Vasopressin biological actions

Many biologically active secreted peptides are also amidated at their carboxyl terminal, and acetylated at their amino-terminal. The consequences of these modifications are (a) to reduce the susceptibility of these peptides to degradative actions of extracellular aminopeptidases and carboxypeptidases after their secretion and (b) to influence the biological activity of the peptides. Corticotropin-releasing factor, gastrin, cholecystokinin and vasopressin require the C-terminal amide for full activity [54—56]. Acetylation of the N-terminus of a-MSH is necessary for activity, whereas acetylation of /3-endorphin inhibits its opioid activity [57], The enzymes responsible for acetylation have been identified from bovine and rat intermediate lobes [57] and enzymes with a-amidation activity have been reported in preparations of pituitary secretory granules [54,55]. 

Neurohypophysial hormones a group of hormones produced in the hypothalamus (not, as the name suggests, in the neurohypophysis see Hypophysis). The action spectrum of these phylogenetically ancient hormones, Oxytocin (see) and Vasopressin (see), extends from an effect on the smooth muscle of the uterus, mammary gland and blood vessels, to an alteration of the permeability of the skin, urinary bladder and kidney tubules. The carrier protein of N.h. is Neurophysin (see). N.h. are small molecules (nonapeptides) and they represent an ideal model for the study of the mechanism of hormone action at a molecular biological level. 

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