Neurohypophysial hormones oxytocin and vasopressin differ in molecular structure and function within the mammalian body. The molecular structure of each of the two hormones slightly differs by two amino acid sequences. Despite the slight molecular variation between the two hormones, each has very different physiological functions. Vasopressin helps regulate water and solute concentrations, while oxytocin plays a role in certain reproductive processes. Differences between these substances are also seen in mood and secretion mechanisms.
Physiological differences between the two similar hormones are due to the slight molecular structure variation. Vasopressin’s amino acid sequence is Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2, while oxytocin is Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2. One pair of amino acids that occur in oxytocin but not vasopressin is isoleucine (Ile) and leucine (Leu). The phenylalanine (Phe) and arginine (Arg) combination is present in vasopressin but absent in oxytocin.
Both oxytocin and vasopressin are synthesized in the hypothalamus and stored in the posterior pituitary gland in the brain. Varying amounts of the hormones are released directly into the brain. The rest of the hormones are secreted into the blood stream by carrier proteins called neurophysin.
Unlike oxytocin, vasopressin plays an important role in fluid homeostasis within the mammalian body by regulating water, glucose and salts. The hormone is commonly referred to as antidiuretic hormone for its water conservation effects on the kidneys by decreasing the formation of urine. Secretion of vasopressin is regulated by osmoreceptors when simulated by factors such as thirst, blood pressure and fluid volume. Other potent stimuli of antidiuretic hormone secretion are nausea and vomiting.
The main difference between oxytocin and vasopressin secretion is oxytocin’s ability to release itself from other tissues including the ovaries and testes; while vasopressin's only secretion location is the posterior pituitary gland. Both genders produce oxytocin, but women produce the hormone in larger quantities than men. Oxytocin is released in large amounts during labor and helps to facilitate breast feeding. In child birth oxytocin is secreted when the fetus simulates the cervix and vagina. After oxytocin is released uterine contractions are enhanced to help induce child birth.
Secretion of oxytocin and vasopressin affects moods and behavior. Women who are lactating tend to have increased levels of oxytocin released in cerebrospinal fluid. Increased oxytocin levels in women have been associated with establishing maternal behavior. Studies involving the brains of non-pregnant animals infused with oxytocin shows rapidly induced maternal behavior. Instead of inducing maternal behavior, vasopressin greatly influences social behavior and social bonding.