The amino acid hydroxyproline constitutes approximately 13 per cent of collagen (1, 2), and 1 to 2 per cent of elastin (2). It is present in no other protein of the body. For this reason, the determination of hydroxyproline has been utilized for the estimation of collagen in various animal tissues (3), and in the fibrinoid material of the subcutaneous nodule of rheumatoid arthritis (4).It is, at the present time, not clear whether in the diseases of the connective tissue, or "collagen diseases," significant alteration and degradation of the protein collagen occurs. The light microscope studies of Klinge (5) and of Bahrmann (6), who observed swelling of collagen in tissue sections of lesions from patients with rheumatic and other diseases, suggested that these changes do occur. Others (7-9) have shown in addition that swelling and focal degeneration of collagen fibers is a common and striking effect of anaphylactoid hypersensitivity reactions.Using the electron microscope, however, Gross (10) and Gale (11) did not find abnormal fibers in material from lesions of rheumatoid arthritis, rheumatic fever, disseminated lupus erythematosus, and scleroderma. Though Wolpers (12) did observe fibrils lacking cross striations in necrotic areas of old rheumatoid nodules, the fibers were normal in non-necrotic areas and in samples of collagen obtained from Arthus lesions. When cross sections of rheumatoid nodules were submitted to careful X-ray diffraction study by Kellgren, Ball, Astbury, Reed, and Beighton (13) In contrast to the preceding workers, Rich, Voisin, and Bang (14) did observe altered fibrils in a small percentage of samples of tissue from Arthus lesions examined with the electron microscope. The fibrinoid material of the subcutaneous nodule of rheumatoid arthritis has recently been extracted (4) and found to contain negligible amounts of hydroxyproline, indicating that, in all probability, it does not contain degraded collagen and arises from other components of the connective tissue.Because hydroxyproline is present almost entirely in collagen, it was felt that if there were a significant deviation from normal in the metabolism of collagen or an increase in degradation of this protein in patients with collagen diseases, these changes might be reflected by increased levels of excretion of this amino acid in urine.
METHODSSixty-four patients were studied, of whom 48 were adults ranging in age from 17 to 74, and 16 were children ranging in age from 5 to 14. Twenty-four of the adults were men and 22 women; all but one of the children were boys. Among the adults, 8 were normal individuals and 16 had rheumatoid arthritis. Eight had one of the collagen diseases, i.e., 2 had disseminated scleroderma; 1, isolated scleroderma; 2, disseminated lupus erythematosus; 1, dermatomyositis; and 2, acute rheumatic fever. Sixteen had one of a group of miscellaneous diseases; these included 4 patients with resolving pneumonia, and one patient each with the following conditions: multiple sclerosis, coronary heart disease, acromegaly...
