Pharm 9 - SNS Agonists Flashcards
From which region of the spinal cord do sympathetic fibres originate?
Thoracolumbar
Most sympathetic post ganglionic neurones release noradrenaline. State two exceptions.
Sweat glands - acetylcholine
adrenal medulla - adrenaline
State two difference between directly and indirectly acting sympathomimetics.
Directly - binds to adrenoceptor and mimic the action of catecholamines by stimulating the receptor
indirectly acting - inhibits uptake and breakdown of the system leading to accumulation of the neurotransmitter in the synaptic cleft
Describe the mechanism of action of the 4 different types of adrenoceptors.
All are G protein coupled
Alpha 1 = PLC –> IP3 + DAG
Alpha 2 = decrease cAMP
beta 1+ 2= increase cAMP
State the main actions of beta-1 receptors
Heart - increase heart rate and contractility
kidneys - increase renin release which increases blood pressure
State the main actions of beta 2 receptors?
- partial bronchodilation
- hepatic glucose output - glycogenolysis + gluconeogenesis
- vasodilation of vessels to skeletal muscle
State some of the effects that are mediated by both alpha and beta receptors.
Exocrine secretions
GIT motility
What receptors are responsible for the production of aqueous humour by the ciliary body?
Beta receptors
State some of the effects of alpha 1 receptors.
vasoconstriction
increased motility and tone of ureters
mydriasis
hepatic glucose output
What is the principle action of beta blockers?
Inhibits beta 1 mediated increase in renin secretion
Describe the relative selectivity of adrenaline and noradrenaline
adrenaline = beta
noradrenaline = alpha
Describe the action of pre-synaptic alpha 2 receptors?
negative influence on noradrenaline synthesis and release
State 5 directly acting SNS agonists.
Phenylephrine – alpha-1 Clonidine – alpha-2 Dobutamine – beta-1 Salbutamol – beta-2 Isoprenaline – beta 1+ beta 2
Describe the development of hypersensitivity following the first exposure.
after the first exposure you generate antibodies to the antigen
these circulate and bind to mast cells
in subsequent exposure, the mast cells have the antibody on the surface
cross linking of the antibodies causes a huge release of stored mediators leading to the symptoms of hypersensitivity
State some of the symptoms of hypersensitivity.
Increase in capillary permeability leads to increased movement of fluid into the tissues.
depletes circulating fluid volume, causing decrease in blood pressure = anaphylactic shock
can also cause contraction of bronchial smooth muscle causing resp distress
Why is adrenaline more effective than noradrenaline in dealing with hypersensitivity?
adrenaline is more selective for beta receptors
so better as causing beta 2 mediated bronchodilation thus opening airways
airways is more important
adrenaline also stimulates heart via b1
acts on alpha 1 to cause vasoconstriction and increase TPR and blood pressure