Theophylline-induced changes in mammalian adenosine deaminase activity and corticosterone status: possible relation to immune response.

Theophylline at low doses (10 mg/kg/day p.o.) under long-term conditions (for 16 consecutive days) increased the adenosine deaminase (ADA) activity in spleen and thymus of adult male albino rats without changing its hepatic ADA activity. Treatment with high doses (20 mg/kg/day p.o.) under similar conditions, on the other hand, decreased the splenic and hepatic ADA activity and increased the thymic ADA activity. This induction of thymic ADA activity, however, was significantly less than that observed with low doses of theophylline. The plasma corticosterone level was increased without changing its adrenal level under similar conditions. This study, thus, indicates that long-term theophylline treatment may potentiate or suppress the immune response, depending on the dose, through the tissue (liver/spleen/thymus)-specific modulation of ADA activity and plasma corticosterone status.