A model to study the dynamics of glomerular ultrafiltration and glomerular capillary permselectivity characteristics

Abstract

A model, based on recent developments of the pore theory of transport across membranes, is developed to describe solute and fluid transport across the glomerular capillary wall. The model allows the prediction of the glomerular capillary permselectivity parameters r o (pore radius), A p l (total capillary pore surface area/capillary thickness), and K f (the hydraulic permeability), as well as the average transmembrane hydrostatic pressure drop ( ΔP ) and the efferent arteriolar colloid osmotic pressure ( π E). The input data required are the glomerular filtration rate, initial glomerular plasma flow, systemic protein concentration, and sieving ratios for a few test solutes of known hydrodynamic radius. The model is then applied to results obtained previously on four groups of Wistar rats with accessible surface glomeruli where direct measurement of ΔP and π E and independent estimates of K f were made by micropuncture techniques. The model predictions are shown to correspond quite closely to direct measurements and previous findings on these rats and would be a useful tool in analyzing the dynamics of glomerular ultrafiltration as well as glomerular permselectivity where direct measurements are difficult or impossible.