Absorption kinetics of dietary hydrolysis products in conscious pigs given diets with different amounts of fish protein. 1. Amino-nitrogen and glucose.

1. Concentrations of amino-nitrogen, glucose, reducing sugars and lactic acid 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 twenty unanaesthetized pigs (initial mean body-weight 52.3 (SEM 0.9) kg) receiving experimental meals (200-1000 g) at 3-4 d intervals from 6-8 to 20 d after surgical implantation of the catheters and electromagnetic flow probe. The semi-synthetic starch-based diets contained variable amounts of fish meal given crude protein (nitrogen x 6.25; CP) concentrations (g CP/kg) of 80 (seven meals), 120 (twenty-two meals), 160 (six meals) and 240 (nine meals). 2. After the meal the concentration of amino-N increased with increasing levels of protein intake and increased more in the portal than in the arterial blood. There were significant relations between amounts of amino-N appearing in the portal blood at various time-intervals after the meal and the level of protein intake. Values for the ratio, amount absorbed within 8 h: amount ingested (absorption coefficient: 0.633 for a mean intake of 13.4 g N) decreased with increasing level of protein intake. 3. There was a rise in glycaemia after the meal, increasing with the amount of carbohydrate eaten, and this was more marked in the portal than in the arterial blood. There were also significant relations between amounts of glucose absorbed and amounts of starch ingested. However, the appearance of glucose in the portal blood was less marked than that of amino-N since the absorption coefficient within 8 h was lower (0.504 for a mean intake of 291 g reducing sugars). This was most probably due to a larger uptake of glucose by the intestinal cell wall. 4. Amounts of lactic acid appearing in the portal vein during the post-prandial period did not depend on amounts ingested; they ranged from 3 to 1.6 g/h from the 1st to the 8th hour after the meal.