Food Components to Enhance Performance An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations (1994) / Chapter Skim
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15. Tyrosine and Stress: Human and Animal Studies
15. Tyrosine and Stress: Human and Animal Studies
Pages 277-300
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From page 277... ...
Providing even a small edge in effectiveness by using a comparatively benign nutritional intervention could, in theory, significantly improve performance on the battlefield, reduce casualties, and conserve critical material resources. In the classic combat scenario, fear, loss of sleep, and exposure to harsh environmental conditions can be expected to produce substantial decrements in performance.
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From page 278... ...
One nutrient that may prevent performance decrements caused by exposure to highly stressful environmental or operational conditions is the amino acid tyrosine. This substance is the precursor of several key brain neurotransmitters and may protect against the severe mental fatigue associated with exposure to life-threatening stressors that can occur in combat and certain other critical military operations.
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From page 279... ...
It is well established that the noradrenergic neurons of the locus ceruleus and hypothalamus participate in the regulation of a variety of functions that are altered during acute stress. Alertness, attention, activity, anxiety levels, blood pressure, and the secretion of certain hormones are all controlled, at least in part, by these neurons (Antelman and Caggiula, 1977; Gray, 1982; Murphy and Redmond, 1975; Stone, 1975~.
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From page 280... ...
This phenomenon has been used to model human clinical depression and posttraumatic stress disorder (Gray, 1982; van der Kolk et al., 1985~. The effects of acute stress are not limited to learning and similar behaviors, but rather, impairments in these behaviors are representative of a broad range of behavioral deficits.
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From page 281... ...
Many popular books and articles, as well as military histories, refer to the adverse consequences of combat stress on the performance of soldiers on the battlefield. In one of the few research studies conducted in a combat situation, the affect of Special Forces soldiers in an isolated outpost, deep in enemy territory during the earlier stages of the war in Vietnam, was assessed (Bourne et al., 1968~.
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From page 282... ...
However, in another group of animals that were given a diet supplemented with tyrosine and that were stressed, the frequency of these spontaneous behaviors did not differ significantly from those in the unstressed control animals. Increased dietary tyrosine apparently protected these animals from the behavioral inhibition produced by the stressor, presumably by augmenting noradrenergic, but also perhaps dopaminergic, neurotransmission (Lehnert et al., 1984a)
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From page 283... ...
Additionally, in a stressful behavioral procedure sometimes considered to be a learned helplessness paradigm and used to screen drugs for their antidepressant activities (the Porsolt swim test [Porsolt et al., 1978~) , significant dose-related potentiation of escape behavior following tyrosine administration has been observed (Gibson et al., 1982~.
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From page 284... ...
pretreatment on duration of immobility in the Porsolt swim test. Just prior to testing, the core body temperature (Tc)
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From page 285... ...
These studies support the hypothesis that tyrosine protects against the adverse effects of acute coldinduced stress on memory consolidation (see Chapter 161. In another animal study conducted at USARIEM, tyrosine reversed the adverse effects of acute exposure to hypobaric hypoxia (Lieberman et al., 1992~.
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From page 286... ...
For example, its acute administration can lower blood pressure in spontaneously hypertensive rats that are subjected to stressful testing conditions (Sved et al., 1979) and raise blood pressure in arrivals made hypotensive by blood loss, which is a model of hemorrhagic shock (Conlay et al., 1981, 19851.
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From page 287... ...
TYROSINE AND ACUTE STRESS: STUDIES IN HUMANS Tyrosine has been administered to normal human subjects in only a few studies, although it may have beneficial effects on the mood states of certain subgroups of depressed patients (Gelenberg et al., 1983~. In studies with normal males, no significant behavioral effects of tyrosine administered orally at a dose of 100 mg/kg of body weight were noted (Lieberman et al., 1983~.
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From page 288... ...
This causes blood and interstitial fluids to pool in the lower extremities because of decreased venous return and increased sympathetic drive (Bonde-Petersen et al., 1984~. Subjects exposed to LBNP initially respond with decreased blood pressure and increased heart rate.
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From page 289... ...
, subjects were able to maintain higher pulse pressures (Figure 15-8~. In addition, changes in auditory-evoked potentials suggestive of increased central nervous system activity were also observed as a consequence of tyrosine administration (Figure 15-91.
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From page 290... ...
The experimental stressor was a 4-h exposure to a combination of hypobaric hypoxia (4,200 and 4,700 m) and cold (15°C)
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From page 291... ...
, and vigilance performance. The experimental stressor was a 4-h exposure to a combination of hypobaric hypoxia (4,200 and 4,700 m)
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From page 292... ...
FIGURE 15-8 Change in mean + standard error of the mean, pulse pressure following treatment with 100 mg of tyrosine per kg of body weight. The experimental stressor was exposure to lower body negative pressure (LBNP)
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From page 293... ...
The adverse effects of hypoxia, cold, lower body negative pressure, and psychological stresses have all been reduced by treatment with tyrosine. This amino acid may have protective effects on behavioral and cardiovascular parameters because it prevents the depletion of central and peripheral catecholamines caused by acute stress.
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From page 294... ...
Caffeine would not be expected to have beneficial effects in high-stress scenarios, and since it can have adverse effects on sleep, it would not be advisable to add it to rations as a generic supplement. Although no adverse effects of tyrosine have been demonstrated, the apparent requirement for it to be used in high doses may preclude its use except in a specially identified form.
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From page 295... ...
Lieberman 1990 Tyrosine decreases physiological stress caused by lower body negative pressure (LBNP)
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From page 296... ...
Dollins, and R.J. Wurtman 1991 Strategies to sustain and enhance performance in stressful environments: The effects of tyrosine pre-treatrnent on lower body negative pressure stress.
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From page 297... ...
Lown, and R.J. Wurtman 1981 Tyrosine administration decreases vulnerability to ventricular fibrillation in the normal canine heart.
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From page 298... ...
Wurtman 1979 Tyrosine administration reduces blood pressure and enhances brain norepinephrine release in spontaneously hypertensive rats.
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From page 299... ...
TYROSINE AND STRESS 299 and norepinephrine as well. The data for the other neurotransmitters are not complete at this point, and I cannot present any information on that.
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