INVESTIGATION OF THE DISTRIBUTION OF EAB-515 TO CORTICAL ECF AND CSF IN FREELY MOVING RATS UTILIZING MICRODIALYSIS

A freely moving rat model was developed to study the CNS distribution of EAB 515 amino-5-phosphonomethyl[1,1'-biphenyl]-3-propanoic acid). M icrodialysis (MD) in the frontal cortex (FrC) and in the lateral ventr icle (LV) of the rat brain was performed to measure the levels of EAB 515 in the cortical extracellular fluid (ECF) as well as in the cerebr ospinal fluid (CSF). The femoral artery and femoral vein were cannulat ed for serial blood sampling and intravenous (iv) drug administration, respectively. EAB 515 was also administered via the intracerebroventr icular (icv) route in a cross-over experiment. The in vivo recovery of EAB 515 across the MD probes was determined by simultaneous retrodial ysis (RD) performed using a hydroxylated analog of EAB 515, as the RD calibrator (RDC). An extremely sensitive and selective on-line HPLC sy stem with native fluorescence detection was developed for the simultan eous analysis of EAB 515 and RDC in microdialysate samples from rat CS F and cortical ECE Unbound concentrations of EAB 515 in the rat plasma were determined by direct injection of plasma ultrafiltrate onto the HPLC column. The validity of the use of RDC as the RD calibrator was d emonstrated by comparing the results of zero-net flux (ZNF) analysis s imultaneously in some experiments. After constant rate iv infusion in rats (n = 12) for 900 min, the average (S.D.) ratio of the levels of E AB 515 in the CSF to those in plasma (C-csf.iv/C-p) was determined to be 17.7 (7.8)% and that in the cortex relative to plasma (C-cortex.iv/ C-p) was 8.3 (4.8)%. In these animals the total body clearance (Cl) of EAB 515 was estimated to be 8.5 +/- 1.6 ml/min/kg. Upon icv administr ation in the lateral ventricle of rats (n = 6), a 136 +/- 42-fold dist ribution advantage in the cortical ECF was determined. These results i ndicate a significant contribution from the transport across the CSF-B rain interface to the total uptake of EAB 515 by cortical tissue.