Studies on the secretion of amino acids and of urea into the gastro intestinal tract of pigs. 2. Net secretion of leucine into the small and large intestines.

The experiment was carried out on 3 pigs of 34 kg body weight equipped with re-entrant cannulas both in the duodenum and terminal ileum. Furthermore, catheters were inserted into the external jugular vein and into the carotid artery. During a preliminary period digesta from both cannulas were collected and stored. This digesta was than reintroduced during a 12 hours period of intravenous infusion of 14C-leucine while outflowing digesta from the proximal parts of the cannulas were collected, stored and analyzed for leucine content, 14C-radioactivity and specific radioactivity of leucine. This paper reports the net secretion of 14C-activity and of 14C-leucine by the small intestine and the recovery of both in the content of the digestive tract at the end of the infusion. It was concluded that endogenous leucine enters the lumen of the small intestine through the intestinal wall mainly in a protein bound form. Free leucine is secreted, however, only in small amounts. Metabolites of leucine were also secreted into or formed in the lumen of the small intestine. A proportion of endogenous leucine was reabsorbed during the passage of digesta along the small intestine.