Makindo Medical Notes

Many of the causes of ADH release are common post-operatively. Poor fluid management can lead to hyponatremia and transient SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion).

About ADH

• ADH (Antidiuretic Hormone) is a nonapeptide hormone (composed of 9 amino acids).
• Produced by neurons in the supraoptic and paraventricular nuclei of the hypothalamus.
• Stored and released from the posterior pituitary gland.
• Acts on the collecting ducts in the kidneys to increase water permeability, leading to water retention.

Stimuli for ADH Release

• Increased plasma osmolality detected by hypothalamic osmoreceptors.
• Decreased volume in atrial stretch receptors.
• Low pressure in arterial baroreceptors.
• Angiotensin II, pain, stress, sleep, and drugs like morphine.

ADH Actions

• Stimulates the sensation of thirst.
• Increases free water reabsorption in the kidney’s collecting ducts.
• Causes arteriolar contraction, raising blood pressure (vasopressor effect).
• Reduces plasma osmolality.

Pathology: SIADH (Excess ADH)

• Presents as hyponatremia and reduced plasma osmolality.
• Cell volume depends heavily on the osmolality changes between extracellular fluid (ECF) and intracellular fluid (ICF).
• Excess ADH release can cause a decrease in serum osmolality.
• Low ECF osmolality leads to cell swelling, including brain swelling.
• Cells respond to swelling by expelling intracellular solutes to restore balance.

Pathology: Diabetes Insipidus (ADH Deficiency)

• Characterized by polyuria (excessive urination) and polydipsia (excessive thirst).
• Presents as hypernatremia and increased plasma osmolality.
• Lack of ADH release causes Cranial Diabetes Insipidus (DI).
• Loss of renal response to ADH leads to Nephrogenic Diabetes Insipidus.

Therapeutic Uses of ADH

• Vasopressin, a synthetic form of ADH, is sometimes used during cardiac arrest in place of adrenaline (epinephrine) with mixed results.
• Administered as a nasal spray to treat nocturnal enuresis (bed-wetting).
• Used to treat Cranial Diabetes Insipidus in synthetic form, delivered via nasal spray.