Arginine vasotocin a key hormone in fish physiology and behaviour: a review with insights from mammalian models.

The arginine vasotocin (AVT) neuroendocrine system clearly provides integrative regulation of many aspects of fish physiology and behaviour, including circadian and seasonal biology, responses to stress, metabolism, reproduction, cardiovascular function, and osmoregulation. These are all considered here providing an important context for the design of experiments and interpretation of results for investigations of specific aspects of AVT function. Salt and water balance is a consistent function from fish to mammals and is examined in more detail. Both AVT and AVP secretion is sensitive to hyperosmotic stimuli and associated cellular dehydration, while hypovolaemia would appear less important. AVT and AVP both mediate renal water conservation, though actions involve different receptors and precise targets in fish (V1) and mammals (V2). The actions of AVT to promote gill NaCl extrusion in fish are conserved in the AVP-induced natriuresis in mammalian kidney to support restoration of plasma osmolality. The AVT/AVP regulatory mechanisms involve both altered neurohypophysial peptide secretion and changes in target-tissue receptor expression/modulation of action. Both mechanisms importantly afford integration with the actions of other related hormone systems.