Cardiovascular Autonomic Pharmacology (B2: W3) Flashcards
What is the efect of cAMP on smooth muscle contraction?
Inhibition of contraction
Where are alpha 1 receptors located and what is their mechanism of action?
- Smooth muscle: blood vessels, eye, gut, bladder sphincter
- Formation of IP3 and DAG (PKC)
- Contraction
Where are alpha 2 receptors located and what is their mechanism of action?
- Presynaptic nerve terminals, some vascular smooth muscle
- Inhibition of neuronal Ca channels, inhibition of adenylyl cyclase
- Constriction
Where are ß1 receptors located and what is their mechanism of action?
- Cardiac myocytes, juxtaglomerular cells
- Stimulation of adenylyl cyclase, increased cAMP
- Response:
- Heart: increasing rate (SA), conduction velocity (AV), contractility rate of relaxation
- Kidney: increase renin secretion
Where are ß2 receptors located and what is their mechanism of action?
- Smooth muscle (airways, blood vessels), ciliary body epithelium, cardiac muscle
- Stimulation of adenylyl cyclase, increased cAMP
- Response:
- Heart: increase heart rate and contractility
- Smooth muscle: relaxation
What are the autonomic effects on the SA node?
- Sympathetic activation of ß1 receptors has a positive chronotropic effect (increases HR)
- Parasympathetic activation of M2 muscarinic receptors has a negative chronotropic effect (decreases HR)
What are the autonomic effects on the AV node?
- Sympathetic activation of ß1 receptors has positive dromotropic effect (increases conduction velocity)
- Parasympathetic activation of M2 receptors has a negative dromotropic effect (decreases HR)
What are the autonomic effects on the ventricular muscle?
- Sympathetic activation of ß1 receptors has a positive inotropic effect (increases contractility)
- Parasympathetic activation of M2 receptors antagonizes sympathetic responses
- In the absence of sympathetic tone, parasympathetic activation has little or no effect on the ventricles
What effect does sympathetic ANS stimulation have on blood vessels
- Alpha 1 receptors cause vascular smooth muscle contraction and constriction of the blood vessels
- ß2 receptors cause relaxation of vascular smooth muscle and dilation of blood vessels
What effect does parasympathetic ANS activation have on blood vessels?
- Parasympathetic activation has little or no effect on most blood vessels
- Exceptions: blood vessels of the face, tongue, genitals, and urinary tract, where parasympathetic stimulation causes vasodilation
What is the receptor sensitivity to Norepinephrine?
ß1 = a1 ≥ a2 > ß2
What is the cardiovascular response to Norepinephrine?
- Increase in diastolic, systolic, and mean arterial pressure
- Decrease in heart rate
Why does heart rate decrease with norepinephrine?
- a1 receptor activitiy causes increase in mean arterial pressur (MAP)
- Baroreceptors sense this reflex, and try to bring it back with an increase in parasympatheti tone
- Decrease HR
- Fast response
What is the receptor selectivity to epinephrine?
ß1 = ß2 > a1 = a2
What is the cardiovascular response to epinephrine?
- Increased heart rate
- Increased systolic BP, decreased diastolic, MAP stays the same
- Decreased peripheral resistance
Why does peripheral resistance decrease in response to epinephrine?
- At low doses, ß2 receptors cause vasodilation
- Decreased diastolic BP
- Similar response to isoproterenol
- At higher doeses, the a1 vasoconstriction can be seen
What is the receptor selectivity of isoproterenol?
ß1 = ß2
What is the cardiovascular response to isoproterenol?
- Increased heart rate
- Increased systolic, decreased diastolic, slight decrease in MAP
- ß2 - peripheral vasodilation
- Large decrease in peripheral resistance