Abstract
The regulatory effect of calcitonin (CT) on succinate dehydrogenase in the hepatic mitochondria of rats was investigated. Administration of CT (80 MRC mU/100 g body weight) produced a significant increase in calcium content and a corresponding elevation of succinate dehydrogenase activity in the hepatic mitochondria. These increases were dose-dependent. CT also increased succinate dehydrogenase activity and calcium content in the hepatic mitochondria of thyroparathyroidectomized rats. The CT-induced increase in enzyme activity was completely reversed by treatment with 1.0 mM ethylene glycol bis- (2-aminoethylether) N, N, N', N'-tetraacetic acid (EGTA). The increased activity was restored by addition of Ca2+ (2.5-25 μM). Trifluoperazine (25 and 50 μM), a calmodulin inhibitor, completely prevented the increase in succinate dehydrogenase activity caused by CT. Insulin (1.0 U/100 g) also increased succinate dehydrogenase activity in the hepatic mitochondria by about 30% (p<0.01), while the enzyme activity was not elevated by thyroxine (10 μg/100 g). The effect of insulin on the enzyme activation was attributed to the elevation of mitochondrial calcium. The present result indicates that succinate dehydrogenase activity is regulated by CT, and that the effect may be mediated through an increase of calcium in the mitochondria.
