Connective Tissue IX. Metabolism of Collagen in Bone of Rat.

Abstract

Previously we reported the metabolism of collagen and elastin in several soft tissues of rat( 1,2). The same method of fractionation cannot be used for bone, since the bone salts diminish the extractability of the solvents used in Lowry's method (3). Demineralizing with citrate-formic acid(4) or EDTA( 5 ) is time consuming and involves the loss of soluble collagen. Because of these difficulties, very little has been written about the metabolism of collagen in bone. Gerber and Gerber studied the metabolism of collagen in the femur of young rats(6). Their observations covered 15-day periods. Soluble collagen was not considered. Recently, we published a method for fractionation of proteins in bone and cartilage(7). With use of this method both soluble and insoluble collagens could be separated from other proteins of bone. Therefore, a more nearly complete picture of collagen metabolism in bone could be drawn.The present study deals with (a) the metabolism of soluble and insoluble collagens in several bones of rats, and (b) a comparison of the metabolism of the soluble and insoluble collagens in rats at different ages.Methods. Female rats 5 weeks, 6 months and 2 years of age, respectively, were injected intraperitoneally with 4.26 pc glycine-2-14C (specific activity 53 pc/mg) per 100 g body weight in physiological NaCl solution. At 1, 3, 7, 11, 20 and 31 days after injection, the 5 weeks and 6 months rats were sacrificed in groups of 4 and the 2-year-olds, in groups of two. Bones were freed of all soft tissue; whole bones were freeze-dried. Sol-The hydroxyproline content of both soluble and insoluble collagens was 12-13%. In preliminary experiments, using I4C-lysine as precursor for the synthesis of bone collagen, radioactive hydroxylysine was recovered from both soluble and insoluble collagen samples. The radioactivity of hydroxylysine and lysine was always proportional to the radioactivity of the collagen sample from which these amino acids were derived. Therefore, in the present study, counting was performed on the collagen samples from both TCA extracts.The specific activity (SA) has been defined as counts per min per mg of collagen nitrogen. A correction for changes in body weight in the 5 weeks old group was made by multiplying the SA of insoluble collagen by the following ratio: (total collagen weight at time of determination, Cf) x (% insoluble collagen at time of determination)/ (total collagen weight at beginning of experiment, Ci) X (% insoluble collagen at beginning of experiment). The ratio Cf/Ci was obtained from Sobel's equation(7a), based on data from studies of femoral bone: log Cf/Ci = 0.78633 log wf/wi and used for all bones (wf and' wi are the body weights at time of determination and at beginning of the experiment, respectively). When this correction factor was applied to data from the 5 weeks old animals, it was found that the total collagen of rat femur increased by an average of 34% in 31 days. The soluble collagen was initially 3.5 to 6.0% of the total, but only 2.0 to 3.0% thirty days later,...

Aging in Connective Tissue: A Dynamic Process*

“…In all instances the maximum incorporation of glycine into soluble collagen occurred early, and the slope of the decay curve was rather sharp. In contrast, the incorporation of glycine into insoluble collagen was at its maximum around the third day, and loss of radioactivity was less marked for the skull than for the other three bony tissues studied (24). In vitro studies of collagen synthesis.…”

“…Certainly it does not suggest that aging is a simple degenerative affair, but that even in a single bodily structure, changes occur which are characteristic for the area and organ involved (20, 21). Glycine‐2‐C 14 was injected intraperitoneally into female rats 5 weeks old and 2 years old respectively, and the rats were sacrificed 1, 3, 7, 11, 20 and 31 days later in order to determine the rapidity and amount of formation of new collagen and the rate of decay in the two groups (24). Data for the soluble and insoluble collagen fractions in the femur, rib, vertebra and skull, plotted on a semilogarithmic scale, are shown in Figure 11.…”

“…The protein‐bound hexosamine of plasma and erythrocytes in both normal and diabetic rats and human beings was studied (17). Experiments concerned with the formation of connective both in vitro and in vivo , using uniformly labeled C 14 ‐lysine and uniformly labeled C 14 ‐proline, have been reported previously (18–24).…”