Corticosterone is a steroid hormone produced by the adrenal glands and classified as a glucocorticoid. This hormone regulates a wide range of physiological processes in many animal species. Unlike humans, where cortisol is the dominant stress hormone, corticosterone is the main glucocorticoid found in most non-human mammals, such as rodents, birds, and reptiles. It helps these organisms maintain homeostasis and respond effectively to environmental challenges.
The Role in the Acute Stress Response
When an animal encounters a perceived threat, the acute stress response is immediately triggered. This rapid, coordinated physiological reaction is governed by a neuroendocrine pathway that mobilizes the body for immediate “fight or flight” action. The release of corticosterone is the final output of this cascade, which begins in the brain.
The process starts when the hypothalamus detects the stressor and releases corticotropin-releasing hormone. This signaling molecule travels to the pituitary gland, prompting it to secrete adrenocorticotropic hormone (ACTH) into the bloodstream. ACTH then acts directly on the adrenal cortex, which synthesizes and releases corticosterone into the circulation.
Corticosterone’s immediate action is to mobilize energy resources throughout the body to fuel the response. It promotes the breakdown of stored energy, such as fat and protein, and increases glucose production in the liver, a process called gluconeogenesis. This surge of available energy ensures that the muscles and brain have the fuel needed to react to the threat. Once the threat has passed, elevated corticosterone acts as a negative feedback signal to the brain. This signal tells the hypothalamus and pituitary gland to cease hormone production, shutting down the stress response and allowing the system to return to baseline.
Systemic Influence on Metabolism and Immunity
Beyond the immediate stress reaction, corticosterone plays a continuous role in regulating the body’s internal environment. Its influence on metabolism extends to maintaining basal blood glucose levels, ensuring a steady energy supply for daily functions. The hormone also modulates how fat is stored and distributed, influencing long-term energy reserves.
Corticosterone also exerts a significant effect on the immune system, primarily functioning as an immunosuppressant. This regulatory action prevents the immune system from overreacting and causing excessive inflammation or tissue damage. It can dampen the inflammatory response and cause a temporary redistribution of immune cells, such as lymphocytes and monocytes, moving them out of circulation. This modulation is a balancing act, limiting inflammation while ensuring the body remains prepared to fight infection.
Corticosterone receptors are widely expressed in the nervous system, giving the hormone a broad influence on brain function. It plays a role in cognitive processes, including memory consolidation, and affects emotional regulation and mood. Corticosterone levels also follow a marked diurnal rhythm in most species. Peak concentrations often correspond to the animal’s waking phase, influencing the sleep/wake cycle.
Corticosterone Compared to Cortisol
The distinction between corticosterone and cortisol is rooted in species differences in hormone production. Corticosterone is the main glucocorticoid in many non-human vertebrates, including rats, mice, birds, and reptiles. Its prevalence in laboratory animals makes it the primary focus of stress research when discussing the effects of these hormones.
In contrast, cortisol is the dominant stress hormone in humans and most primates, carrying out the regulatory functions corticosterone performs in other species. The chemical difference lies in the presence of an extra hydroxyl group on the cortisol molecule. Most corticosterone-dominant species lack the necessary enzyme to perform this modification. While humans produce trace amounts of corticosterone, it is generally considered an intermediate in the pathway to making other steroids, and cortisol takes the physiological lead in managing the stress response and metabolic regulation.
Understanding Chronic Imbalances
While acute, short-term spikes of corticosterone are adaptive and promote survival, maintaining high levels over extended periods leads to detrimental long-term health consequences. This chronic elevation, often resulting from continuous stress, can severely compromise the body’s systems. High corticosterone levels can lead to muscle wasting, as the hormone continually promotes the breakdown of protein for energy.
The sustained immunosuppressive action of chronic high corticosterone can leave the organism vulnerable to infections. It is also associated with metabolic dysfunction, including weight gain and the accumulation of fat, particularly around the abdomen. Chronically high levels can be damaging to brain structures, such as the hippocampus, which is involved in memory and learning, potentially leading to cognitive issues.
Conversely, insufficient production of corticosterone also creates significant issues. Low levels of glucocorticoids can result in chronic fatigue, low blood pressure, and problems with blood sugar regulation. A lack of the hormone’s regulatory influence can lead to an unmodulated inflammatory response, potentially increasing the risk for autoimmune or inflammatory problems. This highlights the necessity of a precise balance, as either too much or too little circulating corticosterone can destabilize the body’s overall function.