Temperature-related reversible birefringence changes in rat tail tendon

By use of a highly sensitive method for measuring slight variations in birefringence it is shown here that a strong reversible correlation exists between rat tail tendon birefringence and temperature. This phenomenon is totally different from the loss of birefringence that results from a denaturation process. Below the threshold temperature leading to denaturation, an increase in temperature is systematically accompanied by a reversible increase in birefringence (0.25% degrees C(-1)). This phenomenon is observed at very fast heating rates (250,000 degrees C s(-1)), such as those induced by pulsed infrared lasers, and confirmed by experiments conducted with slow homogeneous heating of the sample medium (0.1 degrees C s(-1)). The good correlation between birefringence and temperature observed during the fast heating suggests that there are only small modifications of the tissue structure at the fibril level.