The tissue concentrations of corticosterone (Fig. 2) showed similar differences over time to plasma concentrations. In the liver, concentrations of corticosterone were significantly (P < 0.05) greater at 15 min, 30 min and 180 min after ACTH than before injection. In cardiac muscle, the concentrations of corticosterone were significantly (P < 0.05) greater at 15 min and 30 min after ACTH injection than before injection and were significantly decreased (P < 0.05) at 120 min and 150 min after ACTH injection than before injection. In the kidney, the concentrations of corticosterone were significantly (P < 0.01) greater 15 min and 30 min after ACTH injection than before injection. In skeletal muscle, the concentration of corticosterone was significantly (P < 0.01) greater 15 min, 30 min, and 60 min after ACTH injection than before injection.