Endothelial vasodil/vasoconst Flashcards
Major mechanisms controlling peripheral vasc resistance
- Vasoconstrictor receptors
o incr [intra¢ Ca2+] => promote vasoconstriction
o Respond to agonists from neurogenic, humoral, endothelial fct
A1 adrenergic R => NE
Ang II => vasoconstrictor + incr NE release
ET-1 => released from damaged endothelium - Cyclic nucleotide vasodilatory system
o cAMP/cGMP: inhibit vasoconstriction by inhibiting myosin light chain kinase
B adrenergic stimulation=> incr cAMP
NO => incr cGMP
Principal determinant of vasomotor tone (cellular pathways)
depends on final common pathway = cytosolic Ca2+ availability for muscle contraction
* Agonist => G-prot ¢ membrane R => phospholipase C =>
o Diacylglycerol (DG) => Ca2+ dependant prot kinase => Na/H exchanger
o Inositol triphosphate (IP3) => direct cytosolic Ca2+ from SR => available for myosin
Def of endothelial signaling
Small molecule locally produced in arterioles
Local vasodilators
NO
Prostacyclin
ET derived hyperpol factor
Adenosine
Local vasoconstrictors
Endothelin
Factors inhibiting vasodilators activity
Hypoxia
Thrombin
O2-derived free radicals
o Also incr ET1 release
Effect of NO release
released from endothelial ¢ lining blood vessels
Reason why exercise induce vasodilation => vasodilatory local messenger
NO release
* psymp stimulation
* Shear stress 2nd to incr blood flow in normal endothelium
incr cGMP induced vasodilation
Effect of adenosine
Act on adenosine R on vascular SM¢
Inhibit release of NE
Effect of endothelin
release stimulated
Shear stress if damaged endothelium
* Act on ETA R => vasoconstriction
Low doses/physiologic = vasodilatory via ETB => NO release
CNS control of endothelium
Stimulation via
o Ao baro/chemo R => vagus nerve => medulla
ChemoR less important for BP regulation => acidosis or hypercapnia => incr BP
o Carotid sinuses & bodies => glossopharyngeal nerve => medulla
o Cardiopulmonary R
o Stretch R in A, V, PA
Effect of decr BP on CNS
activation of symp + suppression of psymp => incr HR, contractility, arterial + venous vasoconstriction, renin release, Na retention
Effect of incr BP on CNS
carotid + Ao baroR => nucleus solitarius in brainstem => vagal nucleus => vagal stimulation => symp inhibition => decr HR and inotropy => decr CO => decr BP
o Expected reflex bradycardia in acute incr BP
o Carotid sinus massage can also initiate response
What are the neurotransmitter of symp system
Norepinephrine (NE): stimulates
* Myocardial B adrenergic R => incr HR
o HR decr after initial transient incr because pressure sensitive control mechanism
* Vascular A adrenergic R => vasoconst
* Formed in variscosities of terminal nerves
o Dopa + dopamine => amino acid tyrosine
Epinephrine: stimulates
* Myocardial B adrenergic R => incr HR
* Vascular B adrenergic R => vasodilation
o Overall effect: incr systolic BP and decr diastolic BP = stable mean BP
o = incr CO + incr limb blood flow
Type of R of symp system
A adrenergic R
* A1 = vascular SM¢ => vasoconstriction
o Postsynaptic receptors (sarcolemma)
* A2 = adrenergic nerve terminal => inhibit NE release
o Feedback inhibition of its own release
o Presynaptic receptors
B adrenergic R
* B1 = heart => incr contractility + HR
* B2 = sinus node => incr HR
= vascular SM¢ => vasodilation
* B3 = decr contractility
A2 = adrenergic nerve terminal => inhibit NE release
Signaling of symp system once R activated
NE bind to B adrenergic R => stimulatory G protein => activates adenylate cyclase => conversion of ATP => cAMP
* incr opening of Ca2+ channel => promotes Ca2+ entry
* incr release of Ca2+ by SR => incr [Ca2+] => incr contractility
In sinus node: cAMP icnr rate of spontaneous pacemaking
Modulation of symp system
Stimulate NE release: AngII
Inhibit NE release: adenosine, NO, incr psymp activity
Overall adrenergic effect on vascular bed
A1 effects of NE opposed to B2 effects of EPI
NE can stimulate B2 as well
* Major vasoconstrictive effect via A1 because
o A1 anatomically closer vs B2
o # of A1 receptors > vs B2
NT of psymp syst
Ach
R and signal trasmission of psymp syst
- Activation via muscarinic/cholinergic R
o Inhibitory G protein => decr adenylate cyclase activity => decr cAMP
decr contractile force
Effect of psymp activation on SA node
decr rate of depolarization
o Directly inhibit SA node + indirectly via decr cAMP formation
o Act on inward rectifying K+ channels
Effect of psymp activation on vascular SM cells
o Bradykinin release => vasodilation
o Inhibit NE release => indirect vasodilation
Vasoconstrictives hormones
Ang II
Vasopressine/ADH
ET1
Ang II effect on circulation
o Sympathetic activation + baroR in renal vascular bed => renin release => cleave to angiotensinogen => angiotensin I => angiotensin II
o Act on 2 receptors (AT1 and AT2)
Heart: AT2/AT1 ratio = 2/1
* Positive inotrope
* Stimulate myocardial hypertrophy
Vasculature: AT1 => vasoconstriction
incr symp activity: block reuptake + facilitate release of NE
Stimulate secretion of aldosterone => incr Na + H2O retention => incr preload
Vasopressine effect on circ
o Secreted by posterior pituitary gland
OsmoR in hypothalamus
* Dehydration => incr blood osmolality => ADH secretion => incr H2O reabsorption (V2)
Ang II triggered => decr BP or CHF => atrial R => vasoconstriction (V1)
o Receptors: V1 and V2
V1 => vasoconstriction
V2 => renal H2O retention
ET1 effect on circ and R
o Released by endothelial ¢: ET1 produced by vascular endothelium
Potent vasoconstrictor, incr HR, contractility, hypertrophy
Increased by NE and AngII
o Receptors: ETA and ETB
ETA: affinity ET1+ET3>ET2
ETB = equal affinity
NO synthetized by
by endothelial ¢
o From A.A L-arginine + O2
o Action of NO synthetase enzyme => activated by incr [Ca2+]
2 endothelial forms:
* Constitutive: constant production under normal conditions
o Activity is Ca2+ and calmodulin dependent
o Stimulated by Ca2+ release from SR storage
* Inducible: low basal activity in normal conditons
o Activation is Ca2+ independent
o Stimulated by inflammation by bacterial endotoxins/cytokins: TNF, IL
Co-factors: O2, NADPH, tetrahydrobipterin, flavin adenine nucleotide
NO signaling
- Paracrine + autocrine signaling
o Only act locally => limited circulating ½ life
Superanion w high affinity for NO => decr bioavailability
o Diffuse in adjacent vascular SM¢ => activate guanylyl cyclase => incr cGMP => vasodilation
Induce vasodilation by
* Inhibit Ca2+ entry => decr [Ca2+]
* Activate K+ channels => hyperpolarization
* Stim cGMP dependent PK => activate myosin light chain phosphatase
PDE5 rapidly inactivate cGMP in physiologic conditions
Vascular ations
o Direct vasodilation: flow dependent, R mediated
o Indirect vasodilation:
decr vasoconstrictor influences (Ang II, adrenergic)
Mediate psymp induced vasodilation
* incr Ach release from nerve terminal
* decr NE release
o Anti thrombotic effect => inhibit platelets adhesion
o Anti inflammatory effect => inhibit leuco¢ adhesion
o Anti proloferative effect => inhibit SM¢ hyperplasia
NO release triggered by
o Adenosine, Ach, bradykinin, substance P
R linked to R-operated Ca2+ channels
o Shear stress: stretch sensitive Ca2+ channels
Exogenous source of NO
Nitrates
* Short lived free radical => enzymatic release of NO => cGMP stim => decr Ca2+ => vasodilation
o Chronic use => tolerance
Prolonged therapy: formation of peroxynitrite => decr NO synthase activity
* Coronary + peripheral vasodilatory effects
o Preferentially dilates large arteries => decr afterload
o Venodilation => incr venous capacitance => pooling of blood => decr venous return => decr preload
Better venodilator
* Antiaggregatory effects: reverse platelet aggregation via classic pathway
