Adrenoreceptors Actions + Mechanisms

Question 1

A1 receptor

• location
• action when stimulated
• mechanism

Answer 1

Vascular smooth muscle,
Vasoconstriction

Gq- coupled phospholipase C activated- IP3 activated —-> Ca2+ increased.

Question 2

A2 receptor

• location, action, mechanism

Answer 2

Widespread through nervous system

Sedation/ analgaesia/ attenuation of sympathetically mediated responses

Decreases cAMP (via Gi-coupled cyclase activation)

Question 3

B1 receptors

- location, action, mechanism

Answer 3

1. Platelets - platelet aggregation
2. Heart - positive ionotropic, and chronotropic (increase contractility and HR)

(Increase cAMP) Gs- coupled adenylate cyclase activated

Question 4

B2 receptors

• location, action, mechanism

Answer 4

Bronchi, heart, vascular smooth muscle, uterus

Relaxation of smooth muscle

Increased cAMP -> increases Na/K ATPase activity and causes hyperpolarisation.

(Gs- coupled adenylate cyclase activity)

Question 5

B3 receptor

-location, action, mechanism

Answer 5

Adipose tissue

Lipolysis

Increase cAMP (Gs-coupled adenylate cyclase activated)

Question 6

D1 receptor

• location, action, mechanism

Answer 6

1. CNS - modulated extrapyramidal effects
2. peripherally - vasodilation of renal and mesenteric vasculature

Increase cAMP (via Gs-coupled adenylate cyclase activation)

Question 7

D2 receptor

• location, action, mechanism

Answer 7

1. CNS - reduced pituitary hormone output
2. Peripherally - inhibit further noradrenaline release

Decrease cAMP (via Gi- coupled adenylate cyclase inhibition)