Strain of rat skin at constant load (creep experiments): influence of age and desmotropic agents.

Creep experiments were performed on skin strips of rats of various ages (4 weeks to 2 years) and of rats treated with prednisolone acetate or D-penicillamine for 10 days. In one specimen of back skin the ultimate load and tensile strength was measured at an extension rate of 5 cm/min. 50 or 25% of the ultimate load was applied to other specimens of the same skin area. Strain (% extension), time until break, and ultimate extension rate were measured in these samples. The constant load was applied either in a continuous or an intermittent manner. The maturation process (up to an age of 1 year) induced an increase of tensile strength and of ultimate strain followed by a decrease due to the ageing process. Time until break was increased and ultimate extension rate was decreased during the whole life span. These values did not show a maximum or minimum. D-Penicillamine decreased tensile strength, decreased the ultimate strain, shortened the time until break at constant load and increased the ultimate extension rate. Prednisolone increased tensile strength and induced some decrease of ultimate strain and time until break. It was concluded that phenomena like creep indicating the viscosity of connective tissue do not resemble those parameters indicating elasticity behaviour.