2nd lecture - sympatholytics Flashcards
The peripheral nervous system is divided into three sub-systems:
The sensory system
The somatic motor system
The autonomic system
The autonomic system controls
the glands, heart and smooth muscles
The autonomic system is divided into
Sympathetic system – activated during critical situations
Parasympathetic system – active at rest
adrenoblockers can also be called (2)
sympatholytics
or
Adrenergic receptor antagonists
what do Adrenergic receptor antagonists do
Interact with adrenergic receptors and by occupying these sites do not allow an adrenergic agonist access to the receptor.
they block stimulus or action from occuring via the receptors they block
alfa 1 blockade removes the pressor response to what substance?
norepinephrine
alfa blockade not only prevents the pressor response to epinephrine, it converts it to a depressor response (epinephrine reversal).
What type of agonist is epinephrine?
mixed alfa-beta agonist
When alfa-1 receptors are occupied by a blocker, only the vasodilator beta-2 receptors are available for interaction with epinephrine which means that epinephrine causes
a fall in blood pressure.
if alfa1 receptors of blood vessels are occupied by alfa
1 blocking agents, they are no longer available to
mimetics.
an example of a natural alfa-adrenoblocker
ergot alkaloids (dihydroergotamine)
examples of synthetic alfa-adrenoblockers (3)
Phentolamine (α1 and α2, used rarely in vet)
Yohimbine, atipamezole, tolazoline (α2 selective)
Prazosin/pratsiol (α1 mainly)
ergot alkaloids are
fungal toxins found in grains
they are a natural alfa adrenoblocker
severe ergot alkaloid poisoning can cause
strong hypotension, gangrenous necrosis of tissues.
Chronic poisoning - ergotism. Weakness, nausea, headache, vasoconstriction and finally gangrene.
cardiovascular effects of ergot alkaloids
intense spasm of peripheral blood vessels, caused by direct-acting effect on the smooth muscle of the blood vessels.
Higher doses cause hypotension and central blood vessels to dilate (beta2 receptor dominance in the presence of α1 blockade). The heart rate and the tone of smooth muscle organs will increase.
Larger doses block the α1 receptors, α1 receptor-mediated effects of agonists are inhibited. beta receptors are not affected.
clinical use of ergot alkaloids
postpartum uterine contraction strengthening (rarely)
in humans, as a migraine treatment
Synthetic α blocking agents do what
They alter pressor effects of catecholamines (can cause epinephrine reversal), but the total cardiovascular effects are from a variety of factors such as concomitant antihistaminic, antiserotonergic and anticholinergic effects.
prazosin/pratsiol blocks which receptors
alfa 1
α1 adrenoblockers cause blood pressure to drop. This is attributable to the drugs blocking the effect of sympathetic impulses on the smooth muscle of the blood vessels.
At the same time, the effect of β2-receptors that decreases the tone of blood vessels has been maintained – causing blood pressure to decrease even further.
atipamezole/antisedan/sedastop blocks what receptors?
alfa 2
Phentolamine interacts with what receptors?
Phentolamine interacts with α1 and α2 receptors as an antagonist.
It causes a decrease in blood pressure, blood vessels dilate, uterus relaxes.
Prazosin/pratsiol interacts with what receptors?
Selective α1 blocker.
It is used for eliminating peripheral spasms and for decreasing blood pressure.
active ingredient of cardisure and vetmedin
pimobendan, a non-glycoside inotrope
what type of drug is atipamezole
Selective α2 blocker
causes a dilation of blood vessels, increased uterine muscle tone and the dilation of blood vessels in the skin and mucous membranes.
is the reversal agent for common alfa 2 adrenomimetics such as dexmedetomidine
Dexmedetomidine favors what receptors?
is a highly selective α-2 agonist
what type of drug is Mirtazapine
α2-blocker
has antihistamine and antiserotonergic activity.
used as an appetite stimualnt in cats, antidepressant in humans.
