L9: Sympathetic system

What transports Na+ and tyrosine into the axon in the sympathetic system?

Aromatic L-amino acid transporter

What is tyrosine converted into in the sympathetic system?

L-DOPA and then dopamine

How is dopamine transported into vesicles in the sympathetic system?

Via VMAT (vesicular monoamine transporter)

What enzyme converts dopamine into noradrenaline in the sympathetic system?

Dopamine beta-hydroxylase

What causes an increase in intracellular Ca2+ in the sympathetic system?

Activation of Ca2+ ion channels by action potentials

What is released from vesicles in the sympathetic system due to an increase in intracellular Ca2+?

Noradrenaline (NE)

How does NE diffuse across the synapse in the sympathetic system?

To bind to adrenergic receptors on the postsynaptic neuron

What happens to excess NE in the sympathetic system?

It can bind to α2 receptors on the presynaptic neuron to suppress NE release, or it can be recycled via NE transporter and broken down by MAO (monoamine oxidase) and COMT (catechol-O-methyltransferase)

What are the effects of activation of α1 receptors in the sympathetic system?

Vasoconstriction, smooth muscle constriction, GI tract relaxation, glycogenolysis, and K+ release in salivary glands

What are the effects of activation of α2 receptors in the sympathetic system?

Reduction of presynaptic NE release, reduction of insulin secretion, and GI tract relaxation

What are the effects of activation of β1 receptors in the sympathetic system?

Increased contractility and heart rate, and amylase secretion in salivary glands

What are the effects of activation of β2 receptors in the sympathetic system?

Vasodilation, relaxation of smooth muscle, and a slight increase in heart rate and contractility

What are the effects of activation of β3 receptors in the sympathetic system?

Relaxation of bladder detrusor, thermogenesis in skeletal muscle, and lipolysis and thermogenesis in fat cells

What is the mode of action of sympathomimetics?

Sympathomimetics mimic the action of the sympathetic nervous system.

What are the two modes of action of sympathomimetics?

Sympathomimetics can act directly by activating the receptor or indirectly by increasing the release of NE.

What is the action of adrenaline on ß1 receptors?

Adrenaline increases stroke volume and heart rate, leading to higher blood pressure.

What is the action of adrenaline on ß2 receptors?

Adrenaline reduces peripheral resistance (vasodilation) and increases smooth muscle relaxation.

What is the clinical use of adrenaline?

Adrenaline is used in cases of anaphylactic shock, cardiac arrest, and asthma.

What is the action of noradrenaline on ß1 receptors?

Noradrenaline increases stroke volume and heart rate, leading to an increase in blood pressure.

What is the action of noradrenaline on α1 receptors?

Noradrenaline stimulates α1 receptors more than ß2 receptors, resulting in an increase in peripheral resistance (vasoconstriction) and further increase in blood pressure.

What is the clinical use of noradrenaline?

Noradrenaline is used to treat hypertension.

What is the action of isoproterenol?

Isoproterenol acts as a non-selective ß1 receptor agonist, increasing stroke volume and heart rate, and reducing peripheral resistance, resulting in an overall reduction in blood pressure.

What is the clinical use of isoproterenol?

Isoproterenol is used in the treatment of asthma.

What is the action of phenylephrine and oxymetazoline?

Phenylephrine and oxymetazoline are selective α1 receptor agonists, causing vasoconstriction and smooth muscle contraction (except in the GI tract, where the effect is smaller).

What is the clinical use of phenylephrine and oxymetazoline?

They are used as decongestants to reduce nasal mucosal swelling.

What is the action of clonidine?

Clonidine is a selective α2 receptor agonist that inhibits presynaptic NE release, reducing cardiac output and vasoconstriction, and lowering blood pressure.

What is the clinical use of clonidine?

Clonidine is used to treat hypertension.

What is the action of dobutamine?

Dobutamine is a selective ß1 receptor agonist that increases heart contractility and heart rate, resulting in an increase in cardiac output and blood pressure.

What is the clinical use of dobutamine?

Dobutamine is used in the treatment of hypotension and heart failure.

What is the action of terbutaline and salbutamol?

Terbutaline and salbutamol cause vasodilation (without affecting heart rate) and smooth muscle relaxation.

What is the clinical use of terbutaline and salbutamol?

They are used as bronchodilators.

What is the action of mirabegron?

Mirabegron causes urinary bladder and skeletal muscle relaxation.

What is the clinical use of mirabegron?

Mirabegron is used to treat overactive bladder and obesity (lipolysis).

What is the action of tyramine?

Tyramine increases NE release by reversing the action of NE transporter (NET).

What is the clinical use of tyramine?

There is no clinical use for tyramine, but it is found in fermented cheese and can cause a dangerous rise in blood pressure when taken with MAO inhibitors.

What is the action of ephedrine?

Ephedrine increases NE release by reversing the action of NET.

What is the clinical use of ephedrine?

Ephedrine is used as a nasal decongestant.

What is the characteristic of sympatholytics?

Sympatholytics reduce the action of the sympathetic nervous system.

What are the two modes of action of sympatholytics?

Sympatholytics can act directly by blocking receptor activation or indirectly by inhibiting the synthesis of NE.

What is the action of prazosin and tamsulosin?

Prazosin and tamsulosin are selective α1 receptor antagonists that reduce vasoconstriction, leading to vasodilation and a decrease in blood pressure. They also reduce smooth muscle contraction.

What is the clinical use of prazosin and tamsulosin?

They are used to treat hypertension by promoting vasodilation. They are also used in the management of benign prostatic hypertrophy to relax prostate smooth muscle and relieve urinary symptoms.

What is the action of yohimbine?

Yohimbine is a selective α2 receptor antagonist that blocks α2 receptors, leading to an increase in NE release. This results in increased heart contractility and heart rate, smooth muscle relaxation, and potential blocking of serotonin and dopamine receptors.

What is the clinical use of yohimbine?

Yohimbine does not have a clinical use.

What is the action of propranolol?

Propranolol is a non-selective ß receptor antagonist. It reduces heart contractility and heart rate by blocking ß1 receptors and causes vasoconstriction by blocking ß2 receptors. Overall, it reduces cardiac output and blood pressure and can also cause smooth muscle contraction.

What is the clinical use of propranolol?

Propranolol is used in the treatment of angina to promote vasodilation of the coronary artery and reduce the workload of the heart by decreasing heart contractility and heart rate. It is also used for cardiac dysrhythmias and hypertension. However, it may have side effects on bronchoconstriction.

What is the action of atenolol and metoprolol?

Atenolol and metoprolol are selective ß1 receptor antagonists. They reduce heart contractility and heart rate, leading to a decrease in cardiac output and blood pressure. They have no effect on smooth muscle.

What is the clinical use of atenolol and metoprolol?

They are used in the treatment of angina, cardiac dysrhythmias, and hypertension. They are suitable for patients with asthma due to their selective ß1 receptor blocking action.

What is the action of butaxamine?

Butaxamine reduces vasodilation and promotes vasoconstriction. It also causes contraction of other smooth muscles.

What is the clinical use of butaxamine?

Butaxamine does not have a clinical use.

What is the action of methyldopa?

Methyldopa acts as a false transmitter of α-methylnoradrenaline. It is not deaminated by MAO, leading to its accumulation and displacement of NE from synaptic vesicles. It is less active on α1 receptors, resulting in less effective vasoconstriction. It is more active on presynaptic α2 receptors, reducing NE release. Overall, it reduces blood pressure.

What is the clinical use of methyldopa?

Methyldopa is used in the treatment of hypertension.