Nor-adrenaline or Nor-epinephrine
Nor-adrenaline or Nor-epinephrine is the neurotransmitter released by the post ganglionic sympathetic neurons. It also constitutes 10-20% of the catecholamines content of adrenal medulla.
Pharmacological effects of Nor-adrenaline or Nor-epinephrine
Noradrenaline primarily acts on α1, α2 and β1 receptors and has little action on β2 receptors. Nor adrenaline and adrenaline are equipotent on β1 receptors. However noradrenaline is 2-10 times less potent than adrenaline on α receptors.
Effects of Nor-adrenaline on “Blood vessels”
Causes intensive vasoconstriction (α receptor mediated) and peripheral resistance in most vascular beds including cutaneous, mucosal splanchnic, hepatic, renal and skeletal muscle.
Unlike adrenaline, nor adrenaline decreases blood flow to skeletal muscles, because of predominal α action, rather than β2 action.
Effects of Nor-adrenaline on “Blood pressure”
Noradrenaline given either by slow infusion or bolus injection, causes dose related increase in blood pressure. Unlike adrenaline, noradrenaline does not produce the biphasic response.
Effects of Nor-adrenaline on “Heart”
Noradrenaline is a potent myocardial stimulant causes both positive inotropic and positive chronotropic effects (β1 action). Cardiac output is, however, unaffected or decreased due to decreased venous return as a result of predominant vasoconstriction.
In intact animals, there is reflex bradycardia due to stimulation of vagus through baroreceptor mechanism.
Effects of Nor-adrenaline on “Smooth muscles”
Noradrenaline causes relaxation of intestinal smooth muscles (α action) which is lesser than that produced by adrenaline. It has a negligible effect on bronchial smooth muscle (due to lack of action on β2 receptors). It contracts radial muscle of eye (α1 action) and produces mydriasis.
Metabolic effects of Nor-adrenaline or Nor-epinephrine
Noradrenaline produces hyperglycemia and other metabolic effects similar to adrenaline, but these are less pronounced.
Pharmacokinetics of Nor-adrenaline
Noradrenaline is ineffective when given orally due to rapid distribution in GI epithelium and liver. Absorbed noradrenaline is metabolised by MAO and COMT.
Side / Adverse effects of Nor-adrenaline
Similar to adrenaline, but less intensive in nature. Reduced blood flow to vital organs is the major danger with the neither use of nor adrenaline.
Contraindications of Nor-adrenaline
Should not be used during general anaesthesia with halogenated hydrocarbons.
Clinical uses of Nor-adrenaline
- Nor-adrenaline has only limited therapeutic value.
- It may be given as slow drip in hemorrhagic or burn shock, as it increases vascular resistance and blood pressure. However, decreased blood supply to the kidney is a limitation.
