245 Evidence for a New Mechanism Underlying Persistent Visceral Hypersensitivity and Increased Permeability in a Model of Post-Infectious IBS

Abstract

and cortisol responses to stimulation with CRH and ACTH: 1) differ between IBS patients and healthy controls (HCs), 2) are affected by sex and EALs, 3) are associated with GR mRNA expression. Methods: Male and female Rome III+ IBS patients and HCs underwent CRH (1μg/kg ovine) and ACTH (250μg) stimulation tests with serial plasma ACTH and cortisol levels measured. GR mRNA levels were measured from peripheral blood mononuclear cells using real-time PCR. Presence of EALs <18 yrs of age was measured with the Trauma History questionnaire. Linear mixed effects models were used to compare ACTH and cortisol response measured across time between groups with a knot at the peak of the curve to model the rates of change from baseline to peak (rise) and from peak to the last time point (decline). Area under the curve (AUC) was also measured. Results: 60 IBS patients (65%F, mean age 33yrs) and 56 HCs (52%F, mean age 31yrs) underwent hormone stimulation studies. 74 IBS (65%F, mean age 33yrs) and 69 HCs (52%F, mean age 33yrs) had GR mRNA expression levels. A subset (37 IBS, 28 HCs) had both hormone stimulation and GR mRNA studies. 34 (60%) IBS patients and 27 (48%) HCs had +EAL. CRH stimulation test: IBS patients showed a slower rate of decline from peak ACTH levels than HCs (p<0.05). Women with IBS had a slower rate of decline of ACTH (p=0.01) and cortisol (p=0.001) than men with IBS. ACTH stimulation test: Cortisol responses were similar in IBS and HCs, likely due to a significant interaction between IBS and sex (p<0.001). Within women, IBS had a lower cortisol response (AUC) than HCs. In contrast, in men, IBS had a greater cortisol response than HCs. GR mRNA expression: Levels were lower in IBS vs HCs (p= 0.03), which was mainly seen within men. Lower GR mRNA levels were associated with faster rise in ACTH and cortisol responses (p=0.01-0.03). EAL did not have a significant effect on hormone responses. Conclusion: HPA axis response was dysregulated in IBS. The enhanced HPA axis response was associated with downregulation of the GR mediated negative feedback system. Sex differences in the stress response may play a role in the female predominance of IBS.