Ionotropes & Vasoconstrictors Flashcards
(25 cards)
A1 stimulation:
- location of receptor
- action when stimulated
- mechanism
- located in vascular smooth muscle
- vasoconstriction
- Gq-coupled phospholipase C activated: increases IP3: increases CA2+
Reflex bradycardia through baroreflex (increased SVR)
B1 stimulation
Iontropy; especially in chronically failing hearts.
Vasodilation in splanchnic and skeletal muscle beds.
B2 stimulation
iontropy, arterial smooth muscle dilation
Adrenaline
- Adrenergic drug
- A1, A2, beta-receptors
CVS:
Low dose- beta effects: increased CO, increased myocardial O2 demand, lowers arrhythmia threshold and coronary artery dilation.
High dose/ bolus/ infusion- alpha effects: increase SVR
Noradrenaline
- A1, B1
- vasoconstrictor and increases vascular tone
Powerful iontrope with potent B1 activity
Isoprenaline
- b1, b2
- powerful iontropy that results in unfettered tachycardia, no vasoconstriction.
- used to treat bradycardia
Salbutamol
- b2
- treat bronchospasm
Dopamine
- natural catecholamine
- ## A1, B1
Dobutamine
- A1, b1
- relatively selective B1 agonist, causes less tachycardia for given iontropy given A1 activity.
- causes bradycardia indirectly through baroreflex.
Dopexamine
- B1
- splanchnic vasodilation through B1 and dopaminergic receptors
What are inodilators?
Drugs that enhance adrenergic activity through phosphodiesterase inhibition.
Ie. Milrinone and Exoximone
Enhance and restore b-adrenoreceptor function
Levosimendan
?class of drug
?action
- class of iontropes and inodilators
- calcium sensitiser for myocardium
- binds to Troponin C, stabilises the complex and inhibits Troponin I - improves myocardial contraction.
- vasodilation due to antagonism of ATP-K+channel and PDE3 inhibitor
- increases cardiac output
V1 Receptor effect
- vasoconstriction, especially in the gut, skin and skeletal muscle and platelet aggregation
V2 receptor effect
Opens aquaporin channels in renal collecting duct, reduces urine volume
Releases Von Willebrand factor
V3 receptor effect
Mainly CNS activity including ACTH release
Main functions of vasopressin (physiology)
- regulates plasma osmolality
- when plasma osmolarity increases, plasma vasopressin conc increases in step
But
When blood volume reduces there is little effect until loss is significant - at least 10% loss after which plasma vasopressin conc increases exponentially.
Uses of Terlipressin
management of bleeding from oesophageal varices
- vasoconstriction
- reduces portal venous pressure by splanchnic vasoconstriction
Vasopressin uses
- receptors are not found in pulmonary vasculature
- Vasoconstrictor of choice in patients with pulmonary hypertension.
- Haemorrhagic shock, cardiac arrest, hypotension after cardiac surgery, sepsis
Desmopressin uses
Treatment of diabetes insipidus of extrarenal origin
Hydrocortisone uses in CVS physiology
Hypertensive effects of A1 stimulation fades in sepsis and other shock conditions, but hydrocortisone has shown to improve responsiveness to A1 agonists.
Methylene Blue uses
Can restore vascular tone in certain circumstances;
Excess Nitric oxide causes vasodilation and hypotension in sepsis, methylene blue inhibits second messenger guanylate cyclase in nitric oxide vasodilation.
Causes methaemoglobinaemia in high doses 4mg/kg
Phosphodiesterase inhibitors effect on blood pressure?
Increase cardiac output due to the decrease in SVR usually leads to reduction in blood pressure.
Therefore increases blood pressure.
Patient with poor LVF, is hypotensive after cardiac bypass, which drugs appropriate to give immediately?
Adrenaline and Noradrenaline for B1 and B2 activity, need to increase myocardial contractility and cardiac output immediately.
In patient who is hypotensive with poor LVF what supplemental therapy maybe appropriate?
(Methylene blue, vasopressin, noradrenaline, milrinone, levosimendan)
a PDE inhibitor would enhance response to adrenaline eg Milrinone but vasodilation May become a problem.
Levosimendan - added iontropic effect.
