L6 - Drugs Affecting the Vascular System (Part II)

Question 1

What neurotransmitter is involved in noradrenergic transmission?

Answer 1

• Noradrenaline (norepinephrine) is involved in noradrenergic transmission.

Question 2

What are the two types of adrenoceptors that govern noradrenergic transmission?

Answer 2

• Noradrenergic transmission is governed by α- and β-adrenoceptors.

Question 3

What compounds bind to adrenoceptors?

Answer 3

• Catecholamines such as adrenaline, noradrenaline, and isoproterenol bind to adrenoceptors.

Question 4

What is the precursor for adrenaline biosynthesis?

Answer 4

• The metabolic precursor for adrenaline biosynthesis is L-tyrosine, an aromatic amino acid.

Question 5

How is adrenaline synthesized?

Answer 5

• Adrenaline biosynthesis involves several steps:
  1. Tyrosine hydroxylase converts tyrosine to DOPA (inhibited by noradrenaline).
  2. DOPA decarboxylase converts DOPA to dopamine.
  3. Dopamine-β-hydroxylase converts dopamine to noradrenaline.
  4. Phenylethanolamine N-methyltransferase (PNMT) converts noradrenaline to adrenaline.

Question 6

How is noradrenaline transported within neurons?

Answer 6

• Noradrenaline is transported to vesicles in the nerve terminal by transporters. Drugs like reserpine block this transport, causing nerve terminals to be depleted of noradrenaline.

Question 7

How is noradrenaline taken up and metabolized?

Answer 7

• Noradrenaline is taken up by both presynaptic neurons and postsynaptic cells. It is metabolized by monoamine oxidase (MAO). MAO inhibitors, used to treat depression, block this process.

Question 8

What are the main types of adrenoceptors?

Answer 8

• The main types of adrenoceptors are:
  o α1-adrenoceptors
  o α2-adrenoceptors
  o β1-adrenoceptors
  o β2-adrenoceptors

Question 9

α1-adrenoceptors

Answer 9

Found in smooth muscle, activate PLC, and increase IP3, leading to vasoconstriction and smooth muscle contraction.

Question 10

α2-adrenoceptors

Answer 10

Located on nerve terminals, regulate noradrenaline release, and reduce blood pressure when activated by agonists like clonidine.

Question 11

β1-adrenoceptors

Answer 11

Found in the heart, activate adenylate cyclase (AC), increase cAMP, and enhance heart rate and contraction force.

Question 12

β2-adrenoceptors

Answer 12

Found in smooth muscle, activate AC, increase cAMP, and cause smooth muscle relaxation.

Question 13

What drugs affect α1-adrenoceptors, and what are their uses?

Answer 13

• Phenylephrine (agonist) is used as a nasal decongestant by stimulating α1-adrenoceptors.
• Prazosin (antagonist) is used to treat hypertension by blocking α1-adrenoceptors.

Question 14

What drugs affect β1-adrenoceptors, and what are their uses?

Answer 14

• Dobutamine (agonist) is used to treat cardiogenic shock by stimulating β1-adrenoceptors to increase heart rate and contraction force.
• Metoprolol (antagonist, beta-blocker) is used to treat angina, hypertension, and dysrhythmias by blocking β1-adrenoceptors.

Question 15

What are the side effects of salbutamol and propranolol?

Answer 15

• Salbutamol (β2-adrenoceptor agonist) can cause tachycardia as a side effect.
• Propranolol (non-selective β-adrenoceptor antagonist) can cause bronchoconstriction as a side effect.

Question 16

How does the activation of phospholipase C (PLC) affect smooth muscle?

Answer 16

• Activation of PLC by α1-adrenoceptors or muscarinic receptors (M3 subtype) increases IP3 and intracellular calcium, causing smooth muscle contraction.

Question 17

How does adenylate cyclase (AC) affect cardiac and smooth muscle?

Answer 17

• In cardiac muscle, β1-adrenoceptors activate AC, increasing cAMP and causing contraction. In smooth muscle, β2-adrenoceptors activate AC, increasing cAMP, leading to relaxation.

Question 18

How do drugs affecting noradrenergic transmission generally act?

Answer 18

• Drugs affecting noradrenergic transmission may influence neurotransmitter release, reuptake, or receptor activation to modify heart rate, blood pressure, and smooth muscle contraction.