ADH (Vasopressin) – Posterior Pituitary hormones

Antidiuretic Hormone (Vasopressin)

Its main action is to prevent diuresis.

The ADH acts on the distal convoluted tubules of the kidney, producing reabsorption of water, which results in decreased urinary output.

K⁺ is excreted.

The ADH binds to membrane receptors and activates adenylate cyclase.

This results in production of cyclic AMP which will activate the Protein kinase.

The Protein kinase phosphorylates proteins of the microtubules & microfilaments.

The net effect is the reabsorption of water.

The regulation of ADH secretion is through the osmolality of blood.

Decreased osmolality (hemodilution) leads to decreased ADH secretion.

Conversely, increase in osmolality (hemoconcentration or dehydration) leads to stimulation of the secretion of ADH.

It may be

It is characterized by excretion of large volumes of dilute urine.

Hypernatremia and hypertonic contraction of extracellular fluid volume.

Very rare condition.

Excess ADH secretion from ectopic production of ADH by malignant tumors elsewhere.

ADH is continuously secreted.

There are NO control mechanisms.

Generally, there is hypotonic expansion of extracellular volume, but sometimes there is Euvolemia associated with hyponatremia.

It has Slow onset and is mostly asymptomatic.

Acute onset will manifest the symptomatology of water intoxication.