Antidiuretic hormones.

There are at least 3 antidiuretic hormones. Arginine vasopressin is the antidiuretic hormone of most mammals, including man. This function is served by lysine vasopressin in the pig, and by arginine vasotocin in birds, reptiles and amphibians. All 3 hormones are closely related chemieally and act on the kidney in a similar inanner. Arginine vasotocin also exists in fish, in which the antidiuretic response is not known to occur. This antidiuretie hormone appeared, therefore, in vertebrate phylogeny before it acquired antidiuretic function. Anatomic considerations suggest that the fish neurohypophysis serves to regulate adenohypophysial secretion. There is evidence that such a primitive type of neurohypophysial function has persisted throughout subsequent vertebrate evolution.