Central administration of saikosaponin-d increases corticotropin-releasing factor mRNA levels in the rat hypothalamus

Saiko agents, Chinese herbal drugs, stimulate corticotropin-releasing factor (CRF) release from the hypothalamus, adrenocorticotropin (ACTH) secretion and proopiomelanocortin (the precursor for ACTH) gene expression in the anterior pituitary. In the present study, the effect of intracerebroventricular injection of saikosaponin (SS)-a and -d, two of the main components of saiko agents, on hypothalamic CRF gene expression was examined in pentobarbital-anesthetized rats. Administration of SS-d, 0.2–2.0 μg/kg body wt, increased plasma ACTH levels, proopiomelanocortin mRNA levels in the anterior pituitary and the CRF mRNA level in the hypothalamus in a dose-dependent manner, whereas SS-a failed to have an affect on these levels. These findings indicate that SS-d stimulates both CRF gene expression and CRF release, which in turn increases ACTH release and proopiomelanocortin gene expression in the anterior pituitary. Therefore, SS-d is believed to have an important role both in saiko agent-induced CRF release and CRF gene expression in the hypothalamus.