182 R. BRINKMAN 



and for our discussion an important property of collagenic fibres is their 

 metabolic renewal. Neuberger and associates (1951, 1953), with the aid of 

 ^^C-labelled glycine showed that even in adult rats coUagen is continually, but 

 very slowly rebuilt. The turnover mainly occurs in the intracellular "pro- 

 collagens"; if this collagen has been fixed in the insoluble fibrous form no 

 rebuilding can be found. It is very probable, that the formation of fibrous 

 collagen requires the presence of matrix mucopolysaccharides. If the produc- 

 tion of mucopolysaccharides decreases with age, or if it is influenced by 

 irradiation, the build-up of fibres may be changed also for this reason. Many 

 fibre-properties have been shown to change with age (hydrophilia, heat 

 contraction, chemical contraction). This may correlate with the increased 

 content of hydroxyproline in fibres of older animals, possibly giving rise to 

 increased cross-linking (Korenchevsky, 1961). 



Some analogy may be found between the physical properties and the very 

 high dose radiation deterioration of tendon fibrils (Braams, 1961, Braams et 

 al, 1958). 



For elastic fibres, so important for the function of large arteries, Lansing 

 et al. (1951) have described their deterioration and calcification with age and 

 after Jellinek's (1958) description of their extraordinary sensitivity to X- and 

 y-irradiation an interesting analogy appeared to have been found. Unfor- 

 tunately to my knowledge confirmation of Jellinek's results has not been 

 published and I know of attempts to reproduce them which did not succeed. 



It is a general opinion (Korenchevsky, 1961), that for the intercellular 

 medium the quotient amorphous ground substance/collagenic fibres, or the 

 chemoanalytically exjjressed quotient hexosamines/hydroxyproline decreases 

 with age. In the skin of rats, this process is strongly accelerated by moderate 

 irradiation, not only by disappearance of ground substance but also by 

 absolute increase of the collagen content (Kitagawa et al., 1961). 



It has been shown by Glicksman and collaborators (Kitagawa etal., 1961) 

 that this preponderance of collagenic fibres after irradiation may be reversed 

 by treatment with 3-iodoth}'Tonine. If a similar application holds for the rela- 

 tion ground substance/fibres in the walls of large arteries, this may be still 

 more interesting. 



In the opinion of many investigators (Perez-Tamayo, 1961), the mucopoly- 

 saccharide ground substance, in its fibrous framework is not only a two- 

 phase mechanical support for parenchymal and endothelial cells but a con- 

 trolling and controlled environment. For the extracellular tissue fluids, it 

 again forms a functionally important macromolecular polyanionic reticulum. 

 It is partly firmly bound to the fibres, especially to the elastic and reticular 

 fibres, and this often results in membraneous structures in the intimal fene- 

 strated elastica of arteries, in the numerous subcutaneous membranes (Day, 

 1959) and, above all, in the basement membranes around most capillaries. 



