Application of the Renkin function to characterize paracellular pathways in the nasal absorption of FITC-dextrans in rats

The Renkin function was applied to characterize absorption pathways after nasal application in rats. Published data about nasal absorption of FITC labeled dextrans (FDs: MW = 4,400, FD4; = 9,500, FD10; = 38,260, FD40; = 50,700, FD70) were used for the analysis. Data for FD4 and FD40 were used to obtain the equivalent cylindrical pore radius (R) and pore area/length ratio (A/L) as the parameters and data for FD10 and FD70 were used for confirmation of the methodology. The R and A/L obtained were useful not only to predict the apparent absorption clearance of drugs (CLA) but also to examine the enhancing mechanism of poly-L-arginine. The simulation curves of CLA-MW were also obtained by the combination of the Renkin function and the relationship between MW and D. This approach will be useful for the development of efficient delivery systems for peptide and protein drugs, giving valuable information on their absorption pathways.