Drugs and the CVS: vasculature Flashcards
what is released by the SNS to cause vasoconstriction?
noradrenaline
name examples of VSM mediators that cause contractions by increasing [ca2+]
o AngII –>AT1r
o PGG2, PGH2 –>TP (T-prostanoid receptor).
o ET1 –> ETA/B
name examples of endothelial cell agonists that stimulate relaxation by increasing [ca2+]
o NO.
o CNP – C-Type Naturietic Peptide.
o PGI2.
o EDHF – Endothelial Hypopolarising Factor.
state the BP formula
CO x TPR
what vessel contributes the greatest to BP regulation?
arterioles
these exhibit vascular tone and are in a partial state of constriction
what state are arterioles in hypertensive patients in?
raised base vascular tone that increases TPR and therefore BP
what is hypertension the most important risk factor in?
stroke
main risk factor in MI and CKD
what is the overview of hypertension treatment?
o Step 1 – Single Therapy: Under 55 – ACEi or ARB (Angiotensin Receptor Blocker). Over 55, Afro-Caribbean – CCB or Thiazide diuretic.
o Step 2 – Dual Therapy:
ACEi and CCB.
ACEi and thiazide diuretic.
o Step 3 – Triple Therapy:
ACEi, CCB and thiazide diuretic.
o Step 4 – Symptomatic Relief:
- Low-dose spironolactone (diuretic therapy).
- alpha -blockade or beta-blockade.
how is hypertension defined?
a BP consistently higher 140/90 or higher
what stimulates the production of renin?
- reduced sodium reabsorption
- reduced renal perfusion pressure
- increased SNS stimulation
how does ANGII contribute to blood pressure?
- increases thirst sensation (so you drink more)
- activates the SNS
- vasoconstrictor
- salt +H20 retention via aldosterone
what drug eliminates ANGII? what also does it do?
ACEi e.g. enalapril
decreases ANGII production and increases Bradykinin (stops it breakdown by ACE)
less ANGII–> less vasoconstriction
more bradykinin–> more vasodilation
what are the uses of ACEi?
o Hypertension. o Heart failure. o Post MI. o Diabetic nephropathy. o Progressive renal insufficiency. o High CVS-disease-risk patients.
what is the suffix for ACEi?
-pril
what are the main two effect of ACEi in reducing hypertension?
(1) reduction of TPR
(2) reduction of sodium retention
how do ACEi reduce TPR in hypertension ?
accumulation of bradykinin and reduction in ANGII:
- less AT1R mediated vasoconstriction
- more bradykinin mediated vasodilation
how does ACEi reduce sodium retention in hypertension?
less Na+ retained:
- via blocked actions of ANGII on AT1R in the kidney
- therefore less aldosterone secretion due to blocked AT1R in the adrenal medulla
what are the effects of ACEi in heart failure?
(1) reduce TPR
(2) reduce preload
how do ACEi reduce preload in heart failure?
venodilation reduces preload
how do ACEi reduce TPR in heart failure?
- less vasoconstriction via AT1R in peripheral vasculature
- reduced TPR
- decreased after load on the heart so inotropic effects decreased
what drug stops ANGII having its effects?
Angiotension Receptor Blockade (ARB) e.g. losartan prevents binding to AT1 receptors on arteries, kidneys and adrenal cortex
what are the uses of ARBs?
- hypertension
- heart failure
why would an ARB be used over an ACEi?
ARB does not affect ACE so bradykinin is not spared:
- Bradykinin induces cough
- ACEi causes Bradykinin to accumulate causing the cough
what are the side effects of ACEi and ARBs?
Cough – ACEi increased bradykinin Urticaria/angioedema – ACEi rarely. Hypotension Hyperkalaemia Foetal injury Renal failure (in patients with renal artery stenosis)
why is hyperkalaemia a side effect of ACEi and ARBs?
no exchange of K+ occurs with the little Na+ present
Aldosterone has been reduced so K+ loss is not being stimulated
why should ACEi and ARBs not be used in renal failure patients with renal artery stenosis?
these patients cannot maintain adequate glomerular pressure, affecting their GFR (maintained by ANGII essentially)
the drug affects the afferent arteriole and exacerbates this problem by affecting glomerular pressure
what is the process outline involved with calcium in smooth muscle contraction?
o Membrane depolarisation opens VGCC.
o Ca2+ enters and binds calmodulin (CaM).
o Ca2+-CaM complex activates MLCK.
o MLCK mediated phosphorylation –> VSM contraction.
where do DHP selective and non-DHP calcium channel blockers bind (CCB) ?
DHP–> blood vessels
non-DHP–> heart and vessels
example of DHP aka non- rate slowing drug
amlodipine:
no effect on heart
prophylactic treatment of angina
example of non-DHP aka rate slowing drug?
verapamil:
has a negative inotropic effect
which CCB is preferably used in hypertension?
what may be an unwanted side effect?
amlodipine (DHP CCB) due to absence of inotropic effects on the heart
reflex tachycardia due to powerful vasodilation
how do DHPs reduce BP?
remember that DHPs are CCBs:
–>inhibit Ca2+ entry into VSMCs so less contraction of the cells
reduced TPR and therefore BP
what is the preferable treatment for those under 55?
why is this?
ACEi or ARB
- good patient adherence compared to other drugs
- this is due to fewer side effects
- not much difference in their reduction of BP
what is the preferable treatment for those over 55 or of Afro- Caribbean origin?
why is this?
CCB or thiazide diuretic
- they have low plasma renin activity so ACEi will be ineffective
examples of alpha blockers?
prazosin (alpha 1 ant)
phentolamine (non-selective ant)
what is the effect of alpha blockers?
block alpha 1 mediated vasoconstriction
what is the selectivity of prazosin and phentolamine?
prazosin- alpha 1 antagonist
phentolamine- Alpha1/ 2 antagonist
what is the effect of the non-selective nature of phentolamine?
non-selective alpha blocker:
binding to alpha 2 means it blocks NA release negative feedback so enhances NA release and the SNS response, leading to a non-reflex increase in HR.
What is the impact of contraction on arterioles in:
- radius
- resistance
- flow
radius decreases
resistance increases
flow decreases
vasoconstriction
what is the impact of vasodilation on arterioles in:
- radius
- resistance
- flow
radius increases
resistance decreases
flow increases
vasodilation
in what state do arterioles stay?
have a state of partial constriction (vascular tone)
what are the effects of Angiotensin 2?
- increased thirst (via SNS activation)
- vasoconstriction
- salt and water retention
- aldosterone secretion
what are the 3 reasons for renin release?
- low renal Na+ reabsorption
NB water moves with salt - low renal perfusion pressure
- sympathetic nervous system
define hypertension
what is hypertension the single most important risk factor for?
definition: consistently above 140/90 mmHg
strokes (causing 50% of ischaemic stroke)
25% heart failure
what is the ultimate aim for hypertension therapy?
reduce mortality from cardiovascular or renal events
what should be given for hypertension management for under 55?
ACEi or ARBs
what should be given for hypertension manage for over 55s or afro-carribeans?
CCBs or thiazide like diuretic
what is step 2 in hypertension management?
ACEi+ TLD
ACEi+CCB
ARB for afro-carribean
what is the last step in hypertension management in resistant hypertension?
consider further diuretics e.g. low dose spironolactone
consider beta or alpha blocker
what are the clinical uses of ACEi?
Hypertension Heart failure Post-myocardial infarction Diabetic nephropathy Progressive renal insufficiency Patients at high risk of cardiovascular disease
what effect does ATR-1 have?
angiotensin II receptor 1
- -> vasoconstriction
- -> sodium retention in kidney
what effect does bradykinin have?
vasodilation
name an angiotensin receptor blocker and is MoA
Losartan, Irbesartan
- block ATR1 so ANGII effects
- blocks renal and vascular effects
what are the clinical uses of Losartan (ARB)?
hypertension and heart failure
describe ARB and ACEi side effects
- Hypotension (both)
- Hyperkalaemia (both): take care with K+ supplements or K+-sparing diuretics; aldosterone promotes K+ loss so aldosterone inhibitors produce a hyperkalaemia.
- Foetal injury (both)
- Renal failure (in patients with renal artery stenosis; both) :Glomerular filtration is maintained by AngII so you need to be careful in renal failure patients.
- Usually very well tolerated (especially ARB)
- Cough (ACEi) very common
- Urticaria and angioedema (ACEi)
what is the mechanism of action of alpha blockers?
blocker alpha 1 mediated vasoconstriction (skin, mucosal membranes)
e.g. prazosin
why does alpha blockade lead to increased heart rate?
- a non selective alpha blocker like phentolamine (Alpha 1 and 2)
- blocks alpha 2 so no -ve FB on NA release
- enhanced NA effects–> SNS to the heart
- heart rate increase
NB this is not reflexive