Analgesic and Uterine Relaxant Effects of Isoliquiritigenin, a Flavone from Glycyrrhiza glabra

Shaoyao-gancao-tang, a Chinese medicinal formula consisting of peony and licorice has been used for the treatment of dysmenorrhea for thousands of years. The purpose of the present study was to demonstrate the analgesic and uterine relaxant effects of isoliquiritigenin (ISL), a flavonoid isolated from the roots of Glycyrrhiza glabra (a type of licorice). In vitro, isoliquiritigenin caused concentration-dependent inhibition of spontaneous contraction of isolated rat uterus and the contraction induced by various types of stimulants, such as acetylcholine (Ach, 10 mM), KCl (40 mM) and oxytocin (1 mU/mL). The uterine contractile response to cumulative concentrations of CaCl₂ was blocked by 0.1 and 1 mM of isoliquiritigenin. The isoliquiritigenin-induced relaxation was partly inhibited by the nitric oxide synthase (NOS) inhibitor Nv-nitro-L-arginine methylester (L-NAME, 100 mM) and the COX-1/COX-2 inhibitor indomethacin (10mM). In vivo, isoliquiritigenin could cause a significant reduction in the acetic acid-induced writhing response and hot-plate test at the high dose. These results indicate that isoliquiritigenin, a flavonoid isolated from the roots of Glycyrrhiza glabra, not only has a spasmolytic effect on uterine contraction, which is in relation to Ca²⁺ channels, NOS and COX, but also an effective activity in reducing pain.