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hpa axis

The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 80

93. How is adrenal insufficiency related to mast cell disease?

Adrenal insufficiency is when the adrenal glands do not make enough cortisol, a stress hormone your body needs to help your body respond to the things happening inside and around it. Not having enough cortisol is dangerous and can be fatal.

Adrenal insufficiency is not the same as adrenal fatigue. Patients with adrenal insufficiency demonstrate lower than normal levels of cortisol. Adrenal fatigue is a term that is used to describe a similar constellation of symptoms as seen in adrenal insufficiency but without the lower than normal serum cortisol level when tested. Adrenal fatigue is not well accepted in main stream medicine.

There are several steps involved in making cortisol. These steps use hormones to tell the body to make other hormones until cortisol is finally made. The molecules that are involved in getting the body to make cortisol are collectively called the HPA axis.

Mast cells interact with the HPA axis a lot and in several ways. I have written extensively about this before.

The activity of the HPA axis can either activate mast cells or stabilize them. It can tell the body to make epinephrine, which decreases mast cell activation. But it can also tell mast cells to make inflammation.

It also works in the other direction. Mast cell activation can activate the HPA axis or not, but it usually activates it. If mast cells generate enough inflammation, that can turn on the HPA axis, which in turn activates mast cells even more. This basically means that if you have frequent mast cell activation, your body can end up in a constant fight or flight response. The inflammation generated can be enormous.

When the body has been in a stress response for too long, the adrenal glands can stop making cortisol, causing adrenal insufficiency. This can cause mast cell activation.

Steroids like prednisone mimic the action of cortisol, the stress hormone. Steroids are sometimes used to treat mast cell disease. The purpose of the steroids is to make cells like mast cells stop causing inflammation. If you take systemic steroids like prednisone routinely, your body can become confused and stop making cortisol on its own. This means that when you stop taking the prescription, your body will not have enough cortisol, causing adrenal insufficiency. This activates mast cells in a huge way. Patients often have a hard time getting back to a good baseline without steroids if they have been on steroids for a while.

There is an autoimmune disease called Addison’s Disease that causes adrenal insufficiency. MCAS sometimes occurs secondary to Addison’s.

 

For further reading, please visit the following posts:

The effects of cortisol on mast cells: Cortisol and HPA axis (Part 1 of 3)
The effects of cortisol on mast cells: Cortisol and HPA axis (Part 2 of 3)
The effects of cortisol on mast cells: Cortisol and HPA axis (Part 3 of 3)
Corticotropin releasing hormone, cortisol and mast cells
Mood disorders and inflammation: High cortisol and low serotonin

Mood disorders and inflammation: Neurologic effects and treatment (Part 4 of 4)

TNF blockers like Enbrel and infliximab can lower depression independent of improvements with physical symptoms. 62% of patients with treatment resistant depression saw improvement on infliximab versus 33% with standard therapies. Infliximab also improved sleep, allowing patients to stay asleep longer. Infliximab successfully improved depression symptoms in patients with inflammatory disease as well as controls who had elevated CRP and TNF but not on controls with normal CRP and TNF. Patients who were not effectively treated with SSRIs were found to have higher IL-6 and TNF.

Chronic inflammation can cause structural and functional changes in the brain, interfering with its ability to make new connections and damaging existing function. Activation of microglial cells in the nervous system is associated with maladaptive behaviors and decreased brain function seen in bipolar disorder, major depressive disorder and other mood conditions. They also protect neurologic function in multiple sclerosis, Huntington’s and Alzheimer’s. Minocycline, an antibiotic, also has significant anti-inflammatory and neuroprotective effects.

In some encephalitis models, DMARDs can actually restore stem cells of the nervous system, reducing tissue and myelin damage. DMARDs, often used for autoimmune diseases, improve mood symptoms in rheumatoid arthritis patients. They can also mitigate hyperactivity from amphetamines. Clinical trials are currently investigating the full effects of these medications on psychiatric conditions.

Mood stabilizers often have anti-inflammatory effects. In bipolar disorder patients, lithium and valproate decreased IL-6. Medications that act on serotonin and dopamine receptors decrease production of inflammatory molecules like TNF, IL-6 and PGE2. Escitalopram, an SSRI antidepressant, can decrease cortisol production and IL-11.  ACTH production can be induced by fluoxetine.

References:

Furtado M, Katzman MA. Examining the role of neuroinflammation in major depression. Psychiatry Research 2015: 229, 27-36.

Rosenblat JD, et al. Inflamed moods: a review of the interactions between inflammation and mood disorders. Progress in Neuro-Psychopharmacology & Biological Psychiatry 2014; 53, 23-34.

The effects of cortisol on mast cells: Cortisol and HPA axis (Part 1 of 3)

Things I’m not great at: Knowing how many posts I need to cover all the effects cortisol has on mast cells.  So this is the first of three posts on cortisol and mast cells.  Then we will get back to the tables breaking down the effects of hormones on mast cells.
Cortisol is a glucocorticoid steroid hormone with far reaching anti-inflammatory actions. It is the product of a very complex endocrine system called the HPA axis.  HPA stands for hypothalamus-pituitary-adrenal.  The hypothalamus is in the brain and the pituitary is a small structure on the edge of the hypothalamus.  The adrenal glands are above the kidneys.

The hypothalamus, pituitary and adrenal glands all release a number of hormones that affect many bodily functions. Briefly, the hypothalamus receives signals from the nervous system to make corticotropin releasing hormone (CRH).  CRH induces the pituitary to make adrenocorticotropin hormone (ACTH). ACTH induces the adrenal glands to make cortisol.

Cortisol is most well known as the stress hormone, although it has many other functions. It can be released as a response to inflammation or physical or emotional trauma.  In such instances, signals from the nervous system tell the hypothalamus that it needs to make CRH.  CRH triggers vasodilation and increased vascular permeability to allow immune cells move from the bloodstream to inflamed spaces in tissue.  CRH also triggers manufacture of ACTH, which then triggers manufacture of cortisol.

When cortisol levels are high in the adrenal gland, epinephrine can be made from norepinephrine. Cortisol is thought to regulate the enzyme that makes epinephrine at several steps in the process.  Epinephrine is also part of the stress response and participates in the fight-or-flight response.

The role for which glucocorticoids are most often prescribed is suppression of inflammation. Cortisol production is initiated very early in an inflammatory response. Cortisol counteracts vasodilation seen by many inflammatory mediators.  Cortisol also decreases vascular permeability so immune cells are not able to easily leave the bloodstream and move into tissues.  Cortisol also affects gene expression so that inflammatory products are not made as much and anti-inflammatory products are made more.  (This will be discussed in great detail when I cover how cortisol affects mast cells.)

A number of synthetic glucocorticoids, like prednisone and dexamethasone, have similar behaviors and functions. The medication hydrocortisone functions the most like cortisol in the body.  Synthetic glucocorticoids stay in the blood longer and are more bioavailable than cortisol.  The amount of cortisol produced by the body changes throughout the day in time with other functions.  Synthetic glucocorticoids cannot mimic these changes exactly and are thus inferior to cortisol.  Small changes in amount of glucocorticoid can have major effects.

References:

Oppong E, et al. Molecular mechanisms of glucocorticoid action in mast cells. Molecular and Cellular Endocrinology 2013: 380, 119-126.

Varghese R, et al. Association among stress, hypocortisolism, systemic inflammation and disease severity in chronic urticaria. Ann Allergy Asthma Immunol 2016: 116, 344-348.

Zappia CD, et al. Effects of histamine H1 receptor signaling on glucocorticoid receptor activity. Role of canonical and non-canonical pathways. Scientific Reports 2015: 5.

Coutinho AE, Chapman KE. The anti-inflammatory and immunosuppressive effects of glucocorticoids, recent developments and mechanistic insights. Mol Cell Endocrinol 2011: 335(1), 2-13.

Interplay between mast cells and hormones: Part 2 of 8

Hormone Location released Major functions Interaction with mast cells Reference
Beta endorphin Pituitary Inhibits pain signaling In two studies, beta endorphin was shown to induce histamine release from mast cells; however, this phenomenon has not been seen by other researchers.

Sensation of pain activates mast cells and can also trigger endorphin release, so interplay between endorphins and mast cells is possible.

 Kimura T, et al. Intradermal application of nociception increases vascular permeability in rats: the possible involvement of histamine release from mast cells. European Journal of Pharmacology 2000: 407, 327-332.
Brain natriuretic peptide (BNP) Heart Reduce systemic vascular resistance and water, sodium and fat in blood, decreasing blood pressure

Decrease cardiac output

Vasodilator

Relax smooth muscle of airway

 BNP directly activates mast cells in a dose dependent fashion. Yoshida H, et al. Histamine release induced by human natriuretic peptide from rat peritoneal mast cells. Regulatory Peptides 1996: 61, 45-49.
Calcidiol/ Vitamin D3 (inactive) Skin Inactive form of vitamin D3 Vitamin D decreases IgE dependent mast cell activation and cytokine production in a dose dependent fashion.

 

 

 Yip KH, et al. Mechanisms of vitamin D3 metabolite repression of IgE-dependent mast cell activation. Journal of Allergy and Clinical Immunology 2014: 133 (5), 1356-1364.
Calcitonin Thyroid Stimulates bone construction

Promotes retention of calcium in bone

 One report in 1994 noted that serum calcitonin was increased in a patient with SM. Yocum MW, et al. Increased plasma calcitonin levels in systemic mast cell disease. Mayo Clin Proc 1994: 69 (10), 987-990.
Calcitriol/ Vitamin D3 Kidney Promote absorption of calcium and phosphate in GI tract

Inhibit release of parathyroid hormone in kidneys

 Vitamin D decreases IgE dependent mast cell activation and cytokine production in a dose dependent fashion.

 

 

 Yip KH, et al. Mechanisms of vitamin D3 metabolite repression of IgE-dependent mast cell activation. Journal of Allergy and Clinical Immunology 2014: 133 (5), 1356-1364.
Cholecystokinin Small intestine Release of digestive enzymes from pancreas and bile from gallbladder

Suppresses hunger

Stimulates vagus nerve

Decreases gastric emptying and GI motility

Unclear role in medication tolerance and withdrawal

 The form of CCK most predominant in intestine (CCK-33) stabilizes mast cells.

May have a role in preventing mast cell degranulation as a response to food.

 Vergara P, et al. Neuroendocrine control of intestinal mucosal mast cells under physiological conditions. Neurogastroenterology 2002: 14(1), 35-42.
Corticotropin releasing hormone (CRH) Hypothalamus Stimulate ACTH release from pituitary CRH binds to mast cell receptors CRHR-1 and CRHR-2 causing release of VEGF but not histamine, tryptase or IL-8.

CRH is also released by mast cells.

 Theoharides TC, et al. Mast cells and inflammation. Biochim Biophys Acta 2012: 1822(1), 21-33.
Cortisol and other glucocorticoids Adrenal gland (cortex) Breaks down fat in adipose tissue

Drives production of glucose, epinephrine and norepinephrine

Inhibits immune action and inflammation, protein production, and glucose transfer to muscle and adipose tissue

Cortisol has a wide range of other effects

 Glucocorticoids inhibit mediator production in several ways.

Decreases prostaglandin production by decreasing levels of COX-2, an enzyme that makes prostaglandins.

Decreases production of leukotrienes, prostaglandins and thromboxanes by increasing anti-inflammatory molecules.

Triggers release of annexin-1, an anti-inflammatory molecule that is also involved in the mast cell stabilizing mechanism of cromolyn.

Lowers bradykinin levels, decreasing swelling.

Directly interferes with production and secretion of cytokines.

 The role of Annexin-A1/FPR2 system in the regulation of mast cell degranulation provoked by compound 48/80 and in the inhibitory action of nedocromil. International Immunopharmacology 2016: 32, 87-95.

Oppong E, et al. Molecular mechanisms of glucocorticoid action in mast cells. Mol Cell Endocrinol 2013: 380, 119-126.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Author’s note: I tried to hit the high notes here but cortisol has a massive range of effects on immune function, including mast cells, so the next post in this series will be dedicated just to cortisol and the effects on mast cells.

 

 

 

 

Mood disorders and inflammation: High cortisol and low serotonin (Part 2 of 4)

There are multiple suspect pathways for causation of mood dysregulation in the setting of inflammation. One well described model hinges upon the ability of inflammatory mediators to impact the HPA axis, a system of hormone release that drives many physiologic functions in addition to the stress response.  Briefly, the central pathway of the HPA axis is that CRH causes production of ACTH, which causes production of cortisol, a stress hormone and a very potent anti-inflammatory under most circumstances.  Many molecules can affect the signaling of the HPA axis and contribute to inappropriate hormone regulation.

IL-1, IL-6, TNF and IFN-a are all inflammatory mediators released by mast cells and other cells. These mediators all activate the HPA axis, resulting in high production of CRH, ACTH and cortisol via a series of intertwined mechanisms. At the same time, inflammation also makes cortisol less effective.  There are several ways for this to occur. Inflammation can cause cells to make fewer receptors for cortisol, meaning that no matter how much cortisol is made, only a small fraction will be able to act on cells.  Persistently high cortisol levels decrease production of other anti-inflammatory molecules and molecules that mediate the anti-inflammatory action of cortisol.  High cortisol also tells the HPA axis that it doesn’t need to make more cortisol, so even though more may actually be necessary, your body doesn’t know that.

All of these factors coalesce to form a reality where cortisol may be elevated but with little anti-inflammatory effect because of the changes I mentioned above. High cortisol is associated with mood symptoms.

Decrease of serotonin activity is also seen in mood disorders. Tryptophan is a precursor to serotonin, a hormone and neurotransmitter that heavily regulates mood.  Cortisol increases the activity of a molecule called tryptophan 2,3-dioxygenase (TDO), which removes the amino acid tryptophan from the pool of molecules to break down. Inflammatory molecules like interferon increase activity of the enzyme IDO, which decreases serotonin production.  IDO breaks down tryptophan to molecules that cannot be made into serotonin, such as kynerenin and quinolonic acid.  These metabolites have been observed as elevated in models of depression and anxiety.

Another way that inflammatory mediators affect the action of serotonin is to hasten its degradation. Both TNF and IL-6 increase the breakdown of serotonin to 5-HIAA.

References:

Furtado M, Katzman MA. Examining the role of neuroinflammation in major depression. Psychiatry Research 2015: 229, 27-36.

Rosenblat JD, et al. Inflamed moods: a review of the interactions between inflammation and mood disorders. Progress in Neuro-Psychopharmacology & Biological Psychiatry 2014; 53, 23-34.

Diabetes, steroids and hypoglycemia

Following alloxan induction of diabetes, rats overexpress glucocorticoids. This in turn depletes the mast cell populations in the skin, lungs and intestines. Glucocorticoids interfere with production and expression of tissue cytokines and stem cell factor, a growth factor for mast cells.

Several experiments have definitively proven that these steroids are responsible for downregulating mast cell growth and activity. Treating diabetic rats with the steroid receptor blocker RU486 or removing adrenal glands on both sides of the animal causes an increase in intestinal mast cell numbers and IgE formation.

The mechanism by which steroids confer these effects is thought to involve insulin. Glucocorticoids inhibit secretion of insulin in the pancreas. In turn, insulin release decreases systemic glucocorticoids. Additionally, insulin also activates mast cell signaling pathways. In the presence of insulin, antigen induced mast cell degranulation and survival is upregulated. In diabetic rats, administration of insulin recruits mast cells and increases response to antigen. Insulin treatment can reverse the reductions in mast cell populations, histamine production and IgE release seen following alloxan administration.

Increased activity of the HPA axis is often seen in type I and II diabetics, resulting in elevated cortisol. One study showed that appropriate activity can be restored with insulin treatment. This is achieved by a complex mechanism in which expression of glucocorticoid receptor mRNA is elevated in the pituitary, facilitating glucocorticoids to suppress expression of ACTH release.

 

Can hypoglycemia cause mast cell degranulation?

Yes. Activation of histamine 1 and 2 receptors as a result of insulin or hypoglycemia causes release of ACTH. Hypoglycemia (low blood sugar, which can also be induced after administration of insulin) normally increases ACTH levels in the blood. However, higher than normal histamine levels in the blood can interfere with the action of ACTH, which would normally address hypoglycemia via production of glucocorticoids. One study found that this effect can be mostly ameliorated by pretreating with antihistamines, though I suspect in mast cell patients, this may not achieve the full response seen in non-mast cell patients.

 

Can anaphylaxis cause hypoglycemia?

Yes. In instances of severe stress (emotional or physical), corticotropin-releasing hormone (CRH), neurotensin and substance P are released. Among other things, CRH can induce mast cell degranulation (of note, CRH does not directly induce histamine release via degranulation). CRH also causes increased expression of the IgE receptor on mast cells, which increases the likelihood of being stimulated and thus degranulation (this may cause histamine release). In tandem, neurotensin and substance P increases the expression of the CRHR-1 receptor for CRH on mast cells so that they are more sensitive to CRH. Likewise, neurotensin and substance P act on mast cells via receptors to induce degranulation (this causes histamine release). As a result of this degranulation, histamine and other mediators are present to inhibit the action of ACTH, which would otherwise increase blood sugar (via the production of cortisol, epinephrine, and norepinephrine).

 

References:

Carvalho V.F., Barreto E.O., Diaz B.L. et al. (2003) Systemic anaphylaxis is prevented in alloxan-diabetic rats by a mechanism dependent on glucocorticoids. Eur. J. Pharmacol. 472, 221–227.

Carvalho V.F., Barreto E.O., Cordeiro R.S. et al. (2005) Mast cell changes in experimental diabetes: focus on attenuation of allergic events. Mem. Inst. Oswaldo Cruz 100(Suppl. 1), 121–125.

Foreman JC, Jordan CC, Piotrowski W. Interaction of neurotensin with the substance P receptor mediating histamine release from rat mast cells and the flare in human skin. Br J Pharmacol. 1982 Nov;77(3):531-9.

Meng, Fanyin, et al. Regulation of the Histamine/VEGF Axis by miR-125b during Cholestatic Liver Injury in Mice. The American Journal of Pathology, Volume 184, Issue 3, March 2014, Pages 662–673

Theoharides, T., et al. A probable case report of stress-induced anaphylaxis. Ann Allergy Asthma Immunol xxx (2013) 1e2

Kjaer A, et al. Insulin/hypoglycemia-induced adrenocorticotropin and beta-endorphin release: involvement of hypothalamic histaminergic neurons. Endocrinology. 1993 May;132(5):2213-20.

Carvalho V.F, et al. Reduced expression of IL-3 mediates intestinal mast cell depletion in diabetic rats: role of insulin and glucocorticoid hormones. Int. J. Exp. Path. (2009), 90, 148–155.

Carvalho V.F, et al. Suppression of Allergic Inflammatory Response in the Skin of Alloxan-Diabetic Rats: Relationship with Reduced Local Mast Cell Numbers. Int Arch Allergy Immunol 2008;147:246–254.

Carvalho VF, Barreto EO, Diaz BL, Serra MF, Azevedo V, Cordeiro RS, et al: Systemic anaphylaxis is prevented in alloxan-diabetic rats by a mechanism dependent on glucocorticoids. Eur J Pharmacol 2003; 472: 221–227.

S.C. Cavalher-Machado, et al. Down-regulation of mast cell activation and airway reactivity in diabetic rats: role of insulin. Eur Respir J 2004; 24: 552–558.

Diabetes, mast cells and allergic disease

Patients with either type I or II diabetes mellitus demonstrate unusual physiology pertaining to hypersensitivity and mast cell activation. This was first described in 1962, when a paper reported that diabetic animals do not experience anaphylactic shock.   Despite the amount of time that has passed, the reasons for this are still being unraveled.

The role of mast cells in type II diabetes mellitus is more straightforward. When mice are made obese through dietary manipulation, they normally develop glucose intolerance or insulin resistance. If the mice are mast cell deficient, they do not develop these conditions. Transfer of mast cells to mast cel deficient mice was shown to reverse this protection against these complications.

In mice without established type Ii diabetes that were given manipulated diets to induce obesity, treatment with mast cell stabilizers actually prevented the development of type II diabetes. In mice with pre-established type II diabetes, treatment with mast cell stabilizers cromolyn or ketotifen protected against glucose intolerance and insulin resistance. These findings have been replicated in at least one patient, a type II diabetic who had normalized plasma glucose and A1C after six months on cromolyn.

The relationship between mast cells and type I diabetes is far more intricate.   This is mostly understood through a diabetic rat model. It is possible to induce type I diabetes in rats by administering a chemical called alloxan. Triggering diabetes in this way causes a variety of mast cell changes in these animals. The same changes can be seen when causing diabetes via administration of another chemical, streptozotocin.

Diabetic rats have less vascular response to the action of histamine and reduced mast cell degranulation. These animals are resistant to both local and systemic allergic responses, including anaphylaxis.   Mast cell populations become depleted and less likely to activate. When exposed to antigen, diabetic rats have 50% less degranulated mast cells and histamine release compared to non-diabetic controls.

IgE production is also suppressed in diabetic rats, both antigen specific IgE and total IgE. If you transfer mast cells from the spleen and lymph nodes of non-diabetic rats to diabetic rats, IgE production is diminished. Likewise, if mast cells from diabetic rats are transferred into non-diabetic animals, IgE production is restored.

This protection from allergic processes is well established in animals, but also translates to humans. Children with type I diabetes, and their siblings, are less likely to develop asthma. The incidence of bronchial asthma, rhinitis, and atopic dermatitis is lower than predicted in patients with diabetes mellitus.   Risk of death due to anaphylactic shock is significantly reduced in diabetes. This has been attributed to both the depletion of mast cell populations in diabetics, but also to the overproduction of corticosteroids in the body.

 

References:

Carvalho V.F., Barreto E.O., Diaz B.L. et al. (2003) Systemic anaphylaxis is prevented in alloxan-diabetic rats by a mechanism dependent on glucocorticoids. Eur. J. Pharmacol. 472, 221–227.

Carvalho V.F., Barreto E.O., Cordeiro R.S. et al. (2005) Mast cell changes in experimental diabetes: focus on attenuation of allergic events. Mem. Inst. Oswaldo Cruz 100(Suppl. 1), 121–125.

Foreman JC, Jordan CC, Piotrowski W. Interaction of neurotensin with the substance P receptor mediating histamine release from rat mast cells and the flare in human skin. Br J Pharmacol. 1982 Nov;77(3):531-9.

Meng, Fanyin, et al. Regulation of the Histamine/VEGF Axis by miR-125b during Cholestatic Liver Injury in Mice. The American Journal of Pathology, Volume 184, Issue 3, March 2014, Pages 662–673

Theoharides, T., et al. A probable case report of stress-induced anaphylaxis. Ann Allergy Asthma Immunol xxx (2013) 1e2

Kjaer A, et al. Insulin/hypoglycemia-induced adrenocorticotropin and beta-endorphin release: involvement of hypothalamic histaminergic neurons. Endocrinology. 1993 May;132(5):2213-20.

Carvalho V.F, et al. Reduced expression of IL-3 mediates intestinal mast cell depletion in diabetic rats: role of insulin and glucocorticoid hormones. Int. J. Exp. Path. (2009), 90, 148–155.

Carvalho V.F, et al. Suppression of Allergic Inflammatory Response in the Skin of Alloxan-Diabetic Rats: Relationship with Reduced Local Mast Cell Numbers. Int Arch Allergy Immunol 2008;147:246–254.

Carvalho VF, Barreto EO, Diaz BL, Serra MF, Azevedo V, Cordeiro RS, et al: Systemic anaphylaxis is prevented in alloxan-diabetic rats by a mechanism dependent on glucocorticoids. Eur J Pharmacol 2003; 472: 221–227.

S.C. Cavalher-Machado, et al. Down-regulation of mast cell activation and airway reactivity in diabetic rats: role of insulin. Eur Respir J 2004; 24: 552–558.

 

Corticotropin releasing hormone, cortisol and mast cells

The term “HPA axis” refers collectively to the signals and feedback loops that regulate the activities of three glands: the hypothalamus, the pituitary gland, and the adrenal glands. The HPA axis is a critical component of the body’s stress response and also participates in digestion, immune modulation, emotions, sexuality and energy metabolism.

The hypothalamus is part of the brain. It performs several integral functions. It regulates metabolism, makes and releases neurohormones, and controls body temperature, hunger, thirst, circadian rhythm, sleep and energy level. It is also known to affect parenting and attachment behaviors. It effectively turns nervous system signals into endocrine signals by acting on the pituitary gland.

The pituitary gland is a small gland at the bottom of the pituitary. The anterior portion of the pituitary is part of the HPA axis. It makes and releases several hormones, including human growth hormone, thyroid stimulating hormone, adrenocorticotropic hormone (ACTH), prolactin, luteinizing hormone and follicle stimulating hormone. All of these hormones are released when hormones released by the hypothalamus act on the pituitary.

The adrenal glands are located on top of the kidneys. They primarily synthesize and release corticosteroids like cortisol and catecholamines like epinephrine and norepinephrine in response to action by the pituitary.   It also produces androgens and aldosterone.

The hypothalamus synthesizes vasopressin and corticotropin releasing hormone (CRH).   Both of those hormones stimulate the release of ACTH by the pituitary gland. ACTH stimulates the adrenals to make glucocorticoids (mostly cortisol). The cortisol then tells the hypothalamus and pituitary to suppress CRH and ACTH production. This is called a negative feedback loop.

Cortisol acts on the adrenals to make epinephrine and norepinephrine. Epi and norepi then tell the pituitary to make more ACTH, which stimulates the production of cortisol.

When you take steroids regularly, it suppresses ACTH so that your body stops making its own steroids. This is why weaning steroids is very important. By weaning, your body should gradually start making its own cortisol to replace the deficit when you lower your steroid dose. However, this doesn’t always work. People who do not make enough cortisol on their own are called adrenally insufficient and are steroid dependent. People with this condition can suffer “Addisonian crises” if their steroid levels drop dangerously low. This is a medical emergency.

CRH is released by the hypothalamus in response to stress. This drives the production of cortisol to help manage stressful situations of either a physical or emotional nature. Mast cell attacks and anaphylaxis are examples of physically stressful situations that stimulate release of CRH.

CRH binds to CRHR-1 and CHRH-2 receptors on various cells, including mast cells. When it binds to mast cells, it stimulates the release of VEGF, but not histamine, tryptase or IL-8. This type of release is called selective release as it does not involve the release of preformed granules (degranulation.) Additionally, CRH is also released by mast cells. This can act on the mast cells or other cells with CRHR receptors, like those in the pituitary. The exact purpose of mast cells releasing CRH is not clear.

 

References:

Theoharis C. Theoharides, et al. Mast cells and inflammation. Biochimica et Biophysica Acta 1822 (2012) 21–33.