A systemic, endotoxin-induced immune activation leads to decreased visceral sensory and pain thresholds and altered subjective pain ratings in healthy humans.
Growing evidence suggests that systemic immune activation plays a role in the pathophysiology of pain in functional bowel disorders. By implementing a randomized crossover study with an injection of endotoxin or saline, we aimed to test the hypothesis that endotoxin-induced systemic inflammation increases visceral pain sensitivity in humans. Eleven healthy men (mean ± standard error of the mean age 26.6 ± 1.1 years) received an intravenous injection of either lipopolysaccharide (LPS; 0.4 ng/kg) or saline on 2 otherwise identical study days. Blood samples were collected 15 min before and 1, 2, 3, 4, and 6 h after injection to characterize changes in immune parameters including proinflammatory cytokines. Rectal sensory and pain thresholds and subjective pain ratings were assessed with barostat rectal distensions 2 h after injection. LPS administration induced an acute inflammatory response indicated by transient increases in tumor necrosis factor alpha, interleukin 6, and body temperature (all P < .001). The LPS-induced immune activation increased sensitivity to rectal distensions as reflected by significantly decreased visceral sensory and pain thresholds (both P < .05) compared to saline control. Visceral stimuli were rated as more unpleasant (P < .05) and inducing increased urge to defecate (P < .01). Pain thresholds correlated with interleukin 6 at +1 h (r = 0.60, P < .05) and +3 h (r = 0.67, P < .05) within the LPS condition. This report is novel in that it demonstrates that a transient systemic immune activation results in decreased visceral sensory and pain thresholds and altered subjective pain ratings. Our results support the relevance of inflammatory processes in the pathophysiology of visceral hyperalgesia and underscore the need for studies to further elucidate immune-to-brain communication pathways in gastrointestinal disorders.
aInstitute of Medical Psychology and Behavioral Immunobiology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
bDepartment of Trauma Surgery, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
*Corresponding author. Address: Institute of Medical Psychology and Behavioral Immunobiology, University Hospital Essen, Hufelandstr. 55, 45122 Essen, Germany. Tel.: +49 201 723 4502; fax: +49 201 723 5948.
Submitted August 23, 2011; revised November 3, 2011; accepted December 5, 2011.