Bjørn Brodal

Effects of dietary polyamines and clofibrate on metabolism of polyamines in the rat

The activities of catalase, polyamine oxidase, diamine oxidase, ornithine decarboxylase, and peroxisomal beta-oxidation were assayed in homogenates from liver and small intestinal mucosa of rats which had been fed either a diet very low in polyamines or a diet containing five times the levels of dietary polyamines (putrescine, spermine, and spermidine) found in a standard rat diet. In rats fed the high polyamine diet, hepatic activities of catalase and polyamine oxidase were significantly decreased. Levels of the other activities were unchanged, except that intestinal ornithine decarboxylase was decreased. In rats treated simultaneously with clofibrate, the high polyamine diet restored activities of catalase, ornithine decarboxylase, and polyamine oxidase back to levels found in rats fed the low polyamine diet. The expected increase in activity of peroxisomal beta-oxidation was observed, although this was somewhat diminished in rats fed the high polyamine diet. Intestinal diamine oxidase activity was stimulated by clofibrate, particularly in rats fed the high polyamine diet. For the duration of the experiment (20 days), levels of putrescine, spermine, and spermidine in blood remained remarkably constant irrespective of treatment, suggesting that polyamine homeostasis is essentially independent of dietary supply of polyamines. It is suggested that intestinal absorption/metabolism of polyamines is of significance in this respect. Treatment with clofibrate appeared to alter polyamine homeostasis.

The Influence of Haemolysis on the Radioimmunoassay of Insulin

The lysis of erythrocytes interferes with the radioimmunoassay of insulin, causing a destruction of the hormone. The disappearance of insulin in human blood in vitro is measured, as a function of time and the degree of haemolysis, by means of a radioimmunoassay. The insulin degradation after incubation with known amounts of haemolysates for different periods of time is verified using a trichloroacetic acid precipitation technique to obtain an estimate of the remaining intact hormone.

Enzymatic microanalysis of glycogen

A specific and simple enzymatic method for the determination of glycogen in tissue, with a detection limit of about 1 microgram glycogen (6.2 nmol glucosyl residues) is described. Glycogen is converted to 6-phosphogluconate by means of amyloglucosidase, hexokinase, and glucose-6-phosphate dehydrogenase. The increase in NADPH is measured fluorometrically. Muscle tissue (5-20 mg) is hydrolysed in hot KOH (5.4 mol/l), neutralized and analysed. The glycogen-glucosyl content in wet rat diaphragm muscle is about 43 mmol/kg.

Synthesis of phosphoenolphosphate from pyruvate in rat skeletal muscle.

1. The activity of pyruvate kinase, malic enzyme, phosphoenolpyruvate carbonoxykinase and pyruvate carboxylase was measured in muscle tissue. 2. The enzyme assays were critically evaluated. 3. Muscle tissue possesses at the most only residual activities of pyruvate carboxylase and PEP carboxykinase. 4. The pyruvate kinase activity was significantly lowered after a 24 hr fast. 5. Malic enzyme activity was increased after the fast.

Enhanced (Na+, K+)-activated ATPase activity after indirect electric stimulation of rat skeletal muscle in vivo

Abstract A significant increase in sarcolemma bound ATPase activity was obtained after indirect electric stimulation of leg muscles in rats. The enzyme activity was assayed on isolated sarcolemma, and the unstimulated leg served as control. Membrane located 5′-nucleotidase was unaffected by the muscle activity.

Activity of peroxisomal enzymes, and levels of polyamines in LPA-transgenic mice on two different diets

BackgroundIn man, elevated levels of plasma lipoprotein (a)(Lp(a)) is a cardiovascular risk factor, and oxidized phospholipids are believed to play a role as modulators of inflammatory processes such as atherosclerosis. Polyamines are potent antioxidants and anti-inflammatory agents. It was therefore of interest to examine polyamines and their metabolism in LPA transgenic mice.Concentration of the polyamines putrescine, spermidine and spermine as well as the activity of peroxisomal polyamine oxidase and two other peroxisomal enzymes, acyl-CoA oxidase and catalase were measured. The mice were fed either a standard diet or a diet high in fat and cholesterol (HFHC). Some of the mice in each feeding group were in addition given aminoguanidine (AG), a specific inhibitor of diamine oxidase, which catalyses degradation of putrescine, and also inhibits non-enzymatic glycosylation of protein which is implicated in the aetiology of atherosclerosis in diabetic patients. Non-transgenic mice were used as controls.ResultsIntestinal peroxisomal polyamine oxidase activity was significantly higher in LPA transgenic mice than in the non-transgenic mice, while intestinal peroxisomal catalase activity was significantly lower. Hepatic β-oxidation increased in Lp(a) transgenic mice fed the HFHC diet, but not in those on standard diet.Hepatic spermidine concentration was increased in all mice fed the HFHC diet compared to those fed a standard diet, while spermine concentration was decreased. With exception of the group fed only standard diet, transgenic mice showed a lower degree of hepatic steatosis than non-transgenic mice. AG had no significant effect on hepatic steatosis.ConclusionThe present results indicate a connection between peroxisomal enzyme activity and the presence of the human LPA gene in the murine genome. The effect may be a result of changes in oxidative processes in lipid metabolism rather than resulting from a direct effect of the LPA construct on the peroximal gene expression.