Noradrenaline (norepinephrine)

• The sympathetic neurotransmitter in the effector organs.
• It is released from postganglionic fibres and activates both α and ß receptors.
• Infusion starting from 0.05 mcg/kg/min.

Adrenaline (epinephrine)

• Also activates the sympathetic receptors. It is synthesised in the adrenal glands and reaches the sympathetic receptors via the circulation.
• Infusion starting from 0.05 mcg/kg/min.
• At lower doses the inotropic Beta effects are more prominent, at higher doses the pressor alpha effects are more prominent.

Acetylcholine

• The neurotransmitter for the parasympathetic system is acetylcholine.
• This activates two types of acetylcholine receptors, nicotinic and muscarinic receptors.
• Nicotinic receptors are predominantly preganglionic, i.e. in sympathetic and parasympathetic ganglia (i.e. a synapse before the effector organ).
• Muscarinic receptors are postganglionic and are the receptors on effector organs.

Drugs that activate the sympathetic receptors, hence mimicking the activity of the sympathetic nervous system, are called sympathomimetics.