Mechanism of Toona sinensis-stimulated adrenal steroidogenesis in primary rat adrenal cells

Toona sinensis is a well-known nutritious plant food widely distributed in Asia. The effects of aqueous leaf extracts of T. sinensis (TSL-1) on steroidogenesis was examined using primary rat adrenal cells. TSL-1 stimulated corticosterone production in a time- and concentration-dependent manner. Cells were then challenged with forskolin, dibutyryl cyclic AMP (dbcAMP), pregnenolone, progesterone or deoxycorticosterone in the presence or absence of TSL-1 for 6 h to determine the mechanism. TSL-1 could enhance forskolin- and dbcAMP-induced steroidogenesis and promote pregnenolone-, progesterone- and deoxycorticosterone-induced steroidogenesis. Moreover, TSL-1 induced steroidogenic acute regulatory protein (StAR) mRNA and protein expression in rat adrenal cells and increased StAR promoter activity in CHO-K1 cells. Thus, the stimulatory effect of TSL-1 was presumed to be mainly due to methyl and ethyl gallates. Therefore, TSL-1-stimulated corticosterone production requires the participation of cAMP-dependent PKA, steroidogenic enzymes and the expression of StAR, which regulates the rate-limiting step in steroidogenesis.