Concentrations of amino acids (AA) in blood obtained from arterial and portal permanent catheters were measured together with the portal hepatic blood flow-rate during a post-prandial period of 8 h, in nine conscious pigs (initial mean body-weight 49.3 (SEM 1.8) kg) receiving experimental meals (500, 600 or 1000 g) at 3-4 d intervals from 6-8 to 20 d after the surgical implantation of the catheters and electromagnetic flow probe. The semi-synthetic starch-based diets contained variable amounts of fish meal giving crude protein (nitrogen x 6.25; CP) concentrations (g/kg) of 80 (seven meals), 120 (seven meals), 160 (five meals) and 240 (three meals). 2. During the post-prandial period, variations in the individual blood AA concentrations were parallel to those of total amino-N (Rérat et al. 1988) to a greater or lesser extent according to the AA considered. Portal concentrations, which always exceeded arterial ones (except for glutamic acid and glutamine), increased quickly and, after a peak, returned slowly to reach initial values (small intake) or above (large intake) after 8 h. 3. Relations between amounts of each AA appearing during 8 h after the meal and amounts ingested were characterized by a highly significant linear regression (with the exceptions of glutamic acid and cystine). There were also close and significant relations between amounts of AA absorbed during the first 2 and 4 h after the meal and the amounts ingested. 4. For a mean intake of 90 g CP, aromatic AA showed the highest hourly absorption coefficients (about 0.10/h), and sulphur-AA (0.07/h), lysine (0.07/h) and arginine (0.056/h) the lowest ones. Alanine was synthesized (amounts absorbed within 8 h exceeding those ingested) at the expense of glutamic acid (absorption coefficient 0.01/h). 5. For a given period of time, the AA absorption coefficients decreased with increasing intake, but not in the same proportions for all AA, resulting in an enrichment (lysine, arginine, serine, proline) or depletion (branched-chain AA, histidine) of the absorbed mixture. 6. Some substances of the urea cycle were synthesized in rather large amounts in the gut wall (for a mean level of intake of 90 g CP: citrulline 2.41 g/8 h, ornithine 1.09 g/8 h). Blood glutamine was taken up by the gut wall in larger amounts (4.28 g/8 h).
