{"paper_id":"8906b1cb-3c92-4c5e-b004-8daa703cd8b3","body_text":"Abstract\nPurpose\nPain in patients with endometriosis is considered a significant source of stress but does not always correlate with severity of the condition. We have demonstrated that stress can worsen endometriosis in an animal model. Here, we tested the impact of a psychological stress protocol on pain thresholds and pain receptors.\nMethods\nEndometriosis was induced in female rats by suturing uterine horn tissue next to the intestinal mesentery. Sham rats had sutures only. Rats were exposed to water avoidance stress for 7 consecutive days or handled for 5 minutes (no stress). Fecal pellets and serum corticosterone (CORT) levels were measured as an index of anxiety. Pain perception was assessed using hot plate and Von Frey tests. Substance P, enkephalin, endomorphin-2, Mu opioid receptor (MOR), and neurokinin-1 receptor expression in the spinal cord were measured by immunohistochemistry.\nResults\nFecal pellets and CORT were significantly higher in the endo-stress (ES) group than endo-no stress (ENS; P <.01) and sham-no stress groups (SNS; P <.01). The ES rats had more colonic damage (P <.001 vs SNS; P <.05 vs ENS), vesicle mast cell infiltration (P <.01 vs ENS), and more severe vesicles than ENS. The ES developed significant hyperalgesia (P <.05) but stress reversed the allodynic effect caused by endo (P <.001). The MOR expression was significantly reduced in ENS versus SNS (P <.05) and more enkephalin expression was found in endo groups.\nConclusion\nAnimals subjected to stress develop more severe symptoms but interestingly stress seems to have beneficial effects on abdominal allodynia, which could be a consequence of the stress-induced analgesia phenomenon.\nSimilar content being viewed by others\nReferences\nBulun SE. Endometriosis. N Engl J Med. 2009;360(3):268–279.\nSchindler AE. Dienogest in long-term treatment of endometriosis. Int J Womens Health. 2011;3:175-184.\nMcKinnon B, Bersinger N, Wotzkow C, Mueller MD. Endometriosis-associated nerve fibers, peritoneal fluid cytokine concentrations, and pain in endometriotic lesions from different locations. Fertil Steril. 2012;97(2):373–380.\nPractice Committee of the American Society for Reproductive Medicine. Endometriosis and infertility: a committee opinion. Fertil Steril. 2012;98(3):591–598.\nLevy BS, Apgar BS, Surrey ES, Wysocki S. 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