EFFECT OF THYROID HORMONES ON APOPTOSIS IN CHICK SKELETAL MUSCLE CELLS

用分散酶消化法从13日龄鸡胚大腿肌肉中分离成肌细胞。细胞孵育24小时后，向培养基中加入甲状腺激素-甲状腺素（T4）和三碘甲状腺原氨酸（T3），并继续孵育6天。T4和T3均可促进细胞分化，而T3可抑制细胞增殖，但T4不抑制细胞增殖。此外，T3还增加了肌肉蛋白质的降解，降低了DNA含量，而T4没有。因此，DNA裂解和片段化作为凋亡的指标进行了测量，并显示凋亡是由T3诱导的，而不是由T4。蛋白酶体和组织蛋白酶的活性也被测定，以显示与细胞凋亡的关系。结果表明，细胞凋亡和蛋白酶活性之间可能存在关系。本研究表明，T4是一种活性激素，但其作用与T3不同。

Myoblasts were isolated from thigh muscles of 13-day-old chick embryos by digestion with dispase. After the cells were incubated for 24 hours, thyroid hormones -thyroxine (T4) and triiodothyronine (T3) - were added in the medium and the incubation was continued for 6 days. Cell differentiation was increased by both T4 and T3 while cell proliferation was inhibited by T3 but not by T4. Furthermore, muscle protein breakdown wasincreased and DNA content was decreased by T3 but not by T4. Thus DNA cleavage and fragmentation as indices apoptosis were measured and shown that apoptosis was induced by T3 but not by T4. Proteasome and cathepsin activities were also measured to show the relationship with apoptosis. The results indicated a possible relationship between apoptosis and protease activity. The present study shows that T4 is an active hormone but it's role is different from that of T3.