What is the Difference Between Adrenaline and Noradrenaline

The main difference between adrenaline and noradrenaline is that adrenaline/epinephrine is the main hormone secreted by the adrenal medulla whereas noradrenaline/norepinephrine is the main neurotransmitter in the sympathetic nervous system. Furthermore, adrenaline is the main factor which increases metabolism in preparing the body to stress or danger while noradrenaline is responsible for the reflexive changes in cardiovascular tone.

Adrenaline and noradrenaline are two types of hormones and neurotransmitters in the body responsible for the regulation of the homeostasis in order to prepare the body for stressful or dangerous situations by mediating the fight-or-flight response.

Key Areas Covered

1. What is Adrenaline
     – Definition, Structure, Role
2. What is Noradrenaline
     – Definition, Structure, Role
3. What are the Similarities Between Adrenaline and Noradrenaline
     – Outline of Common Features
4. What is the Difference Between Adrenaline and Noradrenaline
     – Comparison of Key Differences

Key Terms

Adrenaline/Epinephrine, Adrenergic Receptors, Fight-or-Flight Response, Noradrenaline/Norepinephrine, Vasoconstriction

What is Adrenaline

Adrenaline or epinephrine is a type of catecholamine exclusively produced in the medulla of the adrenal gland. Moreover, noradrenaline is converted into adrenaline by the action of the enzyme, phenylethanolamine N-methyltransferase (PNMT), which only occurs in the adrenal medulla. Therefore, the production of adrenaline only occurs in the adrenal medulla.

Figure 1: Adrenaline

Furthermore, adrenaline is one of the two mediators responsible for preparation of the body to the fight-or-flight response. Here, adrenaline activates both types of adrenergic receptors. Generally, alpha adrenergic receptors mainly occur in the arteries while beta-adrenergic receptors occur in the heart, lungs, and arteries of skeletal muscles. Some of the main responses produced in the body are as below.

• Increases heart rate and contractility
• Relaxes smooth muscles in the airways to improve breathing
• Constricts blood vessels to increase blood pressure
• Increases blood sugar levels

In addition, adrenaline is important as a medicine to treat low blood pressure associated with septic shock in allergic reactions.

What is Noradrenaline

Noradrenaline or norepinephrine is another type of catecholamine responsible for preparing the body for stressful situations. Both adrenal medulla and postganglionic neurons of the sympathetic nervous system secrete noradrenaline. In general, noradrenaline is produced in the axons of these neurons and stored inside vesicles. When an action potential travels down the neuron, noradrenaline is released into the synaptic gap to stimulate the postsynaptic neuron.

Figure 2: Noradrenaline Function

Moreover, noradrenaline mainly activates beta-adrenergic receptors. Therefore, the main response generated by noradrenaline is vasoconstriction, which narrows blood vessels. This increases the blood pressure in response to acute stress. However, noradrenaline activates beta-adrenergic receptors to a certain degree as well. Due to the effect of noradrenaline in increasing the blood pressure, it serves as an important medicine to increase blood pressure in acute situations like cardiac arrest, spinal anesthesia, septicemia, blood transfusions, and drug reactions.

Similarities Between Adrenaline and Noradrenaline

• Adrenaline and noradrenaline are two types of catecholamines.
• Both are hormones, which can also act as neurotransmitters.
• Their main function is to regulate the homeostasis of the body to prepare to face stressful or dangerous situations. Fight-or-flight response is the name of the response they generate.
• Both substances activate adrenergic receptors: alpha-adrenergic and beta-adrenergic receptors.
• The medulla of the adrenal gland produces both adrenaline and noradrenaline.
• The central nervous system regulates the secretion of both substances. Therefore, they are not under voluntary control.

Difference Between Adrenaline and Noradrenaline

Definition

Adrenaline refers to a hormone secreted by the adrenal glands, increasing rates of blood circulation, breathing, and carbohydrate metabolism and prepares muscles for exertion while noradrenaline refers to a hormone released by the adrenal medulla and by the sympathetic nerves and functions as a neurotransmitter; it is also used as a drug to raise blood pressure. Thus, this is the main difference between adrenaline and noradrenaline.

Production

Moreover, adrenaline is exclusively produced by the medulla of the adrenal gland while noradrenaline is produced by both the medulla of the adrenal gland and the sympathetic nervous system.

Biosynthesis

Another difference between adrenaline and noradrenaline is that the adrenaline is synthesized from noradrenaline while the noradrenaline is synthesized from dopamine.

Chemical Structure

Furthermore, adrenaline contains a methyl group attached to its nitrogen while noradrenaline contains hydrogens attached to nitrogen.

Receptor Activation

Receptor activation is another difference between adrenaline and noradrenaline. Adrenaline activates both alpha and beta adrenergic receptors while noradrenaline only activates alpha adrenergic receptors.

Effect

The four effects of adrenaline are the increase in the heart rate and contractility, relaxation of breathing tubes, increase in blood pressure by vasoconstriction, and the increase of the blood sugar levels while the main effect of noradrenaline is vasoconstriction. Hence, this is another difference between adrenaline and noradrenaline.

Conclusion

Adrenaline is the main hormone secreted by the medulla of the adrenal gland. It activates both alpha and beta-adrenergic receptors. The main function of adrenaline is to increase the metabolism of the body by increasing the blood flow, breathing rate, and glucose availability. On the other hand, noradrenaline is a neurotransmitter, which activates only alpha adrenergic receptors. Therefore, the main effect of this substance is to increase the blood pressure via vasoconstriction. Hence, the main difference between adrenaline and noradrenaline is their effect while preparing the body to stressful situations.

Reference:

1. “Norepinephrine vs Epinephrine: What’s the Difference?” Drugs.com, Drugs.com, Available Here

Image Courtesy:

1. “Adrenaline” By Harbin – Own work (Public Domain) via Commons Wikimedia  
2. “Synapse noradrenergique1” By Pancrat – Own work (CC BY-SA 3.0) via Commons Wikimedia