ZINC-ABSORPTION IN PREMATURE-INFANTS - COMPARISON OF 2 ISOTOPIC METHODS

The fractional absorption of an oral dose of zinc can be measured in a dults when given simultaneously with an intravenous dose and subsequen tly 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 ((x) over bar +/- SD) birth w eight, 29 +/- 4 wk gestational age], an oral dose of either 300 or 120 0 mu g Zn-68 . kg(-1) d(-1) was equilibrated with formula or human mil k and administered simultaneously with either 50 or 100 mu g Zn-70 . k g(-1) d(-1) given intravenously 35 +/- 3 wk postconception. Urine and fecal samples were collected for 3-6 d and analyzed by inductively cou pled plasma mass spectrometry. Endogenous fecal zinc (EFZ) was determi ned from isotopic enrichment, whereas net absorption and retention wer e calculated by traditional methods. The mean fractional absorption ca lculated 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 pg kg(-1) . d(-1). EFZ averaged 390 +/ - 270 mu g kg(-1) . d(-1) and ranged from 48 to 889 mu g . kg(-1) d(-1 ) Net absorption was 220 +/- 316 mu g . kg(-1) d(-1) and net retention was 131 +/- 334 mu g . k(-1). d(-1). True absorption was 373 +/- 161 mu g . kg(-1) . d(-1). Fecal collection is difficult, tedious, and oft en incomplete, and may be replaced by urine collection for the fractio nal absorption of zinc in groups of premature infants.