Adlay is a grass crop which has been used in traditional Chinese medicine and also as a nourishing food. It has been shown to posses anti-allergic, antimutagenic and hypolipemic effects. However, the effects and action mechanisms of crude adlay hull acetone extract (AHA) on adrenal zona fasciculata-reticularis (ZFR) cells are still unclear. This study explored the effects of AHA on corticosterone release. ZFR cells were incubated with AHA in the presence or absence of adrenocorticotropin (ACTH), 8-bromo-cyclic 3′: 5′- adenosine monophosphate (8-Br-cAMP), forskolin (FSK), 25-hydroxy cholesterol (25-OH-cholesterol), pregnenolone, progesterone or deoxycorticosterone. The concentrations of corticosterone or pregnenolone in the media were measured by radioimmunoassay (RIA). The cells were used to measure the expression of steroidogenic acute regulatory (StAR) protein by Western blot. The present data demonstrated that: (1) AHA inhibited ACTH-, 8-Br-cAMP-, forskolin-, 25-OH-cholesterol-, pregnenolone-, progesterone- or deoxycorticosterone-stimulated corticosterone release; (2) AHA (800 μg/ml) caused more pregnenolone release in control group, but not in 25-OH-cholesterol, trilostane or 25-OH-cholesterol+trilostane group; (3) kinetic study showed an uncompetitive inhibition model of AHA to P450 side chain cleavage enzyme (P450scc); (4) kinetic study showed a noncompetitive inhibition model of AHA to 11β-hydroxylase; and (5) AHA inhibited the expression of StAR protein. These results suggest that AHA acts directly upon rat ZFR cells to diminish corticosterone release. These results indicate the inhibitory mechanism of AHA mediates through an inhibition of the activities of the post-cAMP corticosterone synthesis enzymes, i.e. 3β-HSD, 21-hydroxylase, 11β-hydroxylase, and inhibition of StAR protein expression.
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