ZINC KINETICS IN PRETERM INFANTS - A COMPARTMENTAL MODEL-BASED ON STABLE-ISOTOPE DATA

Zinc is an essential nutrient for growth; however, little is known abo ut zinc kinetics (absorption, distribution, and excretion) in preterm infants (<38-wk gestation). Zinc kinetics were studied in two preterm infants (gestational ages, 32 and 33 wk) following oral or intravenous administration of a stable isotope (Zn-70). Plasma, red blood cells ( RBC), urine, and feces were sampled for up to 30 days. Isotope enrichm ent was measured in tissues by inductively coupled plasma (ICP)-mass s pectrometry, and zinc was determined by ICP-atomic emission spectromet ry. Data were analyzed by compartmental analysis using SAAM31. Zinc in take increased during the studies, and, because body zinc was not in s teady state, both tracer (70Zn) and tracee (Zn) data were fitted using analogous models. A model for adults [M. E. Wastney, R. L. Aamodt, W. F. Rumble, and R. I. Henkin. Am. J. Physiol. 251 (Regulatory Integrat ive Comp. Physiol. 20): R398-R408, 1986] was modified to fit data from the preterm infants. RBC data were fitted using one compartment (vs. 2 in adults), and an adult RBC subsystem was included in the model to account for zinc introduced during blood transfusions. Exchange of zin c between compartments that were not sampled was based on zinc distrib ution in neonates. Absorption was 42 and 34%, and endogenous fecal exc retion, based on intravenous data, was 15 mu g . kg(-1). day(-1). The model can be used to quantify changes in zinc kinetics of preterm infa nts with age, weight, and zinc intake for evaluating nutritional requi rements with growth.