Arginine vasopressin or antidiuretic hormone has got name “vasopressin” due to its vasoconstrictor properties. Vasopressin is a posterior pituitary hormone which is essential for the cardiovascular homeostasis. In normal physiological conditions, it helps in regulation of plasma osmolality and volume via its action on the kidney. Other important actions of vasopressin include regulation of vascular smooth muscle tone, control of circadian rhythm, thermoregulation, and adrenocorticotropic hormone release (ACTH).
In recent years, vasopressin has emerged as an important therapeutic option in the treatment of various shock states. Vasopressin has increasingly been used in both pediatric and adult critical care units for the management of central diabetes insipidus, bleeding abnormalities, oesophageal variceal haemorrhage, asystolic cardiac arrest, and various shock states e.g. shock due to ventricular fibrillation, hypovolaemia, sepsis and cardiopulmonary bypass.
Ongoing researches helped in increasing understanding of the endocrine response to shock and importance of vasopressin in their management. Prolonged vasodilatory shock is characterised by relative deficiency of endogenous vasopressin and marked vasopressor effects of the exogenously administered hormone. Sepsis and post cardiopulmonary bypass conditions are the most common causes of vasodilatory shock; however, vasodilation can be a common final pathway of any type of shock. Unlike other vasoconstrictors, vasopressin also exerts some vasodilatory properties which can be due to its action on various receptors, namely V1 vascular, V2 renal, V3 pituitary and oxytocin receptors, and the P2 purinergic receptors producing variable and seemingly contradictory responses.
To better understand the variable responses on the vascular system, which vasopressin exerts, it is prudent to acquire the knowledge of the physiology and action of the different vasopressin receptors. In this chapter, vascular actions of vasopressin along with distribution of the classic vasopressin receptors and signalling pathways will be explored.