Abstract
Background/Aims Lubiprostone, a chloride channel type 2 (ClC-2) activator, was thought to treat constipation by enhancing intestinal secretion. It has been associated with increased intestinal transit and delayed gastric emptying. Structurally similar to prostones with up to 54% prostaglandin $E_2$ activity on prostaglandin E receptor 1 ($EP_1$), lubiprostone may also exert $EP_1$-mediated procontractile effect on intestinal smooth muscles. We investigated lubiprostone's effects on intestinal smooth muscle contractions and pyloric sphincter tone. Methods Isolated murine small intestinal (longitudinal and circular) and pyloric tissues were mounted in organ baths with modified Krebs solution for isometric recording. Basal muscle tension and response to electrical field stimulation (EFS; 2 ms pulses/10 V/6 Hz/30 sec train) were measured with lubiprostone $(10^{-10}-10^{-5}M){\pm}EP_1$ antagonist. Significance was established using Student t test and P < 0.05. Results Lubiprostone had no effect on the basal tension or EFS-induced contractions of longitudinal muscles. With circular muscles, lubiprostone caused a dose-dependent increase in EFS-induced contractions ($2.11{\pm}0.88$ to $4.43{\pm}1.38N/g$, P = 0.020) that was inhibited by pretreatment with $EP_1$ antagonist ($1.69{\pm}0.70$ vs. $4.43{\pm}1.38N/g$, P = 0.030). Lubiprostone had no effect on circular muscle basal tension, but it induced a dose-dependent increase in pyloric basal tone ($1.07{\pm}0.01$ to $1.97{\pm}0.86$ fold increase, P < 0.05) that was inhibited by $EP_1$ antagonist. Conclusions In mice, lubiprostone caused a dose-dependent and $EP_1$-mediated increase in contractility of circular but not longitudinal small intestinal smooth muscles, and in basal tone of the pylorus. These findings suggest another mechanism for lubiprostone's observed clinical effects on gastrointestinal motility.