Adaptive regulation of intestinal lysine metabolism

The metabolism of dietary essential amino acids by the gut has a direct eff ect on their systemic availability and potentially limits growth. We demons trate that, in neonatal pigs bearing portal and arterial catheters and fed a diet containing 23% protein [high protein (HP) diet], more than half the intake of essential amino acids is metabolized by the portal-drained viscer a (PDV). Intraduodenal or i.v. infusions of [U-C-13]-lysine were used to me asure the appearance across and the use of the tracer by the PDV. In HP-fed pigs, lysine use by the PDV was derived almost entirely from the arterial input. In these animals, the small amount of dietary lysine used in first p ass was oxidized almost entirely. Even so, intestinal lysine oxidation (24 mu mol/kg per h) accounted for one-third of whole-body lysine oxidation (77 mu mol/kg per h). Total lysine use by the PDV was not affected by low prot ein (LP) feeding (HP, 213 mu mol/kg per h; LP,186 mu mol/kg per h), In LP-f ed pigs, the use of lysine by the PDV accounted for more than 75% of its in take, In contrast to HP feeding, both dietary and arterial lysines were use d by the PDV of LP-fed pigs in nearly equal amounts. Intestinal lysine oxid ation was suppressed completely. We conclude that the PDV are key organs wi th respect to amino acid metabolism and that the intestines use a dispropor tionately large amount of the dietary supply of amino acids during protein restriction.