Endothelium and Nitric Oxide (Prof Khan) Flashcards
Describe intrinsic local blood flow control factors
Originate from the vessel itself or surrounding tissue- Endothelial fators, myogenic mechanisms, local hormones (bradykinin, histamine), metabolic by-producs/hypoxia.
Describe extrinsic blood pressure regulation factors
Originate from outside of the organ or tissue in which the blood vessel is located- sympathetic nerves and circulating Ang II.
List the 8 main functions of the endothelium
1) Diffusion/permeability barrier
2) Regulate homeostasis and immunogenic processes
3) Regulate vascular tone
4) Regulate inflammation
5) Regulate oxidative stress
6) Regulate vascular growth/remodelling
7) Sense shear and tangential stress
8) Modulates vasoactive substances
Describe laminar blood flow
Blood in the centre of the blood vessel travels with least peripheral resistance
How does endothelium react to blood flow
Detect direction of blood flow and the endothelial cells move according to which way the blood flows (the endothelial cells move compared with no flow, 6 hours of flow and then 24 hours of flow)
List some risk factors for endothelial damage
Vasospasm, DM, hyperlipidaemia, HF, hypertension, inactivity, adiposity, oxidative stress, inflammation/infection and passive smoking
List the two main types of endothelium-derived chemicals and what molecules are included in these
1) Vasodilators: Endothelium-derived relaxing factor; nitric oxide, prostaglandins (PGI2, PGE2) and endothelium-derived hyperpolarising factor (CO, EETs, H2O2, NO and PGI2.
2) Vasoconstritors: Endothelin and prostanoids (thromboxane, PGG2 and PGH2.
How do they test the effects of ACh on the vascular wall
ACh was shown to relax a strip of aorta precontracted with noradrenaline. This is done with an arterial sample organ bath.
List the three types of nitric oxide synthase
- NOS I: Neuronal (nNOS): in neurons
- NOS II: Inducible (iNOS): Macrophages, neutrophils, fibroblasts, VSMC
- NOS III: Endothelial (eNOD): Endothelial cells, cardiac myocytes, osteoblasts, osteoclasts, airway epithelium
What is the chemical reaction that forms nitric oxide
L-arginine, NADPH and O2 react with nitric oxide synthases to produce NO, NADP and L-citruline
Subcellular locations of nNOS, iNOS and eNOS
nNOS = Largely cytosolic iNOS = Cytosolic eNOS = Membrane bound
Regulation of expression of nNOS, iNOS and eNOS
nNOS = Constitutive
Upregulated by SEX hormones and after nerve injury
iNOS = Not normally present
Expression induced by cytokines/endotoxins
eNOS = Constitutive
Upregulated by sex hormones and shear stress
Which NOS types are calcium calmodulin binding dependent
nNOS and eNOS are both activated when calcium is above a normal resting concentration of the cells
Major function of nNOS, iNOS and eNOS
nNOS = Neuronal messenger, cell communication
iNOS = Immunocytotoxicity
eNOS = Relaxation of vascular smooth muscle
What are the actions of NO
1) Scavenged by O2 to form OONO > Nitrate (NO3)
2) Combines oxyhaemoglobin
3) Activates guanylate cyclase in VSMC
4) Lowers intacellular calcium by SERCA uptake into intracellular stores in VSMC
5) Indirect effects: Inhibits PDE, inhibits ET-1 and inhibits renin release
Actions of NO via cGMP
- Stimulate sodium potassium ATPase causing hyperpolarisation
- Inhibits Rho kinase causing reduced contraction
- Modulate calcium
Role of calcium in muscle contraction
1) Increased calcium
2) Increased CaM
3) This changes MLCK to MLCK CaMCA2+
4) This turns mysoin into myosin P
5) To contract, myosin-P binds with actin to form actomyosin-P
Describe local changes in calcium
1) Calcium sparks-activated by calcium entry through VGCC
2) Calcium sparks caused by coordinated opening of RyRc
3) Calcium sparks acts as positive feedback to increase smooth muscle contractility
4) A lot more…
Actions of NO on calcium
- Downregulating IP3 formation (inhibits PLC)
- Decreasing calcium mobilisation through IP3 receptor
- Promoting calcium sequestration in SR
- Reducing calcium influx
- Increasing calcium efflux
Examples of NO donor drugs
Sodium nitroprusside, diethylamine/NO and diethylenetriamine and S-nitrosothiols
CV agents modulating endogenous NO bio activity
- ACEi
- Calcium channel blockers
- Statins
- Beta blockers
- Phosphodiesterase inhibitors
Examples of NO synthesis inhibitors
- Asymmetric dimethylarginine (ADMA)- This is naturally occurring
- Arginine analogues:
1) NG-monomethyl-L-arginine (L-NMMA)
2) NG-nitro-L-arginine methyl ester (L-NAME)
Describe endothelium-derived hyperpolarising factor
Causes an increase in endothelial calcium and activates endothelial SK and IK calcium channels
Describe hyperpolarisation of endothelial cells
Spread to SMC (via gap junctions) and activtaes SMC sodium potassium and/or potassium channels
Describe endothelin
ET1, 2 and 3 are produced on demand through mRNA synthesis. Is induced by Ang II, adrenaline, hypoxia and oxLDL. Is inhibited by shear stress, NO and PGI2
What pathway does endothelin cause vasoconstriction
IP3 pathway
Describe the lead up to ET-1
Pre-pro-ET-1 -> Big ET-1 -> ET-1
What receptors are expressed on the endothelium that initiate ipro-inflammatory signalling pathways
Toll like receptors
Describe TLRs
- TLRs control cytokine production
- Healthy arteries express low levels of TLR2 and 4
Deletion of TLRs prevent what
Atherosclerosis
How to assess endothelial function
- An endothelial -dependent vasodilator (ACh, substance P, bradykinin, serotonin)
- This causes a dilation via the endothelium
- Then a nitrovasodilator is given (GTN or SNP) and this donates NO directly (out with use of endothelium)
What does TLR signalling in macrophages activate
Mitogen and stress-activated protein kinase MSK1 and MSK2
What do MSKs promote
Transcription of genes with anti-inflammatory functions (IL-10 and IL-1 receptor antagonists)
