title: Urinary and faecal excretion of marker calcium (46Ca) by low birthweight infants.
abstract: Low birthweight infants were given calcium enriched in 46Ca in a single feed. The specific activity of successive urine samples showed that the absorption of the marker was largely complete in about 4 hours. The rate of decrease of urinary specific activity after 3 1/2 hours was exponential and very similar in 8 sets of observations in 6 infants. Its extrapolation backwards to 1 hour may indicate the size of the exchangeable calcium pool, usually about 200 mg/kg body weight. Completeness of faecal collection for estimation of 46Ca is essential for accurate determination of true absorption and endogenous faecal excretion of natural Ca. In 5 infants examined, nor marker was detectable in faeces excreted later than 48 hours after the first stool containing marker. Nevertheless, reasons are given why a collection period limited to 48 hours may sometimes involve error.
mesh_terms: D002118:Calcium / Q000378:metabolism* / Q000652:urine; D002127:Calcium Isotopes; D005243:Feces / Q000032:analysis*; D006801:Humans; D007223:Infant; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007408:Intestinal Absorption; D007668:Kidney / Q000378:metabolism; D013997:Time Factors
chemical_list: D002127:Calcium Isotopes; D002118:Calcium