Urea secretion into the colon of sheep and goat

Total urea entry rate into the body pool and urea hydrolysis rate (transfer of endogenous urea into the total gastrointestinal (g.i.) tract) were obtained after single intravenous injections of [14C]urea and from renal urea excretion in sheep and goat. Secretion of endogenous urea into the colon was estimated from the appearance of urea N in the temporarily isolated and perfused colon. Rate of urea secretion into the colon was rather small (0.10-0.31 mmol . h-1). It was only 0.3-1.1% of urea entry rate, or 0.4-7% of urea hydrolysis rate. Urea secretion into the colon increased linearly with increase of plasma urea concentration. Dietary conditions and short-chain fatty acid concentrations in colonic contents had no significant effect on the permeability of the colonic epithelium for urea.