Quercetin, a main flavonoid in onion, inhibits the PGF_2α-induced uterine contraction in vitro and in vivo

Dysmenorrhoea is considered to be caused by excessive levels of prostaglandins, which stimulate abnormal uterine contractions. This study aimed to investigate the modulatory effects of quercetin that is a main flavonoid in onion on uterine contractility and its possible underlying mechanisms. In vitro and in vivo contractile activities of the uteri were determined using uterine horns isolated from adult rats. The results indicated that (1) for contractions induced by PGF_2α-, oxytocin-, and carbachol, quercetin showed the most potent suppressing effect among the tested flavonoids; (2) Ca²⁺-dependent uterine contractions were inhibited by quercetin; (3) quercetin reduced the PGF_2α-elicited Ca²⁺ responses in human uterine smooth muscle cells; (4) quercetin inhibited uterine contractions stimulated by Ca²⁺ channel activator and depolarisation in response to high K⁺; (5) quercetin was able to block Ca²⁺ influx through voltage-operated Ca²⁺ channels in plasma membrane; and (6) quercetin effectively reduced PGF_2α-induced contractions through the administration of increasing doses of 10, 25, and 50 mg/kg in rats. The present findings suggest that onion's major active compound, quercetin, may be a potential adjuvant for treating uterine disorders.