Endocrine

melatonin hormone

By
Proph.Israa

Melatonin also known chemically as N-acetyl-5-methoxytryptamine.

Is a naturally occurring compound found in animals, plants, and microbes.

In animals,circulating levels of the hormone melatonin vary in a daily cycle.

Allowing the entrainment of the circadian rhythms of several biological function .

It produced in the pineal gland which is outside of the blood-brain barrier acts as an endocrine hormone since it is released into the blood

melatonin produced by the retina and the gastrointestinal (GI) tract

INTRODUCTION

Many biological effects of melatonin are produced through activation of melatonin receptors


powerful antioxidant, with a particular role in the protection of nuclear and mitochondrial DNA

Known as the "hormone of darkness", it is secreted in darkness in both day-active (diurnal) and night-active (nocturnal) .

It may also be produced by a variety of peripheral cells such as bone marrow cells, lymphocytes and epithelial cells.

HISTORY

Melatonin receptors

Found in central nervous system and peripheral

tissues

In brain MT1 AND MT2 receptors are found in membranes of neurons of (SCN).

MTI AND MT2 are G-protien-couple receptors.

MT3 receptor is also found which is poorly understood.

G-protein couple receptor

They also called the metabotropic receptor.
Have three subunits
1-Alpha
2-beta
3-gamma
Seven transmembrane receptors.
Called Heptahelical receptor









Working of G-protein Receptor

G-protein couple receptor effector system

1- Adenylate cyclase/C-AMP sytem

2- phospholipase C / inositol phosphate system

Mechenisum of MT1 receptor

Mechenisum of MT2 receptor

SYNTHESIS OF MELATONIN

MELATONIN IN PLANTS

In plants involve regulation of their response to photoperiod, defense against harsh environments, and the function of an antioxidant.

Melatonin has been reported in foodstuffs including bananas and grapes, rice and cereals, herbs, olive oil, wine and beer.

While no food has been found to elevate plasma melatonin levels in humans, when other animals consume melatonin-containing food, blood levels of melatonin do increase

MELATONIN IN ANIMALS

Melatonin can suppress libido by inhibiting secretion of (LH) and (FSH) especially in mammals that have a breeding season when daylight hours are long.

.

In Human

The melatonin signal forms part of the system that regulates the sleep-wake cycle.


Infants melatonin levels become regular in about the third month after birth, with the highest levels measured between midnight and (8 AM).

In humans, 90% of melatonin is cleared through the liver, a small amount is excreted in urine and a small amount is found in saliva.

Light dependence

Production of melatonin by the pineal gland is inhibited by light and permitted by darkness. SO called "the hormone of darkness“.

Its onset called the Dim-Light Melatonin Onset (DLMO).

Secretion in blood peaks in the middle of the night, and gradually falls during the second half of the night.

When used several hours before sleep, the compound shifts the circadian clock earlier, thus promoting earlier sleep onset and morning awakening.

Cont…

It is principally blue light, around 460 to 480nm that suppresses melatonin.

light containing only wavelengths greater than 530 nm does not suppress melatonin in bright-light conditions


Use of blue-blocking goggles the last hours before bedtime advised for people who need to adjust to an earlier bedtime, as melatonin promotes sleepiness.

Melatonin as antioxidant

The discovery of melatonin as an antioxidant was made in 1993.

Melatonin is a direct scavenger of OH, and NO.

Melatonin once oxidized cannot be reduced to its former state because it forms several stable end-products upon reacting with free radicals.

Called terminal or suicidal antioxidant.

MELATONIN IN IMMUNE SYSTEM

immunological effect is thought to result from melatonin acting on high affinity receptors (MT1 and MT2).

melatonin may enhance cytokine production

melatonin might be useful fighting infectious disease including viral, such as HIV and bacterial infections, and cancer.

Endogenous melatonin in human lymphocytes has been related to interleukin-2 (IL-2) production.thats why it enhance immune system.


MELATONIN IN DREAM
Increase in vivid dreaming.

2 to10 mg increase the propensity of falling sleep .

80mg can induce sleep in adult man.

Extremely high doses of melatonin (50 mg) increased REM sleep time . Many drugs such as cannabis increase melatonin synthesis.