Uric acid and urea in human sweat

The present study investigated whether thermal sweating may relieve elevated concentrations of serum uric acid or urea. Concentrations of uric acid and urea were measured in the sweat of sixteen male volunteers, who were treated with external heat after one hour of intense physical exercise. The same analytes were also measured in their urine and serum samples. Furthermore, creatinine and some electrolytes were determined in these specimens. The results show that the concentration of uric acid in the sweat is 24.5 micromol/L, which is only 6.3% of that in serum. The concentration of urea in the sweat is 22.2 mmol/L, which is 3.6 times that in serum. The results indicate that sweat uric acid concentration is quite minimal, and the estimated total uric acid excretion per day in normal physiological range is insignificant. However, the level of sweat urea was found at a much higher concentration than the serum level. No correlation could be established between the level of uric acid in sweat and in serum. There was also no correlation between the level of urea in sweat and that in serum. These results suggest it would not be effective to relieve the elevated serum uric acid concentration by thermal sweating when the renal excretion of uric acid is partly compromised. Nevertheless, the potential of urea excretion via profuse sweating is apparent particularly when the kidneys are damaged or their function is impaired. These findings also suggest that persons who take vigorous exercise or are exposed to hot environments should be well advised to drink adequate fluids since heavy sweating excretes only minimal uric acid, accompanied by significant diminution of urinary output and diminished urinary excretions of uric acid, which may induce elevated levels of serum uric acid.     

Bone marrow fat mobilization in relation to lipid and protein catabolism during prolonged fasting in barn owls

 To assess the role of bone marrow fat in survival during a period of negative energy balance, we investigated the relationship between the time-course of marrow fat mobilization and the metabolic states associated with body fuel utilization during a prolonged fast. In order to mimic the winter fast of the barn owl (Tyto alba), captive birds were subjected to fasts of various durations at 5 °C ambient temperature. Body mass and plasma metabolites were used to determine the metabolic state at the end of fasting. Skeleton composition remained unchanged throughout phase II of fasting, during which the birds essentially rely on lipid fuels. During the following phase III, characterized by an increase in net body protein breakdown, the lipid mass in skeleton marrow decreased sharply by 78%, concomitant with an increase of the bone water content. This marrow fat mobilization occurred in all parts of the skeleton. This observation supports the hypothesis that bone marrow fat is not only involved in local nutrition, but can also be used as a lipid reserve for total energy requirements. However, in contrast to other fat deposits, marrow fat is mobilized only during phase III of the fast, when the last shift from lipid to protein fuel metabolism occurs. Thus, metabolic and/or hormonal changes associated with this transition could be involved in bone marrow fat mobilization. Lastly, our results suggest that the measurement of bone marrow fat can be used as an accurate index of the nutritional status (i.e. phase II or phase III) in barn owls. Accepted: 4 July 1996     

Relationships between amino acid catabolism and protein anabolism in the ruminant

The observed relation found in sheep between the flux rate of an amino acid and the proportion found in whole-body protein suggests that the major immediate fate of an amino acid is its incorporation into tissue protein. This may be true even for dispensable amino acids. In ruminants, there is substantial utilization of several amino acids (serine, glycine, threonine, histidine, and methionine) for the synthesis of methyl groups; the use of these amino acids for gluconeogenesis is limited. There is little evidence that demands of gluconeogenesis limit the availability of amino acids for protein synthesis. Most amino acids are catabolized in the liver but there may be significant catabolism of alanine, aspartate, and glutamate in peripheral tissues, especially muscle. Normally, peripheral catabolism of branched-chain amino acids is significantly less in ruminants than other species. Nevertheless, there is some oxidation of leucine by muscle and this may be substantially increased in the diabetic state. Catabolism of leucine (and perhaps isoleucine and valine) might be inversely related to use for protein synthesis, but there is no evidence of such a relation for other amino acids.     

Regulation of glutamate dehydrogenase activity in relation to carbon limitation and protein catabolism in carrot cell suspension cultures

Glutamate dehydrogenase (GDH) specific activity and function have been studied in cell suspension cultures of carrot (Daucus carota L. cv Chantenay) in response to carbon and nitrogen supply in the culture medium. The specific activity of GDH was derepressed in sucrose-starved cells concomitant with protein catabolism, ammonium excretion, and the accumulation of metabolically active amino acids. The addition of sucrose led to a rapid decrease in GDH specific activity, an uptake of ammonium from the medium, and a decrease in amino acid levels. The extent of GDH derepression was correlated positively with cellular glutamate concentration. These findings strengthen the view that the function of GDH is the catabolism of glutamate, which under conditions of carbon stress provides carbon skeletons for tricarboxylic acid cycle activity.     

Fatty acid-binding protein and its relation to fatty acid oxidation

A relation between fatty acid oxidation capacity and cytosolic FABP content was found in heart and various muscles of the rat. Other tissues do not show such a relation, since they are involved in more or other pathways of fatty acid metabolism. At postnatal development FABP content and fatty acid oxidation capacity rise concomitantly in heart and quadriceps muscle in contrast to in liver and kidney. A dietary fat content of 40 en. % increased only the FABP content of liver and adipose tissue. Peroxisomal proliferators increased fatty acid oxidation in both liver and kidney, but only the FABP content of liver, and had no effect on heart and skeletal muscle. The FABP content of muscle did not show adaptation to various conditions. Only it increased in fast-twitch muscles upon chronic electrostimulation and endurance training.     

Ornithine metabolism in relation to stimulation of urea cycle,induced by high protein diet

Approximate rates of some in vivo ornithine metabolisms in rats were calculated by pulse-labeling data, on the assumption that hepatic metabolite levels are constant during a given 3-min period. The rate of ornithine catabolism was 70–110 nmol/min/g liver; that of urea output was 3–6 μmol/min/g liver; the rotary rate of the “ornithine flux” was 10–12 rpm. A change from a 25 to a 70% casein diet resulted in a 1.5-fold augmentation in the rate of ornithine catabolism and a 1.6-fold increase in the rate of urea output; however, the rate of the “ornithine flux” remained nearly constant These findings suggest that stimulation of the urea cycle is accompanied not by acceleration of the cycle rotation, but rather by increased mass of the metabolite flux.     

Peptidases and amino acid catabolism in lactic acid bacteria

The conversion of peptides to free amino acids and their subsequent utilization is a central metabolic activity in prokaryotes. At least 16 peptidases from lactic acid bacteria (LAB) have been characterized biochemically and/or genetically. Among LAB, the peptidase systems of Lactobacillus helveticus and Lactococcus lactis have been examined in greatest detail. While there are homologous enzymes common to both systems, significant differences exist in the peptidase complement of these organisms. The characterization of single and multiple peptidase mutants indicate that these strains generally exhibit reduced specific growth rates in milk compared to the parental strains. LAB can also catabolize amino acids produced by peptide hydrolysis. While the catabolism of amino acids such as Arg, Thr, and His is well understood, few other amino acid catabolic pathways from lactic acid bacteria have been characterized in significant detail. Increasing research attention is being directed toward elucidating these pathways as well as characterizing their physiological and industrial significance.     

Metabolic control of urea catabolism in Chlamydomonas reinhardi and Chlorella pyrenoidosa.

In the unicellular green alga Chlamydomonas reinhardi (strain y-1), synthesis of the enzymes required for urea hydrolysis is under substrate induction control by urea and under end product repression control by ammonia. Hydrolysis of urea if effected by the sequential action of the discrete enzymes urea carboxylase and allophanate lyase, collectively called urea amidolyase. The carboxylase converts urea to allophanate in a reaction requiring biotin, adenosine 5'-triphosphate, and Mg2+. The lyase hydrolzyes allophanate to ammonium ions and bicarbonate. Neither activity is present in more than trace amounts when cultures are grown with ammonia or urea plus ammonia, or when they are starved for nitrogen for 8 h. Urea in the absence of ammonia induces both activities 10 to 100 times the basal levels. Addition of ammonia to an induced culture causes complete cessation of carboxylase accumulation and an 80% depression of lyase accumulation. Ammonia does not reduce urea uptake by repressed cells, so it does not prevent induction by the mechanism of inducer exclusion. The unicellular green alga Chlorella pyrenoidosa (strain 3 Emerson) also has discrete carboxylase and lyase enzymes, but only the carboxylase exhibits metabolic control.     

Utilisation of Wadden Sea salt marshes by geese in relation to livestock grazing

To arctic breeding geese, the salt marshes of the International Wadden Sea are important spring staging areas. Many of these marshes have always been grazed with livestock (mainly cattle and sheep). To evaluate the influence of livestock grazing on composition and structure of salt-marsh communities and its consequences for habitat use by geese, a total of 17 pairs of grazed and ungrazed marshes were visited both in April and May 1999, and the accumulated grazing pressure by geese was estimated using dropping counts. Observed grazing pressure was related to management status and to relevant vegetation parameters.The intensity of livestock grazing influences the vegetation on the marsh. Salt marshes that are not grazed by livestock are characterised by stands with a taller canopy, a lower cover of grasses preferred by geese, and a higher cover of plants that are not preferred.Overall goose-dropping densities are significantly lower in ungrazed marshes compared to marshes grazed by livestock. Some ungrazed marshes had comparatively high goose grazing pressure, and these were all natural marshes on a sandy soil, or artificial mainland marshes with a recent history of intensive livestock grazing. Goose grazing is associated with a short canopy. The plant communities with short canopy, dominated by Agrostis stolonifera, Festuca rubra and Puccinellia maritima, together account for 85% of all goose droppings in our data.The sites that were not visited by geese differed very little from those that were visited, in the parameters we measured. This might indicate that there was no shortage of available habitat for spring staging geese in the Wadden Sea, in the study period.     

Amino acid repletion does not decrease muscle protein catabolism during hemodialysis

Intradialytic protein catabolism is attributed to loss of amino acids in the dialysate. We investigated the effect of amino acid infusion during hemodialysis (HD) on muscle protein turnover and amino acid transport kinetics by using stable isotopes of phenylalanine, leucine, and lysine in eight patients with end-stage renal disease (ESRD). Subjects were studied at baseline (pre-HD), 2 h of HD without amino acid infusion (HD-O), and 2 h of HD with amino acid infusion (HD+AA). Amino acid depletion during HD-O augmented the outward transport of amino acids from muscle into the vein. Increased delivery of amino acids to the leg during HD+AA facilitated the transport of amino acids from the artery into the intracellular compartment. Increase in muscle protein breakdown was more than the increase in synthesis during HD-O (46.7 vs. 22.3%, P < 0.001). Net balance (nmol.min(-1).100 ml (-1)) was more negative during HD-O compared with pre-HD (-33.7 +/- 1.5 vs. -6.0 +/- 2.3, P < 0.001). Despite an abundant supply of amino acids, the net balance (-16.9 +/- 1.8) did not switch from net release to net uptake. HD+AA induced a proportional increase in muscle protein synthesis and catabolism. Branched chain amino acid catabolism increased significantly from baseline during HD-O and did not decrease during HD+AA. Protein synthesis efficiency, the fraction of amino acid in the intracellular pool that is utilized for muscle protein synthesis decreased from 42.1% pre-HD to 33.7 and 32.6% during HD-O and HD+AA, respectively (P < 0.01). Thus amino acid repletion during HD increased muscle protein synthesis but did not decrease muscle protein breakdown.     

Uric acid correlates to oxidation and inflammation in opposite directions in women

Abstract

Objective: To evaluate the association of uric acid (UA) levels with a panel of markers of oxidative stress and inflammation.

Methods: Plasma UA levels, along with a panel of oxidative stress and inflammatory markers, were measured in 755 Chinese women.

Results: Plasma UA levels were inversely associated with urinary levels of the oxidative stress marker F₂-isoprostanes and positively correlated to levels of inflammatory markers, such as C-reactive protein and some proinflammatory cytokines (tumor necrosis factor-α and interleukin-6) in blood as well as prostaglandin E₂ metabolites in urine.

Conclusions: Plasma UA levels correlate to oxidation and inflammation biomarkers in opposite directions in women.