norepinephrine secretion

Definition

Target type: biologicalprocess

The regulated release of norepinephrine by a cell. Norepinephrine is a catecholamine and it acts as a hormone and as a neurotransmitter of most of the sympathetic nervous system. [GOC:ef, GOC:jid]

Norepinephrine secretion is a complex process that involves the synthesis, storage, and release of norepinephrine from sympathetic nerve terminals.

**Synthesis:** Norepinephrine is synthesized from the amino acid tyrosine. Tyrosine is converted to L-DOPA by the enzyme tyrosine hydroxylase. L-DOPA is then converted to dopamine by the enzyme aromatic L-amino acid decarboxylase. Finally, dopamine is converted to norepinephrine by the enzyme dopamine β-hydroxylase.

**Storage:** Norepinephrine is stored in synaptic vesicles within the nerve terminal. These vesicles are filled with norepinephrine and other neurotransmitters, such as ATP and chromogranin A.

**Release:** When a nerve impulse arrives at the nerve terminal, calcium ions enter the terminal and trigger the fusion of synaptic vesicles with the presynaptic membrane. This fusion releases norepinephrine into the synaptic cleft, the space between the nerve terminal and the target cell.

**Reuptake:** After release, norepinephrine is rapidly removed from the synaptic cleft by reuptake into the presynaptic nerve terminal. This reuptake is mediated by a specific transporter protein called the norepinephrine transporter (NET).

**Regulation:** Norepinephrine secretion is regulated by a variety of factors, including neuronal activity, stress, and the presence of other neurotransmitters. For example, the release of norepinephrine is increased by the activation of β-adrenergic receptors, while it is decreased by the activation of α2-adrenergic receptors.

**Biological Roles:** Norepinephrine is a neurotransmitter that plays a wide variety of roles in the body, including:

* **Regulation of heart rate and blood pressure:** Norepinephrine increases heart rate and blood pressure by stimulating the sympathetic nervous system.
* **Regulation of mood and arousal:** Norepinephrine is involved in the regulation of mood, attention, and alertness.
* **Regulation of sleep and wakefulness:** Norepinephrine plays a role in the regulation of sleep-wake cycles.
* **Regulation of energy metabolism:** Norepinephrine stimulates the breakdown of glycogen and fat, increasing energy expenditure.
* **Regulation of pain perception:** Norepinephrine can block pain signals.

**Disorders:** Disruptions in norepinephrine secretion can lead to a number of disorders, including:

* **Depression:** Low levels of norepinephrine are associated with depression.
* **Anxiety:** High levels of norepinephrine are associated with anxiety.
* **Post-traumatic stress disorder (PTSD):** Dysregulation of norepinephrine levels is associated with PTSD.
* **Attention-deficit/hyperactivity disorder (ADHD):** Disruptions in norepinephrine levels are associated with ADHD.'
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Proteins (1)

Compounds (8)