The Pituitary Gland

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THE PITUITARY GLAND

The Pituitary Gland is divided into 2 areas.

The Pituitary gland
Fig.1: Pituitary gland

The Anterior Pituitary:

  • Under the regulation of the hypothalamus, the anterior pituitary makes and releases a hormone.

Example:

  • Growth Hormone (GH).
  • Thyroid-stimulating Hormone (TSH).
  • Adrenocorticotropin (ACTH).
  • Follicle-stimulating Hormone (FSH).
  • Leutinizing Hormone (LH).
  • Prolactin.

The Posterior Pituitary:

  • Stores and secretes hormones that are made in the hypothalamus.
  • Oxytocin and anti-diuretic hormone (ADH).

ANTERIOR PITUITARY HORMONES

Growth Hormone

  • GHRH (Growth Hormone Releasing Hormone) released from the hypothalamus in regulating the secretion of Growth hormone (GH).
  • GH secretion is high in newborns, till 4 yr of age.
  • Growth of brain and eye independent of growth hormone.
  • Insulin-like growth factor 1 (IGF-1) released from the liver inhibits GH secretion by stimulating somatostatin secretion from the hypothalamus.
  • Sermorelin – a synthetic analog of GHRH. Which is used as a diagnostic agent for testing childhood short stature.

Pharmacological Action:

  • Promotes retention of nitrogen and other tissue constituents.
  • Induces lipolysis especially in adipose tissue.
  • Increases hepatic glucose output.
  • Glycogenolysis in the liver.
  • Is protein anabolic hormone.

Growth Hormone Deficiency:

  • It occurs as a result of damage to the pituitary or hypothalamus by a tumor, infection, surgery, or radiation therapy.
  • In childhood: short stature and adiposity, hypoglycemia.
  • Adults: Generalized obesity, reduced muscle mass.
  • Lack of GH can cause dwarfism.

Growth Hormone Excess:

  • It leading to a benign pituitary tumor.
  • In adults causes acromegaly.
  • If this occurred before the long bone epiphyses close, it leads to the rare condition, gigantism.

Treatment of Excess GH Disorders:

  • Synthetic Somatostatin (Octreotide).
  • DA agonists (Bromocriptine).
  • Surgical removal / Radiotherapy of the tumor.
  • GH Antagonists (Pegvisomant).

ADR:

  • Hypothyroidism, Pancreatitis, Gynecomastia.

Somatostatin:

  • It is a growth hormone release-inhibiting hormone (GHRIH).
  • It is inhibiting the secretion of GH. Also inhibiting the secretion of TSH, insulin, and gastrin.
  • Because of the short half-life and lack of specificity use of somatostatin is very limited.
  • Octreotide, Lanreotide, Seglitide are somatostatin analogs.

Thyroid-stimulating Hormone (TSH) / Thyrotrophin

  • TSH stimulates the secretion of thyroxine (T4) and triiodothyronine (T3).
  • Synthesis and release of TSH by the pituitary are controlled by the hypothalamus.
  • Inappropriate TSH secretion results in hypo or hyperthyroidism.

Adrenocorticotropin (ACTH)

  • Promoting steroidogenesis and stimulates cortisol secretion by the adrenal cortex.
  • Promotes growth of adrenal cortex.
  • Cushing’s syndrome – due to excess production of ACTH from basophil pituitary tumors.

Follicle – Stimulating Hormone (FSH)

  • Females: Stimulates growth and development of ovarian follicles, promotes secretion of estrogen by ovaries.
  • Males: Essential for sperm production.
  • Preparations are available for clinical use:
  • Urofollitropin (a purified form of the urine of postmenopausal women).
  • 2 recombinant forms: follitropin alpha and follitropin beta.

Leutinizing Hormone (LH)

  • Females: Mainly triggers the ovulation, formation of corpus luteum in the ovary, and regulation of ovarian secretion of female sex hormones.
  • Males: Stimulates the testes to secrete testosterone.
  • Lutropin alfa, approved for use in combination with follitropin alfa for stimulation of follicular development in infertile women with profound LH deficiency.

Prolactin

  • Lactotroph cells are responsible for the secretion of prolactin.
  • Its secretion is stimulated by estrogen.
  • Females: stimulates breast development and milk production.
  • Males: involved in testicular function.
  • Prolactin secretion is inhibited by dopamine agonists, which act in the pituitary to inhibit prolactin release, used in the treatment of hyperprolactinemia.

Prolactin Inhibitors:

Bromocriptine:

  • It is an ergot derivative and a potent dopamine agonist.
  • Act on D2 receptor.
  • Inhibit prolactin release.
  • Increases growth hormone release in normal individuals.

POSTERIOR PITUITARY HORMONES

Oxytocin:

  • It is synthesized in the hypothalamus and transported to the posterior pituitary.
  • It is an effective uterine stimulant that produces contraction and is used intravenously to induce or reinforce labor.
  • Induces the release of milk.
  • Suckling sends a message to the hypothalamus via the nervous system to release oxytocin, which further stimulates the milk glands.

Clinical uses of Oxytocin:

  • Induction of labor.
  • Control of postpartum bleeding.

ADR:

  • Fetal distress, placental abruption or uterine rupture, excessive fluid retention.

Vasopressin (Antidiuretic Hormone ADH):

  • Synthesized in the hypothalamus and transported to the posterior pituitary.
  • ADH is to increase water conservation by the kidney.
  • A high level of ADH secretion leads to the reabsorption of water by the kidney.
  • ADH causes peripheral blood vessel constriction to help elevate blood pressure.

Clinical Uses:

  • Diabetes insipidus.
  • Nocturnal enuresis (by decreasing nocturnal urine production).

AE:

• Hyponatremia and seizures.

Synthetic ADH Drugs:

  • Vasopressin, Desmopressin.
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