Theophylline, a non-specific phosphodiesterase inhibitor, has been used for the treatment of asthma for a long time, however, its inhibitory actions on inflammatory cells have not been studied sufficiently. Especially, there are few evidence which indicate anti-inflammatory actions of theophylline when it is administered intravenously. In the present study, we examined the effect of intravenous theophylline on eosinophilia induced by IL-5 in the mouse and rat.
In the mouse, blood eosinophil number was significantly increased 2 hr after intravenous injection of 1 μg/kg mIL-5 (Vehicle; 5.56, mIL-5; 9.01, ×104cells/mL, p<0.01). Intravenous theophylline, administered 30 min after mIL-5 treatment decreased blood eosinophil dose dependently (3 mg/kg; 8.83, 10 mg/kg; 7.13, 30 mg/kg; 5.46, ×104cells/mL). Interestingly, a component ratio of eosinophil in the femoral bone marrow significantly decreased after mIL-5 treatment (Vehicle; 3.62%, mIL-5; 3.00%, p<0.01), and intravenous injection of theophylline inhibited this decrease of component ratio (3 mg/kg; 3.32%, 10 mg/kg; 3.40%, 30 mg/kg; 3.45%). Similar effects of theophylline were also observed in the rat.
These results strongly suggest that intravenous injection of theophylline inhibits mobilization of eosinophil from their internal pool such as bone marrow into the blood. Our results also suggest the clinical efficacy of theophylline when used via intravenous route.