Total parenteral nutrition (TPN) may enhance the growth of some
tumors: this enhanced growth is associated with an increase in the erythrocyte
polyamine levels. The effect of
arginine in TPN on
tumor growth was compared with
ornithine using rats with a transplantable Ward colon
tumor. The relationship of circulating
arginine,
ornithine,
glutamine, and
polyamines with
tumor growth was investigated. For rats fed chow ad libitum, increasing
tumor weights were associated with a linear decrease in the plasma
arginine levels which was consistently lower than that of age-matched non-
tumor bearing (NTB) rats;
ornithine and
lysine levels were not affected. Subsequent experiments suggest that plasma
glutamine levels were also lower in
tumor bearing rats. Pair-fed NTB rats had reduced
arginine but not
glutamine levels in plasma. TPN regimens with
arginine or with
ornithine substituted for
arginine at two levels (equimolar [Orn-Em] or isonitrogenous [Orn-IN]) were given to colon
tumor bearing rats for 8 days. The final
tumor weight of rats which received the
arginine-containing regimen (19.8 +/- 5.7 g, n = 4) (P less than 0.05) was significantly greater than the
tumor weight of rats fed chow ad libitum (12.1 +/- 3.3 g, n = 6). The final
tumor weights of Orn-EM (11.2 +/- 2.6 g, n = 4) or Orn-IN (11.6 +/- 0.8 g, n = 6) were similar to the chow-fed controls. The plasma
arginine levels were elevated, compared with the control, when
arginine was present in the regimen. The plasma
arginine levels of rats which received Orn-EM or Orn-IN were lower than the controls. The plasma
ornithine levels were not affected by
arginine in the regimen but were elevated with increasing levels of
ornithine in TPN. Plasma
glutamine levels were decreased when
arginine was present in the regimen but were elevated when
ornithine was substituted for
arginine. Erythrocyte
putrescine was increased when either
arginine or
ornithine was included in the TPN regimens. These results demonstrate that while
arginine in a parenteral regimen stimulates
tumor growth, substituting
ornithine for
arginine in TPN does not enhance the growth of a transplantable colon
tumor.