STABLE ISOTOPES OF LITHIUM - INVIVO DIFFERENTIAL DISTRIBUTION BETWEEN PLASMA AND CEREBROSPINAL-FLUID

  • 1 January 1982
    • journal article
    • research article
    • Vol. 17  (4) , 413-421
Abstract
Stable and radioactive isotopes of an element were used to study a variety of complex phenomena including metabolic pathways and enzyme reactions. Isotopes of an element are generally not treated in a differential manner. The 2 stable isotopes of Li, one of mass 6 and the other with a mass of 7, are differentially taken up by red blood cells with 6-8% higher quantities of 6Li being accumulated. The in vivo pharmacokinetics of Li isotopes are discussed. Adult cats [19] were given a single dose of either 6LiCl by gastric intubation (1 meq/kg) and 2 wk later the treatment was crossed. Plasma concentrations of the 2 Li isotopes were determined. In another series of studies 19 adult cats were given either 6LiCl or 7LiCl by intubation, CSF and blood samples were collected simultaneously and isotropic Li concentrations of the CSF and plasma were determined. The average plasma concentration of 6Li was higher than 7Li between 2 and 9 h postadministration. The elimination curve for both isotopes had an initial fast and later slow component. For the slow component 6Li had an average half-life of 12.9 and 7Li 15.9 h. Comparison of the CSF/plasma ratio for 6Li and for 7Li indicated that the ratios were higher for 6Li than 7Li 2-6 h after administration. Factors in addition to concentration gradients may influence the transport of Li isolates across the blood-brain barrier. The acute pharmacokinetics of the 2 Li isotopes were apparently not the same in compartmental distribution and rate of disppearance from plasma. 6Li may have a greater toxic or therapeutic effect than 7Li in the treatment of manic-depressive illness in humans.