Collagen, Elastic Tissue and Resorcin Fuchsin

Abstract

IN recent years several investigations^1–3 have thrown doubt on the specificity of resorcin fuchsin as a reliable stain for structures containing the protein elastin. These investigations have also indicated that some alteration in the state of collagen may cause the latter to react with this stain. Partridge⁴ has suggested that this alteration is denaturation and the increase in reactivity which occurs with this change allows the protein to react with phenolic dyes. However, although resorcin fuchsin contains a phenol, the actual basic dyes used in the stain are not phenolic. Furthermore, it can be shown that certain fibres in connective tissue which stain with resorcin fuchsin but which are demonstrably different from the elastic tissue of the aorta, cannot be distinguished from normal collagen using the basic dyes from resorcin fuchsin without additives. Since denatured collagen has an isoelectric point of 4.8 compared with 7.5 (ref. 5) for the normal protein a simple basic dye should distinguish between the two. Such a result could not be obtained in the connective tissues mentioned. It follows, therefore, that connective tissue contains either three types of fibre reactive to resorcin fuchsin, namely, elastic tissue, denatured collagen and a previously undescribed fibre (Fig. 1), or some other aspect of collagen denaturation must be considered in accounting for the similarity in the staining reactions of elastic tissue and denatured collagen. It is the purpose of this communication to suggest that the loss of crystalline structure that occurs when collagen is denatured⁶ accounts for this similarity and disposes of the need to postulate any other resorcin positive fibre in connective tissue.