6. Catecholamine Receptors

Question 1

Alpha 1

Answer 1

Heart, blood vessels, GI SM, liver, radial muscles of eye, sweat glands, ejaculation, prostate, bladder sphincter
Gq/11 -> PLC
1) IP3 -> [Ca2+]
2) DAG -> PKC
-> Vasoconstriction, bladder sphincter closure, glycogenolysis, GI relaxation

Question 2

Alpha 2

Answer 2

Autoreceptors, blood vessels, GI sphincter, GI glands
Gi/o
1) BY -| VGCC
2) Ai -| cAMP -| PKA -| VGCC
Prevents neurotransmitter release
Platelet aggregation
Vasoconstriction
Decrease gland activity

Question 3

Beta 1

Answer 3

Heart, GI SM, kidney
Gs -> cAMP -> PKA
1) Ih current activation by cAMP -> increase heart rate
2) MLC kinase phosphorylation -> inactivation -> contractility
3) VGCC activation
4) Phosphorylation of L-type calcium channels
Increase heart rate and contractility, relaxation of GI tract

Question 4

Beta 2

Answer 4

Skeletal and cardiac vessels, Gi smooth mm, Liver, Ciliary mm, skeletal mm
Gs -> cAMP -> PKA
1) Ih current activation by cAMP -> increase heart rate
2) MLC kinase phosphorylation -> inactivation -> contractility
3) VGCC activation
4) Phosphorylation of L-type calcium channels
Increase heart rate and contractility, relaxation of GI tract

Question 5

Adrenaline

Answer 5

A2 > A1 > B1 > B2

Physiological antihistamine - used in anaphylactic shock

Question 6

Phenylephrine

Answer 6

A1 Receptor Agonist

Raises blood pressure in acute hypotension

Question 7

Clonidine

Answer 7

Slightly A2 selective Receptor Agonist

Antihypertensive

Question 8

Xylazine

Answer 8

A2 selective Receptor Agonist

Used as a veterinary sedative due to CNS effects

Question 9

Isoprenaline

Answer 9

Beta Receptor Agonist

Previous use in asthma treatment (but B1 related tachycardia was problematic)

Question 10

Salbutamol

Answer 10

B2 Selective Agonist, long acting

Used preventatively for asthma

Question 11

Dobutamine

Answer 11

Selective B1 Agonist

Used in acute cardiogenic shock (heart failure) as it has an inotropic effect

Question 12

Prazosin

Answer 12

Selective A1 Antagonist

Used in hypertension

Question 13

Phentolamine

Answer 13

Non selective Alpha Antagonist

Reflex tachycardia

Question 14

Atenolol

Answer 14

Beta 1 Blocker
Used with phenoxybendazole (irreversible alpha antagonist) to combat large release of catelcholamine release following surgery
Used in

Question 15

Labetalol

Answer 15

Combined alpha and beta blocker
Used to treat hypertension in pregnancy
Four isomers with different activity

Question 16

Yohimbine

Answer 16

Alpha 2 selective antagonist

Question 17

Idazoxan

Answer 17

Alpha 2 Receptor Antagonist

Question 18

Propanolol

Answer 18

Non selective beta antagonist

Past use as an antihypertensive - no longer due to bronchoconstriction