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UPTAKE 2 (extra neuronal uptake) : CA are taken into other tissues.
COMT plays a major role in the metabolism of catecholamines particularly in liver.
Beta 1 agonists increase the HR, stroke volume and cardiac output.Beta 2 agonists decrease the total peripheral resistance.
EPINEPHRINECNS : Not significant when given IV because of poor penetration of BBB .PHARMACOKINETICS :Epinephrine, Norepinephrine and Dopamine – ORALLY INACTIVE Epinephrine and Norepinephrine are degraded by MAO and COMT of the intestine wall and liver
Alkaloid from the plant – ephedra vulgaris.Repeated injections produce tachyphylaxis.
Beta 2 agonists :Selectivity of the drugs is not absolute.Stimulation of the heart is the major adverse effect of this group.Beta 2 receptors are also seen in the skeletal muscle – tremors
UPTAKE OF CA :
It is an efficient mechanism after the
release of NE
Axonal uptake (Uptake 1 ) :
Transports NE at a higher rate than E.
Extra neuronal uptake (Uptake 2 ):
CA are taken into other tissues.
by two enzyme systems – .
NE after Uptake -1 into the axoplasm is
acted upon by
NE which diffuses into the circulation is
acted upon by , mainly in the liver
The major metabolites excreted in urine is
(Vanillyl mandelic acid)
Epi→ β1receptors on ventricular myocytes→
↑ force of contraction
Epi→ β1receptors at SA node →↑HR
Cardiac output is determined by heart rate and
CO = HR x SV
At low plasma
Epi, β2 effect
At high plasma
Epi, α1 effect
Arterial BP = CO x PVR
Low doses ↓ PVR (arteriolar dilation in skeletal muscle)
High doses ↑PVR
Acts on α1,α 2 and β1,β2.
Epinephrine increase the HR, systolic
BP and PP.
Its effects on diastolic blood pressure
depends on dose.
At low dose, β2 activation predominates
resulting in decrease of diastolic pressure
and TPR, although mean BP may not
At medium dose, increase in heart rate,
increase in mean blood pressure and
increase in pulse pressure due to both β1
and α1 receptor action.
It increases TPR and both diastolic and
systolic blood pressure.
Positive inotropic action results in increase
of pulse pressure.
Compensatory vagal reflexes tend to
overcome the direct chronotropic action
of NE -- reflex bradycardia may occur.
Beta agonists :β1 and β2
It cause a decrease in peripheral resistance,
a decrease in mean BP due to β2 receptor
action and a reflex increase in heart rate.
Systolic blood pressure does not fall
significantly as diastolic, due to β1 receptor
action, so the pulse pressure increases .
Epi at α1-
receptors on radial
smooth muscle →
Epi at B2-
• peristalsis is reduced, sphincters are
• detrusors relaxed, trigone contractedBladder
• contracts (alpha action), RBCs are pouredSplenic capsule
• neuromuscular transmission is facilitated.
(Tremors due to beta 2 actions)Skeletal muscle
• restlessness , tremors , fall in BP and
• hyperglycemia, lipolysisMetabolic :
• Relaxation at termUTERUS :
Dopaminergic neurons in brain, enteric nervous system
Moderate doses DA:
Stimulate DA receptors in mesenteric and renal vascular beds
Stimulate β1 receptors in heart →↑HR and ↑force of contraction
High doses DA:
Stimulate α1 receptors →vasoconstriction
• ↑ blood flow to kidney
• ↑ cardiac output
• Moderate doses ↑ cardiac
output without ↑PVR
Stimulates β1- and β2-adrenergic receptors, but at
therapeutic doses, β1-effects predominate
Increases force of contraction more than
increases heart rate
↑CO = ↑HR x ↑ ↑ SV
Refractory congestive heart failure
Acts directly on alpha and beta receptors and indirectly
Effective orally - resistant to MAO
Crosses the BBB – CNS stimulation.
Used in bronchial asthma and hypotension
Used occassionally as pressor
Selective alpha1 agonist
Topically as nasal
For producing mydriasis.
Open angle Glaucoma (by
constricting ciliary body
blood vessells IOP)
AE: Rise in BP, After
Used orally as decongestant of upper
respiratory tract, nose, eustachian tube.
Provides symptomatic relief in allergic rhinitis,
common cold, URTI.
AE: rise in BP
Naphazoline, Oxymetazoline, Xylometazoline
Topical nasal decongestants
After congestion less and are longer acting.
Regular chronic use can cause atrophic rhinitis
due to persistent vasoconstriction.
AE: rise in BP