Veterinary Physiology-III

ANTIDIURETIC HORMONE OR VASOPRESSIN

• The vasopressin is a peptide containing   8 amino acids.
• It shows species specificity in its composition.
• In cattle, man and most mammals the main form of vasopressin is arginine‑vasopressin (arginine at position 7 is essential for antidiuretic effect).
• In swine it is lysine‑vasopressin.
• In birds it is arginine‑ vasotocin.
• ADH has a half-life of 18 minutes.
• An increase in osmolality of body fluids due to dehydration of body, hypotension and decreased blood volume, angiotensin II stimulates the osmoreceptrors of the hypothalamus and release ADH.
• ADH acts on the distal tubule and collecting ducts through cAMP mecha­nism and causes increased reabsorption of water.
• Trauma, pain, anxiety and certain drugs also favour the release vasopressin,
• Diluted body fluid and cold environmen­tal temperature inhibit its secretion.
• A deficiency of this hormone leads to increased urine volume (diuresis) resulting in a condition known as diabetes insipidus in the dog, cat and horse.

Pressor Effect of ADH

• ADH shows less prominent constrictor effect on smooth muscles of the vascular system in normal physiological concentrations; may be involved in regulation of blood pressure. During haemorrhage, vasopressin is released in considerable amounts to cause pressor effect.