Observations on predicted brain influx rates of neurotransmitter precursors. Effects of tumor, operative stress with tumor removal, and postoperative TPN of varying amino acid compositions

Abstract

Effects of tumor, operative stress and tumor removal, and postoperative TPN of varying amino acid compositions on brain levels of tryptophan or tyrosine as predicted by their brain influx rates were studied in normals and in malnourished cancer patients. Concentrations of the large neutral amino acids (LNAA) were determined in patients before and after tumor removal, and in postoperative patients before and after receiving either a standard TPN solution (STD-TPN), or a branched-chain amino acid solution (BCAA-TPN). The LNAA were altered in all groups versus normals. Brain influx rates showed the following: in preoperative patients, predicted brain tryptophan levels were below normal (P less than 0.001), whereas tyrosine levels were within or above normal; no significant differences between pre- and postoperative tryptophan or tyrosine levels; postoperative STD-TPN did not change predicted brain tryptophan concentration from preinfusion values, but BCAA-TPN decreased it (P less than 0.001), underscoring the common transport carrier; and preinfusion predicted brain tyrosine levels were decreased (P less than 0.001) by both types of TPN solutions. These results imply low substrate levels for brain serotonin and catecholamine synthesis, possibly affecting functions dependent on their control.

Hypothalamic integration of immune function and metabolism

“…Insulin may contribute to the anorectic effect of IL-1a taking into account that circulating insulin increases after cytokine injection and that there is a negative correlation between food intake and plasma insulin (Sato et al, 2003). It is known that peripheral insulin increase plasma tryptophan and decreases other neutral amino acids (Fernstrom and Wurtman, 1972) that compete with free tryptophan for brain entry (Fernstrom and wurtman, 1972;Landel et al, 1987) leading to an enhanced availability of hypothalamic tryptophan and subsequently to a rise in 5-HT production that may be released after the increase in neuronal activity induced by IL-1a.…”