Simultaneous measurements of capillary diffusion and filtration exchange during shifts in filtration‐absorption and at graded alterations in the capillary permeability surface area product (PS)

Abstract

Following diffusion exchange of Cr-EDTA, using the single injection indicator diffusion method, capillary filtration capacity (CFC) in an isogravimetric rat hindquarter preparation was estimated during artificial perfusion and maximal dilatation. Measurements were performed at constant flow and during shifts in filtration-absorption, alterations of perfused capillary wall area (graded rarification of capillary network by microsphere injection) and altered permeability (i.e., histamine infusion). At maximal vasodilatation CFC was 0.037 .+-. 0.001 ml/min .times. mmHg .times. 100 g and PS [capillary permeability surface area product] for Cr-EDTA 5.67 .+-. 0.13 ml/min .times. 100 g. During filtration or absorption, Cr-EDTA transfer from vessels to interstitium changed only slightly but may differ for solute transfer from interstitium to vessels. Alterations in capillary wall area resulted in proportional changes in PS for Cr-EDTA while CFC changes were always relatively smaller. Histamine increased CFC 3-fold with a marked increase in protein transfer and PS for Cr-EDTA increased marginally. This histamine effect could be due to an increased number of large pores which, because of relative paucity, are of little importance in small molecule diffusion exchange but highly important in convective and macromolecular exchange.