The design and validation of a diet for studies of amino acid metabolism in adult humans

A dietary protocol developed for use in studies of amino acid and protein metabolism is reported in detail. The diet consisted of a mixture of free amino acids, an amino nitrogen-free liquid formula and protein-free cookies. Energy requirement for a group of adult men (n=10) was determined by multiplying each individual's resting metabolic rate, measured by indirect calorimetry, by a factor of 1.7. Subjects maintained a constant weight while consuming the experimental diet and had few complaints regarding palatability during a nine day study period. No significant variation (P=0.69) was evident over a six hour period in measurements of ¹³CO₂ enrichment in the breath of subjects (n=4) consuming small hourly meals of the diet. Dietary adaptation to a constant level of ¹³C enrichment in breath CO₂ with this dietary protocol was accomplished in a short period of time as shown by the lack of change in the mean (±SD) ¹³C enrichments of 0.02764±0.00084, 0.02818±0.00067 and 0.02812 ±0.00062 atoms percent enrichment in subjects (n=7) on days 3, 6 and 9 of the dietary period, respectively. The small within subject variation in repeated ¹³CO₂ enrichment measurements indicates the reliability of the dietary protocol in studies where a steady isotope background is essential. This dietary protocol provides a constant and stable metabolic milieu for studies of amino acid metabolism, especially, for those involving the use of stable isotopes.     

URINARY RIBOFLAVIN METABOLITES FROM RATS

Riboflavin-deficient, male rats were fed [2-¹⁴C] riboflavin to replete the animals prior to collecting ¹⁴C- compounds excreted during a second depletion period. Chromatographic fractionation and microbiological assay before and after acid hydrolysis indicated bound and free metabolites of riboflavin, as well as the vitamin itself.     

VITAMIN A AND THE SYNTHESIS OF A LIPID CONTAINING MANNOSE IN RAT LIVER

A polar metabolite of ¹⁴C-rctinol has been found in a mannolipid synthesized by a membrane-bound polyribosomal fraction from rat liver. Addition of retinal to an in vitro system increased the incorporation of ¹⁴C-inannose into mannolipid and glycoproteins.     

Bacterial colonization of enteral feeding tubes

An in-vitro model system was used to determine the number of bacteria infused into a 'patient' when three types of polyurethane enteral feeding-tubes that had been experimentally contaminated with feed containing K . aerogenes on day I, were then perfused with sterile feed for periods of 8 h on three consecutive days (days 2–4). The tubes were syringed with 20 ml sterile water at regular intervals. Viable counts were made on syringe washings, feed collected from the ends of the tubes and feed from the nutrient containers.
On day 1, the total number of K . aerogenes in feed samples collected from the nutrient containers and the ends of the tubes rose from 10² to 103–10⁴ cfu ml^-1 over 8 h. On days 2–4 no organisms were detected in the feed samples from the nutrient containers whereas viable counts on feed samples collected from the tubes and syringe washings rose from 10⁴ to 10⁷ and from 10¹ to 10⁷ cfu ml^-1 respectively.
It can be concluded that a single incidence of feed contamination could lead to a patient receiving contaminated feed from an enteral feeding-tube colonized with bacteria which will not be detected by normal monitoring of the remainder of the system.     

The Effect of Fasting and Fructose and Glucose Infusion on Gluconeogenesis and Triose Phosphate Flux in Rats in Vivo

Gluconeogenesis was measured quantitatively by mass isotopomer distribution analysis in rats in vivo through determination of the isotopic enrichment of the pool of hepatic triose phosphates, the immediate precursors of glucose, using primarily [2-¹³C]glycerol infusion after fasting, and following fructose and glucose infusion. The results showed that the liver controls gluconeogenesis, the metabolic sources and disposal of triose phosphates, and the contribution of glucose from glycogen in response to alterations in substrate availability.     

INCREASED ENZYME ACTIVITY IN VITRO AND METABOLISM OF SUBSTRATES IN VIVO

¹⁴CO₂ formation from a tracer dose of ¹⁴C-tryptophan or ¹⁴C-tyrosine in rats did not increase in proportion to the increases in the activities of the enzymes tryptophan pyrrolase and tyro transaminase after injection of hydrocortisone. The extent of oxidation was correlated to a greater extent with the amount of non-radioactive amino acid given with the tracer dose than with the increase in enzyme activity.     

THE METABOLISM OF MANNOHEPTULOSE-14 C BY THE RAT

Mannoheptulose induces a hyperglycemia by blocking insulin release, inhibiting synthesis of the hormone, or both. This sugar has been found not to be metabolized to any significant extent in the rat. since only a small percentage of an intravenously administered dose of mannoheptulose-¹⁴ C appeared as ¹⁴CO₂ within six hours. The bulk of the administered radioactivity was excreted in the urine as mannoheptulose.     

Addressing Ceiling Effects in Health Status Measures: A Comparison of Techniques Applied to Measures for People with HIV Disease

Objectives. To compare different approaches to address ceiling effects when predicting EQ-5D index scores from the 10 subscales of the MOS-HIV Health Survey.
Study Design. Data were collected from an HIV treatment trial. Statistical methods included ordinary least squares (OLS) regression, the censored least absolute deviations (CLAD) approach, a standard two-part model (TPM), a TPM with a log-transformed EQ-5D index, and a latent class model (LCM). Predictive accuracy was evaluated using percentage of absolute error ( R ¹) and squared error ( R ²) predicted by statistical methods.
Findings. A TPM with a log-transformed EQ-5D index performed best on R ¹; a LCM performed best on R ². In contrast, the CLAD was worst. Performance of the OLS and a standard TPM were intermediate. Values for R ¹ ranged from 0.33 (CLAD) to 0.42 (TPM-L); R ² ranged from 0.37 (CLAD) to 0.53 (LCM).
Conclusions. The LCM and TPM with a log-transformed dependent variable are superior to other approaches in handling data with ceiling effects.     

Problems with the re-use of enteral feeding systems—a study of the effectiveness of a range of cleaning and disinfection procedures

Although many manufacturer's state that their systems are 'single-use only', some authors are now recommending that enteral feed delivery systems can be re-used, particularly in the home, in order to reduce the expense of enteral feeding.
The purpose of this study was to evaluate the effectiveness of a range of currently recommended cleaning and disinfection procedures in removing bacteria from five commonly used enteral feeding systems. The systems used were, a collapsible, top-fill reservoir with integral giving set, a plastic enteral nutrition bag with side port and integral giving set, and three different types of rigid plastic reservoirs with separate giving sets.
The systems were filled with 1000-ml portions of feed experimentally contaminated with either Klebsiella aerogenes or Escherichia coli and the feed perfused through the systems for 15 h; viable counts increased from 10²-^-10³ to 10⁷-^-10⁹ cfu ml^-1. The systems were then cleaned by a range of methods including rinsing and/or immersing them in sterile water, sterile water and detergent, and/or disinfection with hypochlorite solutions. When the systems were refilled with sterile feed it was found that residual bacteria in the systems multiplied to yield levels ≤10⁹ cfu ml^-1 after 15 h.
The results of the present study demonstrate that none of the methods tested can be recommended as being totally effective in removing bacteria from contaminated systems.     

DIETARY CHOLESTEROL AND LIVER MICROSOMAL FATTY ACID DESATURASES

Dietary cholesterol increased the activity of rat liver microsomal fatty acid Δ⁹ desaturase, decreased that of Δ⁵ and Δ⁶ desaturases, and increased the fluorescence anisotrophy of 1,6-diphenyl-1,3,5-hexatriene.     

Prospective study of food intake and nutritional status in HIV infection

Weight loss is a common feature of Human Immunodeficiency Virus (HIV) infection. The aetiology of such weight loss is multifactorial; however the relative importance of factors involved is unknown. In order to test the hypothesis that a gross reduction of food intake is one of the factors responsible for weight loss seen in HIV disease, we prospectively measured food intake for 7 days in 11 male HIV antibody positive subjects and nine male control subjects. Anthropometric measurements were taken to assess nutritional status and fat absorption was assessed using 1–¹⁴C Triolein breath test. In the 3 months preceding the study mean weight loss was 3.9±1.2 kg. (s.e.m.) for the HIV antibody positive group. Protein and energy intakes were not significantly different between the two groups. HIV infected subjects had significantly lower mid-arm muscle circumference (MAMC) and grip strength (GS). Fat malabsorption of a minor degree was detected in only three subjects. These data suggest that constitutionally well HIV infected subjects have reduced MAMC and GS in the face of apparently adequate protein and energy intakes.     

ASCORBIC ACID AND THE CATABOLISM OF CHOLESTEROL

Guinea pigs with a latent, chronic ascorbic acid deficiency were injected with 26-¹⁴C-cholesterol and the conversion of the labeled chofesterol into bile acids was estimated by following the output of ¹⁴CO₂ for several weeks. Deficient guinea pigs accumulated serum and tissue cholesterol and had a lower output of ¹⁴CO₂ than did the controls. In addition, the turnover time of the labeled cholesterol was less than that of contols. From these, as well as previous results, it was concluded that adequate tissue concentrations of ascorbic acid were necessary for conversion of cholesterol to bile acids.     

LINOLEIC ACID METABOLISM IN THE CAT

When linoleate (18:2ω-6) is the only source of essential fatty acid in cat diets, the level of arachidonate (20:4ω-6) in plasma falls. Little ¹⁴C-arachidonate is formed when ¹⁴C-linoleate is fed to kittens even though feeding ¹⁴C-8, 11, 14-eicosatrienoate (20:3ω-6) caused significant arachidonate formation. Is this an essential fatty acid?     

Galactose Toxicity and Alterations in Brain Metabolism in the Chick

Chicks fed a diet containing 40 per cent galactose incorporated less ³²P into brain phosphatidylinositol than did controls. The levels of brain glucose and ATP uere also significantly reduced in the groups fed galactose, and galactose levels were greatly increased. The reduction in glucose level and in the synthesis of phosphatidylinositol may be related to the convulsive seizures in chicks fed galactose. The chick appears to be a sensitive model system for study of metabolic changes produced by high tissue levels of galactose.     

INTERACTION OF RETINOL AND RETINOIC ACID WITH THE NUCLEUS

Intracellular binding proteins for retinol and retinoic acid have been described. A nuclear retinoic acid receptor also has been detected. Pure cellular retinol-binding protein, containing bound labeled retinol was found to bind to isolated, purified rat liver nuclei. The binding was highly specific and saturable, showing about 3 times 10⁵ specific binding sites per nucleus.     

ADULT HEART CELLS ARE TARGETS FOR 1,25-DIHYDROXYVITAMIN D3

Nanomolar amounts of 1,25-dihydroxyvitamin D₃ stimulate the uptake of ⁴⁵Ca into heart myocytes in culture.     

Application of Hazard Analysis Critical Control Points system to enteral tube feeding in hospital

An HACCP system was implemented for the quality assurance of preparation, storage and delivery of enteral feeds to patients in hospital. Routine methods of feed preparation, storage and delivery to patients were studied and a flow chart was initially made. After identifying hazards, an HACCP team was assembled, a flow chart was modified and critical control points were defined using a decision tree. Control measures for each step of the process and its monitoring and corrective measures to be applied were also defined. In addition, feed samples were analysed for microbiological quality and feed storage temperatures were also recorded, before and after the implementation of the HACCP system. When the control measures were applied and monitored, the hazard was reduced. Bacterial counts in feed were reduced from 10⁵ cfu mL^–1 to < 10¹ cfu mL^–1. The results show that contamination of enteral feed may be reduced or eliminated if a systematic approach such as HACCP is applied effectively.     

The male antifertility activity of 6-Chloro-6-deoxyglucose

6-Chloro-6-deoxy[U-¹⁴C]glucose is not metabolised by mature boar spermatozoa nor has it any specific inhibitory action on their metabolic activity in vitro. The compound is metabolised by the male rat and the identification of two urinary metabolites as -chlorohydrin and 3-chlorolactate confirmed that (S)-3-chlorolactaldehyde is produced by this species in vivo. A tissue distribution study revealed that radioactivity from 6-chloro-6-deoxy[U-¹⁴C]glucose was more concentrated in rat caudal spermatozoa than in any other of the major tissues.     

METABOLISM OF PYRIDOXINE IN THE MOUSE

Quantitation of the levels of the different froms of vitamin B₆ at varying times following injections of ¹⁴C-pyridoxine into mice generally reflects the activities of the phosphokinase, oxidase, and transminases involved in the interconversions.     

EFFECT OF MEALS ON IRON ABSORPTION

The type of meal fed before and after a ⁵⁹Fe test meal affects whole-body retention of iron.