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D A Hems

Publications and source records attributed to D A Hems.

At least 73 records · Page 4Linked to original sources
PubMed1973

Plasma lipoproteins and the synthesis and turnover of plasma triglyceride in normal and genetically obese mice.

1. Lipoproteins in the plasma of mice were characterized by agarose-gel chromatography and polyacrylamide-gel electrophoresis: genetically obese (ob/ob) mice exhibited hyperlipoproteinaemia (compared with lean mice), largely owing to an increase in the concentration of cholesterol in high-density lipoprotein. Plasma concentrations of triglyceride and phospholipid were not markedly increased in genetically obese mice. 2. The formation of glycerolipids in liver and plasma was investigated with (14)C-labelled precursors. The synthesis of hepatic triglyceride and phospholipid from glucose or palmitate was enhanced in ob/ob mice, compared with lean mice. The rate of entry of triglyceride into plasma, calculated from the time-course of incorporation of (14)C from [(14)C]palmitate into plasma triglyceride, was increased in ob/ob mice (0.5mumol of fatty acid/min, compared with 0.2 in lean mice). 3. The removal from plasma of murine lipoprotein triglyceride-[(14)C]fatty acid was increased in ob/ob mice (half-time 2.2min, compared with 7.2min in lean mice). Similar results were obtained with an injected lipid emulsion (Intralipid). 4. From these measurements, estimates of the rates of turnover of plasma triglyceride in mice (fed on a mixed diet, female, 3 months old) are about 1.0mumol of fatty acid/min in ob/ob mice, and 0.25 in lean mice. 5. The major precursor of hepatic and plasma triglyceride in lean and ob/ob mice was calculated to be plasma free fatty acid. 6. These results are discussed, in connexion with the role of the liver in triglyceride metabolism in mice, especially in relation to genetic obesity.

Animals↗
PubMed1973

Stimulation by vasopressin of glycogen breakdown and gluconeogenesis in the perfused rat liver.

1. Vasopressin (anti-diuretic hormone, [8-arginine]vasopressin) stimulated the breakdown of glycogen in perfused livers of fed rats, at concentrations (50-600muunits/ml) that have been reported in the blood of intact rats, especially during acute haemorrhagic shock. 2. In perfused livers from starved rats, vasopressin (30-150muunits/ml) stimulated gluconeogenesis from a mixture of lactate, pyruvate and glycerol. 3. Vasopressin prevented accumulation of liver glycogen in the perfused liver of starved rats, or in starved intact rats. 4. The action of vasopressin on hepatic carbohydrate metabolism thus resembles that of glucagon; the minimum effective circulating concentrations of these hormones are of the same order (100pg/ml). 5. The stimulation of hepatic glucose output by vasopressin is discussed in connexion with the release of glucose and water from the liver.

Animals↗
PubMed1972

Carbohydrate metabolism in the isolated perfused rat kidney.

1. Anaerobic formation of lactate from glucose by isolated perfused rat kidney (411mumol/h per g dry wt.) was three times as fast as in aerobic conditions (138mumol/h per g). 2. In aerobic or in anaerobic conditions, the ratio of lactate production to glucose utilization was about 2. 3. Starvation or acidosis caused a decline of about 30% in the rate of aerobic glycolysis. 4. The rate of formation of glucose from lactate by perfused kidney from a well-fed rat, in the presence of 5mm-acetoacetate (83mumol/h per g dry wt.), was of the same order as the rate of aerobic glycolysis. 5. During perfusion with physiological concentrations of glucose (5mm) and lactate (2mm) there were negligible changes in the concentration of either substrate. 6. Comparison of kidneys perfused with lactate, from well-fed or starved rats, showed no major differences in contents of intermediates of gluconeogenesis. 7. The tissue concentrations of hexose monophosphates and C(3) phosphorylated glycolytic intermediates (except triose phosphate) were decreased in anaerobic conditions. 8. Aerobic metabolism of fructose by perfused kidney was rapid: the rate of glucose formation was 726mumol/h per g dry wt. and of lactate formation 168mumol/h per g (dry wt.). Glycerol and d-glyceraldehyde were also released into the medium. 9. Aerobically, fructose generated high concentrations of glycolytic intermediates. 10. Anaerobic production of lactate from fructose (74mumol/h per g dry wt.) was slower than the aerobic rate. 11. In both anaerobic and aerobic conditions the ratio [lactate]/[pyruvate] in kidney or medium was lower during perfusion with fructose than with glucose. 12. These results are discussed in terms of the regulation of renal carbohydrate metabolism.

Acetoacetates↗
PubMed1972

Glycogen synthesis in the perfused liver of the starved rat.

1. In the isolated perfused liver from 48h-starved rats, glycogen synthesis was followed by sequential sampling of the two major lobes. 2. The fastest observed rates of glycogen deposition (0.68-0.82mumol of glucose/min per g fresh liver) were obtained in the left lateral lobe, when glucose in the medium was 25-30mm and when gluconeogenic substrates were present (pyruvate, glycerol and serine: each initially 5mm). In this situation there was no net disappearance of glucose from the perfusion medium, although (14)C from [U-(14)C]glucose was incorporated into glycogen. There was no requirement for added hormones. 3. In the absence of gluconeogenic precursors, glycogen synthesis from glucose (30mm) was 0-0.4mumol/min per g. 4. When livers were perfused with gluconeogenic precursors alone, no glycogen was deposited. The total amount of glucose formed was similar to the amount converted into glycogen when 30mm-glucose was also present. 5. The time-course, maximal rates and glucose dependence of hepatic glycogen deposition in the perfused liver resembled those found in vivo in 48h-starved rats, during infusion of glucose. 6. In the perfused liver, added insulin or sodium oleate did not significantly affect glycogen synthesis in optimum conditions. In suboptimum conditions (i.e. glucose less than 25mm, or with gluconeogenic precursors absent) insulin caused a moderate acceleration of glycogen deposition. 7. These results suggest that on re-feeding after starvation in the rat, hepatic glycogen deposition could be initially the result of continued gluconeogenesis, even after the ingestion of glucose. This conclusion is discussed, particularly in connexion with the role of hepatic glucokinase, and the involvement of the liver in the glucose intolerance of starvation.

Animals↗
PubMed1972

Metabolism of glutamine and glutamic acid by isolated perfused kidneys of normal and acidotic rats.

1. When isolated kidneys from fed rats were perfused with glutamine the rate of ammonia release at pH7.4 (110-360mumol/h per g dry wt.) was one to two times that of glutamine removal. Glucose formation from 5mm-glutamine was 16mumol/h per g. If kidneys were perfused with glutamine at pH7.1 (10-13mm-sodium bicarbonate) there was no increase in glutamine removal or in the formation of ammonia or glucose. 2. When isolated kidneys from fed rats were perfused with glutamate at pH7.4, glucose formation was 59mumol/h per g, glutamine formation was 182mumol/h per g and ammonia release was negligible. At pH7.1 glutamine synthesis was inhibited and formation of ammonia and glucose were increased. 3. In perfused kidneys from acidotic rats, which had received 1.5% (w/v) NH(4)Cl to drink for 7-10 days, gluconeogenesis from glutamine was enhanced (101mumol/h per g). Glutamine removal and ammonia formation were also increased, compared with the rates in perfused kidney from normal rats. The extra glutamine consumed was equivalent to the extra glucose formed. 4. When the kidney from the 7-10-day-acidotic rat was perfused with glutamate gluconeogenesis was increased (113mumol/h per g). Synthesis of glutamine was decreased, and ammonia release was approximately equal to the rate of glutamate removal. 5. The time-course of these metabolic alterations was investigated after the rapid induction of acidosis by infusion of 0.25m-HCl into the right side of the heart. The increase in gluconeogenesis from glutamine developed gradually over several hours. When kidneys from 6h-acidotic rats were perfused with glutamate, formation of glucose and glutamine were both rapid. 6. In acidotic rat kidneys perfused with glutamine, tissue concentrations of glutamate and glucose 6-phosphate were increased compared with those in control perfused kidneys from non-acidotic rats. 7. The results are discussed in terms of control of the renal metabolism of glutamine. In particular, it is suggested that in acidotic rats glucose formation is the major fate of the carbon of the extra glutamine utilized by the kidney, and that inhibition of glutamine synthetase could contribute to the increase in intracellular ammonia concentration in the kidney.

Acidosis↗
PubMed1971

Effects of metabolic acidosis and starvation on the content of intermediary metabolites in rat kidney.

1. Metabolite contents were determined in freeze-clamped kidney from acidotic and starved rats in order to elucidate the rate-controlling steps which are responsible for the acceleration of gluconeogenesis in these situations. 2. In the kidney of rats which were made mildly acidotic by replacing drinking water with 1.5% ammonium chloride for 7 to 10 days (when the plasma bicarbonate concentration was 20mm) the content of phosphoenolpyruvate was increased from the control value of 35 to 63nmol/g and that of 3-phosphoglycerate from 85 to 154nmol/g. 3. Similar but smaller changes in these metabolites occurred in the kidney of starved rats but there were no such changes in the kidney of rats 12h after an infusion of 0.25m-hydrochloric acid, although plasma bicarbonate concentration fell to about 10mm on this treatment. 4. The renal concentration of glucose 6-phosphate was not raised in rats that received ammonium chloride, but was increased in starved and acutely acidotic rats. 5. The concentrations of alpha-oxoglutarate, malate and citrate were less than half the normal value in the kidney of both groups of acidotic rats. These changes can be accounted for on the basis of equilibrium relationships among reversible reactions, particularly as a result of the rise in intracellular ammonia content. A less marked decrease in alpha-oxoglutarate and malate was found in the kidney of starved rats. 6. The renal cortical cytoplasmic oxaloacetate concentration was calculated to be decreased in acidotic and starved rats. 7. These results are discussed in the light of the known enhancement by acidosis and starvation of renal gluconeogenesis. In particular they support the suggestion that the phosphoenolpyruvate carboxykinase reaction is a site of control of gluconeogenesis in kidney in these conditions.

Acidosis↗
PubMed1971

Carbohydrate metabolism of the isolated perfused liver of normal and genetically obese--hyperglycaemic (ob-ob) mice.

1. A technique for perfusion of the mouse liver has been developed, and aspects of carbohydrate metabolism have been investigated in the perfused liver of normal and genetically obese mice, homozygous for the recessive gene ob. 2. Rates of gluconeogenesis in perfused mouse liver were faster than those reported for slices of mouse liver, particularly from lactate and pyruvate. 3. The rate of glycogen breakdown to glucose, but not to lactate, was faster in liver from fed obese mice. 4. The capacity for glycogen synthesis from glucose was enhanced in liver from 20h-starved obese mice. 5. The capacity for gluconeogenesis from a number of substrates was not significantly altered in livers from fed or starved obese mice when compared with that of lean mice. 6. These results suggest that the liver contributes to the hyperglycaemia of the obese mice by increased glycogenolysis, and that liver glycogen in obese mice is maintained by synthesis from dietary glucose.

Alanine↗
PubMed1970

Effects of ischaemia on content of metabolites in rat liver and kidney in vivo.

1. The time-course of changes in content of intermediates of glycolysis in rat liver and kidney cortex after severance of blood supply was investigated. 2. The decline in content of ATP was more rapid in kidney (1.7-0.5mumol/g in 30s) than in liver (2.7-1.6mumol/g in 60s). In both tissues AMP and P(i) accumulated. 3. Net formation of lactate was 1.7mumol/g during the second minute of ischaemia in liver from well-fed rats, 1.1mumol/g in liver from 48h-starved rats, and about 1.0mumol/g during the first 30s of ischaemia in kidney. Net formation of alpha-glycerophosphate was rapid, especially in liver. 4. In kidney the concentration of beta-hydroxybutyrate rose, but that of alpha-oxoglutarate and acetoacetate decreased. 5. In both organs the concentrations of fructose diphosphate and triose phosphates increased during ischaemia and those of other phosphorylated C(3) intermediates decreased. 6. The concentration of the hexose 6-phosphates rose rapidly during the first minute of ischaemia in liver, but decreased during renal ischaemia. 7. In kidney the content of glutamine fell after 2min of ischaemia, and that of ammonia and glutamate rose. 8. The redox states of the cytoplasmic and mitochondrial NAD couple in kidney cortex were similar to those in liver. 9. The regulatory role of glycogen phosphorylase, pyruvate kinase and phosphofructokinase is discussed in relation to the observed changes in the concentrations of the glycolytic intermediates.

Acetoacetates↗
PubMed1969

Effects of added nucleotides on renal carbohydrate metabolism.

1. The regulatory effects that adenine nucleotides are known to exert on enzymes of glycolysis and gluconeogenesis were demonstrated to operate in kidney-cortex slices and in the isolated perfused rat kidney by the addition of exogenous ATP, ADP and AMP to the incubation or perfusion media. 2. Both preparations rapidly converted added ATP into ADP and AMP, and ADP into AMP; added AMP was rapidly dephosphorylated. AMP formed from ATP was dephosphorylated at a lower rate than was added AMP, especially when the initial ATP concentration was high (10mm). Deamination of added AMP occurred more slowly than dephosphorylation of AMP. 3. Gluconeogenesis from lactate or propionate by rat kidney-cortex slices, and from lactate by the isolated perfused rat kidney, was inhibited by the addition of adenine nucleotides to the incubation or perfusion media. In contrast, oxygen consumption and the utilization of propionate or lactate by slices were not significantly affected by added ATP or AMP. 4. The extent and rapidity of onset of the inhibition of renal gluconeogenesis were proportional to the AMP concentration in the medium and the tissue, and were not due to the production of acid or P(i) or the formation of complexes with Mg(2+) ions. 5. Glucose uptake by kidney-cortex slices was stimulated 30-50% by added ATP, but the extra glucose removed was not oxidized to carbon dioxide and did not all appear as lactate. Glucose uptake, but not lactate production, by the isolated perfused kidney was also stimulated by the addition of ATP or AMP. 6. In the presence of either glucose or lactate, ATP and AMP greatly increased the concentrations of C(3) phosphorylated intermediates and fructose 1,6-diphosphate in the kidney. There was a simultaneous rise in the concentration of malate and fall in the concentration of alpha-oxoglutarate. 7. The effects of added adenine nucleotides on renal carbohydrate metabolism seem to be mainly due to an increased concentration of intracellular AMP, which inhibits fructose diphosphatase and deinhibits phosphofructokinase. This conclusion is supported by the accumulation of intermediates of the glycolytic pathway between fructose diphosphate and pyruvate. 8. ATP or ADP (10mm) added to the medium perfusing an isolated rat kidney temporarily increased the renal vascular resistance, greatly diminishing the flow rate of perfusion medium for a period of several minutes.

Adenine Nucleotides↗