ABSTRACT
This chapter summarizes the state of the knowledge of the role of neurohypophysial hormones arginine vasotocin and isotocin in fish osmoregulation. The new experimental approaches and modern techniques addressed to arginine vasotocin and isotocin gives a promise to elucidate a role of both nonapeptides in fish osmoregulation. It is a well-established fact in mammals that neurohypophysial hormone arginine vasopressin regulates water and ions transport by epithelia by stimulating adenylate cyclase via V2-type receptors. The vasotocin and isotocin precursor sequences consist of a signal peptide, hormone and neurophysin. Both pro-vasotocin and pro-isotocin have elongated carboxyl-terminals with a leucin-rich segment similar to copeptine-like sequence of vasopressin precursor, but its glycosylation does not appear to be possible. There are three main organs engaged in osmoregulation in fish: gill, gastrointestinal tract and kidney. Cortisol, prolactin and growth hormone have been well documented to be involved in osmoregulation in fish since the sixties.
