TABLE Hormones of the Posterior Lobe of the Pituitary Gland21.4 Hormone Composition Source Major Functions Oxytocin Polypeptide containing 9 amino acids Cell bodies of neurons located in the supraoptic and paraventricular nuclei of the hypothalamusa Stimulates activity of the contractile cells around the ducts of the mammary glands to eject milk from the glands; stimulates contraction of smooth muscle cells in the pregnant uterus Antidiuretic hormone (ADH; vasopressin) Polypeptide containing 9 amino acids; two forms: arginine-ADH (most common in humans) and lysine-ADH Cell bodies of neurons located in the supraoptic and paraventricular nuclei of the hypothalamusa Decreases urine volume by increasing reabsorption of water by collecting ducts of the kidney; decreases the rate of perspiration in response to dehydration; increases blood pressure by stimulating contractions of smooth muscle cells in the wall of arterioles a Immunocytochemical studies indicate that oxytocin and ADH are produced by separate sets of neurons within the supraoptic and paraventricular nuclei of the hypothalamus. Biochemical studies have demonstrated that the supraoptic nucleus contains equal amounts of both hormones, whereas the paraventricular nucleus contains more oxytocin than ADH, but less than the amount found in the supraoptic nucleus.