LG 07 adrenal biochemistry

What inhibits the type 2 11ß-hydroxysteroid dehydrogenase?

Glycyrrhetinic acid! Found in black licorice!!

Result of excessive corticosterone

HTN and hypokalemia!

What plasma level of K will stimulate the release of aldosterone, high or low K?

High K stimulates the release of aldosterone!

What is the overall cause in the serum due to aldosterone release?

Higher Na and lower K!

What is the name of the substrate which is synthesized into aldosterone, cortisol, DHEA, testosterone, estradiol........

Cholesterol is the starting point!!

Embryologic origin of the adrenal gland

Cortex: derived from mesoderm Medulla: derived from neural crest cells

Talk about cortisol binding to its receptor

Cortisol binds to its intracellular receptor. When cortisol binds to this receptor, it releases a heat-shock protein (chaperonen) that exposes a nuclear localization signal.

What other substance will you have extremely high levels of in 17alpha-hydroxylase deficiency?

Extremely high levels of corticosterone!

Anatomy of the adrenal cortex

From outer to inner: Zona glomerulosa —> zona fasciculata —> zona reticularis

Function of ß-endorphin

Gene has potent opioid action in the CNS!

How do you test a cortisol deficiency?

Give ACTH (Co-syntropin) stimulation test. If cortisol does not go up here, this tells you that you have an end organ adrenal gland problem!

If we had cortisol excess, how would we determine where in the pathway the issue is at?

Give the patient a potent steroid, dexamethasone (potent synthetic cortisol). This potent steroid should inhibit CRH and ACTH should fall significantly! If they do not fall, there is an issue with CRH/ACTH secretion (like an ACTH generating tumor).

What causes hyperpigmentation in cushing's disease?

MSH binding to the MSH receptor!!!

Where is the only place in the body Epi is released?

Medulla of adrenal gland!!

Where do melanocortins bind?

Melanocortin 1 receptors (MC1R) on melanocytes to disperse pigment granules!

What cells in the hypothalamus make and secrete CRH?

Paraventricular cells!

What are the rate limiting steps in this cholesterol pathway?

Passage of cholesterol into the mitochondria which requires steroidogenic acute regulatory protein (StAR) However if StAR is sufficient, then, the rate limiting step is the first reaction that takes place in the mitochondria which is side-chain cleavage of cholesterol

What can 3ß-hydroxysteroid dehydrogenase act on?

Pregnenolone, 17-hydroxypregnenolone, or dehydroepiandrosterone (DHEA)!

Presentation of 21-hydroxylase deficiency

Presents in infancy (salt waisting) or childhood (precocious puberty). XX virilization.

What can 21-hydroxylase act on?

Progesterone or 17-hydroxyprogesterone! Progesterone —> 11-deoxycorticosterone 17-hydroxyprogesterone —> 11-deoxycortisol

What type of hormone is corisol?

Steroid!

What is this final breakdown product? This can be measured in the urine for evaluation of how much Epi and NE we have being released?

Vanillylmandelic acid! Also, sulfates and glucuronides are often added in the liver and gut and are excreted in urine which can also be measured.

Are there issues with aldosterone clinically with 11ß-hydroxylase deficiency?

We do not make aldosterone here. However, high levels of 11-deoxycorticosterone and 11-deoxycortisol have mineralocorticoid activity causing HTN even though we do not have any aldosterone!

What is the very first chemical reaction to produce NE and/or Epi?

We have to convert phenylalanine to tyrosine! This step requires tetrahydrobiopterin!

Result of no cortisol in 11ß-hydroxylase

We will have congenital adrenal hyperplasia (CAH) due to extremely high ACTH!

Function of heat-shock protein, chaperonen

When there is no hormone (cortisol) bound, it covers a nuclear localization signal.

What is the result of the side-chain cleavage reaction?

When we cut the side chain, we make the precursor to all steroids, pregnenolone

What will result in a deficient 11ß-hydroxylase? What will we not make here? What will you have in excess?

Will not make cortisol or or aldosterone! Because we are not making these, we will have a TON of testosterone.....

Results of the excess testosterone in 11ß-hydroxylase deficiency

XX virilization!

Does cortisol have any CNS effects?

Yes! Cortisol acts on higher brain centers to alter mood and cognition

Are the adrenal medulla and cortex connected?

Yes! There is a portal circulation in which blood that perfused the cortex also perfuses the medulla!

What does the adrenal cortex secrete?

Zona glomerulosa —> mineralocorticoids (aldosterone) Zona fasciculata —> glucocorticoids (cortisol) Zona reticularis —> androgens (DHEA)

Where does aldosterone bine?

1 - binds to a LOW affinity receptor which is a glucocorticoid receptor that cortisol binds to with a high affinity called the mineralocorticoid receptor (MR) 2 - binds to a HIGH affinity receptor called the mineralocorticoid receptor

Function of 11ß-hydroxylase

11-deoxycorticosterone —> corticosterone 11-deoxycortisol —> cortisol

In the cells that express an aldosterone receptor however, what do they express?

11ß-hydroxysteroid dehydrogenase, however, this one is type 2!

What enzymes are lacking in the zona glomerulosa?

17alpha hydroxylase!! Because the glomerulosa cannot make cortisol!

What is the predominant cause of CAH?

21-hydroxylase deficiency!

How does ACTH release cortisol?

ACTH binds to all three cortical cell types via the melanocortin 2 receptor (G-protein coupled activating adenylyl cyclase). Phosphorylation increases side chain cleavage and increases synthesis of StAR LDL receptor, and other Cyt P450 enzymes, increasing synthesis of cortisol

Talk about the synthesis of ACTH

ACTH is processed from a much large "polyprotein" expressed from the pro-opiomelanocortin gene!

What is the principle regulator in the secretion of Epi?

Ach is secreted from the preganglionic sympathetic fibers of the splanchnic nerves and are the principal regulators of adrenomeddulary hormone secretion

What would phenotype be if side chain cleavage rxn/or StAR failed?

Adrenal insufficiency/failure (lack of cortisol), do not make any steroids. Gross accumulation of lipoid in StAR deficiency because the system will try to drive synthesis of those steroids and will cause deposition of lipids. Gonadal failure, 46XY would appear female.

Do glucocorticoids function with or against insulin?

Against insulin! Glucocorticoids like to release glucose!

Other products of pro-opiomelanocortin gene

Alpha and gamma melanocortins! Also, ß-endorphin is made!

How does angiotensin II signal to release aldosterone?

Binds to G-protein coupled receptors that activates phospholipase C and IP3 mobilized calcium and DAG which activates PKC and calcium calmodulin kinases that lead to depolarization of glomerulosa plasma membrane and a sustained calcium influx that activates side chain cleavage and delivery of cholesterol to the mitochondria.

In glucocorticoid responsive cells, how else can cortisol be obtained?

By the reduction of cortisone to cortisol via 11ß-hydroxysteroid dehydrogenase (11ßHSD)

How does ACTH weakly stimulate aldosterone release?

By the same PKA mechanism that functions to secrete cortisol!

MOA of how CRH stimulates ACTH release

CRH travels via portal circulation to anterior pituitary and binds to CRH G-protein coupled receptors on corticotrophs which activated adenylyl cyclase and the PKA pathway to activate calcium channels and secrete ACTH

Who breaks down catecholamines?

Catecholamine-O-methyltransferase (COMT)! Then, the second enzyme is monoamine oxidase which converts Epi and NE to the final breakdown product. The order here of enzymes do not matter!

Picture, what is causing this?

Caused by a 21-hydroxylase issue (but this is the non-salt waiting form)! We know it is a non-salt waiting form because he survived infancy! Picture of description on next flashcard.

What does cortisol do to immune system and what does it do to bones? Function in intestines?

Cortisol decreases inflammation and immune responses! (Cortisol bound receptor forms heterodimers with NF-kB and represses txn of pro-inflammatory mediators) —> promotes release of neutrophil from bone marrow and decreases circulating lymphocytes. In the bone, cortisol decreases function of osteoblasts. In gut, cortisol interferes with calcium absorption.

Talk about cortisol feedback

Cortisol feeds back on hypothalamus and the anterior pituitary. The most important feedback location however is the anterior pituitary, this is where strongest feedback is at. ACTH should fall then.

What is the main endogenous glucocorticoid in the body?

Cortisol!

Reproductive symptoms of cushing's syndrome

Decreased libido, in women, ammenorrhea (due to cortisol-mediated inhibition of gonadotropin release)

Effects of 21-hydroxylase deficiency. Talk about mineralocorticoid, cortisol, sex hormones, BP, and K levels!

Decreased mineralocorticoids, decreased cortisol, increased sex hormones, decreased BP, increased K levels.

What happens when dopamine is formed?

Dopamine enters granule with help of the carrier VMAT1

Location of NE formation and Epi formation

Dopamine hydroxylase is found on inner membrane of granules and thus, NE is formed inside the granule. However, NE has to move into the cytosol to be acted on by the SAM pathway to form Epi. Then Epi is placed back in the granules for storage

What is dopamine converted into? And where are we at now?

Dopamine is converted into NE inside the granule!

What is PKU due to?

Due to decreased phenylalanine hydroxylase or decreased tetrahydrobiopterin (BH4) cofactor. Tyrosine here becomes essential!

How is aldosterone broken down?

Inactivated by the liver by reduction and attachment of glucuronic acid and cleared in the bile

Talk about innervation of the chromaffin cells

Innervated by preganglionic sympathetic fibers that stimulate the release of the catecholamines

From prognenolone, what is the next step?

It can go via different pathways with really no order! Pregnenolone can be acted on by 17alpha-hydroxylase to make 17-hydroxypregnenolone. Or, pregnenolone can be acted on by 3ß-hydroxysteroid dehydrogenase to make progesterone.

When you have a ton of cortisol around, what can its activity look like? Clinical symptoms of this?

It can have some aldosterone like activity! In fact, it will bind to the same receptor that aldosterone binds to. Thus, in cushing's syndrome we can see hypokalemia, HTN, edema.

What does 11ßHSD require?

It is NADPH dependent, thus, it is called 11ßHSD type 1

Cortisols function in adipose tissue and what does this lead to clinically?

It stimulate the mobilization of fat. Although, not understood completely, this mobilization occurs from subQ fat in the extremities and turns it into central fat. Because of this, individuals with high levels of cortisol (cushing's syndrome), have a buffalo hump and/or moon face!

How does K signal to release aldosterone?

K stimulates aldosterone secretion by DIRECTLY depolarizing the plasma membrane

What is the phenotype for cushing's syndrome?

Moon face, buffalo hump, skinny extremities (due to the peripheral fat (subQ) being moved), muscle waiting, hyperglycemia,

What does the NE now have to do if we need Epi?

NE has to leave to go back to the cytosol for methylation of the NE to make Epi! Epi goes back into granule now and is released via exocytosis

Is aldosterone regulation and cortisol regulation the same?

No! Aldosterone is regulated via angiotensin II (RAAS) and cortisol is regulated via ACTH!

Will aldosterone levels in 17alpha-hydroxylase deficiency be high too?

No! Aldosterone will be normal here because there is a rate limiting step involved in aldosterone synthesis! Actually, aldosterone might even be low due to suppression by RAAS due to the HTN from the excessive corticosterone.

Is there a feedback loop in the Epi and NE release pathway?

No!! Because the catecholamine effects are brief, less than 10 seconds!

What stimulates activity of both tyrosine and dopamine hydroxylase?

Sympathetic stimulation and ACTH!

If you have a tetraydrobiopterin defect, what is effected?

The conversion of phenylalanine to tyrosine via phenylalanine hydroxylase and ALSO, the conversion of tyrosine to DOPA via tyrosine hydroxylase is also affected!!!

What beginning reactions are in the cytosol when synthesizing NE and Epi?

The conversion of tyrosine through to the conversion to dopamine

What would happen if you could not make cortisol besides adrenal insufficiency?

The lack of cortisol will drive production of ACTH! ACTH here will stimulate adrenal growth like mad!! This is called congenital adrenal hyperplasia (CAH)!

What types of cells are in the adrenal medulla and what do they do?

The medulla, being of neural origin, contains chromaffin cells which produce catecholamines Epi and NE!

What is the stimulation for synthesis of aldosterone?

The most important stimulation of aldosterone synthesis and secretion is angiotensin II. K ion concentration is also a potent stimulus. ACTH does bind in the zona glomerulosa (as it does in all 3 levels), but it does not have much effect on aldosterone synthesis

What cells receive the highest concentration of cortisol and aldosterone?

The portal circulation in the adrenal gland delivers the highest concentration of cortisol and aldosterone to the chromaffin cells!

However, what "saves" these cells where cortisol binds to its aldosterone receptors?

These cells have an enzyme that converts cortisol into cortisone!!! But when there is a lot of cortisol, this enzyme has trouble keeping up!

What will result in a deficient 17alpha-hydroxylase?

These patients cannot make cortisol or testosterone. Due to the testosterone deficiency here, 46XY will again appear female.

What is the non-salt waiting form of the 21-hydroxylase deficiency

These patients have a 21-hydroxylase deficiency in the fact that their 21-hydroxylase only binds and works on progesterone and NOT 17-hyrodyprogesterone! Thus, these patients still make aldosterone however they do not make any cortisol!

What are chromaffin cells?

They are the structural and functional equivalents of the postganglionic neurons in the sympathetic nervous system!! They secrete the catecholamines!

What step in this pathway do postganglionic neurons lack?

They lack NE ability to leave to go into cytosol to form Epi! This only occurs in the medulla cells (chromaffin cells)!

What will cortisol AND aldosterone bind to?

They will both bind to the aldosterone receptor!!

How do we get formation of aldosterone? Location of this in the body?

This ONLY occurs in the zona glomerulosa!! Aldosterone synthase works on corticosterone to produce aldosterone.

What happens next after the heat shock protein chaperonen is displaced by cortisol binding to its receptor?

This allows the bound hormone receptor to travel to the nucleus where it will bind typically as a dimer and will affect txn! It can also bind as a homodimer and binds to specific DNA response elements (looks like that the homodimer is the one that results in gene txn)

Function of this 11ß-hydroxysteroid dehydrogenase type 2?

This enzyme is NAD+ dependent! Thus, this converts us the opposite way as type 1. It oxidizes cortisol to cortisone and inactivates it.

What happens when aldosterone binds mineralocorticoid receptor?

This is the high affinity receptor remember! This will then bind to DNA and up regulates a group of kinases called SGK (serum glucocorticoid regulated kinases), upregulates Na/K ATPases, the Na/K/Cl cotransporter, and apical Na channels in certain cells of the distal tubule and collecting duct.

In a baby, what is absolutely required for treatment in StAR/side chain cleavage defects?

Treatment with aldosterone (Fludrocortisone) is MUCH more important than treatment with cortisol because without aldosterone, baby could not regulate Na or K levels!