Influence of ovariectomy on extracellular fluid volume in rats: Assessmentof extracellular fluid volume by means of bromide

There is considerable evidence that the extracellular fluid volume (ECV) ma y change in disease states or during longitudinal intervention studies. The refore, the measurement of ECV is important for studying body composition i n patients and laboratory animals. We present a modified plasma bromide (Br -, non-radioactive) assay using anion-exchange chromatography, in which a s mall blood sample of 200 mu L (100 mu L of plasma) appeared to be enough to reproducibly measure ECV. The inter- and intra-assay accuracy of the Br- a nalysis ranged from -1.6% to 0.9% and from -0.5% to 0%, respectively The in ter- and intra-assay precision ranged from 1.3% to 1.7% and from 0.6% to 1. 2%, respectively. This modified precise and accurate Br- analysis in a smal l blood sample was applied to investigate whether the ECV changed in rats a fter ovariectomy Ovariectomy significantly (P <.05) reduced the ECV as comp ared with results in SHAM rats. This observation indicates that a change in clinical condition may change ECV, which has consequences for the determin ation of, for example, the fractional absorption and the relative bioavaila bility of compounds principally distributed through the ECV.