The effects of quercetin on intestinal and vascular smooth muscle

In this study, researchers from the University of Alberta in Canada investigated quercetin and its effect on gallbladder smooth muscle, in particular, if it could relax gallbladder smooth muscles. The results of their study were published in the journal Nutrition Research.

• Quercetin is a phytoestrogen and a flavonoid that can relax intestinal and vascular smooth muscle.
• The researchers used an in vitro technique to determine the effects of quercetin on gallbladder strips and which system(s) mediated the relaxation.
• They used paired t-tests and considered differences between means of P < .05 significant.
• They reported that the addition of quercetin before cholecystokinin or potassium chloride (KCl) produced a significant (P < .001) decrease in the amount of tension (0.80 ± 0.04 vs. 0.48 ± 0.04 g cholecystokinin octapeptide and 0.8 ± 0.06 vs. 0.54 ± 0.05 g KCl, respectively).
• When they added protein kinase C (PKC) inhibitors bisindolymaleimide IV and chelerythrine Cl? simultaneously, they observed a significant (P < .001) reduction in the quercetin-induced relaxation (45.7 percent ± 4.3 percent vs. 27.6 percent ± 3.4 percent).
• They also used protein kinase A (PKA) inhibitor 14-22 amide, myristolated to determine if PKA mediated the quercetin-induced relaxation. They found that it significantly (P < .05) decreased the amount of quercetin-induced relaxation (40.4 percent ± 3.7 percent vs. 34.5 percent ± 3.3 percent).
• 2-APB (51.2 percent ± 3.5 percent vs. 14.8 percent ± 3.6 percent) and l-NG-methyl-l-arginine acetate salt (45.7 percent ± 4.2 percent vs. 35.2 percent ± 3.6 percent) – a nitric oxide synthase inhibitor – also significantly (P < .001) reduced the amount of quercetin-induced relaxation.
• KT5823, a PKC inhibitor, had no effect on the quercetin-induced relaxation.
• The researchers also found that quercetin blocked extracellular Ca2+ entry, affecting downstream events, such as activation of PKC, PKA, intracellular Ca2+ release, and activation of nitric oxide synthase.
• Quercetin relaxed cholecystokinin octapeptide and KCl-induced tension in a concentration-dependent manner.

Based on these findings, the researchers concluded that quercetin can induce relaxation of gallbladder smooth muscle via multiple signaling pathways.

Journal Reference:

Kline L, Karpinski E. QUERCETIN RELAXES GUINEA PIG GALLBLADDER STRIPS. Nutrition Research. October 2016;36(10):1098–1104. DOI: 10.1016/j.nutres.2016.09.008