| Question | Answer |
| Agonist | An agent binding to a receptor to stimulate a response
White sympathetic a and b receptors, an agonist can be called
A sympathetic agonist
A sympathomimetic agent
An adrenergic agonist
An adrenoreceptor agonist |
| Direct vs indirect effects | Direct - noradrenaline, adrenaline, isoprenaline - act directly on receptor
Indirect - tyramine, ephedrine and amphetamine - increase release of transmitter
Sympathetic denervation blocks their effects |
| How do we know there are different receptors | Same conc, same compound, same animal - can give different effects
Adrenaline increases BP in contracting vascular smooth muscle
Adrenaline and ergot decreases BP by relaxing smooth muscle |
| Potency order - Ahlquist | Divided receptors into alpha and beta
Decided potency order using isolated and in vivo smooth muscle preparations
Alpha - Noradrenaline> adrenaline > Isoprenaline
Beta - Isoprenaline > Adrenaline > Noradrenaline |
| Types of receptors in key locations | Heart - alpha 1
Blood vessels - Alpha 1 and 2 and Beta 2
Bronchi - Alpha 1 and Beta 2
GIT - Alpha 1 and Beta 1
Liver - Alpha 1 and Beta 2
Eye - Alpha 1
Skeletal muscle - Beta 2 and 3
Adipose tissue - Beta 3 |
| Modulation of effects by baroreceptors | Isoprenaline binds solely to beta receptors
Causes a decrease in resistance due to vasodilation
Increase in heart rate due to baroreceptor reflex
Overall decrease in BP |
| Non-selective adrenoreceptor agonists | Adrenaline and noradrenaline
Non-selectivity limits use, as well as being unstable
Risk of ventricular fibrillation
Used in anaphylactic shock to reverse bronchospasm and vasoconstriction
Used in acute cardiac failure to stimulate the heart |
| Selective alpha 1 agonists | Phenylephrine - counter acute hypotension, treat nasal decongestion and cause mydriasis
Xylometazoline - nasal decongestion
Metaraminol - acute hypotension, partially IAS
Vascular and uterine smooth muscle contraction, salivary secretion |
| Selective alpha 2 agonists | Clonidine - anti hypertensive, central and peripheral actions
Xylazine - sedative effects via CNS
Presynaptic to decrease transmitter release, platelet aggregation, vasoconstriction |
| Selective beta 1 agonists | Isoprenaline - cardiac stimulant
Dobutamine - cardiogenic shock, ionotropic support in infarction
Increase rate and force of heart contraction, relax GI smooth muscle |
| Selective beta 2 agonists | Isoprenaline - cardiac stimulant
Salbutamol, terbutaline - short acting bronchodilators
Salmeterol - long acting, preventative
Bronchodilation, vasodilation, especially coronary and skeletal muscle beds, uterine relaxation, glycogenolysis |
| Adrenoreceptor antagonists - Ergot | First discovered were ergot alkaloids by Dale - ergot poisoning
Includes histamine, ACh, tyramine
Derivatives of lysergic acid - ergotamine and ergometrine
Partial alpha agonist as well as antagonist - stimulate then block |
| Alpha antagonists | Phentolamine - non-selective, associated with raised heart rate as it blocks alpha 2 feedback
Prazosin - selective alpha 1 used as an antihypertensive
Phenoxybenzamine - irreversible non-selective used to prevent swings in BP and heart rate in surgery |
| Main drawback of alpha antagonists | Postural Hypotension
Blocking alpha receptors removes the reflex that prevents blood pooling in the legs |
| Beta antagonists | Propranolol - non-selective so risk of bronchodilation, fatigue and claudication
Atenolol - beta 1 selective so less likely to give bronchodilation
Both give cold hands and feet
Used in hypertension, cardiac dysrhythmia and angina |
