Serotonin

(5-Hydroxytryptamine)

SEROTONIN

SEROTONIN

• An important neurotransmitter

• Regulates mood, sleep, appetite, and temperature regulation, as well as the perception of pain, the regulation of blood pressure, and vomiting

SEROTONIN

• A local hormone (Autacoid) in the gut

• It is a component of the platelet clotting process

Tryptophan

• amino acid precursors of Serotonin (source like banana)

psilocybin, mescaline, LSD

hallucinogen compounds ex:

Psychedelic drugs

Hallucinogen aka

Indoleamine

hallucinogenic property due to

5-hydroxyindole acetaldehyde

Intermediate product

• diagnostic agent for tumor especially for  carcinoid tumor

5-hydroxyindoleacetic acid (5-HIAA) used

5-hydroxyindoleacetic acid (5-HIAA)

major product

Brain

• Regulates mood, sleep, appetite 

• depression , anxiety, & insomnia

⬇ Serotonin =

• Serotonin syndrome (headache, confusion, hypertension

⬆ Serotonin

(Neurotransmitter)

• temperature regulation

• Perception of pain

• Regulation of blood pressure

• Vomiting

Brain

Neurotransmitter

Melatonin

Platelets

Small intestine 

(Enterochromaffin cells)

DISTRIBUTION

N-acetyl-5-methoxytryptamine

Melatonin

Melatonin

N-acetyl-5-methoxytryptamine 

• Regulate sleep-wake behavior of human 

Melatonin

N-acetyl-5-methoxytryptamine 

methoxylated and N-acetylated product of serotonin found in the pineal gland.

Platelets

component of the platelet clotting process (aggregation)

• enterochromaffin cells of the gastrointestinal tract. 

Approximately 90% of serotonin is found in the

Small intestine 

(Enterochromaffin cells)

• ⬆ Increases GIT motility

Serotonin agonist - Used to manage constipation

Enterochromaffin cells

Small intestine

Bezold-Jarisch reflex

Serotonin III associated in chemoreceptors reflex like the

1. Hypotension

2. Bradycardia

3. Apnea

Bezold-Jarisch reflex

MECHANISM OF ACTION

• Serotonin acts on several classes of 5HT1-receptor, which are are located on cell membranes of many tissue:

• contracts arterial smooth muscle, especially in carotid and cranial circulation

5HT1 Stimulates

5HT1

• At presynaptic sites, neuronal serotonin release is inhibited.

• causes contraction of vascular and intestinal smooth muscle and ⬆ increase microcirculation and vascular permeability

5HT 2 stimulates

5HT2

• CNS - mediates hallucinogenic effects (due to indoleamine) 

• area postrema - cause nausea and vomiting

• Stimulation on peripheral sensory neurons - cause pain

5HT3

• In the GIT, these receptor mediate an ⬆ increase in secretion and peristalsis (wavelength motion particularly in the digestive system) 

5HT4

5HT V, VI, VII

These receptors have been cloned and appear to be coupled to various second-messenger, but their function is unclear

5HT3 receptor

• in the GIT and in the vomiting center of the medulla participate in the vomiting reflex

5HT3 receptor

A potent stimulant of pain and itch sensory nerve endings and is responsible for some of the symptoms caused by insect and plant stings

AIRWAYS

• Facilitate acetylcholine release from bronchial vagal nerve ending

• Bronchoconstriction

• May also cause hyperventilation (rapid breathing cause by annxiety/panic) as a result of the chemoreceptor reflex or stimulation of bronchial sensory nerve ending

AIRWAYS

• skeletal muscle and heart, where it dilates blood vessels.

Powerful vasoconstrictor except in

• Initially, there is a ⬇ decrease in heart rate, cardiac output, and blood pressure caused by the  chemoreceptor response

• In phase 1 Bezold-Jarisch reflex happens

• Triphasic blood pressure response 1

• Following this ⬇ decrease, blood pressure increases as a result of vasoconstriction

• Mid pressor case

• Triphasic blood pressure response 2

• The third phase is again a ⬇ decrease in blood pressure attribute to vasodilation in vessel supplying skeletal muscle

• Triphasic blood pressure response 3

• Powerful stimulant of gastrointestinal smooth muscle, ⬆ increasing tone and facilitating peristalsis.

GIT

• 5HT4 receptor in the Enteric Nervous System = ⬆ increased acetylcholine 

= Stimulation of some Diarrhea, Urination

GIT Activation of

GIT

• Mediates a motility enhancing/prokinetic effect of selective serotonin agonist such as cisapride (for constipation)

5HT2 receptor

SKELETAL MUSCLE receptor

• Malignant hyperthermia (common side effects of Anesthetic agents, ⬆ high body temp due to overactivit of muscle producing heat)

SKELETAL MUSCLE

• Condition precipitated by certain anesthetic and neuromuscular agents

That results in severe hyperthermia due to skeletal muscle overactivity and metabolic and autonomic instability

SKELETAL MUSCLE