Formononetin Relaxes Cholecystokinin‐ and KCl‐induced Tension in Guinea Pig Gallbladder Strips

Abstract

Formononetin, a phytoestrogen and isoflavone, relaxed cholecystokinin octapeptide‐ (CCK) and KCl‐induced tension in a concentration dependent manner. An in vitro technique was used to determine which system(s) mediated the relaxation. Paired t‐tests were used; differences between mean values of p<0.05 were considered significant. Adding formononetin prior to CCK or KCl produced a significant decrease in the amount of tension {1.2±0.07 vs. 0.81±0.05 g CCK, (p<0.001); 0.84±0.04 vs. 0.74±0.05 g KCl, p<0.01}. When the PKC inhibitors bisindolymaleimide IV and chelerythrine Cl− were used together, a significant (p<0.01) reduction in the formononetin‐induced relaxation (78.1±4.5 vs. 69.7±3.4%) was observed. Genistein, a protein tyrosine kinase inhibitor, significantly (p<0.01) decreased the amount of formononetin‐induced relaxation (72.2±6.5 vs. 59.3±6.5%). To determine if PKA mediated the formononetin‐induced relaxation, PKA inhibitor 14–22 amide myristolated (PKA‐IM) was used. PKA‐IM had no significant effect on the amount of formononetin‐induced relaxation. Neither the use of 2‐APB, a blocker of intracellular Ca2+ release; KT5823, a blocker of PKG; or L‐NMMA, a nitric oxide synthase inhibitor, had a significant effect on the amount of formononetin‐induced relaxation. The formononetin‐induced relaxation of CCK‐ or KCl‐induced tension was mediated by blocking extracellular Ca2+ entry which then affected downstream events such as activation of PKC and protein tyrosine kinase.