Temperature-related reversible birefringence changes in rat tail tendon

By use of a highly sensitive method for measuring slight variations in bire fringence it is shown here that a strong reversible correlation exists betw een rat tail tendon birefringence and temperature. This phenomenon is total ly different from the loss of birefringence that results from a denaturatio n process. Below the threshold temperature leading to denaturation, an incr ease in temperature is systematically accompanied by a reversible increase in birefringence (0.25% degrees C-1). This phenomenon is observed at very f ast heating rates (250,000 degrees C s(-1)), such as those induced by pulse d infrared lasers, and confirmed by experiments conducted with slow homogen eous heating of the sample medium (0.1 degrees C s(-1)). The good correlati on between birefringence and temperature observed during the fast heating s uggests that there are only small modifications of the tissue structure at the fibril level. (C) 2000 Optical Society of America OCIS codes: 260.1440, 170.6920, 120.5410, 350.5340, 170.4580.