What governs noradrenergic transmission?
Alpha (α) and beta (β) adrenoceptors that bind catecholamines such as adrenaline, noradrenaline, and isoproterenol.
What is the precursor of adrenaline and noradrenaline?
L-tyrosine, an aromatic amino acid found in body fluids.
What enzyme converts tyrosine to DOPA?
Tyrosine hydroxylase (TH), which is inhibited by noradrenaline.
What enzyme converts DOPA to dopamine?
DOPA decarboxylase.
What enzyme converts dopamine to noradrenaline?
Dopamine-β-hydroxylase (DBH).
What enzyme converts noradrenaline to adrenaline?
Phenylethanolamine N-methyltransferase (PNMT).
Where is noradrenaline stored before release?
In vesicles within noradrenergic neurons.
What drug blocks the transport of noradrenaline into vesicles?
Reserpine; it depletes nerve terminals of noradrenaline and is used to treat hypertension.
How is noradrenaline reabsorbed after release?
By uptake into presynaptic neurons (U1) or postsynaptic cells (U2).
What enzyme metabolizes noradrenaline?
Monoamine oxidase (MAO).
What are MAO inhibitors used for?
Treating depression by preventing the breakdown of monoamines.
What drugs inhibit noradrenaline uptake transporters?
Cocaine and amphetamines.
What is the effect of inhibiting noradrenaline reuptake?
Increased noradrenaline concentration in the synaptic cleft, enhancing sympathetic effects.
What are the four main types of adrenoceptors?
α1, α2, β1, and β2.
What type of receptor are all adrenoceptors?
G-protein coupled receptors (GPCRs).
Where are α1-adrenoceptors located?
On smooth muscle (e.g., blood vessels).
What is the mechanism of α1-adrenoceptor activation?
They activate phospholipase C (PLC), increasing IP3 and intracellular Ca2+, causing smooth muscle contraction and vasoconstriction.
Give examples of α1 receptor drugs and their uses.
Agonist: phenylephrine (nasal decongestant); Antagonist: prazosin (antihypertensive).
Where are α2-adrenoceptors located?
On presynaptic noradrenergic neurons.
What is the function of α2-adrenoceptors?
They inhibit adenylate cyclase, reducing cAMP and decreasing noradrenaline release (negative feedback).
Give examples of α2 receptor agonists and their effects.
Clonidine and α-methylnoradrenaline; they reduce blood pressure by inhibiting noradrenaline release.
Where are β1-adrenoceptors found?
In the heart.
What is the mechanism of β1-adrenoceptor activation?
They activate adenylate cyclase, increasing cAMP and Ca2+, leading to increased heart rate and contractility.
Give examples of β1 receptor drugs and their uses.
Agonist: dobutamine (treats cardiogenic shock); Antagonist: metoprolol (beta-blocker for angina, hypertension, arrhythmias).
