Ipamorelin accelerates colonic transit and restores feeding in postoperative ileus rats
Background
Postoperative ileus (POI) is a transient but debilitating cessation of coordinated gastrointestinal motility following abdominal surgery, prolonging hospital stays and increasing morbidity. Current standard-of-care options remain limited and largely supportive. Ghrelin, an endogenous gut peptide, is known to stimulate appetite and enhance gastric motility through the GHSR (growth hormone secretagogue receptor), making GHSR agonism a rational pharmacological target for restoring gut function after surgery. Ipamorelin is a selective, pentapeptide growth hormone secretagogue and GHSR agonist with a distinct receptor-selectivity profile compared with earlier ghrelin mimetics such as GHRP-6, motivating its evaluation in surgical gut-motility disruption.
Study Design
Fasted male rats underwent laparotomy and intestinal manipulation to induce POI. A dye marker was infused into the proximal colon at the end of surgery to measure colonic transit time (time to first bowel movement) as the primary endpoint. Ipamorelin (0.01–1 mg/kg), GHRP-6 (20 µg/kg), or vehicle (saline) were administered via intravenous bolus. Two dosing regimens were tested: a single post-surgical dose and a 2-day repetitive regimen of four doses per day at 3-hour intervals. Cumulative fecal pellet output, food intake, and body weight were monitored for 48 hours post-surgery.
Results
A single dose of ipamorelin 1 mg/kg or GHRP-6 20 µg/kg each significantly decreased the time to first bowel movement compared with vehicle, indicating accelerated colonic transit after surgery. However, neither single-dose compound produced significant changes in cumulative fecal output, food intake, or body weight gain over 48 hours. The repetitive dosing regimen told a markedly different story:
Repetitive dosing of ipamorelin at 0.1 mg/kg or 1 mg/kg (four doses/day for 2 days) significantly increased cumulative fecal pellet output, food intake, and body weight gain versus vehicle — effects not achieved with a single dose at any tested concentration.
The dose-response across 0.01–1 mg/kg revealed that the lowest dose (0.01 mg/kg) was insufficient to accelerate transit even in single-dose conditions, while both 0.1 mg/kg and 1 mg/kg were effective under the repetitive regimen. The finding that sustained GHSR activation — rather than a single bolus — is required to normalize comprehensive gut recovery metrics suggests a threshold of receptor engagement needed to restore full post-surgical GI function.
Key Findings
- Single dose ipamorelin (1 mg/kg, IV) decreased time to first bowel movement vs. vehicle
- Single dose GHRP-6 (20 µg/kg, IV) also shortened time to first bowel movement
- Single dosing had no effect on fecal output, food intake, or body weight at 48 h
- Repetitive dosing (0.1 or 1 mg/kg, 4×/day × 2 days) significantly increased fecal output, food intake, and body weight gain
- Dose range tested for ipamorelin: 0.01–1 mg/kg IV; 0.01 mg/kg was insufficient
Why It Matters
Sustained, multi-dose ipamorelin infusion is required to fully restore gut function after surgery — a single bolus only partially addresses POI by accelerating initial transit without correcting the broader recovery deficit. For clinicians and protocol designers, this suggests that post-surgical ipamorelin regimens should be structured as repeated intravenous infusions over at least 48 hours rather than a one-time administration. The 3-hour dosing interval used here provides a concrete scheduling anchor for future clinical protocol development, though translation from rodent to human dosing is not yet established. The comparison with GHRP-6 confirms the ghrelin-mimetic class is mechanistically viable for POI, positioning ipamorelin — with its selectivity profile — as a candidate for further clinical investigation.
