Abstract
Mammals adapted to a great variety of habitats with different accessibility to water. In addition to changes in kidney morphology, e.g. the length of the loops of Henle, several hormone systems are involved in adaptation to limited water supply, among them the renal-neurohypophysial vasopressin/vasopressin receptor system. Comparison of over 80 mammalian V2 vasopressin receptor (V2R) orthologs revealed high structural and functional conservation of this key component involved in renal water reabsorption. Although many mammalian species have unlimited access to water there is no evidence for complete loss of V2R function indicating an essential role of V2R activity for survival even of those species. In contrast, several marsupial V2R orthologs show a significant increase in basal receptor activity. An increased vasopressin-independent V2R activity can be interpreted as a shift in the set point of the renal-neurohypophysial hormone circuit to realize sufficient water reabsorption already at low hormone levels. As found in other desert mammals arid-adapted marsupials show high urine osmolalities. The gain of basal V2R function in several marsupials may contribute to the increased urine concentration abilities and, therefore, provide an advantage to maintain water and electrolyte homeostasis under limited water supply conditions.
Highlights
Over a period of 170 million years of mammalian evolution species adapted to a great variety of habitats with different accessibility to water
All members of the vasopressin receptor family belong to the superfamily of rhodopsin-like G protein-coupled receptors (GPCR)
The V2R is a key component in regulating the renal water reabsorption but its contribution to adaptation of mammals to different water accessibility was not investigated yet
Summary
Over a period of 170 million years of mammalian evolution species adapted to a great variety of habitats with different accessibility to water. Several mammals managed adaptation to conditions of water restriction among them desert rodents and elephants. Other closely related mammals such as Baikal and California seals managed adaptation to fresh and sea water conditions, respectively. There is strong evidence that, besides morphological modifications in the kidney [3,4], several hormone systems [5], among them the renal-neurohypophysial hormone system of vasopressin, are involved in adaptation to differences in fresh water supply [6]. The peptides of the vasotocin/vasopressin/oxytocin family are evolutionary old hormones which are already found in agnate bony and cartilaginous fishes [7,8,9]. Along with the divergence of the vasopressin/oxytocin peptides their receptors developed co-evolutionary and in mammals at least two of the various vasopressin receptor subtypes and one oxytocin receptor became established within all the genomes investigated so far. In mammals V1 vasopressin receptors (V1aR, V1bR) are involved in blood pressure regulation and central feedback mechanism whereas the V2 vasopressin receptor (V2R) maintains the water balance and electrolyte homeostasis
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