University of Helsinki, Helsinki 2006
A novel assay method for measuring added plasma caesium and its application in the measurement of short-term kinetics
Doctoral dissertation, October 2006.
The aim of this thesis was to develop a new simple method for measuring added caesium (Cs) in blood plasma and to use it in the study of short-time plasma kinetics.
The new method, based on isotopic dilution, is analogous to radioimmunoassay. The dispersive complex salt ammonium-iron(III)-hexacyanoferrate(II) (AFCF) has a very high affinity towards Cs+. In a mixture of plasma, AFCF and added radioactive Cs tracer (134Cs), the amount of AFCF-bound activity depends o n the amount of stable Cs in plasma. This bound activity is separated from soluble activity by co-precipitating AFCF with plasma proteins using trichloroacetic acid and measured using a standard gamma counter. Using standard samples prepared from plasma collected prior to an intravenously given Cs dose, the Cs concentration in plasma samples after the dose can be determined. The qualitative detection limit for the method is around 0.2 µmol l-1, and the practical limit for quantitative results around 1 µmol l-1.
Using this method, short-term plasma kinetics after an intravenous dose of Cs was measured in both goats and horses. The values measured for goats were very similar to those using 134Cs as a tracer in another study.
The rate constant for the removal of Cs from the bloodstream was initially above 0.1 min-1, but decreased within 40 min to a value below 0.02 min-1. From 2 to 40 min, the plasma concentration can be approximated with a biphasic exponential decay curve. Exercise speeds up the rate of Cs removal from blood. Between 30 and 40 min after the start of exercise, the rate of Cs removal was twice as high in exercising individuals compared to resting individuals (0.06 min-1 vs. 0.03 min-1). Stimulation of muscle sodium-potassium pumps (Na, K-ATPase) is a plausible explanation for the increased removal of Cs from blood during exertion.
At 30 min after dosing, the tissues with the highest 134Cs content were the gastrointestinal tract (22% of original dose), skeletal muscle (14% of dose) and the kidney (13%). A likely location for the large unrecovered portion of the original dose (38%) was connective tissue. Incorporation in one or several of these tissues probably explains the rapid initial removal of Cs from circulation.
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© University of Helsinki 2006
Last updated 04.10.2006