the proximal straight tubule, but not as much in convoluted portions, whereas glucose-6-phosphatase rose modestly in both parts of the proximal tubule and fructose bisphosphatase rose only in the straight tubule, especially the early segment. It is suggested that ammoniagenesis can accompany gluconeogenesis in the proximal convoluted tubule but not in the straight segment.

Acidosis↗
PubMed1978

Distribution of gamma-aminobutyric acid, glycine, glutamate and aspartate in the cochlear nucleus of the rat.

The distributions of gamma-aminobutyric acid (GABA), glycine, glutamate and aspartate were measured in cochlear nuclei of two rats by quantitative histochemical mapping procedures. The levels and distributions in the two rats were comparable, and resembled those previously reported for cat cochlear nucleus. The results are consistent with a concept that these putative transmitter amino acids have similar levels and distributions in the cochlear nucleus among mammals.

Aminobutyrates↗
PubMed1978

Measurement of metabolites in single preimplantation embryos; a new means to study metabolic control in early embryos.

Methods are described for preparing and analyzing single preimplantation mouse embryos for a variety of metabolites and cofactors (glucose-6-P, fructose-6-P, fructose-1,6-bisphosphate, ATP, AMP, Pi, citrate, isocitrate, alpha-ketoglutarate, and malate). Oil-well and enzymatic cycling techniques are combined to provide the sensitivity needed to measure the amounts present (10(-12) to 1o(-15) moles). After experimental treatment, embryos are collected on glass slides and freeze-dried. They can then be stored indefinitely under vacuum at -25 degrees C without deterioration. With these procedures, the embryos were collected at successive stages of development and subjected to starvation and refeeding with glucose, pyruvate or both. The results confirm the existence of a block at early stages at the P-fructokinase step. This may be due to inhibition by the very high citrate levels present. The data suggest that glycolysis is turned on late in preimplantation development by the rise in fructose-6-P, a deinhibitor of P-fructokinase. In the citrate cycle, no step between citrate and alpha-ketoglutarate is rate-limiting, but a step between alpha-ketaglutarate and malate appears to impede the flux at early embryonic stages.

Adenosine Monophosphate↗
PubMed1977

Organic acid and potassium accumulation in guard cells during stomatal opening.

Leaflets of Vicia faba L. with either open or closed stomata were quick-frozen and freeze-dried. Individual guard cell pairs and pure samples of palisade parenchyma, spongy parenchyma, and epidermis lacking guard cells were dissected from the leaflets, weighed, and assayed for organic acids or K(+).K(+) was measured by a new enzymatic method. In guard cells of open stomata, as compared to closed stomata, K(+) was 2- to 4-fold higher, malic acid 6-fold higher, and citric acid 3-fold higher. Both aspartic and glutamic acids were also higher, but the amounts present were low compared to malic and citric acids. Isocitric acid was significantly higher in one experiment, but not in another. Glyceric acid was not increased. Succinic acid was too low to detect by the method used; but in guard cells of open stomata the concentration must have been less than 2% of that of malic acid. Malic acid was higher in the palisade parenchyma from the leaflet with open stomata. The ion balance shows that malic and citric acids provide much of the counter ion for the K(+) taken up during stomatal opening.

Journal Article↗
PubMed1977

Enzymic assay of 10 to 10 moles of sucrose in plant tissues.

Procedures are described for measuring sucrose in plant extracts or freeze-dried tissue in the range between 10(-7) and 10(-14) moles. The method is based on the destruction of pre-existing glucose and fructose, followed by the hydrolysis of sucrose and reduction of NADP(+) by a series of coupled enzymic reactions. Depending on the sensitivity required, the NADPH is determined directly with a spectrophotometer or a fluorometer, or is amplified as much as 30,000 times before fluorometric assay. The procedures suggested for the macro level are simpler than current methods, and those suggested for microanalysis are several orders of magnitude more sensitive.With this technique, single palisade parenchyma cells and single spongy parenchyma cells of Vicia faba leaflets were each found to contain about 2.2 pmoles of sucrose.

Journal Article↗
PubMed1976

Distribution of 3':5'-cyclic AMP and 3':5'-cyclic GMP in rabbit retina in vivo: selective effects of dark and light adaptation and ischemia.

By use of highly sensitive radioimmunoassays, 3':5'-cyclic AMP (cAMP) and 3':5'-cyclic GMP (cGMP) were measured in individual layers of light- and dark-adapted rabbit retinas, and the effects of ischemia were determined. In light-adapted retinas, cGMP levels ranged 50-fold, with over 90% of the total concentrated in the photoreceptor cells. The layer of outer segments contained 95 mumol/kg of dry weight, or three times the concentration present in the remainder of the photoreceptor cell layers. By contrast, levels of cAMP varied only 4-fold; the lowest level (6 mumol/kg of dry weight) was found in the outer segment layer and the highest level (22 mumol/kg of dry weight) in the inner segment layer of the photoreceptor cells. Dark adaptation elevated cGMP levels only in retinal layers containing photoreceptor cells, and the greatest proportional increase was observed in the synaptic layer of photoreceptor cells. Dark adaptation also caused increases of cAMP that were restricted to the outer plexiform and outer nuclear layers. Ischemia lowered cGMP levels, but only in retinal layers containing photoreceptor cells, and elevated cAMP levels, primarily in the inner layers of the retina. The effects of ischemia were greater in the dark-adapted than in light-adapted retinas. These results indicate that cGMP and cAMP levels in retina are influenced by the light adaptational state, that ischemia markedly modifies these processes, and that the effects of both light exposure and ischemia are regionally selective.

Animals↗
PubMed1976

Direct quantitation of amino acid transport and metabolism in segments of individual nephrons.

A new approach to amino acid transport in kidney is described which may be useful for study of renal transport in general. The amino acid is given in threshold and above threshold loads along with inulin as a glomerular filtrate marker. The kidney is quickly frozen at --60 degrees. Frozen 16 mum sections are dried at --40 degrees, and identified parts of single nephrons are analyzed for amino acid given, certain metabolites and inulin. The relationship of amino acid to inulin along the tubule is used to indicate changes relative to the glomerular filtrate. With either aspartate or glutamate loads, both amino acids accumulate to high levels in segments in which transport is believed to take place (proximal convoluted and straight tubules). Glutamine also accumulates to a high degree, but only in the proximal straight tubule.

Amino Acids↗