Stimulation of the pituitary-adrenocortical axis by saikosaponin of Bupleuri radix.

Abstract

The effects of saikosaponin-a, -c and -d, isolated from the roots of Bupleurum falcatum on plasma ACTH and corticosterone concentrations in unanesthetized or pentobarbital-anesthetized rats were determined by radioimmunoassay and by the competitive protein binding method. A single dose of saikosaponin-a (5 mg/kg, i.p.) or -d (2.5 mg/kg, i.p.) significantly increased plasma ACTH and corticosterone levels 30 and 60 min after the treatment, but saikosaponin-c at a dose of 100 mg/kg had no effect. I.p. administration of saikosaponin-a or -d, but not -c, induced a transient hyperglycemia and a transient hypoinsulinemia. Dexamethasone pretreatment depressed the saponin-induced increase of both corticosterone and glucose. Treatment with hexamethonium partially depressed the saponin-induced responses in plasma corticosterone, but treatment with diphenhydramine did not.