Abstract:
Two methods are described for measuring the filtration coefficient of individually perfused frog mesenteric capillaries. Both methods involve the perfusion of capillaries via a micropipette with a solution in which a small number of human red cells are suspended. After a short period of perfusion, the capillary is occluded at a point some 500 ,um or more downstream from the point of cannulation. Movements of the red cells in the isolated capillary micropipette system are interpreted to be the consequence of fluid movements across the capillary wall. The filtration coefficient of the capillary is determined either (method I) from a series of different filtration rates measured at different capillary hydrostatic pressures when intracapillary colloid osmotic pressure is constant, or (method II) from the changes in filtration rate as the fluid within the capillary concentrates at a constant pressure. Values for the filtration coefficient obtained by both methods have a skewed distribution. Determinations made by method I at 14-16°C have a peak value of 2 x 10-3 vm.sec-1 . cm H20-1 and determinations made by method II at 22-26°C have a peak value of 5 x 10-3sjm . sec- . cm H20 -1. The assumptions underlying both methods are discussed and a mathematical model of the change in protein concentration in a closed off capillary at constant pressure is presented in the appendix.
