Effect of thyroxine on the function of rabbit skeletal muscle sarcoplasmic reticulum

: Thyrotoxicosis in rabbits was induced by prolonged intraperitoneal injection of L-thyroxin. The development of thyroxicosis was assoiated with a decreased Ca2+ accumulation rate by sarcoplasmic reticulum (SR) fragments and a lowered Ca2+ dependent ATPase activity. As compared to the analogous parameters in normal animals. Ca2+ accumulation rate and ATPase activity of thyrotoxicosis animals decreased by 60 and 25%, respectively. The changes in the specific parameters of SR were also observed during incubation of normal SR samples in the medium containing thyroxin (10-5 M). The changes seen in SR functioning in thyrotoxicosis animals are likely to be related to structural rearrangements of lipoprotein surroundings of Ca-ATPase.