Chronic naltrexone treatment of rats: effects on gastrointestinal opioid peptide content

Morphine Promotes Colonization of Anastomotic Tissues with Collagenase - Producing Enterococcus faecalis and Causes Leak

BACKGROUND

Despite ever more powerful antibiotics, newer surgical techniques, and enhanced recovery programs, anastomotic leaks remain a clear and present danger to patients. Previous work from our laboratory suggests that anastomotic leakage may be caused by Enterococcus faecalis strains that express a high collagenase phenotype (i.e., collagenolytic). Yet the mechanisms by which the practice of surgery shifts or selects for collagenolytic phenotypes to colonize anastomotic tissues remain unknown.

METHODS

Here, we hypothesized that morphine, an analgesic agent universally used in gastrointestinal surgery, promotes tissue colonization with collagenolytic E. faecalis and causes anastomotic leak. To test this, rats were administered morphine in a chronic release form as would occur during routine surgery or vehicle. Rats were observed for 6 days and then underwent exploratory laparotomy for anastomotic inspection and tissue harvest for microbial analysis. These results provide further rationale to enhanced recovery after surgery (i.e., ERAS) programs that suggest limiting or avoiding the use of opioids in gastrointestinal surgery.

RESULTS

Results demonstrated that compared to placebo-treated rats, morphine-treated rats demonstrated markedly impaired anastomotic healing and gross leaks that correlated with the presence of high collagenase-producing E. faecalis adherent to anastomotic tissues. To determine the direct role of morphine on this response, various isolates of E. faecalis from the rats were exposed to morphine and their collagenase activity and adherence capacity determined in vitro. Morphine increased both the adhesiveness and collagenase production of four strains of E. faecalis harvested from anastomotic tissues, two that were low collagenase producers at baseline, and two that were high collagenase producers at baseline.

CONCLUSION

These results provide further rationale to enhanced recovery after surgery (i.e., ERAS) programs that suggest limiting or avoiding the use of opioids in gastrointestinal surgery.

Beta-funaltrexamine blockade of opioid-induced inhibition of somatostatin secretion from rat stomach

Opioid peptides are potent inhibitors of gastric somatostatin secretion. In the current investigation the effect of mu-opioid receptor blockade on responses to [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAGO) was studied. Gastric inhibitory polypeptide (GIP; 1 nM) -stimulated secretion of immunoreactive somatostatin was almost completely inhibited by DAGO (1 microM). The mu-receptor antagonists, beta-funaltrexamine and naloxonazine, blocked the effect of DAGO. Pretreatment of rats with beta-funaltrexamine, 24 h prior to perfusion, reduced the percentage inhibition by DAGO from 88.6 +/- 5.2% to 50.7 +/- 9.3%. These studies support the involvement of mu-opioid inhibitory receptors in the regulation of gastric somatostatin secretion.