Influence of desmotropic drugs on viscoelastic properties of rat tail tendons. Hysteresis experiments.

The influence of several desmotropic drugs (D-penicillamine (D-Pc) at doses of 300 and 1000 mg/kg p.o., a lathyrogenic drug, e.g. aminoacetonitrile (AAN) at doses of 100 and 300 mg/kg p.o. and a glucocorticoid, e.g. prednisolone acetate at doses of 2 and 10 mg/kg s.c.) on viscoelastic properties of rat tail tendons has been studied after 10 days' administration. In this experimental series not only the ultimate values (ultimate load, tensile strength, ultimate load of elasticity, ultimate strain), but also the hysteresis loops after 2, 4, 6 and 8% strain were evaluated. The ultimate values showed similar results as found in earlier experimental series, e.g., an impressive decrease after D-Pc treatment, a less pronounced decrease after AAN and an increase after prednisolone acetate. At extension degrees below rupture the values of stress, modulus of elasticity and energy input showed the same pattern. In contrast, energy dissipation as indicated by the area between the hysteresis loop showed a different pattern. Consequently, the ratio between energy dissipation and energy input, which is the characteristic parameter of the hysteresis phenomenon, was highly increased by D-Pc and only barely influenced by AAN. In contrast, prednisolone acetate reduced this ratio. A similar pattern was found for residual extension. Since the hysteresis phenomenon can be regarded as a parameter of plasticity of tail tendons one can conclude that D-Pc increases plasticity, AAN has only a slight influence and prednisolone acetate decreases plasticity.