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., 1967)

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 BEISEL, 1977)