Absorption of Na, H ions and short chain fatty acids from the sheep colon

The interrelationship between the absorption of Na, H ions and short chain fatty acids (SCFA) and the secretion of HCO3 in the sheep colon was studied using an in vivo perfusion technique. 1. Under control conditions net SCFA absorption was 62.9 +/- 6.1 mmol . h-1, net Na absorption 49.8 +/- 7.6 mmol . h-1. HCO3 accumulated in the colon lumen at a rate of 5.1 +/- 2.9 mmol . h-1. 2. When 30, 50, or 70% of the Na in the perfusion solution were replaced by Li, Na transport was gradually inhibited and even abolished when 70 mmol . 1(-1) of Li were present. SCFA absorption also decreased, however, to a lower degree. 3. Net Na transport was higher in the presence than in the absence of SCFA. This difference disappeared when Na transport was inhibited by Li. 4. HCO3 accumulation in the colon lumen significantly increased with increasing Li concentrations up to a maximum of 21.7 +/- 7.1 mmol . h-1 when 50% of Na were replaced by Li, however, only in the presence of SCFA. 5. Neither increasing Li concentrations nor the presence or absence of SCFA influenced the H ion disappeared from the perfusion solution. 6. These results indicate that net absorption of Na and SCFA in sheep colon are closely linked to the availability of H ions.