Effects of short chain fatty acids and K on absorption of Mg and other cations by the colon and caecum.

The influence of short chain fatty acids (SCFA) on Mg, Na, and water absorption was studied in the rat distal colon and caecum using an in vivo luminal perfusion technique. The effect of SCFA on K absorption by the distal colon and the effect of K on Mg absorption by the distal colon and caecum were also investigated. Butyrate (60 mmol/l) or a mixture of SCFA (60 mmol/l acetate, 20 mmol/l propionate, 10 mmol/l butyrate) stimulated Mg and K absorption by the distal colon, while Na and water absorption was not affected. The effect on Mg absorption was pH-dependent. In the caecum, butyrate enhanced Na and water absorption, but not Mg absorption. Acetate (60 mmol/l) did not influence electrolyte absorption by either intestinal segment. K (30 mmol/l) inhibited Mg absorption by the distal colon, but not by the caecum. It is concluded from these findings that SCFA deriving from fermentation of carbohydrates in the large intestine stimulate Mg, K, and Na absorption by delivering protons to Mg++/H+, K+/H+ and Na+/H+ exchangers located in the apical membrane of the epithelium. K seems to inhibit Mg absorption in the colon by affecting a mechanism which does not respond to SCFA.