Adenosine

Question 1

Where are Adenosine receptors found ?

Answer 1

It is a CNS neuromodulator, its receptors are mainly located in (specific A1):
-Brain
-Spinal cord
-Lungs
-Heart
-Testis
-Autonomic nerve terminals
(For type 2 Adenosine receptors, mainly : brain, lungs, heart &spleen)

Question 2

In depth explanations in terms of its receptors on the molecular level (coronary vessels example) ?

Answer 2

Adenosine receptors are bound to a G-protein, when Adenosine binds to it, a cascade of reactions is launched causing the production of Adenyl Cyclase, AMPc &Protein kinase.
All these 3substances bring about the opening of K+ channels, inducing K+ efflux which causes Hyperpolarisation &vascular relaxation.
Increased AMPc inhibits Myosin light chain kinase reducing Contraction in consequence.

Question 3

Adenosine in coronary vessels ? (sort of a repetition)

Answer 3

Adenosine receptors are coupled to G proteins, when adenosine binds to its receptor, a cascade of reactions in induced :
production of Adenyl Cyclase, AMPc &Protein Kinase –>
K+ Channels openning –>
K+ efflux (out of the cell) –>
Hyperpolarisation = Vascular relaxation

Question 4

Adenosine in pacemaker (meaning, in SA node : sinatrial node) ?

Answer 4

Chronotrope (-) et Dromotrope (-)

This mainly occurs in the AV node, so Adenoside is referred to as atrioventricular blocker.

Question 5

Adenosine in sympathetic nerve terminals ?

Answer 5

binding to purinergic receptors present on autonomic nerve terminals leads to inhibition of Nor-adrenaline release.

Question 6

Chronotrope ?

Answer 6

Frequence cardiaque

Question 7

Bathmotrope ?

Answer 7

Excitabilité cardiaque

Question 8

Inotrope ?

Answer 8

Contractilité cardiaque

La capacité des cellules cardiaques de se contracter en reponse au potentiel d’action.

Question 9

Dromotrope ?

Answer 9

Vitesse de la conduction de l’influx nerveux des fibres myocardiaques.

Question 10

Indication ?

Answer 10

A first-line diagnostic &therapy agent in the treatment of Supra Ventricular Tachycardia SVT
tachycadie supraventriculaire

Question 11

Adenosine comes in what form ?

Answer 11

Adenosine is always administered intravenously. Usual initial dose is at 6mg, 12 mg

Question 12

How is Adenosine administered ?

Answer 12

-Rapid bolus IV injection into the vein.
-or into an IV line : large-borne cannula, immediately followed by a flush; 20ml of 0.9% NaCl
(evidence is shown the cardiac monitor within 10-15 seconds)

Question 13

Duration of effect and half time in plasma ?

Answer 13

Adenosine has a duration effect that is very short due to the quick uptake by the cells, its half life is of 10 seconds.

Question 14

Important AE ?

Answer 14

Bradycardia &asystole (possibly)
deeply unpleasant feeling pf sinking in the chest, breathlessness &a sense of impending doom ( inevitably but briefly)

Question 15

Important cautions ?

Answer 15

Adenosine should not be administered to patients who cannot support its transient bradycardiac effects; patients with hypotension, coronary ischemia &decompensated heart failure
It induces bronchospasm in susceptible patients, so it should be avoided in asthma &COPD patients.

Question 16

Important interactions ?

Answer 16

Dipyridamole blocks cellular uptake of Adenosine (dose should be halved)
Theophyline, amynophylline &Caffeine are competitive antagonists of adenosine.