Rapid determination of whole-body bicarbonate kinetics by use of a digital infusion

Accurate determination of substrate oxidation rates from breath 13CO2 levels often requires information on the bicarbonate status of the subject. We have developed a rapid method to obtain a complete set of bicarbonate kinetic parameters, prime bicarbonate pools with 13C, clamp breath 13CO2 levels rapidly and accurately with predetermined ranges, and provide a steady base-line enrichment of 13C for a subsequent substrate oxidation measurement. The method consists of administering NaH13CO3 intravenously as a combination of a bolus dose, an exponentially decreasing infusion, and a constant infusion. A Harvard model 2729 microprocessor-controlled syringe pump was modified for external control and coupled to a Hewlett-Packard HP-85 desk-top computer to deliver the complex infusion. An infusion algorithm that would rapidly attain and maintain an increase of 50% 13C enrichment of breath CO2 was derived by using the SAAM-27 program to interrogate a three-compartmental model of bicarbonate kinetics in normal, fasted, resting adult subjects. When the method was tested on five adult fasted subjects who had rested for 1.5 h, plateau enrichments were achieved within 10–20 min. The bicarbonate pool sizes and kinetic parameters obtained by compartmental analysis of their 13CO2 data were used to obtain a refined infusion protocol, which resulted in more rapid attainment of plateau enrichments. If carried out immediately before a substrate oxidation test, the method can provide a complete description of bicarbonate kinetics for use in the compartmental and noncompartmental analysis of substrate catabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Download Full-text

Whole-body protein metabolism in lactating and nonlactating women

Journal of Applied Physiology ◽

10.1152/jappl.1989.66.1.370 ◽

1989 ◽

Vol 66 (1) ◽

pp. 370-376 ◽

Cited By ~ 7

Author(s):

K. J. Motil ◽

C. M. Montandon ◽

D. L. Hachey ◽

T. W. Boutton ◽

P. D. Klein ◽

...

Keyword(s):

Protein Metabolism ◽

Whole Body ◽

Constant Infusion ◽

Dietary Intakes ◽

Adaptive Responses ◽

Body Protein ◽

Lactating Women ◽

Dietary Nutrients ◽

Amino Acid Flux

The adaptive responses of body protein metabolism to lactation were characterized in women at 1, 5, and 12 mo postpartum and in nulliparous controls during a controlled diet of measured protein and energy intakes by nitrogen balance, a constant infusion of [13C]bicarbonate, and a primed constant infusion of [1–13C]leucine and [alpha-15N]-lysine. Dietary energy intakes in the lactating women were 27% greater than those in the nulliparous controls. Despite these differences, lactating women had significantly lower nitrogen balances compared with the nonlactating women (-4.0 +/- 37.8 vs. +44.7 +/- 30.8 mg.kg-1.day-1). No significant differences in amino acid flux, oxidation, or incorporation into protein were detected during fasting conditions in the two groups of women. However, significantly positive associations were noted between dietary intakes and the variables of protein metabolism in the lactating women. A more complete understanding of the mechanisms that regulate the disposition of dietary nutrients into maternal body stores or milk production will enhance the determination of nutrient requirements in lactating women.

Download Full-text

Altered lipid kinetics in adjuvant recombinant human growth hormone-treated multiple-trauma patients

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1994.267.4.e560 ◽

1994 ◽

Vol 267 (4) ◽

pp. E560-E565 ◽

Cited By ~ 1

Author(s):

M. Jeevanandam ◽

S. R. Petersen

Keyword(s):

Growth Hormone ◽

Multiple Trauma ◽

Human Growth Hormone ◽

Recombinant Human Growth Hormone ◽

Human Growth ◽

Whole Body ◽

Constant Infusion ◽

Control Group ◽

Trauma Patients ◽

Oxidation Rates

Adjuvant recombinant human growth hormone therapy during the postinjury period may improve the efficiency of utilization of body energy stores. In a group of 20 severely injured highly catabolic hypermetabolic adult multiple-trauma victims, we have investigated the basic lipid kinetics of trauma (study I) and its modification after 7 days of intravenous feeding (total parenteral nutrition) with (group H, n = 10) or without (group C, n = 10) daily rhGH (0.15 mg somatotropin.kg-1.day-1) intramuscular injections (study II). Whole body lipolysis rate (2-stage primed constant infusion of 10% glycerol), substrate net oxidation rates (indirect calorimetry), and plasma levels of hormones were determined. Compared with the control group (group C) the treatment group (group H) showed significantly (P = 0.006) enhanced rates of lipolysis and free fatty acid reesterification (10 +/- 2 to 18 +/- 2 kcal.kg-1.day-1, P = 0.05). As a function of resting energy expenditure (REE), a trend of increased net glucose oxidation [32 +/- 10 vs. 56 +/- 7% REE, not significant (NS)] and decreased fat (40 +/- 8 vs. 25 +/- 5% REE, NS) and protein oxidation rates (28 +/- 2 vs. 19 +/- 2% REE, P = 0.007) were also indicated. The simultaneous operation of increased lipolytic and reesterification processes may allow the adipocyte to respond rapidly to changes in peripheral metabolic fuel requirements in injury.

Download Full-text

Rapid determination of kinetic parameters for the electrocatalytic reduction of dioxygen by vitamin B12 adsorbed on glassy carbon electrode

Electrochimica Acta ◽

10.1016/0013-4686(93)80112-d ◽

1993 ◽

Vol 38 (15) ◽

pp. 2297-2303 ◽

Cited By ~ 13

Author(s):

Qingsheng Qiu ◽

Shaojun Dong

Keyword(s):

Vitamin B12 ◽

Kinetic Parameters ◽

Glassy Carbon Electrode ◽

Glassy Carbon ◽

Rapid Determination ◽

Carbon Electrode ◽

Electrocatalytic Reduction

Download Full-text

Whole body leucine flux in HIV-infected patients treated with or without protease inhibitors

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00067.2005 ◽

2006 ◽

Vol 290 (4) ◽

pp. E685-E693 ◽

Cited By ~ 3

Author(s):

Magali Prod’homme ◽

Cécile Rochon ◽

Michèle Balage ◽

Henri Laurichesse ◽

Igor Tauveron ◽

...

Keyword(s):

Amino Acid ◽

Protein Metabolism ◽

Glucose Infusion ◽

Fat Free Mass ◽

Whole Body ◽

Constant Infusion ◽

Body Protein ◽

X Ray ◽

Immunodeficiency Virus

The present study was carried out to assess the effects of protease inhibitor (PI) therapy on basal whole body protein metabolism and its response to acute amino acid-glucose infusion in 14 human immunodeficiency virus (HIV)-infected patients. Patients treated with PIs (PI+, 7 patients) or without PIs (PI−, 7 patients) were studied after an overnight fast during a 180-min basal period followed by a 140-min period of amino acid-glucose infusion. Protein metabolism was investigated by a primed constant infusion of l-[1-13C]leucine. Dual-energy X-ray absorptiometry for determination of fat-free mass (FFM) and body fat mass measured body composition. In the postabsorptive state, whole body leucine balance was 2.5 times ( P < 0.05) less negative in the PI+ than in the PI− group. In HIV-infected patients treated with PIs, the oxidative leucine disposal during an acute amino acid-glucose infusion was lower (0.58 ± 0.09 vs. 0.81 ± 0.07 μmol·kg FFM−1·min−1 using plasma [13C]leucine enrichment, P = 0.06; or 0.70 ± 0.10 vs. 0.99 ± 0.08 μmol·kg FFM−1·min−1 using plasma [13C]ketoisocaproic acid enrichment, P = 0.04 in PI+ and PI− groups, respectively) than in patients treated without PIs. Consequently, whole body nonoxidative leucine disposal (an index of protein synthesis) and leucine balance (0.50 ± 0.10 vs. 0.18 ± 0.06 μmol·kg FFM·−1·min−1 in PI+ and PI− groups respectively, P < 0.05) were significantly improved during amino acid-glucose infusion in patients treated with PIs. However, whereas the response of whole body protein anabolism to an amino acid-glucose infusion was increased in HIV-infected patients treated with PIs, any improvement in lean body mass was detected.

Download Full-text

Effects of oral contraceptives on glucose flux and substrate oxidation rates during rest and exercise

Journal of Applied Physiology ◽

10.1152/japplphysiol.00693.2002 ◽

2003 ◽

Vol 94 (1) ◽

pp. 285-294 ◽

Cited By ~ 48

Author(s):

Sang-Hoon Suh ◽

Gretchen A. Casazza ◽

Michael A. Horning ◽

Benjamin F. Miller ◽

George A. Brooks

Keyword(s):

Oral Contraceptives ◽

Substrate Oxidation ◽

Metabolic Effects ◽

Whole Body ◽

Moderate Intensity ◽

High Dose ◽

Moderate Intensity Exercise ◽

Oxidation Rates ◽

Glucose Flux ◽

Hormone Analogs

We examined the effects of oral contraceptives (OC) on glucose flux and whole body substrate oxidation rates during rest (90 min) and two exercise intensities [60-min leg ergometer cycling at 45 and 65% peak O2 uptake (V˙o 2 peak)]. Eight healthy, eumenorrheic women were studied during the follicular and luteal phases before OC and the inactive and high-dose phases after 4 mo of a low-dose, triphasic OC. Subjects were studied in the morning 3 h after a standardized (308 kcal) breakfast. There were significant reductions in glucose rates of appearance and disappearance during exercise of both intensities with OC but not rest. There were no phase effects on substrate oxidation during rest or exercise. These results are interpreted to mean that, in women fed several hours before study, 1) OC decreases glucose flux, but not overall carbohydrate and lipid oxidation rates during moderate-intensity exercise; and 2) synthetic ovarian hormone analogs in the doses contained in OC have greater metabolic effects on glucose metabolism during exercise than do endogenous ovarian hormones.

Download Full-text

The contribution of phenylalanine to tyrosine metabolism in vivo. Studies in the post-absorptive and phenylalanine-loaded rat

Biochemical Journal ◽

10.1042/bj2100811 ◽

1983 ◽

Vol 210 (3) ◽

pp. 811-817 ◽

Cited By ~ 28

Author(s):

L L Moldawer ◽

I Kawamura ◽

B R Bistrian ◽

G L Blackburn

Keyword(s):

In Vivo Studies ◽

Whole Body ◽

Constant Infusion ◽

Substantial Contribution ◽

Oxidation Rates ◽

Plasma Phenylalanine ◽

Tyrosine Oxidation ◽

Tyrosine Metabolism ◽

Plasma Tyrosine

1. Rates of appearance and oxidation of plasma L-leucine, L-phenylalanine and L-tyrosine, as well as conversion of plasma phenylalanine into plasma tyrosine, were determined in 90-120 g rats after overnight starvation and while receiving 115-120 mumol of L-phenylalanine/h. 2. In the post-absorptive state, plasma tyrosine and phenylalanine appearances were similar, despite the fact that 22% of plasma tyrosine appearance could be attributed to the hydroxylation of phenylalanine. 3. A constant infusion of 115-120 mumol of L-phenylalanine/h did not significantly alter plasma leucine kinetics, but increased appearance of plasma phenylalanine and tyrosine. The percentage of phenylalanine and tyrosine appearance that was oxidized increased from 12.1% and 24.4% to 37.3% and 48.0% respectively. In phenylalanine-loaded rats, 72% of plasma tyrosine appearance could be attributed to the conversion of phenylalanine. 4. Whole-body tyrosine oxidation measured from a continuous infusion of either L-[14C]tyrosine or L-[14C]phenylalanine differed by 165%. 5. It can be concluded that, in the post-absorptive state, phenylalanine hydroxylation makes a substantial contribution to the plasma appearance of tyrosine and is significantly increased when phenylalanine is administered. The disposal of excess infused phenylalanine is a result of a greater percentage of plasma phenylalanine being converted into tyrosine and a greater proportion of tyrosine being further oxidized. However, apparent tyrosine oxidation rates estimated from plasma tyrosine specific radioactivities and appearance of expired 14CO2 during administration of [14C]tyrosine are underestimates of true rates, in part because tyrosine generated from phenylalanine hydroxylation is catabolized without freely equilibrating with the plasma compartment.

Download Full-text

Hemodialysis stimulates muscle and whole body protein loss and alters substrate oxidation

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.2002.282.1.e107 ◽

2002 ◽

Vol 282 (1) ◽

pp. E107-E116 ◽

Cited By ~ 176

Author(s):

T. Alp Ikizler ◽

Lara B. Pupim ◽

John R. Brouillette ◽

Deanna K. Levenhagen ◽

Kali Farmer ◽

...

Keyword(s):

Amino Acids ◽

Muscle Protein ◽

Substrate Oxidation ◽

Whole Body ◽

Constant Infusion ◽

Acid Oxidation ◽

Protein Breakdown ◽

Protein Loss ◽

Body Protein ◽

Protein Calorie Malnutrition

The hemodialysis (HD) procedure has been implicated as a potential catabolic factor predisposing the chronic HD (CHD) patients to protein calorie malnutrition. To assess the potential effects of HD on protein and energy metabolism, we studied 11 CHD patients 2 h before, during, and 2 h after HD by use of primed constant infusion of l-[1-13C]leucine andl-[ ring-2H5]phenylalanine. Our results showed that HD led to increased whole body (10%) and muscle protein (133%) proteolysis. Simultaneously, whole body protein synthesis did not change, and forearm synthesis increased (120%). The net result was increased net whole body protein loss (96%) and net forearm protein loss (164%). During the 2-h post-HD period, the muscle protein breakdown trended toward baseline, whereas whole body protein breakdown increased further. Substrate oxidation during the post-HD was significantly altered, with diminished carbohydrate and accelerated lipid and amino acid oxidation. These data demonstrate that hemodialysis is an overall catabolic event, decreasing the circulating amino acids, accelerating rates of whole body and muscle proteolysis, stimulating muscle release of amino acids, and elevating net whole body and muscle protein loss.

Download Full-text

Model for determination of 13C substrate oxidation rates in humans in the fed state

American Journal of Clinical Nutrition ◽

10.1093/ajcn/41.6.1277 ◽

1985 ◽

Vol 41 (6) ◽

pp. 1277-1282 ◽

Cited By ~ 14

Author(s):

P J H Jones ◽

P B Pencharz ◽

L Bell ◽

M T Clandinin

Keyword(s):

Substrate Oxidation ◽

Fed State ◽

Oxidation Rates

Download Full-text

Rapid Determination of Ammonia in a Perchloric Acid Supernate from Blood, by Use of an Ammonia-Specific Electrode

Clinical Chemistry ◽

10.1093/clinchem/19.10.1162 ◽

1973 ◽

Vol 19 (10) ◽

pp. 1162-1169 ◽

Cited By ~ 32

Author(s):

Henning F Proelss ◽

Billy W Wright

Keyword(s):

Perchloric Acid ◽

Rapid Determination ◽

Clinical Status ◽

Accurate Determination ◽

Ammonia Nitrogen ◽

Blood Proteins ◽

Exchange Method ◽

Time Required ◽

Sensitivity Specificity

Abstract A simple, rapid method was developed for accurate determination of ammonia in whole blood. Blood proteins were precipitated with perchloric acid (8 g/dl) and the free ammonia liberated in the supernate on alkalinization was measured directly with an ammonia-specific electrode after adjusting the sample temperature to 25 °C. Some variables affecting precision, accuracy, and electrode performance were studied. Sensitivity, specificity, and interferences are discussed. The tentative normal range is 28 ± 14 µg of ammonia nitrogen per deciliter. The coefficient of variation was 4.8% in the "normal," 3.6% in the "abnormal" range. Abnormal values were correlated with clinical status. Recoveries averaged 99.3%. Correlation with an established ion-exchange method for plasma ammonia was 0.994. Total time required for a complete assay is 15 min.

Download Full-text