The effect of hyperglycaemia on cerebral potentials evoked by rapid rectaldistension in healthy humans

Background Acute hyperglycaemia affects the perception of sensations arisin g from the gastrointestinal tract. The mechanisms responsible for this effe ct are unknown. Recordings of cerebral evoked potentials (EPs) can be used to assess the integrity of visceral afferent pathways. Our aim was to deter mine whether hyperglycaemia affects EPs elicited by rectal distension in he althy humans. Materials and methods Twelve healthy men, aged 19-31 years, were studied. A manometric catheter, incorporating a rectal balloon, was positioned 7-10 c m from the anal verge. Balloon distensions at both 'low' (similar to 20 mL) and 'high' (similar to 28 mL) volumes were performed, in a single-blind, r andomized order, during both euglycaemia (4 mmol L-1) and hyperglycaemia (1 2 mmol L-1). EPs were recorded from a midline scalp electrode (Cz, Internat ional 10-20 system) and averaged for each series of 50 distensions. EP late ncies and interpeak amplitudes were calculated. Results Polyphasic EPs were recorded in all but one subject. Although the b lood glucose concentration had no significant effect on the latencies of th e EP peaks elicited by either 'low'- or 'high'-volume balloon distension, t he interpeak amplitude (P1-N1) was greater during hyperglycaemia than durin g euglycaemia at the 'low' balloon volume (6.3 +/- 1.2 mu V vs. 4.8 +/- 1.0 mu V, P < 0.05). The blood glucose concentration had no significant effect on the perception of rectal balloon distension. Conclusions We conclude that in normal subjects acute hyperglycaemia increa ses the amplitude of the cerebral EP elicited by rectal balloon distension at low balloon volumes, suggesting that the effects of hyperglycaemia on ga strointestinal sensation may be mediated by central mechanisms.