1.4. Catabolic losses
A catabolic response occurs with all infections even when they are
subclinical and not accompanied by infection (BEISEL et al., 1967;
BEISEL, 1972; 1975; BEISEL and WANNEMACHER, 1980; KEUSCH and FARTHING, 1986).
Under the stimulus of the release of interleukin-1 and tumor necrosis factor by
phagocytic cells, endocrine changes are initiated that lead to the mobilization
of amino acids from the periphery, primarily from skeletal muscle. Amino acids,
such as those of the branched-chain group (BCAAs), are utilized as energy
sources leading to the synthesis of alanine or glutamine. BCAAs are rapidly
taken up by the liver and utilized for gluconeogenesis, while alanine and
glutamine serve as intestinal fuels, for regulation of acid-base and for
gluconeogenesis by the kidney.
Amino acids, such as phenylalanine and tryptophan, which cannot be
metabolized in skeletal muscle, are released in elevated amounts (WANNEMACHER,
1977). Figure 1 shows that in a young man with tularemia more than two
thirds of the negative nitrogen balance was due to this metabolic response and
the remainder to a spontaneous decrease in food intake (BEISEL et al.,
1967). Figure 2 shows that even an individual with completely
asymptomatic Q-fever can be in cumulatively increasing negative nitrogen balance
for as long as 21 days (BEISEL et al., 1967).
In INCAP experience with metabolic studies in children, infections
are always associated with a period of negative nitrogen balance, even in the
case of immunization with yellow fever vaccine which provokes no symptoms
(GANDRA and SCRIMSHAW, 1961). The response to these asymptomatic infections is
qualitatively similar to those with the typical clinical disease.
Figure 1. The components of the
negative N balance during the acute phase of tularemia in an adult male subject
are shown. The white area represents that proportion resulting from decreased N
intake due to anorexia and the shaded area that due to the catabolic response.
(From BEISEL et al.,
Figure 2. Nitrogen balance data in a
subject who remained asymptomatic despite subclinical Q-fever.
This individual showed neither an elevation of rectal
temperature above 100° F nor diminution of dietary intake despite the
presence of Coxiella burnetii in the blood over an 8-day period. (From