Measurement of unbound caffeic acid in rat blood by on-line microdialysis coupled with liquid chromatography and its application to pharmacokinetic study

To monitor the levels of caffeic acid in rat blood, an on-line microdialysi s system coupled with liquid chromatography was developed. The microdialysi s probe was inserted into the jugular vein/right atrium of male Sprague-Dau ley rats. Caffeic acid (100 mg/kg, i.v.) was then administered via the fem oral vein. Dialysates were automatically injected onto a liquid chromatogra phic system via an on-line injector. Samples were eluted with a mobile phas e containing methanol-100 mM monosodium phosphoric acid (35:65, v/v, pH 2.5 ). The UV detector wavelength was set at 320 nm. The detection limit of caf feic acid was 20 ng/ml. The in vivo recoveries of the microdialysis probe f or caffeic acid at 0.5 and 1 mu g/ml were 48.34+/-2.68 and 47.64+/-3.43%, r espectively (n = 6). Intra- and inter-assay accuracy and precision of the a nalyses were less than or equal to 10% in the range of 0.05 to 10 mu g/ml. Pharmacokinetics analysis of re suits obtained using such a micro dialysis- chromatographic method indicated that unbound caffeic acid in the rat fitte d best to a biexponential decay model. (C) 1999 Elsevier Science B.V. All r ights reserved.