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

Acute hyperglycaemia affects the perception of sensations arising from the gastrointestinal tract. The mechanisms responsible for this effect are unknown. Recordings of cerebral evoked potentials (EPs) can be used to assess the integrity of visceral afferent pathways. Our aim was to determine whether hyperglycaemia affects EPs elicited by rectal distension in healthy humans.

Twelve healthy men, aged 19-31 years, were studied. A manometric catheter, incorporating a rectal balloon, was positioned 7-10 cm from the anal verge. Balloon distensions at both 'low' ( approximately 20 mL) and 'high' ( approximately 28 mL) volumes were performed, in a single-blind, randomized order, during both euglycaemia (4 mmol L-1) and hyperglycaemia (12 mmol L-1). EPs were recorded from a midline scalp electrode (Cz, International 10-20 system) and averaged for each series of 50 distensions. EP latencies and interpeak amplitudes were calculated.

Polyphasic EPs were recorded in all but one subject. Although the blood glucose concentration had no significant effect on the latencies of the EP peaks elicited by either 'low'- or 'high'-volume balloon distension, the interpeak amplitude (P1-N1) was greater during hyperglycaemia than during euglycaemia at the 'low' balloon volume (6.3 +/- 1.2 microV vs. 4.8 +/- 1.0 microV, P < 0.05). The blood glucose concentration had no significant effect on the perception of rectal balloon distension.

We conclude that in normal subjects acute hyperglycaemia increases the amplitude of the cerebral EP elicited by rectal balloon distension at low balloon volumes, suggesting that the effects of hyperglycaemia on gastrointestinal sensation may be mediated by central mechanisms.