Levels of lysine and methionine in portal blood of rats following protein feeding

Some aspects of the digestion of proteins

“…Heat-damaged or indigestible proteins caused lower rises in portal levels than did unheated or easily digested proteins (Denton & Elvehjem, 1953;Wu, 1954;Wheeler & Morgan, 1958;Guggenheim, Halevy & Friedmann, 1960;Buraczewski, 1966). Rapidly digested proteins such as gelatin and gluten caused higher increases than did more slowly digested proteins, and the feeding of poorly digested or heat-damaged proteins produced falls in systemic blood plasma amino acids.…”

Relationship of blood plasma free amino acids and ingested protein in swine

“…They concluded, however, that a direct relationship between the postprandial plasma amino acid pattern and the amino acid composition of the ingested protein did exist. Guggenheim et al (1960) and Goldberg and Guggenheim (1962) similarly reported that the extent and duration of a rise in concentration of lysine and methionine in portal plasma of rats during digestion were not in complete agreement with the amino acid composition of the protein source.…”

“…The interaction of amino acids occurring during their absorp tion has been emphasized by Nasset (1957). Indirect evidence of preferential absorption of individual amino acids from mixtures has been obtained from studies of amino acid patterns in portal plasma following the ingestion of a protein meal (Dent and Schilling, 1949 ;Guggenheim et al, 1960).…”

“…Many researchers seem to agree that the concentration of blood plasma free amino acids, after ingesting different proteins, corresponds roughly to the amino acid composition of the protein fed. However, the lack of a consistent correla tion has been repeatedly demonstrated (Frame, 1958;Longnecker and Hause, 1959;Guggenheim et al, 1960;and Goldberg and Guggenheim, 1962). Almquist (1954) sunmarized the literature on blood plasma amino acids of the chicken in relation to the amino acid composition of the diet, and concluded that in the chick there is a high degree of correlation between the free amino acid content of plasma and the amino acid composi tion in the dietaiy protein.…”

Blood plasma free amino acid studies in swine

“…When several types of carbohydrates were studied for their effect on amino acid absorption (Guggenheim et al, 1960), lactose was found to induce the highest lysine peak, fructose the longest duration of the lysine increase, whereas dextrose depressed the usual rise of lysine found after a soybean test meal. Furthermore, starch, lactose and fructose caused a higher rise of methionine than sucrose or dextrose.…”