Now oxytocin is in a chemist’s court…
Oxytocin is generated in magnocellular neurosecretory cells in the supraoptic nucleus and paraventricular nucleus of the hypothalamus and it is discharged into the blood from the posterior lobe of the pituitary gland. Some neurons in the paraventricular nucleus that project to other parts of the brain and to the spinal cord are also responsible for the generation of the hormone. Oxytocin, a nonapeptide contains the sequence cysteine – tyrosine – isoleucine – glutamine – asparagine – cysteine – proline – leucine – glycine (CYIQNCPLG). Sulfur bridge is formed by the the cysteine residues. Molecular mass of the hormone is approximately 1007 daltons. Now from the structural point of view oxytocin resembles vasopressin (cysteine – tyrosine – phenylalanine – glutamine – asparagine – cysteine – proline – arginine – glycine), also a nonapeptide with a sulfur bridge, whose sequence differs from oxytocin by 2 amino acids. Oxytocin and vasopressin were isolated and synthesized by Vincent du Vigneaud in the year 1953. This was the work for which he received the Nobel Prize in Chemistry in 1955 with the citation: “for his work on biochemically important sulphur compounds, especially for the first synthesis of a polypeptide hormone.”. Oxytocin and vasopressin are the only two well known hormones released by the human posterior pituitary gland to act at a distance. On the other hand, oxytocin neurons make other peptides, including corticotropin-releasing hormone (CRH) and dynorphin. But they act locally. It is worthy to mention that magnocellular neurons that make oxytocin are adjacent to magnocellular neurons that make vasopressin, and are similar in many respects.
