THE DISTAL COLON PROVIDES RESERVE STORAGE CAPACITY DURING COLONIC FLUID OVERLOAD

Background-In addition to its absorptive function the capacity of the colon to retain fluid might be relevant in compensating for increased fluid loads and prevention of diarrhoea. The distal colon is considere d to be mainly a conduit without extensive storage function. Aims-To e valuate colonic volume capacity in a model of pure osmotic diarrhoea.M ethods-A non-absorbable, iso-osmotic solution (OS) containing polyethy lene glycol (500 ml) was infused into the caecum of nine healthy volun teers; the control group (n=5) received an equal amount of an easily a bsorbable electrolyte solution (ES). Fluids were radiolabelled with te chnetium-99m and gamma camera images were obtained for 48 hours. Count s in the proximal and distal colon were measured and regional and over all colonic transit and stool output were quantified. Results-After OS , in contrast to ES, faecal output was increased significantly (p<0.05 ), but colonic transit after OS was not different from transit after E S (p>0.05). This indicates storage of OS in the colon: after OS infusi on, counts in the proximal colon decreased linearly while the distal c olon stored approximately 30% of radioactivity for the whole 48 hour s tudy period. After OS, stool output correlated with distal (p<0.01), b ut not with proximal (p>0.05), colonic transit. In constrast, after ES , stool output was determined by proximal colonic transit (p<0.05) but not by transit through the distal colon (p>0.05). Conclusion-The dist al colon retains nonabsorbable fluid volumes extensively. In our model transit through the distal colon-but not the proximal colon-determine d the time at which diarrhoea occurred.