title: Noninvasive measures of radiolabeled dextran transport in in situ rabbit lung.
abstract: Dextrans are nontoxic and can be obtained in a wide variety of molecular weights. The purpose of this study was to label 6-kDa and 40-kDa dextrans with gamma- (99mTc) and positron- (18F) emitting radioisotopes and monitor their transport across the pulmonary microvascular barrier.
  
  
  METHODS
  External scan measurements for radiolabeled uncharged dextrans, albumin and red blood cells were obtained in eight blood-perfused in situ rabbit lung preparations. After 3 hr of external scanning, the lungs were removed for postmortem and extravascular distribution volume calculations. Extravascular distribution volumes were obtained in six additional rabbits following 4 hr of dextran perfusion to compare the effect of time. The normalized slope index (NSI), a measure of transvascular transport rate, was calculated for each diffusible tracer.
  
  
  RESULTS
  The mean NSI for albumin (0.001676 +/- 0.000537 min-1) was significantly lower than NSI for the 40-kDa dextran (0.002303 +/- 0.0005426 min-1) as well as the 6-kDa dextran (0.004312 +/- 0.001134 min-1). The difference between the 6-kDa and the 40-kDa dextrans was also significant. After 4 hr of equilibration, distribution volumes were not significantly different than those obtained at 3 hr.
  
  
  CONCLUSIONS
  Dextrans can be radiolabeled with gamma and positron emitters and small dextrans traverse the lung microvascular barrier more rapidly than albumin. Our results suggest that the use of small dextrans rather than albumin can reduce scan times in clinical applications and minimize motion artifact associated with the noninvasive gamma detection method.
authors.affiliation: Department of Biomedical Engineering, School of Engineering, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: V J
authors.initials: VJ
authors.lastname: Abernathy
authors.forename: N A
authors.initials: NA
authors.lastname: Pou
authors.forename: T L
authors.initials: TL
authors.lastname: Wilson
authors.forename: R E
authors.initials: RE
authors.lastname: Parker
authors.forename: S N
authors.initials: SN
authors.lastname: Mason
authors.forename: J A
authors.initials: JA
authors.lastname: Clanton
authors.forename: L J
authors.initials: LJ
authors.lastname: Baudendistel
authors.forename: R J
authors.initials: RJ
authors.lastname: Roselli
mesh_terms: D000818:Animals; D002199:Capillary Permeability / Q000502:physiology*; D003911:Dextrans / Q000493:pharmacokinetics; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics; D007553:Isotope Labeling; D008168:Lung / Q000000981:diagnostic imaging* / Q000378:metabolism; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics; D011817:Rabbits; D011877:Radionuclide Imaging
chemical_list: D003911:Dextrans; D005462:Fluorine Radioisotopes; D015609:Organotechnetium Compounds; C034146:technetium Tc 99m dextran