Differential responding of autonomic function to histamine H₁ antagonism in irritable bowel syndrome

Background: The role of histamine in the pathophysiology of irritable bowel syndrome (IBS) is largely unknown. Dysfunction of the autonomic nervous system (ANS) in IBS patients is also not fully confirmed. We hypothesized that blockade of histamine H₁ receptors affects ANS responses differently between IBS subjects and controls. Methods: Subjects were 12 IBS subjects and 12 age- and sex-matched controls. Either 100-μg-kg^-1 chlorphenamine or the same amount of saline was administered on different days. The rectum was stimulated with electrical currents of 0-mA (sham) or 30-mA. Autonomic nervous system function was measured using mean arterial pressure (MAP), heart rate (HR), high frequency (HF) component of HR variability, low frequency/high frequency ratio (LF/HF ratio) and plasma catecholamines and histamine. Subjective perceived stress during the examination was evaluated on an ordinate scale. Key Results: Mean arterial pressure showed significant effects of diagnosis (P-<-0.05) and drug-×-diagnosis interaction (P-<-0.05). The MAP significantly increased after chlorphenamine administration in IBS subjects, but not in controls. Heart rate revealed a significant drug effect (P-<-0.001), which decreased after chlorphenamine administration in controls, but not in IBS subjects. Perceived stress significantly increased by rectal stimulation (P-<-0.001) and a significant stimulus-×-diagnosis interaction (P-<-0.05) was revealed, indicating greater reduction in IBS subjects by chlorphenamine.Conclusion & Inferences- Sympathetic vasomotor tone in IBS subjects differentially responded on administration of a histamine H₁ antagonist to that of controls. These findings suggest an increased histaminergic activity in IBS subjects.