How to write a nursing essay on CATECHOLAMINES PATHWAYS

Catecholamines are hormones produced by the adrenal glands. They are responsible for the flight and fight responses in the body. The main catecholamines are Norepinephrine (NE), dopamine (DE), and epinephrine (adrenaline) (Hobert, 2018). Serotonin is a   monoamine oxidase catecholamine.

SEROTONIN PATHWAY

Figure 1

L-tryptophan

Tryptophan hydroxylase

L-5hydroxytryptophan

Aromatic L-amino acids decarboxylase

5-hydroxyindole acetaldehyde

Aldehyde dehydrogenase

5-hydroxyindole acetic acid

Serotonin (5-HT) – Raphe nuclei controls the release of 5-HT to other parts of the brain. It is crucial for controlling the digestion process, mood, and sleeping. It is abundant in the brain and is linked to anxiety, depression, impulsivity, sexual drive, social interactions, and migraine (Höglund et al., 2019). Decreased levels of serotonin production cause migraine episodes. In addition, it promotes the constriction of blood vessels in the case of an injury and aggregation of platelets to reduce hemorrhage. 90% of serotonin is present in the gastrointestinal playing a role in GI motility and nausea. Increased production of serotonin circulating in the blood triggers serotonin syndrome. This is characterized by headaches, agitation, confusion, red flushed skin, hyperthermia, hypertonia, sweating, and tachycardia.

Dopamine, Norepinephrine, and epinephrine

Figure 2

Tyrosine hydroxylase         DOPA decarboxylase

Tyrosine                               DOPA                       dopamine

Tetrahydrobiopterin             Pyridoxal phosphate

Dopamine                             norepinephrine                          epinephrine

Ascorbate                                       S-Adenosyl-L-methionine

Dietary proteins provide tyrosine, which is then carried from the bloodstream into the brain. There are unique enzymes that serve as a catalyst for each stage in the production of catecholamines. Tyrosine hydroxylase, which controls the total rate of DA and NE production, is the pathway’s rate-limiting enzyme.

Dopamine (DA) – this neurotransmitter plays an essential role in the reward pathway located at the ventral tegmental area in the nucleus accumbens (Hobert, 2018). Other functions include the inhibition of prolactin, regulation of behavior and cognition, motor functions, and maintenance of physiological functions such as digestion. It is synthesized both in the CNS and the peripheral nervous system.

Norepinephrine (NE) – this is a key component of the sympathetic nervous system. Increased production affects the CNS by enhancing concentration, increasing attention span, vigilance, and energy. In the PNS, it results in increased heart rate, hypertension, diverting blood circulation to the vital organs, and increased glucose (Hobert, 2018). The locus coeruleus regulate amounts of NE in the forebrain.

 

 

 

Biosynthetic Pathway for Catecholamines

Figure 3

L-Phenylalanine

( 6BH4)                                                        Phenylalanine hydroxylase

6BH4

L-Tyrosine

6BH4                                               Tyrosine hydroxylase

L-Dopa

Pyridoxal phosphate                                  L-aromatic amino acid decarboxylase

Dopamine

Ascorbate                                                 Dopamine- β-hydroxylase

Norepinephrine

S-Adenosyl-L-methionine                              Phenylethanolamine- N-methyltransferase

 

Epinephrine

Hydroxylation step

Phenylalanine hydroxylase converts phenylalanine to tyrosine. In this step, the substrate is molecular oxygen, and Tetrahdrobiopterin is the cofactor.

Tyrosine hydroxylase is found in all cells that synthesize catecholamines, and it hydroxylates tyrosine to L-DOPA (Hobert, 2018). The cofactor 6BH4 is found in subsaturating concentrations.

 

Decarboxylation

Aromatic amino acid decarboxylase converts L-Dopa to dopamine. Pyridoxal phosphate, an active form of vitamin 6, is a cofactor in this step and is necessary to facilitate a conversion (Hobert, 2018). Aromatic amino acid decarboxylase catalyzes other reactions, including converting tryptophan to tryptamine and 5-hydroxytryptophan to serotonin.

Hydroxylation

Dopamine-β-hydroxylase hydroxylates dopamine to Norepinephrine with ascorbic acid as the cofactor. This step utilizes oxygen and copper in the active site. Fumarate is utilized as a modulator (Hobert, 2018).  The reactions in this step are irreversible. Other end products apart from NE are water and dehydroascorbate.

Methylation

Phenylethanolamine N-methyltransferase methylates NE to epinephrine with s-adenosyl methionine acting as the catalyst (Gao et al., 2018). Glucocorticoids induce this step.

 

 

References

Gao, J., Cahill, C. M., Huang, X., Roffman, J. L., Lamon-Fava, S., Fava, M., Mischoulon, D., & Rogers, J. T. (2018). S-Adenosyl Methionine and Transmethylation Pathways in Neuropsychiatric Diseases Throughout Life. Neurotherapeutics, 15(1), 156–175. https://doi.org/10.1007/s13311-017-0593-0

Hobert, O. (2018). Figure 6, Neurotransmitter pathways. Www.ncbi.nlm.nih.gov. https://www.ncbi.nlm.nih.gov/books/NBK154158/figure/neuronalgenome_figure6/

Höglund, E., Øverli, Ø., & Winberg, S. (2019). Tryptophan Metabolic Pathways and Brain Serotonergic Activity: A Comparative Review. Frontiers in Endocrinology, 10. https://doi.org/10.3389/fendo.2019.00158

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