Serum mitochondrial aspartate aminotransferase in patients with polymyositis.

The clinical significance of serum aspartate aminotransferase (GOT) isozymes was studied in 18 patients with polymyositis. Abnormally high levels of mitochondrial GOT (mGOT) (6.2 +/- 1.2 IU/L, mean +/- SEM; normal, less than 2.0 IU/L) and cytosol GOT (sGOT) (95 +/- 21.6 IU/L; normal, less than 25 IU/L) were observed in sera. In polymyositic muscles, the sGOT level was significantly decreased but mGOT was not. The levels of serum sGOT and mGOT and the ratio of mGOT/tGOT before corticosteroid therapy correlated well with the severity of muscle weakness. Serial determination of CPK, sGOT, and mGOT during corticosteroid therapy revealed that mGOT most rapidly returned to normal. Exercise did not increase serum mGOT in polymyositis.