[Determination of bacterial N portions in feces and differently collected ileum chymus from swine]

Endogenous proteins in the ileal digesta of adult humans given casein-, enzyme-hydrolyzed casein- or crystalline amino-acid-based diets in an acute feeding study

BACKGROUND/OBJECTIVES

To ascertain if the form of dietary nitrogen (free amino acids (AA), small peptides, or intact protein) affects the endogenous nitrogen containing substances lost from the upper digestive tract of humans.

SUBJECTS/METHODS

Digesta were collected via a naso-ileal tube from the terminal ileum of 16 adult humans in a single parallel study following an acute feeding regimen. Subjects were given an iso-nitrogenous and isocaloric test meal containing 150 g of casein (CAS) (n=6), enzyme-hydrolyzed casein (HCAS) (n=5) or crystalline AA (n=5) dissolved in 550 ml of water, as the sole sources of nitrogen.

RESULTS

The mean concentrations and flows of total nitrogen, protein nitrogen, and soluble protein nitrogen passing the terminal ileum were significantly higher (P <0.01) for the CAS and HCAS test-meal groups compared to the AA meal group. Dietary CAS and HCAS had a considerable influence on digesta mucin concentrations and flows compared to free AA (+41%). Only 3-4% of the total nitrogen remained unidentified.

CONCLUSIONS

The form of dietary nitrogen (protein, small peptides or free AA) had an acute effect upon the secretion or reabsorption of endogenous proteins in the small intestine of healthy humans, as evident from significant differences in both the quantity and composition of the proteins found in digesta at the end of the ileum.

Endogenous proteins in terminal ileal digesta of adult subjects fed a casein-based diet

BACKGROUND

Although there are several published estimates of the endogenous amino acid composition of ileal digesta in humans, to our knowledge, there are no systematic studies of ileal digesta endogenous proteins.

OBJECTIVES

We determined the nature and composition of endogenous nitrogen-containing substances lost from the upper digestive tract of humans.

DESIGN

Digesta were collected from the terminal ileum for a period of 8 h by using a nasoileal tube in 6 adult subjects fed a single meal that contained 22% of casein as the only source of nitrogen.

RESULTS

The total nitrogen that passed the terminal ileum was 39.3 mg/g native digesta dry matter. Of this amount, 86% was proteinaceous, ~60% was bacterial protein, ~7% was soluble-free protein, ~15% was mucin protein, and ~5% was protein from intact mucosal cells. For nonprotein nitrogen, ~5% of the total nitrogen was ammonia, and ~4% of the total nitrogen was urea. Bacterial and human mucosal cellular DNA nitrogen were collectively ~0.5% of the total nitrogen. Approximately 30% of the nonprotein nitrogen (4% of the total nitrogen) remained unidentified. This amount was assumed to include free amino acids, RNAs, amines, and the tetrapyrroles bilirubin and biliverdin. Bacterial nitrogen, combined with ammonia and urea nitrogen, represented >68% of total ileal nitrogenous losses.

CONCLUSIONS

Findings are presented on the endogenous nitrogen-containing compounds that left the terminal ileum. Of particular significance is the observation that mucin was the most abundant truly endogenous component within the terminal ileal digesta. Bacterial protein, which was strictly nondietary rather than endogenous, contributed the highest proportion, by far, of nondietary protein, the result of which makes a significant contribution to published estimates of ileal endogenous amino acids and protein. The high concentration of bacterial protein and the presence of ammonia and urea nitrogen indicate potentially substantial microbial activity within the human distal small intestine.

[The effect of a different protein and fiber intake on the ileal flow of endogenous protein in 15N-labeled swine]

The endogenous N in ileal digesta of pigs was estimated in two experimental variants. In variant 1 the crud protein content of a wheat-maize-fish meal diet was 18% and the crude fibre content was 1.9% (diet 1) and 2.7% resp. (diet 2). In variant 2 the crude protein content was 12.5% (wheat-maize-diet) and the crude fibre content was 4.1% (diet 3) and 5.5% resp. (diet 4). The higher crude fibre content of the diets 2-4 was provided by means of a supplementation with partially hydroyzed straw meal plus pectin (2:1 w/w). Four miniature pigs with an average initial body weight of 29 kg, were fitted with a ileocaecal re-entrant cannula and received each one of the four different diets. 15NH4Cl, added to the diets, was given for 5 days (150 mg 15N-excess/kg0.75 BW*d) to label the animals with 15N. Ileal digesta, urine and faeces were collected over 24 hours on 8th, 10th and 12th day after the first intake of 15N. The 15N-excess of urine N was used as the comparative measure of 15N-excess of endogenous protein. The amount of nitrogen collected in ileal digesta was in order of the diets 1-4 = 258, 299, 200 and 224 mg/kg0.75 BW*d and of these amounts were 50.1, 52.1, 56.1 and 50.4% of endogenous origin. This were corresponding, after conversion into crude protein to 9.1, 11.2, 10.8 and 11.0 g/100 g crude protein intake or 16.9, 19.7, 13.8 and 13.4 g/kg dry matter intake, respectively. The bacterial N-flow were in order the diets 1-4 = 94.0; 72.7; 55.8 and 52.6 mg/kg0.75 BW*d and 73, 46, 50 and 47% resp. of the endogenous N or 36, 24, 28 and 24% of the ileal total N. The results show, that the absolute amounts of endogenous and bacterial N at the terminal ileum were significantly increased by a higher crude protein content of the diet. The percentage of endogenous and bacterial N on the total N of the ileal digesta was not affected neither by the crude protein content of the diets nor by the fibre supplements.

[Comparison of methods for determining the prececal nutrient digestibility and amino acid absorption of swine with ileorectal anastomoses and ileocecal bridge cannulas]

The apparent precaecal nutrient digestibility and amino acid (a.a.) absorption of 10 diets were estimated in pigs with end-to-side ileorectal anastomoses (IRA) as well as with ileocaecal re-entrant cannulae (IZB). The digestibilities of organic matter and crude carbohydrates were significantly higher in IRA pigs than in IZB pigs in two resp. three diets only. There were no practical important differences for the digestibilities of crude protein and crude fat in all diets. Out of the 180 a.a. absorption comparisons only 20 (i.e. 11%) showed differences larger than 5%-units. The absorption rates of several a.a. were lower in IRA than in IZB pigs and of some other a.a. on the contrary. The methionine absorption of five legume diets and one barley + lysine diet were up to 15% resp. 4%-units lower in IRA pigs. Possibly this was due to the activity of microbes in the rectum in connection with a small intake level of protein bound methionine. In order to minimize such a falsification it is proposed to use the end-to-end anastomosis. The deviations in the apparent a.a. absorption between IRA and IZB pigs can be explained partly by differences in the quantity of precaecally excreted endogenous a.a. per 100 g DM intake.