ACE Inhibitors (Dawes) Flashcards
Describe the physiological effects of the RAAS system
Renin-angiotensin-aldosterone system
1) Regulates…
- Blood pressure
- Intravascular volume/Na+/K+
- Fetal development
2) Juxtaglomerular cells
- produce circulating renin
3) Renin-angiotensin-aldosterone system can also be l_ocally produced_ via myocardium, vascular endothelium, adrenal (drugs target both the local systems and the renal system)
Describe the pathophysiological effects of RAAS
RAAS has increased activity in congestive cardiac failure (CCF) and hypertension.
‘Because increased amounts of angiotensin can cause increased vascular tone, thus vasoconstriction.
It is also involved in _congestive heart failure (CHF) progressi_on.
It has adverse c_ardiovascular effects._
- Cardiac hypertrophy
- Atherosclerosis development and plaque rupture
- Pro-inflammatory/pro-oxidant (pro-oxidant effect can kick start atherosclerosis and deposition of collagen)
RAAS has close relationship with s_ympathetic nervous system_
Describe the RAAS pathway
Renin is produced by juxtaglomerular apparatus of the kidneys. Renin converts angiotensinogen to angiotensin I. Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE).
- ACE also break down bradykinin to inactive fragments.
Angiotensin II is vasoactive molecule, can bind to both type 1 (AT-1) and type 2 (AT-2) receptors
- Type 1 receptor is responsible for aldosterone secretion, vasoconstriction, classic angiotensin actions
- Type 2 receptor is responsible for antagonistic effect to type 1 receptors, anti-proliferative effects.
Conversion of AT-I to AT-II isn’t just by ACE, but also by other proteases including chymase, trypsin and cathepsin
Production of aldosterone have negative feedback, which inhibit production of renin.
What pathway does the ACi inhibit and what pathway does the AIIA inhibit?
What are the effects of Angiotensin II?
Angiotensin II is vasoactive molecule, can bind to both type 1 (AT-1) and type 2 (AT-2) receptors
- Type 1 receptor is responsible for aldosterone secretion, vasoconstriction, classic angiotensin actions
- Type 2 receptor is responsible for antagonistic effect to type 1 receptors, anti-proliferative effects.
- Conversion of AT-I to AT-II isn’t just by ACE, but also by other proteases including chymase, trypsin and cathepsin*
- Production of aldosterone have negative feedback, which inhibit production of renin.*
What are the consequences of ACE inhibitors?
ACE inhibitors inhibit angiotensin converting enzyme
- Decrease activities of angiotensin II (and aldosterone)
- Increase plasma levels of bradykinin (decreased breakdown of bradykinin)
- Change concentration of other vaso-active peptides
What is the role of bradykinin?
Bradykinin is an inflammatory mediator. It is a peptide that causes blood vessels to dilatE
Describe the role of Angiotensin II antagonists
AT-II antagonists inhibit solely angiotensin II type 1 (AT-1) receptors. They have suffix –sartan.
- Decrease activities of angiotensin II (and aldosterone)
- Inhibit type 1 receptors, and augment type 2 receptors, leading to higher beneficial effects
Describe the negative feedback mechanism of ACE inhibitors and Antgiotensin II antagonists
They also block negative feedback mechanism of aldosterone.
- This leads to an i_ncrease in renin_ activity.
- This augments conversion of angiotensinogen to angiotensin I
- Angiotensin I undergoes a shunt pathway mediated by ACE2 to produce increased angiotensin-(1-9), which have antihypertensive and anti-proliferative effects (beneficial).
What are some pathophysiologic effects of AT-II that are blocked by ACE inhibitor and AT-11 antagonists?
1) Cardiac myocytes
2) Fibroblasts
3) Peripheral Arteries
4) Coronary arteries
Blocked By ACE Inhibitor And AT-II Antagonists
What are some pathophysiologic effect of AGII that are blocked by ACE inhibitor and AT-11 antagonists?
1) Cardiac myocytes
2) Fibroblasts
3) Peripheral Arteries
4) Coronary arteries
Decreased Production Caused By ACE Inhibitor And AT-II Antagonists
What are the benefits of ACEi?
1) Initially
2) Later
Angiotensin Converting Enzyme (ACE) Inhibitors and Angiotensin II Receptor Antagonists
Plasma effects in first few weeks include:
- Decreases AT-II concentration
- Decreases aldosterone concentration
- Increases a_ngiotensin-(1-7_) and angiotensin-(1-9)
But later…
- Start to increase circulating [AT-II] and [aldosterone] due to c_hymase activity_ (not inhibited by ACE inhibitors)
- Negative feedback(?)
- Unknown local tissue levels? Other vasoactive peptides
-
Increases bradykinin (ACEi long term beneficial effect), which augments endothelial function by increasing NO production
- Vaso-relaxation
- Increases endothelial function
Name a common ACE inhibitor
- Cilazapril 0.5-5mg od (used in NZ)
Name a common Angiotensin Antagonist
- Candesartan 4-32mg od (used in NZ) (renal 60% excretion, bile 40% excretion)
What are the pharmacodynamics of ACEi and AHA?
-
Vasodilatation
- Decreases arterial and venous pressure
- Decreases ventricular preload (end diastolic volume) and afterload (stress in LV wall during ejection)
-
Decreases blood volume (therefore decreases preload)
- Natriuresis (aldosterone helps Na+ retention and K+ excretion, therefore aldosterone inhibition leads to natriuresis)
- Diuresis
-
Decreases sympathetic activity
- This is important because these drugs also act as a vasodilator. If you give a normal vasodilator, heart respond by increasing HR and SV via SNS. However, SNS is inhibited by these drugs.
- Decreases cardiac and vascular hypertrophy
What are the Contraindications of ACEi and AIIA? (Cautions with use)
- Hyperkalaemia
- Renal impairment
- _Volume deplete/_diuresed patients
- _Bilateral renal artery stenosis **_(absolute contraindication)
- Efferent arteriole is normally under vasoconstrictive tone mediated by AT-II, which sets up pressure gradient to help filter blood in glomerulus
- If there is bilateral renal artery stenosis in afferent arterioles, it will reduce renal perfusion over time, which decreased pressure gradient. This is sensed by pressure sensors, leads to more AT-II production to increase efferent arteriole tone (to maintain gradient).
- If ACEi or AIIA is given to bilateral renal artery stenosis, increased compensatory efferent tone is antagonized, which causing decreased pressure gradient and decreased renal perfusion, hence deterioration of renal function = AKI
- _Pregnancy **_(absolute contraindication) (ACEi/AII crosses placenta)
