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-injection of adrenaline has two kinds of effects
-vasoconstriction in certain vascular beds: rise in arterial pressure
-vasodilation in other tissues
-If animal is injected with ergot, adrenaline caused a fall in arterial pressure
-This showed there were two different receptors and are classified according to the potency of catecholamines. A: noradrenaline > adrenaline > isoprenaline B: isoprenaline > adrenaline > noradrenaline
Key location and effects of
Receptor stimulation: AGONIST: An agent binding to a receptor and stimulates a response With sympathetic a & b receptors : agonist may be referred to as
-the agonist can act directly or indirectly (or a combination of both)
-Direct action on receptor
-Indirect action to release noradrenaline
-tyramine, ephedrine, amphetamine (displaces NA from the storage vesicles) Noradrenline and adrenaline
-these are non selective adrenoreceptor agonists - activates alpha and beta receptors. There is also a danger of ventricular fibrillation
-noradrenaline is more potent that adrenaline in activating alpha1, beta1 receptors
-adrenaline is more potent than noradrenaline in activating a2 and b2 receptorss
-its use is limited to severe acute conditions Anaphylactic shock: reverses bronchospasm Heart stimulation (negative as it leads the ventricular dysrhythmias) Acute cardiac failure: heart stimulation, vasoconstriction (negative as it increases peripheral resistance, this increases the workload of the heart Also applied with local anaesthetics: the vasoconstriction mediated by the adrenaline increases the time period and increases the concentration of the local anaesthetic in a certain place.
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