Hormones of the Hypothalamus

The hypothalamus is a region of the brain. It contains several types of neurons responsible for secreting different hormones.

Thyrotropin-releasing hormone (TRH)
Gonadotropin-releasing hormone (GnRH)
Growth hormone-releasing hormone (GHRH)
Corticotropin-releasing hormone (CRH)
Somatostatin
Dopamine

All of these are released into the blood in the capillaries and travel immediately – in portal veins – to a second capillary bed in the anterior lobe of the pituitary, where they exert their effects.

All of them are released in periodic spurts. In fact, replacement hormone therapy with these hormones does not work unless the replacements are also given in spurts.

Two other hypothalamic hormones:

Antidiuretic hormone (ADH) and
Oxytocin

travel in the neurons themselves to the posterior lobe of the pituitary where they are released into the circulation.

Link to diagram of the endocrine glands (92K)

Thyrotropin-releasing hormone (TRH)

TRH is a tripeptide (GluHisPro).
When it reaches the anterior lobe of the pituitary it stimulates the release there of

thyroid-stimulating hormone (TSH)
prolactin (PRL)

Gonadotropin-releasing hormone (GnRH)

GnRH is a peptide of 10 amino acids. Its secretion at the onset of puberty triggers sexual development.

Primary Effects	Secondary Effects
FSH and LH Up	estrogen and progesterone Up (in females)
FSH and LH Up	testosterone Up (in males)

The signal that stimulates GnRH secretion - Link.

After puberty, a hyposecretion of GnRH may result from

intense physical training
anorexia nervosa

Synthetic agonists of GnRH are used to treat

inherited or acquired deficiencies of GnRH secretion.
prostate cancer. In this case, high levels of the GnRH agonist
- reduces the number of GnRH receptors in the pituitary, which
- reduces its secretion of FSH and LH, which
- reduces the secretion of testosterone, which
- reduces the stimulation of the cells of the prostate.

Growth hormone-releasing hormone (GHRH)

GHRH is a mixture of two peptides, one containing 40 amino acids, the other 44.

As its name indicates, GHRH stimulates cells in the anterior lobe of the pituitary to secrete growth hormone (GH).

Corticotropin-releasing hormone (CRH)

CRH is a peptide of 41 amino acids.

As its name indicates, its acts on cells in the anterior lobe of the pituitary to release adrenocorticotropic hormone (ACTH)

CRH is also synthesized by the placenta and seems to determine the duration of pregnancy.

Description of the mechanism.

It may also play a role in keeping the T cells of the mother from mounting an immune attack against the fetus. [Discussion]

Somatostatin

Somatostatin is a mixture of two peptides, one of 14 amino acids, the other of 28.

Somatostatin acts on the anterior lobe of the pituitary to

inhibit the release of growth hormone (GH)
inhibit the release of thyroid-stimulating hormone (TSH)

Somatostatin is also secreted by cells in the pancreas and in the intestine where it inhibits the secretion of a variety of other hormones.

Dopamine

Dopamine is a derivative of the amino acid tyrosine. Its principal function in the hypothalamus is to inhibit the release of prolactin (PRL) from the anterior lobe of the pituitary.

Antidiuretic hormone (ADH) and Oxytocin

These peptides are released from the posterior lobe of the pituitary and are described in the page devoted to the pituitary.

ADH

Oxytocin

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30 July 2005