Pharmacological Actions of Epinephrine and Norepinephrine

These flashcards summarize key concepts related to the pharmacological actions and clinical uses of epinephrine, norepinephrine, and their receptor interactions, based on the lecture notes.

What are the two main groups of receptors through which Epinephrine and Norepinephrine act?

α-adrenoceptors and β-adrenoceptors.

What are the functions of α1-receptors?

α1-receptors are mainly excitatory and present in smooth muscles.

Where are α2-receptors mainly present and what is their action?

α2-receptors are mainly present in neuronal sites and are inhibitory.

What is the primary location where β1-receptors are found and their action?

β1-receptors are mainly present in cardiac muscles and are excitatory.

What functions do β2-receptors facilitate?

β2-receptors are mainly inhibitory in smooth muscles and excitatory in cardiac and skeletal muscles.

Where are β3-receptors primarily located and what actions do they stimulate?

β3-receptors are mainly present in fat cells (excitatory) and bladder neck smooth muscles (inhibitory).

What metabolic actions are associated with β2-adrenoceptors?

Glycogenolysis.

What is the effect of β3-adrenoceptors on lipolysis?

Stimulates lipolysis with the subsequent release of fatty acids from adipose tissue.

What role do β1-adrenoceptors play in Na+ and K+ homeostasis?

Stimulates renin secretion, leading to Na+ retention and K+ excretion.

What is the effect of epinephrine on smooth muscles?

Epinephrine can cause bronchodilation and relaxation of the uterus after the 20th week of pregnancy.

How does the presence of a-blockade affect epinephrine's action on blood pressure?

Epinephrine will lead to hypotension instead of hypertension.

What is the primary medical use of epinephrine in emergencies?

It is life-saving in anaphylactic shock due to its vasoconstriction and bronchodilation effects.

What are the possible side effects of epinephrine?

Hypertension, arrhythmias, palpitations, and CNS side effects such as anxiety.

What is a significant contraindication for using epinephrine?

It may precipitate acute myocardial infarction.

What treatment should be given for acute epinephrine toxicity?

Chlorpromazine (a-blocker) or sodium nitroprusside (direct vasodilator).

How is noradrenaline distinct in its action from epinephrine?

Noradrenaline causes marked vasoconstriction that may lead to tissue gangrene and decreases heart rate due to reflex vagal stimulation.

What is dopamine primarily used for?

Dopamine is used in cases of bradycardia and may help in shock with renal impairment.

What is the main action of isoprenaline?

Isoprenaline primarily acts as a vasodilator and increases heart rate.

At what concentration does dopamine act as a D1-agonist, and what is its effect?

At low concentrations, dopamine is a D1-agonist leading to vasodilation of renal blood vessels.

What risks are associated with high concentrations of dopamine?

Vasoconstriction leading to hypertension and potential gangrene.

For which patient population is dobutamine primarily used?

Dobutamine is used for severe acute or refractory chronic heart failure.

What is a unique characteristic of dobutamine in terms of its cardiac effect?

Dobutamine primarily stimulates cardiac contractility more than heart rate.

What effect can α1-agonists have on smooth muscle contractions?

α1-agonists can result in vasoconstriction and increase blood pressure.

What are potential side effects of α2-agonists?

Ocular irritation, CNS adverse effects, and respiratory arrest in young children.

Why is phenylephrine preferred over atropine for mydriasis?

Phenylephrine does not induce cycloplegia.

What are the common side effects associated with β2-agonists?

Fine tremors, headache, and palpitations.

What is a potential issue with the use of β2-agonists over time?

Tolerance may develop with prolonged use.

What is the primary use of mirabegron?

Mirabegron is introduced for the treatment of hyperactive bladder.

What happens with the use of local nasal decongestants like naphazoline?

They may cause rebound nasal congestion.

What determines the preferred route of administration for dobutamine?

Dobutamine is administered via IV infusion due to its short action and need for careful titration.

What are the effects of α2-agonists when applied systemically?

Act as sympatholytics by inhibiting presynaptic α2 receptors.

What are some adverse effects of topical brimonidine use?

Red eye, ocular irritation, and respiratory arrest in young children.

What drug is used to manage acute heart failure after cardiac surgery?

Dobutamine.

What is a selective use for midodrine?

Chronic orthostatic and postprandial hypotension.

What neurotransmitter can dopamine be converted into?

Norepinephrine (noradrenaline).

How does α1-agonist lead to bradycardia?

It may cause reflex vagal stimulation, especially in cases of marked hypotension.

Describe the primary cardiovascular effect of dopamine at moderate concentrations.

Dopamine increases heart rate and contractility.

In what situation would ephedrine be preferred over other adrenergics?

In spinal shock as it stimulates norepinephrine release.

What is the therapeutic use of β2-agonists during pregnancy?

Inducing uterine relaxation to prevent premature labor.

What effect does reflex sympathetic stimulation have on heart rate when blood pressure decreases?

It leads to an increase in heart rate.

What warning is associated with the utilization of isoprenaline in patients?

It can precipitate anginal attacks.