M1i: Adrenergic Receptors

Adrenergic Receptors
Adrenergic Receptors1

*The concentration of Isoprel necessary to activate an α receptor is so large, it can essentially be thought of as a pure β-agonist

α1 RECEPTOR: POST SYNAPTIC

  • G Protein: Gq
  • 2nd msg: stimulates PHOSPHOLIPASE C → ↑IP3 & DAG → opens Ca2+ channel
  • Location
    • Smooth m. → VC
    • Cardiac → weak +ve inotropy, weak -ve chronotropy
    • Metabolic → ↑BSL (inhibits insulin secretion, stimulates glycogenolysis & gluconeogenesis)

α2 RECEPTOR: PRE SYNPATIC (peripherally) & POST SYNAPTIC (CNS)

  • G Protein: Gi­
  • 2nd msg: Inhibits AC → ↓cAMP = ↓Ca2+
    • Opens K+ channels → membrane hyperpolarisation
  • Location
    • CNS = Post synaptic nerve terminals ↓ outflow
    • Peripheries = pre-synaptic nerve terminals inhibit NA release by -ve feedback
    • Platelets = ↓plat aggregation

β1 RECEPTOR: POST SYNAPTIC

  • G Protein: G5
  • 2nd msg: ↑AC → ↑cAMP → ↑Ca2+
  • Location
    • Heart = +ve inotropy, chronotropy, dromotropy
    • Metabolic = lipolysis = ↑FFAs & insulin
    • Renal = ↑RENIN by stimulating juxtaglomerular cells → formation AII → VC

β2 RECEPTOR: POST SYNAPTIC

  • G Protein: G5
  • 2nd msg: AC = ↑cAMP
    1. Cardiac cells → ↑Ca2+
    2. Smooth m. → inhibits MLCK
    3. Liver → activates glycogen phosphorylase
  • Location
    • Heart = ↑FoC
    • Smooth m. = relaxes smooth m. of uterus, bronchi, vessels
    • Skeletal m. = fine tremor

Adrenergic Receptor System Summary

Adrenergic Receptor System Summary