Zinc absorption in premature infants: comparison of two isotopic methods.
(73/75)
The fractional absorption of an oral dose of zinc can be measured in adults when given simultaneously with an intravenous dose and subsequently measuring the ratio of the double isotopic enrichment of urine. To test this method in very-low-birth-weight (VLBW) premature infants [n=5 females and 7 males, 1160 +/- 290 g (chi +/- SD) birth weight, 29 +/- 4 wk gestational age], an oral dose of either 300 or 1200 micrograms 68Zn.kg(-1).d(-1) was equilibrated with formula or human milk and administered simultaneously with either 50 or 100 micrograms 70Zn.kg(-1).d(-1) given intravenously 35 +/- 3 wk postconception. Urine and fecal samples were collected for 3-6 d and analyzed by inductively coupled plasma mass spectrometry. Endogenous fecal zinc (EFZ) was determined from isotopic enrichment, whereas net absorption and retention were calculated by traditional methods. The mean fractional absorption calculated from urine was 0.22 +/- 0.09 and from feces it was 0.25 +/- 0.07. Zinc intake averaged 1821 +/- 330, fecal excretion 1637 +/- 419, and urinary excretion 67 +/- 30 micrograms.kg(-1).d(-1). EFZ averaged 390 +/- 270 micrograms.kg(-1).d(-1) and ranged from 48 to 889 micrograms.kg(-1).d(-1). Net absorption was 220 +/- 316 micrograms.kg(-1).d(-1) and net retention was 131 +/- 334 micrograms.kg(-1).d(-1). True absorption was 373 +/- 161 micrograms.kg(-1).d(-1). Fecal collection is difficult, tedious, and often incomplete, and may be replaced by urine collection for the fractional absorption of zinc in groups of premature infants. (+info)
Zinc absorption and intestinal losses of endogenous zinc in young Chinese women with marginal zinc intakes.
(74/75)
The objective of this study was to determine fractional absorption of exogenous zinc and intestinal excretion of endogenous zinc in women of childbearing age whose habitual dietary zinc intake was marginal. The target population (L group) comprised residents of a remote farming village in northeast China and the control subjects (M group) were residents of Beijing. Mean (+/-SE) calculated dietary zinc intakes were 5.2 +/- 0.2 and 8.1 +/- 0.2 mg/d, respectively. The phytate-zinc molar ratio in the diet of both groups was approximately 10:1. 70Zn was administered intravenously before breakfast and 67Zn orally with three main meals in 1 d. Subsequently, all feces were collected quantitatively until the second visible marker had been excreted and 12-h urine samples were collected on days 3-9. Fractional absorption was determined by measuring cumulative fecal excretion of nonabsorbed 67Zn and endogenous fecal zinc by isotope-dilution technique (70Zn). Fractional absorption values for L and M groups, respectively, were 0.31 +/- 0.03 and 0.34 +/- 0.03 (P=0.45). Corresponding figures for endogenous fecal zinc were 1.30 +/- 0.07 and 2.34 +/- 0.20 mg Zn/d (P<0.001). Both the estimated total size of the pools of zinc that exchange with zinc in plasma within 2 d (r=0.762, P<0.001) and the excretion of endogenous zinc in the feces (r=0.706, P<0.0001) were positively correlated with calculated total daily zinc absorption. We conclude that fractional absorption of zinc does not differ between women consuming marginal and adequate quantities of zinc in their diets, but endogenous zinc is conserved effectively by the intestine in women whose habitual dietary zinc is marginal. (+info)
A compartmental model of zinc metabolism in healthy women using oral and intravenous stable isotope tracers.
(75/75)
A mathematical model of zinc metabolism in six healthy women (average age: 30 +/- 11 y) was developed by using stable isotopes of zinc. After equilibration on a constant diet containing 7.0 mg Zn/d, an oral tracer highly enriched in 67Zn and an intravenous tracer highly enriched in 70Zn were administered simultaneously. Multiple plasma and 24-h urine samples were collected for the next 7 d with complete fecal collections for 11 d. Tracer-trace ratios in plasma, urine, and feces were calculated from isotope ratios of 67Zn to 66Zn and 70Zn to 66Zn measured by using inductively coupled plasma-mass spectrometry. An a priori identifiable model composed of seven compartments was developed to describe the kinetics of both tracers as well as that of naturally occurring zinc. The parameters of the model were fitted to the data by using the SAAM-CONSAM modeling software and were estimated with good precision. Several important, not directly measurable zinc variables were estimated (mean +/- SEM) from the model including the fractional absorption from the gastrointestinal tract (0.279 +/- 0.043), the rates of endogenous secretion (2.79 +/- 0.49 mg/d) and excretion (2.01 +/- 0.35 mg/d), the fractional turnover rate of the plasma pool (131 +/- 20/d), and the sizes (7.2 +/- 1.2 and 77.1 +/- 6.4 mg) and fractional turnover rates (22.3 +/- 7.1 and 1.49 +/- 0.18/d) of the fast and slow tissue pools equilibrating with the plasma, respectively. (+info)