Relative and absolute changes in soluble and insoluble collagen pool size in skin during normal growth and with...

Absolute and relative changes in 0.5M acetic acid soluble and insoluble collagen were followed in the whole skins of young rats fed an adequate diet (18% lactalbumin) for 495 days (n = 92) and a low-protein (3% lactalbumin) diet for 210 days (n = 94). In well-nourished rats, the soluble collagen pool size reached a maximum at approximately 100-140 days of age whereas the insoluble pool tended to increase throughout the period of observation. Thus, the percent soluble collagen increased to a maximum of approximately 80% of total collagen at 40-50 days, thereafter declining progressively to about 20% by 495 days. In contrast, the size of the soluble collagen pool remained constant in protein-restricted rats, but with insoluble collagen increasing linearly throughout, although achieving only a level of about 1/6th of that reached in well-nourished rats. In the restricted rats, percent soluble collagen decreased rapidly and remained at about 25% of total between 80 and 210 days. These data were used to develop prediction equations for the size (mumoles hydroxyproline) of the soluble and insoluble collagen pools in healthy and protein-restricted rats. Hence, where A = days of age, the equations were, respectively: 0.414 X 10(-3) A - 0.390 A2 + 86.9 A - 1800; 0.262 X 10(-2) A3 + 0.793 A2 - 26.5 A + 272; 0.236 A + 155; and 5.07 A - 38.5. These findings are discussed with reference to possible mechanisms responsible for conversion of soluble to insoluble collagens in skin of well-nourished and growth-retarded rats.