Ca. Barth et al., SOYBEAN TRYPSIN INHIBITOR(S) REDUCE ABSORPTION OF EXOGENOUS AND INCREASE LOSS OF ENDOGENOUS PROTEIN IN MINIATURE PIGS, The Journal of nutrition, 123(12), 1993, pp. 2195-2200
It was the purpose of this study to define whether trypsin inhibitors
impair protein digestibility via enhanced loss of exogenous or endogen
ous protein by quantifying those losses using the homoarginine techniq
ue, recently developed in this laboratory. Pigs fitted with permanent
ileal T-cannulas were fed test meals containing homoarginine-labeled p
rotein. The meals contained casein and increasing doses of trypsin inh
ibitors (Experiment 1) or alternatively either heat-treated or raw gro
und soybeans (Experiment 2). Following a casein meal (425 mmol nitroge
n, no trypsin inhibitors), ileal protein was predominantly of endogeno
us rather than of exogenous origin (105 vs. 9 mmol nitrogen). Addition
of isolated trypsin inhibitors (3000 mg) enhanced appearance of both
endogenous and exogenous protein at the ileum (by 73 and 9 mmol nitrog
en, respectively). Feeding raw instead of heat-treated soybeans in one
single test meal caused a significant increase of endogenous protein
from 217 +/- 42 to 263 +/- 47 mmol (mean +/- SEM) and of exogenous pro
tein from 16 +/- 3 to 48 +/- 14 mmol. If fed continuously for 1 wk, a
raw soybean diet caused endogenous protein loss to rise significantly
from 221 +/- 26 to 432 +/- 85 mmol. We conclude that ingestion of food
containing trypsin inhibitor affects nitrogen balance more by losses
of amino acids of endogenous secreta than by losses of dietary amino a
cids.