Analysis of the low part of stress-strain curves in rat skin. Influence of age and desmotropic drugs.

Stress-strain behaviour of skin strips in rats at different ages or after treatment with prednisolone or D-penicillamine has been analyzed. Special attention has been paid to the lower part of the stress-strain curves. A "hump" at an extension degree of 30% of original length was noted. When rats of different ages were compared this phenomenon was observed predominantly at an age of 2 months. Futhermore, this hump was remarkable in rats treated with prednisolone. When the stress-strain curves of rats at different ages or after treatment were averaged and normalized, the most pronounced deviations were found at an age of 2 months or after prednisolone treatment. The maximum of deviation from Hooke's law occurred at a relative extension degree of 70%. Thus, the maturation process and the influence of corticosteroid affected mostly the second part of the stress-strain curve. In order to evaluate further the stress-strain curves 3 consecutive tangents of the stress-strain curves indicating modules of elasticity were evaluated. The first and second modules of elasticity showed a minimum at an age of 2 months, whereas the ultimate elasticity modules increased with maturation up to a maximum at 12 months followed by a decrease similar to that observed in tensile strength at an age of 24 months.