Allostasis

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Allostasis (composed of the Greek "allo" for "variable" and "stase" for "standing" , usually translated literally as "achieving stability through change" ) describes the process by which the body in demanding situations ( stress ) through physiological and changes in psychological behavior and maintains stability, including future stresses. This adaptation reaction is basically adaptive at first , but is associated with increased physical demands and thus greater “wear and tear”.

variability

The central variability in the allostasis concept is assigned the greatest importance for the fact that complex organisms can adapt to changing environmental and living conditions. According to the authors, the allostasis concept extends the simpler homeostasis concept, according to which the body in every situation v. a. strives to maintain an inner balance. According to the more dynamic allostasis concept, the brain in particular plays a key role in allostatic reactions to complex problem situations and the anticipation of upcoming stresses. The allostasis reaction is mediated v. a. by hormones of the hypothalamus-pituitary-adrenal cortex axis (also called HPA axis in German after Hypothalamic-Pituitary-Adrenal Axis ), catecholamines and cytokines .

Types

McEwen and Wingfield have suggested dividing allostatic responses into two different types:

  • A type 1 allostatic reaction is triggered when the actual demand for energy exceeds the supply, so that a metabolic emergency program is activated, which leads to energy savings and the mobilization of reserves. After the failure has ended, the normal life cycle can be continued.
  • Type 2 allostasis is triggered when the expected energy demand exceeds the expected supply. This reaction can also occur when there is currently sufficient energy supply. Typical triggers are psychosocial stressful situations.

Both forms of allostasis go hand in hand with an increased release of cortisol and catecholamines . With regard to thyroid homeostasis , the answer is nuanced. Here, type 1 allostasis leads to a low concentration of the thyroid hormone triiodothyronine (T3), while the T3 level is increased in type 2 allostasis.

Allostatic load

Permanent allostatic activation as a result of chronic stress is also described as an allostatic load or overload. Such chronic physiological activation can damage various organ systems. Chronic stress loads have the strongest effects on mental health and the risk of cardiovascular diseases, but diseases of the musculoskeletal system, metabolism and the immune system are also favored.

A permanent allostatic load is of particular importance for the brain itself. While controllable stress leads to stabilization, uncontrollable stress leads to a destabilization of central nervous structures. This particularly affects the few areas of the brain in which a new generation of nerve cells ( neurogenesis ) is possible in humans , such as the hippocampus . A particularly close connection is established between allostatic load, changes in the hippocampus and depression . But various other psychological problems are also closely related to chronic stress ( diathesis stress model ).

Trigger situations - social stress

In principle, every uncontrollable stress reaction can activate the HPA axis and thus the allostasis reaction. However, social stressors are of particular importance for the HPA axis . For example, experiences of exclusion lead to a strong activation of the HPA axis . However, the strongest and most reliable HPA axis activation occurs in degradation situations; H. Situations associated with feelings of shame and humiliation. Social-evaluative situations are therefore also used to experimentally activate the HPA axis .

The allostatic load and its health effects are also seen as important partial causes that an extremely stable connection between the social and health situation is found everywhere around the world ( health inequality ). The allostatic burden that accumulates over life seems to be dependent on the social situation, which can lead to earlier aging and greater exposure to various diseases, depending on the social situation.

Interventions: From Homeostasis to Allostasis

The allostasis concept has significant implications that go beyond the homeostasis concept for the level at which interventions should start. Sterling, the founder of the allostasis concept, clarifies this for arterial hypertension as follows:

“ Homeostasis identifies the most obvious causes; z. B. Essential hypertension is attributed to too much salt water in too little vessel volume. Medicines should therefore reduce salt and water, increase the volume and block feedback mechanisms that counteract this. Allostasis attributes high blood pressure to the brain. Since the brain chronically assumes a need for high pressure, it mobilizes all the mechanisms at the lower level: holding back salt and water through the kidneys, increasing the appetite for salt. Accordingly, allostasis would start therapeutically at a higher level - reduce the need and increase the feeling of control - so that the brain can turn down its prediction and relax all the mechanisms at the lower level. "

Going beyond the homeostasis concept, according to the allostasis concept, the brain is regarded as the most important organ of the stress reaction, as it regulates subordinate systems based on problem analysis and anticipation of future needs. Interventions that only focus on the regulation of these subordinate systems therefore lead to compensatory evasive reactions controlled by the central nervous system. According to the allostasis concept, the brain as the central stress organ should move into the center of all interventions. Since the strongest triggers for allostasis reactions are social stressors, a change in social conditions is ascribed the most important role.

Individual evidence

  1. ^ A b P. Sterling, J. Eyer: Allostasis: a new paradigm to explain arousal pathology. In: S. Fisher, J. Reason (Eds.) Handbook of life stress, cognition and health, Wiley & Sons, New York, 1988, pp. 631-651.
  2. ↑ a b c d B. S. McEwen, JC Wingfield: The concept of allostasis in biology and biomedicine. Horm Behav, 43 (2003) 2-15.
  3. ↑ a b c d P. Sterling: Allostasis: a model of predictive regulation. Physiol Behav, 106 (2012) 5-15. doi : 10.1016 / j.physbeh.2011.06.004
  4. ↑ BS McEwen: Interacting mediators of allostasis and allostatic load: towards an understanding of resilience in aging. Metabolism, 52 (2003) 10-16.
  5. ↑ Apostolos Chatzitomaris, Rudolf Hoermann, John E. Midgley, Steffen Hering, Aline Urban, Barbara Dietrich, Assjana Abood, Harald H. Klein, Johannes W. Dietrich: Thyroid Allostasis – Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming . In: Frontiers in Endocrinology . 8, July 20, 2017. doi : 10.3389 / fendo.2017.00163 . PMID 28775711 .
  6. ^ BS McEwen, E. Stellar: Stress and the individual. Mechanisms leading to disease. Archives of internal medicine, 153 (1993) 2093-2101.
  7. ↑ GP Chrousos: Stress and disorders of the stress system. Nature reviews. Endocrinology, 5 (2009) 374-381. doi : 10.1038 / nrendo.2009.106
  8. ^ S. Leka, A. Jain: Health Impact of Psychosocial Hazards at Work: An Overview. In: WHO (ed.), WHO, Geneva, 2010.
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  10. ↑ G. Huether: The central adaptation syndrome: psychosocial stress as a trigger for adaptive modifications of brain structure and brain function. Prog Neurobiol, 48 (1996) 569-612. PMID 8809909
  11. ^ Vaishnav Krishnan, Eric J. Nestler: The molecular neurobiology of depression. Nature, 455 (2008) 894-902.
  12. ↑ BS McEwen, PJ Gianaros: Central role of the brain in stress and adaptation: links to socioeconomic status, health, and disease. Ann NY Acad Sci, 1186 (2010) 190-222. doi : 10.1111 / j.1749-6632.2009.05331.x
  13. ↑ KD Williams: ostracism. Annu Rev Psychol, 58 (2007) 425-452. doi : 10.1146 / annurev.psych.58.110405.085641
  14. ↑ SS Dickerson, ME Kemeny: Acute stressors and cortisol responses: a theoretical integration and synthesis of laboratory research. Psychological bulletin, 130 (2004) 355-391. doi : 10.1037 / 0033-2909.130.3.355
  15. ↑ C. Kirschbaum, KM Pirke u. a .: The 'Trier Social Stress Test' - a tool for investigating psychobiological stress responses in a laboratory setting. Neuropsychobiology, 28 (1993) 76-81. 119004 [pii]
  16. ↑ Michael G. Marmot: Status syndrome: How your social standing directly affects our health and longevity. Paperback ed., Transferred to digital print 2009 ed., Bloomsbury, London, 2004. ISBN 0-7475-7408-1
  17. ^ A b R. M. Sapolsky: The influence of social hierarchy on primate health. Science, 308 (2005) 648-652. doi : 10.1126 / science.1106477
  18. ↑ T. Seeman, E. Epel et al. a .: Socio-economic differentials in peripheral biology: cumulative allostatic load. Ann NY Acad Sci, 1186 (2010) 223-239. NYAS5341 [pii] doi : 10.1111 / j.1749-6632.2009.05341.x
  19. ↑ P. Sterling: Principles of allostasis: optimal design, predictive regulation, pathophysiology and rational therapeutics. In: Jay Schulkin (Ed.) Allostasis, homeostasis and the costs of physiological adaptation, Cambridge University Press, Cambridge, 2004, ISBN 0521811414