Charles S. Irving

UTILIZATION OF DIETARY CEREAL BY YOUNG INFANTS

The direct demonstration of cereal utilization by 16 healthy 1-month-old infants was achieved by tracing the appearance in breath CO2 of carbon derived from the fed cereal. These oxidation rates were compared with rates obtained from the feeding of glucose and glucose polymers. Fermentation of unabsorbed carbohydrate by the colonic flora was assessed by measurement of breath H2. Stools from four infants were analyzed for the quantity of carbon that originated from the cereal. Oxidation rates were not significantly different (mean = 31.2% of the dose fed). Mean peak hydrogen production was 39.8, 29.1, and 18.6 ppm for cereal, glucose polymers, and glucose, respectively. Cereal carbon was detected in the stools of two infants (3.7% and 13.1% of the ingested load). We conclude that young infants can utilize cereal, although absorption is not always complete. Hydrogen production increases with carbohydrate complexity; participation of colonic bacterial fermentation increases the net absorption of cereal.

Characterization of HCO3−/CO2 Pool Sizes and Kinetics in Infants

The first bicarbonate pool sizes and kinetic data necessary for the interpretation of substrate oxidation studies have been determined in six fed, nonacidotic infants, ages 2.5 to 5 months. Following an intravenous bolus of NaH13CO3 (50 mumol/kg), breath samples were collected over 240 min for the analysis of breath 13CO2. Each breath 13CO2 disappearance curve was fitted to a multicompartmental bicarbonate model previously derived in adults. The mean sizes of the three bicarbonate pools were: 7.4 +/- 0.8 mmol/kg (central pool), 15.1 +/- 4.8 mmol/kg (rapidly exchanging peripheral pool), and 8.8 +/- 3.5 mmol/kg (slowly exchanging peripheral pool). The mean percentage dose recovery was 57 +/- 10%. The pool sizes suggested that extensive metabolic exchange of carbon between HCO3- and organic metabolites occurred in the infant.

Effect of infant age on aminopyrine breath test results.

ABSTRACT: The aminopyrine breath test has been used in adults as a measure of hepatic N-demethylase activity. In order to study maturational changes in enzyme function, 13C aminopyrine (2 mg/kg) was administered orally to infants (n = 16) between the ages of 1 and 38 wk. Breath samples were collected for 6 h after administration of the labeled aminopyrine for the measurement of 13CO2 enrichment. Using a number of different scoring methods to quantitate 13CO2 elimination of breath, demethylation of aminopyrine was found to be positively correlated to age. By 20 wk of age, some infants had rates of elimination similar to those measured in adults. Absorption was excluded as a limiting variable, because no improvement in oxidation rates was found when the aminopyrine was readministered as an intravenous bolus. Changes in nutritional status and route of feeding (enteral versus parenteral) did not prevent the effect of maturation on aminopyrine elimination. Conclusions: 1) maturational differences are seen in the metabolism of aminopyrine; 2) these differences may reflect immaturity of N-demethylase activity or diversion of the liberated formaldehyde into biosynthetic rather than oxidative pathways.

New evidence for taurine biosynthesis in man obtained from 18O2 inhalation studies

The ability of adult humans to synthesize taurine was assessed by measurement of the 18O content of urinary taurine in eight subjects following 60 minutes inhalation of 18O2 (97% 18O). All subjects had at least one 3-hour urine collection in which the mole ratio of 18O-taurine to taurine was at least three times greater than the standard deviation of the stable isotope measurement. The peak mole ratios of 18O-taurine/16O-taurine ranged from 0.0075 to 0.015. These data indicated that adult human subjects have a significant ability to synthesize taurine.

Carbohydrate malabsorption in infants with diarrhea studied with the breath hydrogen test.

Fermentation of malabsorbed carbohydrate (CHO) reaching the colon was studied by measuring peak breath hydrogen (H2) production between feedings in 28 H2-producing hospitalized infants with diarrhea. Patients who required fewer than six days of hospitalization had lower breath H2 values when tested soon after admission than those who required longer stays. Patients hospitalized for more than five days had lower H2 amounts at discharge than on admission. Peak breath H2 values decreased when glucose was substituted for glucose polymers in formulas, or when the formula was fed by continuous drip via a nasogastric tube instead of by orally administered bolus. Glucose-positive and acidic stools were encountered occasionally and were associated with decreased H2 levels. The responses of H2 levels, stool pH, and glucose excretion after changes in patient management or intestinal metabolism of CHO reflect alterations in the balance between proximal intestinal absorption and distal colonic fermentation. Malabsorbed CHO that reaches a competent colon is utilized via microbial conversion, as indicated by high H2 levels, in the absence of glucose-positive and acidic stools. The presence of glucose in the feces or acidic stools indicates an inability of the colon to completely metabolize and absorb CHO or its products of fermentation.

Isolation and derivatization of plasma taurine for stable isotope analysis by gas chromatography-mass spectrometry

Abstract A method for the isolation and derivatization of plasma taurine is described that allows stable isotope determinations of taurine to be made by gas chromatography-mass spectrometry (gc-ms). The isolation procedure can be applied to 0.1 ml of plasma: the recovery of plasma taurine was 70–80%. For gc separation, taurine was converted to its dimethylaminomethylene methyl ester derivative which could not be detected by hydrogen flame ionization, but could be monitored readily by NH3 chemical ionization mass spectrometry. The derivatization reaction occurred partially on-column and required optimization of injection conditions. Using stable isotope ratiometry multiple ion detection, [M + 2 + H] + [M + H] + ion ratio of natural abundance taurine was determined with a standard deviation of less than ±0.07% of the ratio. The [1,2-13C]taurine/taurine mole ratios of standard mixtures could be accurately determined to 0.001. This stable isotope gc-ms method is suitable for studying the plasma kinetics of [1,2-13C]taurine in infants who are at risk with respect to taurine depletion.

Coordination and Binding of Taurine as Determined by Nuclear Magnetic Resonance Measurements on 13C-Labeled Taurine

A number of pharmacological actions of taurine (5,8,9,16,17,19, 21,30,31) on central nervous and peripheral tissues have suggested that taurine might modulate cation flux (15) by either direct (10, 13) or indirect interactions (4) with calcium. The ability of taurine to influence calcium flux by direct coordination with calcium depends on the fraction of free intracellular calcium which can be trapped by taurine. The fraction of calcium that exists as a taurine complex can be estimated readily from intracellular taurine, calcium and hydrogen ion levels, and the formation constants of taurine-calcium complexes. The latter formation constants can be determined in vitro and applied to in vivo conditions. Dolara and coworkers (11,12) using calcium-taurine formation constants estimated from natural abundance 13C chemical shift titration curves, have calculated that approximately 8% of the total calcium in mammalian myocardium exists in taurine complexes. The inherent difficulties associated with making very precise measurements on noisy, low sensitivity natural abundance 13C NMR spectra suggested that the determination of calcium-taurine formation constants be repeated using 13C enriched taurine. We have determined 13C chemical shift titration curves of the calcium-taurine system using 13C-taurine and have obtained new formation constants for calcium-taurine complexes by rigorous complex equilibrium analysis of the titration curves. These formation constants predict that only neglible amounts of calcium are bound directly to taurine at the taurine and calcium levels found in myocardial cells. Additional 13C NMR measurements of taurine in solution have revealed some unexpected electronic properties of the molecule, which may be important to its biological function.

Stable isotope study of plasma taurine kinetics in rhesus monkey

Taurine is one of the most abundant amino acids in mammals and there is increasing evidence for the importance of taurine during development. Plasma taurine kinetics in a rhesus monkey was studied using [1,2-13C2]taurine. Taurine in plasma was derivatized to its dimethylaminomethylene methyl ester, separated on a gas chromatographic column, and the [M+2+H]+/[M+H]+ ion ratio was measured by ammonia chemical ionization mass spectrometry. The results were comparable to those obtained from the simultaneous radioisotope tracer study using [35S]taurine. This stable isotope method requires only 200 microliters of plasma for precise and accurate determination and is suitable for taurine kinetic studies in human infants.

Effect of a simethicone-containing tablet on colonic gas elimination in breath

The effect of a tablet containing the antiflatulent, simethicone, on intestinal hydrogen (H2) elimination in breath was studied. In three trials, normal subjects (age 12–52 years) received, on subsequent days, lactulose or lactulose with two tablets of either simethicone or placebo in randomized order. Breath samples were collected over 210 min and analyzed by gas chromatography for H2. The time course of H2 expiration above baseline levels was calculated and compared for the three tests. No significant differences in transit time were found. Cumulative H2 expiration was significantly lower after simethicone compared to placebo. H2 production from stool incubated with simethicone or placebo indicated that the drug had no effect in reducing the fermentative production of H2in vitro. Interestingly, the vehicle present in the tablets could be fermented by intestinal bacteria. Simethicone reduced the amount of H2 eliminated in breath, but this effect was offset partially by H2 production from the fermentation of unabsorbable substances used in the formulation of the tablets.

[13C]Acetate Oxidation in Infants After Oral Versus Rectal Administration: A Kinetic Model

Summary: To study the fate of volatile fatty acids (VFA) in the large bowel, we compared the rate of oxidation of 13C-labeled VFA administered rectally with that of the orally administered substrate. On two different days, 1-[13C]acetate was administered rectally or orally to five infants recovering from diarrhea. Breath samples were collected over 4 h and analyzed for 13C enrichment of breath CO2 by gas isotope ratio mass spectrometry. The percent dose recoveries of 13C in breath were fitted to multicom-partmental models using the SAAM-27 program. Following model development procedures, the oral acetate breath test curves could be accounted for only by a compartmental model in which labeled acetate underwent absorption into and mixed with a systemic pool before oxidation took place. The rectal acetate breath test curves could be accounted for by a simpler model in which oxidation occurred directly in the compartment in which the rectal acetate was administered, and required no rate-limiting absorptive process. Our results indicate that the labeled acetate was oxidized more rapidly when the substrate was administered rectally than orally. This observation points to the direct utilization of volatile fatty acids within the colon.