Adrenal Medulla – Epinephrine and Norepinephrine
Stimulation
1. Stimulation of sympathetic nervous system
2. Innervation of adrenal medulla by preganglionic sympathetic fibers by release of
acetylcholine
3. Medulloadrenal cells/Chromaffin cells/modified postganglionic neurons release
catecholamines into blood
Products – catecholamines: amine hormones, derived from tyrosine (hydrosoluble)
•Types and prevalence – synthesized by two different Chromaffin cells
◦Norepinephrine./noradrenaline- primary form
▪Adult – 20%
▪Dog/horse – 20-25%
▪Cat – 40%
▪Whale/hen/ fetus – more than epinephrine
◦Epinephrine/adrenaline – derived from norepinephrine
▪Adult – 80%
▪Dog/horse – 75-80%
▪Cat – 60%
◦Dopamine
•Half life - 2 minutes
•Location of synthesis, storage and secretion – adrenal medulla (chromaffin cells)
1. Passage of Tyrosine from blood to chromaggin cell due to sympathetic stimulation
2. Norepinephrine is synthesized in cytoplasm
3. Stress stimulates hypothalamus, which releases ACTH which releases Cortisol which comes
inside the chromaffin cell and synthesizes PNMT enzyme
4. Norepinephine enters neurosecretory granule of chromaffin cell, where it is transformed into
epinephrine
5. Sympathetic stimalation leads to release of Acetylcholine in synaptic cleft, which activates
nicotinic acetylchline receptors on chromaffin cell membrane
6. Na+ enters chromafin cell and triggers an action potential
7. Action potential activates Calcium voltage gated channel
8. Entrance of Ca2+ inside chromaffin cell allows release of epitnephrine of chromaffin
granules in blood
9. Epinephrine binding to different receptors for different responses
Alpha1 Alpha2 Beta1 Beta2
1. Binding of
epinephrine/norepinephri
ne
2. Activation of
phospholipase C
3. Cascade of action
4. Tissue response
1. Binding of
epinephrine/norepinephri
ne
2. Inhibition of adenylate
cyclase phosphorilation
of cAMP
3. No tissue response
1. Binding of epinephrine/norepinephrine
2. Activation of adenylcyclase which, in association
with ATP, phosphorilates cAMP
3. Tissue response
Contraction of vascular smooth muslce Relaxation of vascular smooth muscle, stimulation of
force of contraction and heart rate and metabolism
(beta 2)
10. When blood is saturated with epinephrine, it will associate with ATP, and bind to receptor on
chromaffin cell which will stimulate G protein action of closing voltage gated channels
