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Nor adrenaline act on what sympathetic receptors

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norepinephrine adrenergic receptor affinity alpha1 alpha2 beta1 official pharmacology

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norepinephrine adrenergic receptors

Noradrenaline (norepinephrine) acts mainly on adrenergic sympathetic receptors:
  • α1 receptors: strong action
    Causes vasoconstriction and raises blood pressure.
  • α2 receptors: strong action
    Mainly presynaptic, reduces further noradrenaline release.
  • β1 receptors: moderate action
    Increases heart rate, contractility, and renin release.
  • β2 receptors: very little action
    So it produces minimal bronchodilation or skeletal-muscle vasodilation compared with adrenaline.
Summary: Noradrenaline is predominantly an α1, α2, and β1 agonist, with negligible β2 activity. Adrenergic receptor effects are mediated through α and β receptors on target organs, as described in Bailey and Love's Short Practice of Surgery, p. 7655-7672.

Isoprenaline

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isoproterenol adrenergic receptors

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isoproterenol nonselective beta adrenergic agonist receptor pharmacology

Isoprenaline (isoproterenol) is a non-selective β-adrenergic agonist:
  • β1: strong stimulation - increases heart rate and cardiac contractility.
  • β2: strong stimulation - causes bronchodilation and vasodilation in skeletal-muscle vessels.
  • α1 and α2: essentially no action.
So: Isoprenaline = β1 + β2 agonist, no significant α action. It may lower peripheral vascular resistance and arterial pressure because of β2-mediated vasodilation. Guyton and Hall Textbook of Medical Physiology, p. 2899-2900; Barash, Cullen, and Stoelting's Clinical Anesthesia, p. 2856-2860.
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