Cytosolic aminopeptidase (c-AP: EC 3. 4. 11. 1) is contained in the cytosolic fraction of hepatic cells, lymphocytes, leukemia and lymphoma cells, and other kinds of cells. Elevations of the level of this enzyme in sera have been observed in patients with hepatic diseases or lymphoproliferative disorders. Moreover, increases in c-AP activity have been observed in patients with several viral infections. In this study, the c-AP activity of patients with viral infections was found gradually to begin to increase during the prodromal phase along with increase in lactate dehydrogenase (LD: EC 1. 1. 1. 27) activity, rapidly increased with the appearance of rash, and returned to the normal reference interval more quickly than did LD. Since there were no associated increases in liver-derived enzymes, this increase in c-AP probably originated from lymphocytes and not hepatic cells. We conclude that the measurement of c-AP activity of importance for the diagnosis and follow-up of patients with certain viral infections.
The effect of hypoxia on serum ketone body levels was studied in rats and cultured hepatocytes. When rats inhaled a gas-mixture composed of 25% air in N2, the sum of their ketone bodies (β-hydroxybutyrate plus acetoacetate) increased gradually after 2 hour, reaching 293% of the original level after 4 hour. The acetoacetate/β-hydroxybutyrate ratio decreased appreciably from 0.58 to 0.28 in the same 4 hour period. In cultured rat hepatocytes, the ketone-body ratio also decreased with lowering oxygen tension. However, the exposure of the cells to hypoxia depressed the accumulation of ketone-bodies, indicating that the increase in the sum of serum ketone bodies induced by the exposure of rats to hypoxia was due to a decrease in their utilization in extrahepatic tissues. The determination of the sum of ketone bodies and of the ketone body ratio provides valuable information for the severity and diagnosis of hypoxia due to diminished lung function.