Antidiuretic hormone or Vasopressin
The Antidiuretic hormone or 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 and 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 osmoreceptors 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 Antidiuretic hormone or Vasopressin 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 hemorrhage, vasopressin is released in considerable amounts to cause pressor effect.