What receptors do Noradrenaline act on in airways? What effect does it have?
What drug is its synthetic agonist and for what condition. (2)
- B2 receptors, allows bronchodilation
2. Salbutalmol for Asthma
What receptors do Noradrenaline act on in the heart? What effect does it have?
What is it’s antagonist, and for what condition? (2)
- B1 receptors, causes increased force of contraction.
2. Beta-blockers, to reduce high blood pressure (hypertension).
- What is tachyphylaxis?
2. How does Receptor down-regulation occur (tolerance)? (2)
- Tachyphylaxis is quick and short term receptor desensitisation.
- A longer term effect when receptors are lost from cell surface and take longer to recover.
What are extra Mexhanisms drug effect can be lost?
- Exhaustion of mediators
- Increased metabolisation of drug
- Physiological adaptation (new cells lacking receptors)
- Active extrusion of drug from a cell e.g Cancer and bacteria.
Why do unwanted effects occur? Are agonists and antagonists more likely to produce secondary reaction? (2)
- The same drug can can interact with different of same type of receptor but at different sites in body.
- Antagonists as more likely to interact with multiple receptor types.
Hypertension involves high cardiac output and peripheral resistance which causes HBP.
How can the parasympathetic and sympathetic system be exploited to reduce hypertension? (3)
Goal: to reduce cardiac output and peripheral resistance.
By INCREASING parasympathetic system activity - relaxation of heart muscles.
By DECREASING sympathetic system activity
Parasympathetic System: Acetylcholine (also carbochal and pilocarpine) can be used to decrease heart rate.
How does it work, and how can the effect be sustained? What are its limitations?
What are its side effects? (4)
- Binds to M2 receptor, which slows down contraction.
- Prevent breakdown of acetylcholine by inhibiting acetylcholineesterase.
- Only has modest effect as no effect on peripheral resistance
- Acetylcholine binds to muscarinic receptors and nicotinic receptors around the body, hence causes Bronchoconstriction in Lungs, visual disturbances, salivation, tears etc
Sympathetic system: An adrenoceptor antagonist (e.g carvedilol, Labetalol) can inhibit noradrenaline to reduce heart rate.
What receptors does noradrenaline bind to and what are its effects? (3)
How would reducing heart rate work?
- Noradrenaline binds to B1 receptors in for heart muscle contraction; B2 receptors (airways, blood vessels and lungs) for vasodilation and Alpha adrenoceptors (smooth muscle) for vasoconstriction.
- These receptors are gcoupled proteins so 2nd messenger plays role in different outcomes.
- Antagonist would reduce noradrenaline action.
Sympathetic System: How can action of nasal receptors be exploited to treat the common cold?
What are the side effects? (3)
- Nasal Decongestants (phenylephrine) are alpha-adrenoreceptor agonists. Increasing vasoconstriction and reducing secretions to reduce blood flow.
- Increased peripheral resistance causing reduced blood flow to skin and gut, and increased blood pressure.
This is limited effect when local effect so safe as nasal spray.
What receptors do Salbutamol bind to have effect of treatment?
Is the parasympathetic or sympathetic system being increased or decreased?
B2 receptors. It is an agonist and increases bronchodilation.
Increasing sympathetic system and reducing parasympathetic system.