The Effect of PAK1 Knockout on the Efficacy of Metoclopramide in a Murine Model of Postoperative Ileus

Abstract

Postoperative ileus (POI) is characterized as a decrease in gastrointestinal motility following a surgical procedure. POI is one of the most common postoperative complications in the United States and presents a considerable cost in both financial terms and patient morbidity. Metoclopramide is a prokinetic agent which antagonizes dopamine receptors in the enteric nervous system (ENS) and is currently employed to treat POI. Reviews of the literature have shown metoclopramide to be ineffective in the treatment of POI. We have shown that intestinal smooth muscle is dysfunctional in animal models of POI, which may account for the lack of response to prokinetics such as metoclopramide. We have also shown that PAK negatively regulation myosin light chain phosphorylation in a POI model and PAK inhibition can improve smooth muscle contractility. Based on these data, we hypothesize that the response to metoclopramide will be improved in PAK1 knockout mice compared to wildtype mice after gut manipulation to induce POI. PAK1 homozygous knockout strains and C57BL/6 wildtype mice of both sexes were used. Mice of both genotypes were divided into four groups: 1) sham surgery and vehicle; 2) POI and vehicle; 3) sham surgery and 0.1mg/kg metoclopramide; 4) POI and 0.1mg/kg metoclopramide. Sections of whole ileum were harvested 24 hours post‐surgery and suspended in 37°C buffered Krebs solution while muscle contractility was measured. Amplitude, frequency, tone, and integral were calculated and a carbachol dose response curve was generated in the organ bath. As expected, a significant decrease in baseline integral and contraction amplitude, and agonist induced contractility was observed in the POI groups compared to the sham surgery groups. Contractility and responsiveness to carbachol improved in PAK1 knockout; however, response to metoclopramide was not significantly different between PAK1 knockout and wildtype mice. We conclude that PAK1 inhibition partially attenuates the development of POI but does not improve the response to metoclopramide.