Diurnal variation of abdominal motor responses to colorectal distension and plasma cortisol levels in rats.

Most patients with functional bowel disorders complain of daytime symptoms while they remain asymptomatic at night. As symptoms are associated with heightened visceral sensitivity, we hypothesized that circadian fluctuations of the visceral sensory function occur. At four different timepoints (06.00, 12.00, 18.00 and 24.00 h), colorectal distensions (CRD) were performed in fasting conscious male Lewis rats using a balloon catheter and a barostat device. The abdominal wall contractions (behavioural pain response) were assessed during colorectal distension by abdominal wall electromyography (EMG). Plasma levels for endogenous cortisol were determined simultaneously at these timepoints. EMG responses to CRD were significantly (P < 0.05) higher at midnight and in the early morning. Plasma cortisol levels peaked in the evening. In night-active Lewis rats, the behavioural pain response to noxious visceral stimulation is augmented at night and fluctuations of visceral sensitivity are accompanied by circadian changes of plasma concentrations of endogenous cortisol. We conclude that there are marked circadian fluctuations in visceral sensory functions. Thresholds are low during time periods of normal behavioural activity. These findings suggest that fluctuation of the sensory functions may be linked to the circadian variability of symptoms in patients with functional GI disorders.

Long-term effects of transient chemically induced colitis on the visceromotor response to mechanical colorectal distension.

Acute gastrointestinal infections with transient mucosal inflammation frequently precede the onset of functional GI disorders with altered visceral sensory function. We hypothesized that an acute inflammation of the mucosa is linked to long-lasting alterations of afferent visceral pathways. Utilizing abdominal wall electromyography, we tested the visceromotor response to tonic rectal distension (60 mm Hg/3 min) in fasted, conscious, male Lewis rats (n = 40) with a barostat device before and 2, 4, 15, and 17 weeks after rectal instillation of saline or trinitrobenzenesulfonic acid plus ethanol. Tissue samples from paired controls were obtained to assess histologic tissue alterations. Inflammatory changes were present up to 2 weeks after acid/ethanol instillation but not after saline instillation. Compared to baseline measurements, the visceromotor response to colorectal distension increased significantly and reached a maximum 17 weeks (P < 0.001) after induction of colitis, while it decreased in control experiments (P < 0.05). In conclusion, these data suggest that an acute inflammation has long-term effects on somatosensory functioning.