Inhibitory effects of daidzein on intestinal motility in normal and high contractile states.

Daidzein is a naturally occurring compound and has various health benefits. However, its effects on intestinal smooth muscle contractility remain unknown. The present study was to characterize the effects of daidzein on the contractility of isolated jejunal smooth muscle and its underlying mechanisms. Ex vivo assay was selected as the major method to determine the effects of daidzein on the contractility of isolated jejunal smooth muscle fragment (JSMF). Daidzein (5-160 µmol/L) inhibited the contractility of JSMF in normal contractile state and in a dose-dependent manner. Daidzein also inhibited the contractility of JSMF induced by ACh, histamine, erythromycin and high Ca²⁺, respectively, and decreased charcoal propulsion in the small intestine in vivo. The inhibitory effects of daidzein were partially blocked by phentolamine or propranolol and were abolished in the presence of varapamil or at Ca²⁺-free assay condition. However, the inhibitory effects of daidzein on jejunal contraction were not significantly influenced by nitric oxide (NO) synthase inhibitor L-NG-nitro-arginine (L-NNA). Daidzein was also found to directly inhibit the phosphorylation and Mg²⁺-ATPase activity of smooth muscle myosin. The results implicated that α- and β-adrenergic receptors were involved in the inhibitory effects produced by daidzein rather than via NO pathway. As a phytoestrogen, daidzein has shown its potential value in relieving the hypercontractility of small intestine.