DR Medhat MRCP

Example of GP-CR → Adrenergic receptors :
■ α-1 (Agonist → phenylephrine)
• Vasoconstriction
• Relaxation of GI smooth muscle
• Salivary secretion
• Hepatic glycogenolysis
■ α-2 (Agonist → clonidine)
• Mainly presynaptic : inhibition of transmitter release (inc NA, Ach from
autonomic nerves)
• Inhibits insulin
• Platelet aggregation
■ β-1 (Agonist → dobutamine)
• Mainly located in the heart
• ↑Heart rate + force
■ β-2 (Agonist → salbutamol)
• Vasodilation
• Bronchodilation
• Relaxation of GI smooth muscle
■ β-3 (Agonist → being developed, may have a role in preventing obesity)
• Lipolysis
• Pathway :
All are G-protein coupled
α-1: activate phospholipase C → IP3 → DAG
α-2: inhibit adenylate cyclase
β-1: stimulate adenylate cyclase
β-2: stimulate adenylate cyclase
β-3: stimulate adenylate cyclase
Second messengers :
• Cyclic AMP
o Activation of G-protein coupled receptors → activate this pathway.
o e.g Transmitters e.g muscarenic A.ch , GABA-B ,Adrenaline,nor adrenaline
Hormones : mnemonic→ Glucagon & GRH in FLAT CAMP
- Glucagon - FSH - LH -ACTH - TSH - CRH - MSH - PTH
- GRH - Calcitonin
• Phosphoinositides (IP3) AND/or Calcium
o E.g. mnemonic GTAG → GnRH , TRH ADH, Gastrin .
• Protein(tyrosine) kinase activity
o e.g. Insulin, growth hormone and factor, prolactin, oxytocin, erythropoietin.
• Cyclic GMP
o e.g. vasodilators → ANP, nitric oxide
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