Skeletal formula of propranolol, the first clinically successful beta blocker
Skeletal formula of noradrenaline
Dichloroisoprenaline, the first beta blocker
Norepinephrine degradation. Metabolizing enzymes are shown in boxes.
Norepinephrine (labeled "noradrénaline" in this drawing) processing in a synapse. After release norepinephrine can either be taken up again by the presynaptic terminal, or broken down by enzymes.
Schema of the sympathetic nervous system, showing the sympathetic ganglia and the parts of the body to which they connect.
Brain areas containing noradrenergic neurons.
Chemical structure of octopamine, which serves as the homologue of norepinephrine in many invertebrate species

Beta blockers are competitive antagonists that block the receptor sites for the endogenous catecholamines epinephrine (adrenaline) and norepinephrine (noradrenaline) on adrenergic beta receptors, of the sympathetic nervous system, which mediates the fight-or-flight response.

- Beta blocker

This hypotension is sensed by the baroreceptor reflex, which results in increased sympathetic nerve firing on the heart, releasing norepinephrine.

- Phentolamine

It also has usefulness in the treatment of cocaine-induced cardiovascular complications, where one would generally avoid β-blockers (e.g. metoprolol), as they can cause unopposed α-adrenergic mediated coronary vasoconstriction, worsening myocardial ischemia and hypertension.

- Phentolamine

Beta blockers, which counter some of the effects of noradrenaline by blocking their receptors, are frequently used to treat glaucoma, migraine, and a range of cardiovascular problems.

- Norepinephrine

Other appropriate antihypertensive drugs to administer during hypertensive crisis resulting from stimulant overdose are vasodilators such as nitroglycerin, diuretics such as furosemide, and alpha blockers such as phentolamine.

- Beta blocker

Drugs such as phentolamine that act on both types of receptors can produce a complex combination of both effects.

- Norepinephrine
Skeletal formula of propranolol, the first clinically successful beta blocker

1 related topic with Alpha

Overall

Normal remnant adrenal gland (left) with a pheochromocytoma (right) involving the adrenal medulla

Pheochromocytoma

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Rare tumor of the adrenal medulla composed of chromaffin cells, also known as pheochromocytes.

Rare tumor of the adrenal medulla composed of chromaffin cells, also known as pheochromocytes.

Normal remnant adrenal gland (left) with a pheochromocytoma (right) involving the adrenal medulla
Adrenal gland; the medulla (center, red) is the origin of the adrenal gland
There are two adrenal glands, highlighted in yellow, on top of each of the kidneys
Structure of epinephrine
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FDG PET – the tumor is appreciated as the dark structure in the patient's left chest. Darkened structures at head of patient is brain, in the abdomen are the kidneys, in the pelvis is the bladder. These are normal.
Histopathology on the resected tumor confirms the diagnosis, by typical features as shown.
Patient receiving radiation therapy to the region of the head and neck. Full facial mold is in-place to protect areas where they do not want exposure
Top: Purple lesions are metastatic disease detected with DOTATATE imaging. Bottom: Same patient. Purple lesions are metastatic disease detected with FDG PET
Likelihood of diagnosis when an adrenal-nodule is identified; pheochromocytoma is in yellow near the top-right corner
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The Zebra has become a powerful symbol in the pheochromocytoma advocacy community and represents the rare medical cases that are more likely to be misdiagnosed

3) Toxic Myocarditis: Even in patients without myocardial damage, excessive catecholamines can result in abnormal ST changes on an ECG. Norepinephrine (a catecholamine) is hypothesized to result in damaged cardiac tissue by inhibiting coronary blood flow and depriving cells of oxygen, thus resulting in ischemic tissue. Fortunately, following tumor excision and the subsequent quelling of catecholamines, the damage has been proven reversible.

2) Pharmaceutical Interference: Many prescription, over-the-counter, and illicit substances can interfere with the proper collection of plasma metanephrines and lead to false-positive results. Providers should review a patient's medication list in-detail and have a discussion if temporarily discontinuing any of the interfering medications is possible. The most reported medications to result in falsely elevated metanephrines include: β-adrenoceptor blockers, phenoxybenzamine, tricyclic antidepressants, monoamine oxidase inhibitors, serotonin norepinephrine reuptake inhibitors (SNRI), and methyldopa. As the majority of these medications are commonly prescribed for psychiatric conditions, a conversation with the prescriber may be necessary to facilitate alternative therapeutic options while the patient is undergoing evaluation for a pheochromocytoma. After any possible prescription medications have been held, it is important to review any over-the-counter medications/supplements as well as the commonly used acetaminophen and pseudoephedrine cause false elevations in metanephrine levels. Finally, it is important to have open, non-judgemental discussions about the patient's recreational substance use. Amphetamines, nicotine, and cocaine can result in marked plasma norepinephrine levels.

1) Hypertension: In the pheochromocytoma patient, postoperative hypertension could indicate incomplete tumor resection or another tumor of unknown location. However, the traditional, non-specific causes of postoperative hypertension including pain, fluid overload, and essential hypertension must also be considered. A perioperative hypertensive crisis is first treated with a 5.0 milligram (mg) intravenous bolus of phentolamine, with additional 5.0 mg dose every ten minutes until the blood pressure falls within an acceptable range. If the blood pressure is only minimally elevated, the patient can resume their alpha and beta-adrenoceptor antagonist from prior to surgery.