THE EXCRETION MECHANISM OF THE SPIN-LABEL PROXYL CARBOXYLIC-ACID (PCA) FROM THE RAT MONITORED BY X-BAND ESR AND PEDRI

Proton electron double resonance imaging (PEDRI) was used for monitori ng in vivo the distribution, metabolism and, in particular, the excret ion mechanism of the exogenous nitroxide free radical proxyl carboxyli c acid (PCA) in the rat. PCA clearance half-lives through liver, abdom inal vessels, and renal tissues were determined from a series of PEDRI images for normal rats (n = 5) and rats treated with probenecid (n = 5), a competitive inhibitor of the tubular secretion process, The appr oximately doubled renal half-lives of the treated animals suggest that tubular secretion accounts for about 50% of PCA renal loss in the nor mal rat and reabsorption is insignificant, PCA binding to bovine serum albumin was investigated by X-band ESR and the bound fraction was fou nd to be less than 10% of the total PCA. Most probably, PCA binds to h ydrophilic sites, Blood PCA concentration investigated by X-band ESR e xhibited biphasic behavior and PEDRI results confirmed the in vivo met abolic reduction of PCA by rat liver cells.