Rectal absorption of short chain fatty acids in the absence of chloride.

The absorption of short chain fatty acids by the human rectum in the absence of chloride has been studied using a dialysis bag technique. Absorption rates of sodium, water, and short chain fatty acids were unchanged on replacing chloride with sulphate. Final concentrations of bicarbonate were 35.4 +/- 3.4 mmol/l in the presence of chloride and 37.1 +/- 5.2 mmol/l in the absence of chloride. The rates of movement of bicarbonate into the dialysates were similar. If bicarbonate is secreted in exchange for chloride then it also appears to be secreted in exchange for absorbed short chain fatty acids.