Evolution of Active Neurohypophysial Principles Among the Vertebrates

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Abstract
Nine active neurohypophysial peptides have been identified among the vertebrates. Arginine-vasotocin appears to be the most primitive. It occurs in cyclostomes and among representative species from all major branches of vertebrate phylogeny. The eight other neurohypophysial principles are presumed to have evolved from arginine-vasotocin after one or more reduplications of the primitive arginine-vasotocin gene. Argininevasotocin cannot be detected in the adult mammalian neurohypophysis but it has been found in the pineal and subcommissural organs of adult mammals. Arginine-vasotocin may be released into the cerebrospinal fluid and influence functions mediated by hypothalamic hypophysiotropic factors. The primitive functions of arginine-vasotocin are not clear. They may relate to cardiovascular regulation since vascular responses to arginine-vasotocin can be demonstrated in species representing all major branches of vertebrate evolution.