title: Red blood cell (RBC) volume can be independently determined in vivo in the sheep using ovine RBCs labeled at different densities of biotin.
abstract: BACKGROUND
  To investigate the pathophysiology of anemia and responses to red blood cell (RBC) transfusions and erythropoietin, repeated measurement of the circulating red blood cell volume (RCV) would be useful. Ovine erythropoiesis is similar to human erythropoiesis. Accordingly, a method for measuring RCV using either human or sheep RBCs labeled at different biotin densities has been previously validated in vitro. Here preclinical studies validating this method for in vivo measurement of circulating RCV in sheep are reported.
  
  
  METHODS
  For each sheep, autologous RBCs were biotinylated were at four discrete densities (12, 24, 48, and 96µg biotinylation reagent/mL RBCs). The densities were mixed and infused intravenously. Blood was sampled five times over 1 hour beginning at 4 minutes. RCV values were determined based on dilution of each population of biotinylated RBCs and by the [(14) C]cyanate method.
  
  
  RESULTS
  There was no difference among RCVs measured at all densities through 16 minutes; however, by 60 minutes, RBCs biotinylated at the highest density overestimated RCV by 7.6%. RCV values increased 41% over the hour, consistent with equilibration with a pool of RBCs sequestered in the spleen. RCV by the [(14) C]cyanate method paralleled results by the biotin method but averaged 8% greater.
  
  
  CONCLUSIONS
  These studies provide evidence that all four densities of biotinylated RBCs can be used in sheep to simultaneously and independently determine RCV. We speculate that the multidensity biotinylation method will be useful both for multiple simultaneous measurements and for repeated measurement of circulating RCV and blood volume in humans.
authors.affiliation: Department of Biochemistry & Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA. mockdonaldm@uams.edu
authors.forename: Donald M
authors.initials: DM
authors.lastname: Mock
authors.forename: Nell I
authors.initials: NI
authors.lastname: Matthews
authors.forename: Shan
authors.initials: S
authors.lastname: Zhu
authors.forename: Leon F
authors.initials: LF
authors.lastname: Burmeister
authors.forename: M Bridget
authors.initials: MB
authors.lastname: Zimmerman
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Strauss
authors.forename: Robert L
authors.initials: RL
authors.lastname: Schmidt
authors.forename: Demet
authors.initials: D
authors.lastname: Nalbant
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Freise
authors.forename: Peter
authors.initials: P
authors.lastname: Veng-Pedersen
authors.forename: John A
authors.initials: JA
authors.lastname: Widness
mesh_terms: D000818:Animals; D001710:Biotin / Q000737:chemistry / Q000493:pharmacokinetics; D019921:Biotinylation / Q000379:methods*; D048429:Cell Size; D004906:Erythrocyte Count; D004912:Erythrocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D006400:Hematocrit / Q000379:methods; D006403:Hematologic Tests / Q000379:methods; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D009994:Osmolar Concentration; D012756:Sheep / Q000097:blood; D013194:Staining and Labeling / Q000379:methods*
chemical_list: D006454:Hemoglobins; D001710:Biotin