Experimental Methods to Examine Substances and Pharmacological Possibilities to Influence the Permeability of the Blood-Lymph Barrier

Abstract

It is generally recognized that abnormalities of the permeability of the plasma-lymph barrier occur in certain diseases, for example rheumatic conditions, purpura and especially inflammatory states. These permeability abnormalities are connected with edema formation. There are various drugs which are claimed to be “capillary-active” in the sense that they can “seal” the plasma-lymph barrier or in other words that they can reduce excessive and abnormal permeability. This claim is, however, not so widely accepted. For the experimentalist, and in particular the pharmacologist, who wants to study the effects and the mechanism of action of these “capillary-active” drugs, there is an abundance of methods — too many for me to describe here. Because of the drawbacks of most methods we use the following technique. We cannulate the rat’s thoracic duct and give the animal a continuous infusion of polyvinylpyrrolidone (PVP) of intermediate molecular weight. We then measure the rate of lymph flow and the PVP and protein concentrations in the plasma and the lymph and calculate the concentration ratios (Fig. 1). This procedure has certain disadvantages. Permeability is known to vary from one organ to another, but what we collect from the rat is mixed lymph from a variety of organs.