Surplus dietary tryptophan reduces plasma cortisol and noradrenaline concentrations and enhances recovery after social stress in pigs

Social stress occurs in intensive pig farming due to aggressive behavior. This stress may be reduced at elevated dietary levels of tryptophan (TRP). In this study, we compared the effects of high (13.2%) vs. normal (3.4%) dietary TRP to large neutral amino acid (LNAA) ratios on behavior and stress hormones in catheterized pigs ( approximately 50 kg BW), which were exposed to social stress by placing them twice into the territory of a dominant pig ( approximately 60 kg) for 15 min. Pre-stress plasma TRP concentrations were 156+/-15 vs. 53+/-6 micromol/l (p<0.01) in pigs on the high vs. normal TRP diets, respectively. Pre-stress plasma cortisol and noradrenaline concentrations were twofold (p<0.01) and 1.4-fold (p<0.05) lower but plasma adrenaline concentration was similar in pigs on the high vs. normal TRP diets, respectively. During the social confrontations, pigs on the high vs. normal TRP diets show a tendency towards reduced active avoidance behavior (3.2+/-1.1 vs. 6.7+/-1.2 min, p<0.1) but their physical activity (8.5+/-0.6 vs. 10.2+/-0.8 min) and aggressive attitude towards the dominant pig (11+/-3 vs. 7+/-2 times biting) were similar. Immediate (+5 min) post-stress plasma cortisol, noradrenaline and adrenaline responses were similar among dietary groups. After the social confrontations, the post-stress plasma cortisol, noradrenaline and adrenaline concentrations and/or curves (from +5 min to 2 h) were lower/steeper (p<0.05) in pigs on the high vs. normal TRP diets. In summary, surplus TRP in diets for pigs (1) does not significantly affect behavior when exposed to social stress, (2) reduces basal plasma cortisol and noradrenaline concentrations, (3) does not affect the immediate hormonal response to stress, and (4) reduces the long-term hormonal response to stress. In general, pigs receiving high dietary TRP were found to be less affected by stress.

Serotonergic modulation of mismatch negativity

Neurochemical mechanisms mediating the interaction between emotional and cognitive processing are not yet fully understood. Here, we utilized acute tryptophan depletion (ATD) to reduce the brain synthesis of serotonin (5-HT), which is thought to have a central role in regulation of emotions and mood in humans. ATD effects on event-related potentials and magnetic fields were studied using a passive odd-ball paradigm in a randomized, double-blinded, controlled, cross-over design. Auditory responses were recorded simultaneously with high-resolution magnetoencephalography (MEG) and electroencephalography (EEG) in 14 healthy subjects, 5 h after ATD or a control condition. ATD significantly increased depressed mood and lowered plasma tryptophan concentration (total tryptophan decreased by 75%, free tryptophan decreased by 39%). As compared with the control condition, ATD increased the amplitudes of mismatch negativity (MMN) to duration and frequency changes and decreased the latencies of magnetic MMN to frequency changes in the hemisphere ipsilateral to the ear stimulated. Further, ATD modulated N1m latencies and decreased P2m source activity. ATD increased the interhemispheric latency difference of MMNm to frequency changes. No effects on P50 were observed. The present results suggest serotonergic modulation of preattentive auditory change detection, suggested to initiate involuntary attention shifting in the human brain.

A comparison in normal individuals and sickle cell patients of reduced glutathione precursors and their transport between plasma and red cells

INTRODUCTION

Reduced glutathione is an important antioxidant in red cells whose depletion may contribute to the pathophysiology of sickle cell disease. The current study was designed to examine the availability of reduced glutathione precursors (glutamate, cysteine, glycine and possibly glutamine) together with the activity of the main transport pathways for their uptake (system ASC for cysteine and glycine; system gly for glycine).

MATERIALS AND METHODS

Blood samples were obtained from normal (HbAA, HbA cells) and sickle cell disease patients (HbSS, HbS cells); amino acids were measured by HPLC; and transporter activity was measured by radioactive tracer fluxes (using serine and glycine for activity of system ASC; and glycine for that of system gly).

RESULTS

Plasma concentrations of cysteine and glycine were increased and concentrations of all amino acids were elevated in HbS cells. The activity of system ASC was increased in HbS cells (both transport capacity and affinity were elevated for serine transport; transport capacity only for glycine). Activity of system gly was also increased (twofold increase in V(max) for glycine flux), though not significantly. Oxygenation also increased the activity of both transporters in normal and HbS cells. CO prevented deoxy-inhibition of glycine transport. Staurosporine (5 microM) inhibited O(2)-stimulated glycine transport through system ASC. It also inhibited the absolute magnitude of transport through system gly, but the O(2)-dependent flux was unaffected.

CONCLUSION

Low reduced glutathione levels in HbS cells were not due to decreased substrate availability and O(2) stimulated transport of reduced glutathione precursors in both normal and HbS cells, through a mechanism that is likely to involve Hb and possibly protein phosphorylation.

Antagonists of the system L neutral amino acid transporter (LAT) promote endothelial adhesivity of human red blood cells

The system L neutral amino acid transporter (LAT; LAT1, LAT2, LAT3, or LAT4) has multiple functions in human biology, including the cellular import of S-nitrosothiols (SNOs), biologically active derivatives of nitric oxide (NO). SNO formation by haemoglobin within red blood cells (RBC) has been studied, but the conduit whereby a SNO leaves the RBC remains unidentified. Here we hypothesised that SNO export by RBCs may also depend on LAT activity, and investigated the role of RBC LAT in modulating SNO-sensitive RBC-endothelial cell (EC) adhesion. We used multiple pharmacologic inhibitors of LAT in vitro and in vivo to test the role of LAT in SNO export from RBCs and in thereby modulating RBC-EC adhesion. Inhibition of human RBC LAT by type-1-specific or nonspecific LAT antagonists increased RBC-endothelial adhesivity in vitro, and LAT inhibitors tended to increase post-transfusion RBC sequestration in the lung and decreased oxygenation in vivo. A LAT1-specific inhibitor attenuated SNO export from RBCs, and we demonstrated LAT1 in RBC membranes and LAT1 mRNA in reticulocytes. The proadhesive effects of inhibiting LAT1 could be overcome by supplemental L-CSNO (S-nitroso-L-cysteine), but not D-CSNO or L-Cys, and suggest a basal anti-adhesive role for stereospecific intercellular SNO transport. This study reveals for the first time a novel role of LAT1 in the export of SNOs from RBCs to prevent their adhesion to ECs. The findings have implications for the mechanisms of intercellular SNO signalling, and for thrombosis, sickle cell disease, and post-storage RBC transfusion, when RBC adhesivity is increased.