title: A multiple infusion start time (MIST) protocol for stable isotope studies of fetal blood.
abstract: A new approach utilizing multiple infusion start times for two stable isotopes of leucine was applied to seven pregnancies in order to assess equilibration times for isotopic studies when a single fetal blood sample is available. Two infusates, one containing l -[1-(13)C]-leucine and the other l -[5,5,5-D3]-leucine, were given as a primed constant infusion in the maternal circulation at fetal blood sampling (FBS). In five patients l -[1-(13)C]-leucine infusion was started at time zero (T(0)) whereas l -[5,5,5-D3]-leucine infusion began 30 min later, and both were continued until the umbilical sample was obtained at 149.7+/-8.8 min. In order to assure non-steady state conditions, in two patients the first infusion started at T(0)and the second 17 and 6 min before FBS was performed at 115 and 154 min, respectively. The fetal/maternal ratio for l -[5,5,5-D3]-leucine over the fetal/maternal ratio for l -[1-(13)C]-leucine was 0.98+/-0.03, indicating steady state conditions for both infusions for the first six patients. In the last patient the ratio was 0.51, indicative of non-steady state conditions for the shortest infusion time. Our results show that a single fetal sample can provide data for fetal amino acid enrichments reflecting multiple time points. Leucine steady state is achieved 20 min after a primed continuous infusion both in the maternal and fetal circulations.
authors.affiliation: Department of Obstetrics & Gynecology, DMSD San Paolo, University of Milano, Via A. di Rudini' 8, 20142 Milan, Italy.
authors.forename: C L
authors.initials: CL
authors.lastname: Paolini
authors.forename: A M
authors.initials: AM
authors.lastname: Marconi
authors.forename: A W
authors.initials: AW
authors.lastname: Pike
authors.forename: P V
authors.initials: PV
authors.lastname: Fennessey
authors.forename: G
authors.initials: G
authors.lastname: Pardi
authors.forename: F C
authors.initials: FC
authors.lastname: Battaglia
mesh_terms: D001786:Blood Glucose / Q000032:analysis; D002245:Carbon Dioxide / Q000097:blood; D002247:Carbon Isotopes / Q000008:administration & dosage* / Q000097:blood; D005260:Female; D005312:Fetal Blood / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007651:Keto Acids / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D007930:Leucine / Q000008:administration & dosage* / Q000097:blood; D008431:Maternal-Fetal Exchange; D010100:Oxygen / Q000097:blood; D011247:Pregnancy
chemical_list: D001786:Blood Glucose; D002247:Carbon Isotopes; D007651:Keto Acids; D002245:Carbon Dioxide; D019344:Lactic Acid; C013082:alpha-ketoisocaproic acid; D007930:Leucine; D010100:Oxygen