The neurohypophysis: recent developments.

The hormones of the neurohypophysis, vasopressin and oxytocin, have now been shown to be synthesized as part of a prohormone complex that includes a vasopressin-neurophysin and oxytocin-neurophysin, respectively. In addition, for vasopressin, there is a glycopeptide as part of the prohormone. For each hormone the prohormone is packaged into neurosecretory granules and transported via axons to the posterior pituitary gland. In addition to this "classic" system, axons containing neurohypophyseal hormones project to the median eminence for release into portal vessels, and to other areas of the brain and spinal cord where the peptides may function as neurotransmitters rather than as hormones. As neurotransmitters, the neurohypophyseal hormones may be involved in the regulation of certain autonomic functions. Vasopressin and oxytocin are secreted into the cerebrospinal fluid where there is a diurnal rhythmic secretion of the peptides in several animal species (some species have a predominant rhythm of vasopressin and others a rhythm of oxytocin). Neurohypophyseal peptides are synthesized in some non-neuronal tissues where the function is unknown, and recently a novel peptide with similarities to oxytocin and vasotocin has been identified. The relationship of this novel peptide to the neurohypophyseal peptides is unknown. These new developments are likely to elucidate many new functions for the hormones of the neurohypophysis.