The biochemical properties of tendon and skin as influenced by long term glucocorticoid treatment and food restriction.

The influence of long term systemic glucocorticoid treatment and food restriction on the mechanical properties of muscle tendons and skin was investigated. A group of male, albino rabbits received prednisolone intramuscularly for 63 days. Another group was food restricted to achieve the same weight loss as the prednisolone treated group. The untreated control group had free access to food and water. Peroneus tertius and longus tendons and strip specimens of lumbal skin were tested in a materials testing machine. Long term prednisolone treatment reduced the dry weights of the muscle tendons, with no change in collagen content and "stress"-strain parameters. The elastic stiffness measured after exhaustion of the viscosity in the tendons was found to be increased. The collagen content of skin was reduced, which resulted in a weakening of the skin as such. However, the extensibility of the skin strips was reduced and the maximum "stress" value, i.e. load value normalized to collagen content, was increased. The food restriction did not change the mechanical properties of muscle tendons. For skin the collagen content was reduced and so were the maximum load and "stress" values after food restriction. It is concluded that both long term glucocorticoid treatment and food restriction reduce the amount of collagen and strength of skin, consistent with clinical experiences. However, in long term glucocorticoid treatment the remaining collagen has increased stability, probably caused by a changed cross-linking pattern, in contrast to a reduced stability of skin collagen in food restriction. Skin is thus influenced more easily than muscle tendon.