Vasopressin (argipressin), a cyclic nine-peptide synthesized by hypothalamic neurons, is one of the hormones involved in peptide prohormone synthesis. Vasopressin is involved in the regulation process of hypothalamic-pituitary-adrenal axis, increasing the amount of solute free water reabsorbed from the renal tubule's colate back into the circulation, narrowing arteries to increase pressure, enhancing the stimulating effect of corticotropin releasing factor to regulate pituitary corticotropin secretion. Vasopressin acts as a neurotransmitter during nerve conduction by binding to specific G-protein-coupled receptors.