Anti-inflammatory effect of saikogenin A

Saikogenin A, an anti-inflammatory drug, is present in the crude extract of a Chinese herbal plant called Tsai-Fu. Saikogenin A was less effective in adrenalectomized rats than in normal rats in reducing the carrageenin-induced edema. Serum corticosterone and ACTH were increased in the saikogenin A-treated rats, supporting the view that stimulation of hypothalamopituitary-adrenal system is responsible for the anti-inflammatory effect of saikogenin A. This is further supported by the findings that saikogenin A did not affect the spontaneous release of corticosterone but it facilitated the ACTH-induced release. In addition, cyclic AMP in isolated pituitary and adrenal glands was increased by saikogenin A. A role for cyclic AMP as the second messenger is thus considered. Otherwise, the direct action of saikogenin A on the process of inflammation cannot be ruled out because saikogenin A also functioned in the adrenalectomized rats and it inhibited the release of histamine induced by compound 48/80. Reduction of the vascular permeability was also observed in the saikogenin A-treated rats. These results suggest that the anti-inflammatory action of saikogenin A are due to an increase in corticosterone caused by the release of ACTH and a direct effect on the process of inflammation.