28/01/2025
The Hypothalamic-Pituitary-Adrenal Axis, or HPA Axis, is a bidirectional neuroendocrine network that modulates our adaptive stress response. The activation loop begins in the hypothalamus with corticotropin-releasing hormone (CRH). Once released, CRH binds to receptors on the anterior pituitary gland resulting in the subsequent release of adrenocorticotropic hormone (ACTH). In turn, circulating ACTH binds to its own receptors on the adrenal cortex, thereby stimulating cortisol production. Ultimately, cortisol levels serve as a negative feedback mechanism, modulating hypothalamic CRF and pituitary ACTH release to achieve homeostasis. The HPA Axis also interacts with the limbic system, pivotal to memory and emotional respons.
Our resident microbes continuously interact with the HPA axis, and their influence begins very early in life. Animal studies have shown that the lack of commensal gut microbes contributes to exaggerated HPA Axis activity that can be reversed with a single Bifidobacterium species, but the window for modulating appropriate HPA response is a very narrow one. , stress and HPA Axis activation can directly impact the gut microbiota composition. Studies have demonstrated that extended stress can significantly alter the microbiome and elevate levels of interleukin-6 and monocyte chemotactic protein in the blood.
