The significance of tryptophan in human nutrition

Summary Aside from its role as one of the limiting essential amino acids in protein metabolism, tryptophan (TRP) serves as precursor for the synthesis of the neurotransmitters serotonin and tryptamine as well as for the synthesis of the antipellagra vitamin nicotinic acid and the epiphyseal hormone melatonin.By involvement in so manifold pathways, TRP and its metabolites regulate neurobehavioral effects such as appetite, sleeping-waking-rhythm and pain perception. TRP is the only amino acid which binds to serum albumin to a high degree. Its transport through cell membranes is competetrvely inhibited by large neutral amino acids (NAA). The TRP/NAA ratio in plasma is essential for the TRP availability and thus for the serotonin synthesis in the brain.Due to its high TRP-concentration, human milk protein provides optimal conditions for the availability of the neurotransmitter serotonin. Low protein cow's milk-based infant formulas supplemented with-lactalbumin — a whey protein fraction containing 5.8% TRP — present themselves as a new generation of formulas, with an amino acid pattern different from the currently used protein mixtures of adapted formulas, resembling that of human milk to a much higher degree.     

The quantitative production of interferon by mitogen-stimulated mouse lymphocytes as a function of age and its effect on the lymphocytes proliferative response.

Interferon production by mitogen-stimulated mouse spleen cells increases as the age of the cell donor increases and also varies with with the strain of the cell donor. Exogenous interferon added to mouse spleen cell cultures at dose levels known to be produced by the cells causes a reduction in the proliferative response of T cells to mitogen stimulation. Since the spleen cells from old mice respond poorly to mitogen stimulation, it may be possible that the interferon elaborated by these cells is adversely affecting the mitogen assay.     

Venous versus arterialised venous blood for assessment of blood glucose levels during glucose clamping: comparison in healthy men.

The aim of this study was to investigate the influence of the arteriovenous (A-V) gradient in blood glucose concentrations at low and high insulin levels on the determination of glucose requirements during glucose clamping in 9 healthy, insulin sensitive, male volunteers. In a random order two clamps were performed, once using arterialised venous blood (A Clamp, mean pO2 = 11.5 +/- 0.36 kPa, 86 +/- 2.7 mmHg), and once using venous blood (V clamp, mean pO2 = 7.9 +/- 0.21 kPa, 59 +/- 1.6 mmHg). Insulin levels were maintained at 48 +/- 2.4 mU/l from 0-180 min and at 1054 +/- 114 mU/l from 180-360 min. Elevation of insulin levels caused a significant rise of the A-V gradient: from 0.3 +/- 0.1 to 0.5 +/- 0.1 mmol/l (p < 0.05) and from 0.2 +/- 0.1 to 0.3 +/- 0.1 mmol/l (p < 0.05) during the A and V clamps, respectively. Despite these A-V glucose gradients no significant differences were found for the glucose requirements during the last 30 min of each period of insulin infusion between the A and V clamps: 43.70 +/- 3.4 vs 44.8 +/- 2.8 mumol.kg-1.min-1 during the low insulin level and 77.3 +/- 5.0 vs 76.2 +/- 3.4 mumol.kg-1.min-1 during the high insulin level. We conclude that the A-V glucose gradient, even at high insulin levels, does not influence the assessment of glucose requirements to a measurable extent, allowing the use of the simpler technique of taking venous rather than arterialised venous blood for the measurements of glucose levels during glucose clamping.