208 H. B. LAMBERTS 



these fibres must be goiiig on contmuously and for this an intact mucopoly- 

 saccharide matrix is fundamental. With age, turnover decreases sharply; with 

 development of atheromatosis sulphation may again increase markedly 

 (Kirk, 1959). 



It is important to know how the sulphation rate behaves after irradiation. 

 In the study of Lmdsay et al. the earliest observable radiation lesion is located 

 in the intimal fenestrated membrane and the intimate generic relationship of 

 this membrane to the enveloping mucopolysaccharide matrix is stressed by 

 them. This study was mainly structural and I will now supplement it by 

 some functional observations on the irradiated, non-living aortic intima, 

 indicating the functional importance, and the radiation sensitivity of the 

 subendothelial "gel filtration layer" or "basement membrane", covering the 

 fenestrated elastic membrane on the luminal side. 



Firstly, direct evidence of a radiation effect was found in measuring the 

 injection pressure in the aortic wall during irradiation in a way analogous to 

 that used for skin (Brinkman et al., 1961). The instantaneous droj) of the 

 injection pressure during the irradiation clearly demonstrates an increased 

 permeabiHty to water (Fig. 4), caused by depolymerization of the muco- 

 polysaccharides in the matrix and possibly in the membraneous structures 

 which have a close relation to the matrix. The possibility that radiochemical 

 changes in the matrix substance will cause changes in the development of its 

 fibrous and lamellar structures, e.g. in the basement membrane, should not be 

 overlooked and in fact this possibility is really a probability (Perez-Tamayo, 

 1961; Gersh and Catchpole, 1960; Lindsay and Chaikoff, 1955; Weiss, 1962). 



Impairment of the fmiction of the aortic basement membrane or "gel 

 filtration layer" by irradiation is shown in the results of the following 

 experiments in which we studied the diffusion rate of several dyes by different 

 techniques. In the simplest experiment in this series we irradiated pieces of 

 excised aorta (cow, pig, sheep) with a dose of 2,000 r (50 kV) after which one 

 drop of a saturated trjrpan-blue solution was placed on the endothelial 

 surface and was left there, the pieces being kept for 15 hours in a wet chamber at 

 room temperature. In the irradiated pieces the trypan-blue penetration was 

 regularly 2 to 3 times as deep, in the same time, as in the non-irradiated control 

 pieces (Fig. 5). 



In the next experiment intimal membranes having a thickness of ±0-35 

 mm were prepared by peeling them off freshly excised aortae. They were 

 fixed over 15 mm bore Incite tubes, which were afterwards filled to 1 cm 

 height with a salt solution and immersed in the same solution. The diffusmg 

 solute, haematoporphyrine, was added to the salt solution in the tubes. 

 Diffusion of this dye through the intimal membrane could easily be detected 

 and estimated by the observation of red fluorescence in the immersion bath. 

 The probability of photodynamic effects, made it necessary to perform these 



