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Medsci305 > Lecture 6&7: Drugs Affecting The Vasculature > Flashcards

Lecture 6&7: Drugs Affecting The Vasculature Flashcards

0
Q

What are the main mediators sourced from the vascular endothelium?

A

Prostanoids - relaxes SM, inhibits platelet aggregation via activation of adenylate Cyclase.

Nitric oxide - relaxes SM via activation of Guanylate Cyclase. Especially important in resistance vessels. Also inhibits SMC proliferation, platelet adhesion and aggregation and monocytes adhesion and migration.

Peptides - e.g. Angiotensin II and endothelin are potent endothelium derived vasoconstrictor peptides.

Endothelium derived hyperpolarising factors.

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1
Q

What is the result of increased cAMP and cGMP in smooth muscle?

A

Increased levels of cAMP and cGMP cause relaxation.
CAMP causes MLCK to inactivate. It may also facilitate the calcium efflux pump to decrease intracellular calcium levels.

CGMP opposes the agonist induced increases in calcium

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2
Q

Which vasodilator substances act via endothelial NO production?

A

Acetylcholine and bradykinin. The NO is derived from arginine and produced when calcium concentrations increase in the endothelial cell.

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3
Q

How do nitrates cause smooth muscle relaxation?

A

By activating guanylate Cyclase to increase cGMP production. CGMP opposes the intracellular calcium levels.

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4
Q

What is renin?

A

Proteolytic enzyme secreted by the juxto glomerular apparatus in response to various physiological stimuli e.g. Fall in concentration in the distal tubule and fall in renal perfusion pressure.

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5
Q

What stimulates renin secretion directly?

A

Renal Sympathetic nerve activity
Beta adrenoreceptor agonistS
Prostaglandin I2

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6
Q

What inhibits renin secretion?

A

Angiotensin II and atrial natriuretic peptide.

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7
Q

What does renin act on?

A

Angiotensinogen to form angiotensin I

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8
Q

What is angiotensin converting enzyme?

A

Membrane bound enzyme found on the surface of endothelial cells, particularly abundant in the lung.

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9
Q

What is the role of ACE?

A

Converts angiotensin I to angiotensin II which is a potent vasoconstrictor.

It also inactivates bradykinin and several other peptides

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10
Q

What are the main effects of angiotensin II?

A

The main actions are mediated via receptors AT1 and AT2.

Generalised vasoconstriction, especially marked in the efferent arterioles of the kidney
Increased release of NA from sympathetic nerve terminals which reinforces vasoconstriction and increases rate and force of contraction of the heart,
Stimulation of proximal tubular reabsorption of Na+
Secretion of aldosterone from the adrenal cortex
Cell growth in the heart and arteries

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11
Q

How do l type calcium channel antagonists work on the vasculature?

A

They cause generalised arterial vasodilation although individual agents have distinct patterns of regional potency.

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12
Q

Where do dihydropyridines preferentially act?

A

Of the vascular smooth muscle

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13
Q

Where does verapamil act?

A

It also acts on the heart

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14
Q

Where does Diltiazem act?

A

On both the heart and vasculature

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15
Q

Which drugs activate potassium channels?

A

Cromokalim and minoxidil

16
Q

What is the mechanism of potassium channel agonists?

A

They relax smooth muscle by selectively increasing the membrane permeability to K+.
This hyperpolarises the cells and switches off the voltage dependent calcium channels resulting in reduced calcium levels to mediate relaxation of the heart.

17
Q

When is minoxidil used?

A

As a last resort in treating severe HT in unresponsive patients. It causes hair growth and marked salt and water retention so it is usually prescribed with a loop diuretic.

18
Q

Which drugs act via cyclic nucleotides?

A

Dopamine
Haloperidol
Nitroprusside

19
Q

What are the directly acting vasodilator drugs?

A

Calcium antagonists, (verapamil, nifedipine, Diltiazem)
Potassium channel agonists (minoxidil, cromokalim)
Drugs which influence the cytoplasmic cyclic nucleotide concentrations (dopamine, haloperidol, nitroprusside)

20
Q

How does dopamine affect the vasculature?

A

Dopamine has mixed vasodilator and vasoconstrictor actions. It selectively dilates renal vessels and increases cAMP by activating adenylate Cyclase. Dopamine is a precursor to noradrenaline.

21
Q

What is haloperidol?

A

Dopamine receptor antagonist

22
Q

What are the effects of dopamine on the heart?

A

Its effects result from agonist actions on the α- and β- adrenorceptors as well as the dopamine receptors.
Blood pressure increases slightly but the main effects are vasodilation in the renal circulation and increased cardiac output

23
Q

What is nitroprusside?

A

Powerful vasodilator which ears with tissue sulfhydryl groups under physiological conditions to yield NO.
It acts equally on arterial and venous smooth muscle however it can only be given intravaneously.

24
Q

Where do organic nitrates preferentially act?

A

They preferentially dilate the capacitance vessels and muscular arteries

25
Q

How do natriuretic peptides cause vasodilation?

A

They activate membrane bound form of guanylate Cyclase which is directly linked with natriuretic peptide receptors

26
Q

What are examples of natriuretic peptide drugs?

A

Anaritide, omapatrilat

27
Q

Which phosphodiesterase inhibitors are non selective?

A

Methylxanthines such as theophylline which are used in asthma
Papaverine

28
Q

What is the mechanism of methylxanthine?

A

They act in non vascular smooth muscle and the CNS. They are also purine receptor antagonists

29
Q

What is the mechanism of papaverine?

A

It is closely related to morphine however its main mechanism is to relax smooth muscles in blood and elsewhere involving a combination of PDE inhibiton as will as blocking of calcium channels

30
Q

What are the selective type II PDE inhibitors?

A

Milrinone, cilostazole.
These increase cAMP by blocking its break down.
They increase mortality in heart failure despite demonstrating short term heamodynamic improvement.

31
Q

What are the selective PDE type V inhibitors?

A

Sildenafil.This inhibits the breakdown of cGMP which allows penile erection to occur (as normally NO activates guanylate Cyclase to mediate relaxation for erection).

32
Q

What do the two main groups of indirectly acting vasodilator drugs inhibit?

A

The sympathetic vasoconstriction

RAAS

Medsci305 (17 decks)

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