184 E. BEINKMAN 



the membrane is built up as a lamellated dense polymerization of mucopoly- 

 saccharide ground substance around aTvery fine reticular network, a radiation 

 sensitivity might be expected in analogy, with that of cutaneous or aortic 

 matrix. Enzymes Hke the hyaluronidase complex not only hydrolyze the 

 diffuse ground substance but attack basement membranes as well (Gersh, 

 1952), so the presence of mucopolysaccharides is to be expected there. 



If the basement membrane is a dense network of very elastic (Nagel, 1934) 

 and very fine (40-50 A) reticular fibres, bedded in mucopolysaccharide ground 

 substance its permeability for water and small molecular solutes will depend 

 on the ground substance/fibre ratio. If the ground substance is disappearing 

 slowly (ageing) or somewhat more quickly (irradiation) elastic retraction of 

 the network might decrease basement membrane permeability. Gersh and 

 Catchpole (I960) explain the apparent difference in thickness of basement 

 membranes as concluded from their visibility either m the light or in the 

 electron microscope by suggesting that this membrane normally occurs in a 

 slightly corrugated state. Also from this one might expect a tightening up if 

 the ground substance disappears. 



I must now restrict further consideration of a possible radiation influence 

 on the permeability of basement membranes to one instance, radiation 

 nephrosclerosis. Another instance, not a delayed but a very early effect will 

 be described in the "basement membrane" of the aortic endothelium, by Dr. 

 Lamberts. 



Kadiation nephrosclerosis has been known for some time and results of 

 recent work appear to agree on the cause: i.e. intercapihary glomerular 

 sclerosis, not distinguishable from the same process in ageing. 



Electron microscopy has definitely proved that the chief ultrafiltration 

 barrier in glomeruli is the basement membrane between capillary endothelium 

 and visceral epitheHum. The endothelium is highly fenestrated and the 

 epithelium is not a continuous layer. The membrane is not a simple sieve, but 

 a gel-like structure with two fine fibrillar components embedded in an 

 amorphous matrix (Farquhar e^ aL, 1961). It is not a perfect ultrafilter and the 

 few macromolecules which have permeated appear to be collected by pino- 

 cytosis in the elaborate foot process arrangement, formed by the visceral 

 epitherlium adjoining the basement membrane. This epithelial activity is 

 greatly enhanced when challenged, e.g. when increased quantities of proteins 

 appear in the basement membrane filtrate such as in the nephrotic syndrome. 

 If, initially, the membrane permeability increases by irradiation a similar 

 process might be expected and this could be at the base of the glomerular 

 intercapillary hypertrophy described by recent authors (Guttman and Kohn, 

 1960; Niissel and Schunk, 1961) as the late characteristic change after total- 

 body irradiation. 



The literature on radiation nephrosclerosis as a late effect in many 



