VARIATIONS IN PERMEABILITY ALONG INDIVIDUALLY PERFUSED CAPILLARIES OF THE FROG MESENTERY

Abstract

When single capillaries in the exposed transilluminated frog mesentery were perfused with solutions containing patent blue V (molecular radius 0.7 nm), unbound T1824 [Evans blue] (molecular radius 1.3 nm) and T1824-albumin (molecular radius 3.6 nm), the colored molecules initially appeared to enter the extracapillary tissues more easily at some places than at others along the length of the vessels. Three patterns of extravascular distribution were observed. In high frequency unevenness patent blue V and unbound T1824 1st appeared outside the capillary as spots, bars or bands set at intervals 30-80 .mu.m apart along the length of the vessel. In low frequency unevenness, occuring at later times the extravascular dye was unevenly distributed on a much larger scale, with lengths of vessel of up to 400 .mu.m surrounded by little extravascular dye separating similar lengths around which much dye had accumulated. This pattern of distribution was seen for all 3 solutes. In arteriovenous gradient perfusions with all 3 solutes resulted in more extracapillary coloration accumulating around the venous ends of the capillaries. The distribution of extracapillary solute reflected the distribution of permeability along the length of the capillary. The variations in permeability were attributed to an uneven distribution of small pores along the capillary rather than to presence of large pores.