Hormones of the Hypothalamus

The hypothalamus is a region of the brain. It secretes a number of 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, travel immediately to 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 neurons to the posterior lobe of the pituitary where they are released into the circulation.

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.

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

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 groth 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.

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

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)

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.