Dopamine beta-hydroxylase in rat serum and lymph: changes with age and effect of cold exposure.

The pH optimum for rat serum dopamine beta-hydroxylase (DBH) (3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating)(EC 1.14.17.1) was 4.0 in acetate buffer; other requirements were as reported by others. DBH activity in serum of 20-day-old fetuses is slightly higher than in that of their mothers. Levels of the enzyme in blood a few hours after birth are almost five times greater than in the adult, remain high during the suckling period, then drop rapidly during the 4th week after birth to about three times the adult level, which is then slowly reached over the next few weeks. These fluctuations in serum DBH activity coincide with the period of intense development and maturation of the sympathetic nervous system. There was not significant effect of cold exposure on blood DBH activity when newborn, suckling, weanling or adult warm- and cold-acclimated rats were exposed to cold. Similarly, exposure to cold that elicited two- to three-fold increases in O2 consumption failed to increase DBH activity in thoracic duct lymph. Therefore serum and lymph DBH activities are not sensitive indices of sympathetic secretory activity in the intact rat.     

Alteration in skeletal muscle mitochondria of cold-acclimated rats: Association with enhanced metabolic response to noradrenaline

This paper reports a search for structural changes in skeletal muscle mitochondria of cold-acclimated rats. Histochemical studies (succinic dehydrogenase) show that there appears to be a higher proportion of red fibers in the semitendinosus muscle of the cold-acclimated rat and that the white region of this muscle contains fibers which resemble intermediate fibers. Electron micrographs show an apparently larger number of small mitochondria in both red and white fibers. Counts of mitochondria isolated from skeletal muscle show that there are more mitochondria per gram of both red and white muscle in the cold-acclimated rat than in the non-acclimated control rat. Each mitochondrion contains less protein and less cytochrome oxidase. Thus the mitochondrial mass per gram of red and white muscle is not altered, as indicated by the unchanged content of mitochondrial protein and of cytochrome oxidase per gram of muscle. Thus there appears to be a repackaging of mitochondrial material into smaller units in the skeletal muscle of the cold-acclimated rat. The alteration is shown to be associated with the adaptive state of the rat. No change occurs in muscle mitochondria of cold-acclimated rats in which the development of the enhanced metabolic response to noradrenaline, a measure of the extent of adaptation, is inhibited by treatment with oxytetracycline. The change in skeletal muscle mitochondria disappears when the enhanced metabolic response to noradrenaline in rats which are already cold-climated is reversed by treating the rats with oxytetracycline while they continue to live in the cold. The change in muscle mitochondria also disappears when the cold-acclimated rat undergoes deacclimation after return to room temperature. The alteration in muscle mitochondria is thus not associated either with shivering or with a high metabolic rate. Skeletal muscle of the cold-acclimated rat is known to be an important site of heat production in the course of nonshivering thermogenesis; that is, it can undergo a considerable increase in metabolic rate in the absence of shivering on exposure of the cold-acclimated rat to cold. The metabolic basis of nonshivering thermogenesis is in an enhanced capacity of the tissues of the cold-acclimated rat, principally skeletal muscle, to respond by an increase in metabolic rate to the large amounts of noradrenaline secreted by the nerve endings of the sympathetic nervous system as a consequence of cold-exposure. The mechanism by which the metabolic response to noradrenaline in the cold-acclimated rat can be enhanced is unknown. The structural alteration observed in the skeletal muscle mitochondria of the cold-acclimated rat may indicate a functional alteration responsible for the enhanced capacity of the muscle to respond to noradrenaline by an increase in metabolic rate.     

Improved automated method for determining vitamin C in plasma and tissues.

An improved automated method for determining vitamin C in plasma and tissues is described. Total vitamin C was determined after oxidation to dehydroascorbic acid by reaction with 2,4-dinitrophenylhydrazine. The recovery of ascorbic acid added to plasma was 98 to 101% with a coefficient of variation of 1.8%. Interaction between samples with low, medium, and high concentrations was 1% and the coefficient of variation on 60 replicate analyses of plasma was 2.0%. In the analysis of 16 samples of rat plasma, results obtained by the automated method were essentially the same as those obtained by the original manual method. It was possible to determine vitamin C in 0.15 ml of plasma containing as little as 1.2 μg/ml. Vitamin C was also measured in extracts of rat heart, spleen, kidneys, adrenals, liver, and brain.     

Die Bedeutung des Erhaltungsstoffwechsels und der „maximalen”︁ Ausbeute

This paper examines the microbial denitrification of a medium containing acetate as C-source and of an industrial effluent containing volatile fatty acids as main components a ndphenolics as minor components. Values for m and Y_max are represented. It has been concluded that the maintenance coefficient comprises also those processes not involved in the maintenance metabolism of the cells. The least fraction of the rate of substrate utilization of this extended maintenance metabolism has been expressed by m · 100/q_max. From the values of Y_max a P/2e-ratio < 1 and the equation of cell synthesis have been evaluated.     

The biogeochemistry of two eutrophic marine lagoons and its effect on microphytobenthic communities

This paper summarizes the results of a study on the biogeochemistry of two eutrophic marine lagoons. The lagoons investigated were the Bassin d'Arcachon situated on the Atlantic coast, and Étang du Prévost on the Mediterranean coast. The sites chosen for this study were characterized by the presence of dense communities of microphytobenthos. Both lagoons receive a large input of nutrients but they differ in several aspects. The Bassin d'Arcachon receives a large amount of iron. Iron is of great importance in reducing the effects of eutrophication. Ferric iron is an efficient scavenger of phosphate and it has been proposed that this is one of the mechanisms that controls primary productivity and algal growth in this lagoon. The mechanisms of phosphate mobilization were studied by using sediment slurries. These experiments demonstrated that not only ferric iron but presumably also calcium was responsible for phosphate binding. Another effect of the high iron content in the Bassin d'Arcachon was the precipitation of sulfide as iron sulfide or pyrite. In the Étang du Prévost sulfate reduction resulted in the accumulation of free sulfide. The relative low content of iron in Étang du Prévost not only allowed the formation of free sulfide but may also have limited the binding capacity of phosphate in the sediment. On the other hand sulfate reduction was not important for the release of phosphate from the sediment. In Étang du Prévost primary productivity is nitrogen rather than phosphorus limited. In contrast in the Bassin d'Arcachon primary productivity was presumably mostly phosphate limited. In Étang du Prévost the non-heterocystous cyanobacterium Oscillatoria sp. was the dominant nitrogen-fixing species. Heterocystous species were excluded from this lagoon as a result of the presence of free sulfide. It was demonstrated that heterocystous cyanobacteria are more sensitive towards sulfide than non-heterocystous species. The absence of free sulfide explained the presence of the heterocystous cyanobacterium Anabaena sp. in Bassin d'Arcachon.