Effects of Blood Flow on Diffusion Kinetics in Isolated, Perfused Hindlegs of Cats

Abstract

Diffusion of antipyrine (Ap), urea, 4 acetyl amino antipyrine (4AAAp) and sucrose from blood to tissues in the isolated, perfused hindlegs of cats was studied by measurement of arterial blood concentrations for 2 to 3 hours after their addition to the blood. Ap, urea and 4AAAp diffused into total tissue water and sucrose into interstitial water. For all 4 solutes, the diffusion curves were double exponentials. Mathematical analysis of results indicates that the vascular bed of perfused tissues is divided into 2 parellel regions, one well perfused and the other poorly perfused. Regions differ in their response to vasoactive agents (chloral hydrate and Pitressin) and are not identified with any of the component tissues of the hindleg. Evidence is cited from the literature indicating that such a double circulation is present in tissues of intact animals. Diffusion of Ap into the well perfused tissue compartment is limited by blood flow over the experimental range; diffusion of the other solutes is a function of blood flow and the permeability of both capillary walls and tissues. A general relation between tissue dialysance (a quantity analogous to clearance), blood flow and permeability is described.