Physiology of the vasculature

Question 1

Give three causes of hypertension

Answer 1

Secondary to CHD

Volume overload in circulation (Valve defects)

Pressure overload (narrowed valves or pH)

Question 2

What is Raynaud’s disease

Answer 2

Inappropriate vasoconstriction of smaller arteries/ arterioles

White, then blue fingers, then redness due to reactive hyperaemia after return of blood flow.

Severe cases cause ulceration and gangrene

Treated with vasoactive therapies

Question 3

Give the structure of the artery wall

Answer 3

Tunica externa, media and intima

Smooth muscle sits within the tunica media.

Question 4

What is the importance of endothelium in heart disease

Answer 4

Dysfunctional/ activated endothelium lead to CV disease.

Question 5

What is the glycocalyx

Answer 5

Layer on top of the endothelium made up of carbohydrate chains that stick out. These act to prevent cells adhering to molecules on the endothelial surface.

Question 6

How is the glycocalyx implicated in activated/dysfunctional endothelium

Answer 6

Results in glycocalyx shedding, this is an important response for inflammation and healing. It also represents the initial stage of atherosclerosis

Monocytes are able to bind and translocate across the epithelium. Once inside the artery wall they begin engulfing lipids and initiating atherosclerosis.

It also disturbs blood flow

Question 7

Outline the steps of vascular smooth muscle contraction

Answer 7

Rapid Ca influx, Ca interacts with calmodulin which activates mysoin light chain kinase (MLCK)

MLCK phosphorylates inactive myosin which can then interact with actin leading to crossbridge formation and contraction.

Myosin phosphatase inactivates myosin

in smooth muscle myosin needs to be phosphorylated to be active and the phosphatase is always active.

Question 8

What alternative ways are there to cause smooth muscle contraction

Answer 8

Receptors that activate 2nd messengers like IP3, these act on channels at the SR and cause Ca depletion from intracellular stores.

Question 9

Give 5 non calcium channel receptors that increase Ca

Answer 9

Endothelin A/B

TP (Prostanoid)

AT1 (Angiotensin)

Histamine

Noreadrenaline

All are GPCRs

Question 10

Give 4 examples of calcium channels

Answer 10

Voltage senstive (L-type)

Receptor operated (P2X)

TRP channels

Store operated (Ora1)

Question 11

How do K channels induce relaxation and give examples

Answer 11

K channels lead to K efflux which hyperpolarises the cell.
Hyperpolarisation reduces intracellular calcium. Calcium no longer activates MLCK - No active myosin so relaxation of smooth muscle.

Eg BK channels, SK channels, B-agonists (via By -G protein)

Question 12

How do Gs coupled receptors lead to smooth muscle relaxation and give examples

Answer 12

Gs coupled receptors lead to an increase in cAMP via adenylyl cyclase. High intracellular cAMP reduces Ca conc. Again this leads to a reduction in activated MLCK, then activated myosin

Question 13

How does nitric oxide lead to relaxation of cmooth muscle

Answer 13

Nitric oxide freely diffuses into smooth muscle and activates guanylyl cyclase, this increases cGMP which activates PKG.

PKG can directly inhibt the conc of intracellular Ca

OR it can activate myosin phosphatase which will inactivate MLCK

Question 14

What role does PDE have in smooth muscle relaxation

Answer 14

PDE hydrolyses cAMP and cGMP. If it was to do so then relaxation would be inhibited (PDE inhibitors can be used for this reason)

Question 15

Where is eNOS located

Answer 15

Epithelial cell caveolae

Question 16

What 3 mechanisms inhibit eNOS

Answer 16

1. Smoking
2. High glucose/ insulin: Insulin signalling activates AKT which phosphorylates eNOS, loss of IRS therefore causes dysregulation of NO
3. oxLDL depletes cholesterol from caveolae. This leads to a loss of eNOS

The overall effect of these is to increase BP

Question 17

How do endothelial derived prostanoids regulate smooth muscle contraction

Answer 17

ROS or increased calcium in endothelia activate COX1/2 activity.
This leads to an increase in the conversion of arachidonic acid to prostaglandin H2. PGH2 is the precursor to 3 proteins

1. ThromboxanA2
2. PGE2
3. PGI2

These have effects on vascular smooth muscle receptors.

Question 18

How does PGI2 (prostacyclin) regulate smooth muscle contraction

Answer 18

Acts on IP-R which activates AC leading to increased intracellular cAMP and relaxation

Question 19

How does PGE2 regulate vasoconstriction

Answer 19

Acts on EP-R (1-4) depending on which EP-R it binds depends on if it activates or inactivates the production of cAMP

Question 20

How does TxA2 regulate vasoconstriction

Answer 20

Acts on the TP receptor which induces PLC activation. This increases IP3 production and subesequent Ca and activation of myosin - contraction

Question 21

What role does PKA have in regulation of vasoconstriction

Answer 21

PKA can be activated by cAMP and leads to the activation of myosin phosphatasem inactivating myosin and relaxing smooth muscle

Question 22

How do endothelial derived endothelins regulate vasoconstriction

Answer 22

A stimulus (hypoxia, thrombin, Glucose) leads to the transcription of big endothelin. Big endothelin is converted to ET-1 by ECE (endothelin converting enzyme). ET-1 binds either ETA or ETB receptors. Both of these receptors activate PLC and lead to IP3 production, then calcium release which binds calmodulin and activates MLCK. This phosphorylates myosin and leads to its activation and subsequent contraction of smooth muscle.

Question 23

What is the feedback mechanism in place in endothelial derived endothelins

Answer 23

Endothelial cells express the ETB receptor. The ET-1 produced from big endothelin acts on the endothelial cells themselves. This increases intracellular Ca in the endothelia which stimulates the production of NO via eNOS. NO has two effects.

1. Inhibition of ECE
2. NO diffuses into vascular smooth muscle cells to induce relaxation.

Question 24

How does angiotensin II activity regulate vasoconstriction

Answer 24

Angiotensin I is converted to angiotensin II by ACE on endothelial cells. Angiotensin II binds AT1 on vascular smooth muscle cells. This has a long term and a short term effect.

Long term: Activation of MAPK - Long term VSM gene expression that makes it more contractile

Short term: PLC activation, IP3, Ca, Myosin activity

Question 25

What goes wrong in ageing and disease with respect to BP

Answer 25

1. Atherosclerosis - separates endothelial cells from vascular smooth muscle causing their dysregulation
2. Loss of glycocalyx
3. Calcification stiffens the artery
4. Loss of elastin stiffens the artery.
5. Reduced NO due to diet smoking and hypoxia

All these aid to an increase in BP

Question 26

Give examples of 3 NO donors and their uses

Answer 26

1. Glyceryl trinitrate (nitroglycerate) - treatment for angina. It is converted to NO rapidly by a mitochondrial aldehyde dehydrogenase enzyme. It increases blood flow to ischaemic heart muscle.
2. Nitroprusside - intravenously administered for hypertension
3. Inhaled NO - Used in severe pulmonary hypertension

Question 27

Give 3 examples of endothelial derived prostanoids and their uses

Answer 27

1. Iloprost - Stable analogue of PGI2 - acts on the IP-R which is Gs coupled - increases cAMP and decreases Ca and contraction. Used in pulmonary hypertension and Raynauds disease.
2. Epoprostenol - IP-R agonist with some uses in pulmonary hypertension
3. Corticosteroids - suppress formation of prostaglandins and prevent shock. Used in hypotension

Question 28

Give an example of an endothelin directed therapeutic.

Answer 28

Bosentan is an ETA/ETB inhibitor thats non specific to both receptors and is used in the treatment of pulmonary hypertension.

Question 29

Give examples of ACE inhibitors and their uses.

Answer 29

1. ACE inhibitors - Captopril blocks the active site of the ACE by competing with angiotensin I

Enalapril, Lisinopril - Better molecular fits than captopril. They require conversion to an active metabolite and is longer lasting.

Used in hypertension and heart failure but can cause hypotension, cough, protein urea

Question 30

Give examples of AT1 receptor inhibitors

Answer 30

The sartans e.g Losartan and valsartan

These lower BP by preventing the binding of angiotensin II to AT1

They also inhibit the production of angiotensin I at the level of the kidney.

Question 31

What are the targets of directly acting therapeutics.

Answer 31

1. Activation of adenylyl/guanylyl cyclases and K efflux channels
2. Deactivation of calcium channels and alpha adreno receptors.

Question 32

Give an example of a K channel agonist

Answer 32

Minoxidil, an anti hypotensive.

Diagoxide

Nicorandil

Question 33

Give an example of calcium channel blockers

Answer 33

Nifedipine, used for hypertension and Raynauds.

Verapamil, Diltiazam

Question 34

Why are SNS-acting drugs not commonly used in hypertension treatment

Answer 34

Rarely used due to the multiple severe side effects.

Question 35

Give an example of a PDE inhibitor

Answer 35

Sildenafil = viagra

Used for pulmonary hypertension

Don’t use with other treatments that increase NO. As none is being hydrolysed NO can cause dangerously low blood pressure.