title: Abnormal fluid homeostasis in apelin receptor knockout mice.
abstract: The apelinergic system, comprised of apelin and its G protein-coupled receptor (APJ; APLNR as given in MGI Database), is expressed within key regions of the central nervous system associated with arginine vasopressin (AVP) synthesis and release as well as in structures involved in the control of drinking behaviour, including the magnocellular neurones of the hypothalamus, circumventricular organs, and the pituitary gland. This localisation is indicative of a possible functional role in fluid homeostasis. We investigated a role for APJ in the regulation of fluid balance using mice deficient for the receptor. Male APJ wild-type and knockout (APJ(-/-)) mice were housed in metabolic cages to allow determination of water intake and urine volume and osmolality. When provided with free access to water, APJ(-/-) mice drank significantly less than wild-types, while their urine volume and osmolality did not differ. Water deprivation for 24 h significantly reduced urine volume and increased osmolality in wild-type but not in APJ(-/-) mice. Baseline plasma AVP concentration increased comparably in both wild-type and APJ(-/-) mice following dehydration; however, APJ(-/-) mice were unable to concentrate their urine to the same extent as wild-type mice in response to the V2 agonist desmopressin. Analysis of c-fos (Fos as given in MGI Database) mRNA expression in response to dehydration showed attenuation of expression within the subfornical organ, accentuated expression in the paraventricular nucleus, but no differences in expression in the supraoptic nucleus nor median pre-optic nucleus in APJ(-/-) mice compared with wild-type. These findings demonstrate a physiological role for APJ in mechanisms of water intake and fluid retention and suggest an anti-diuretic effect of apelin in vivo.
authors: Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Bristol BS1 3NY, UK.
authors: Emma M
authors: EM
authors: Roberts
authors: Michael J F
authors: MJ
authors: Newson
authors: George R
authors: GR
authors: Pope
authors: Rainer
authors: R
authors: Landgraf
authors: Stephen J
authors: SJ
authors: Lolait
authors: Anne-Marie
authors: AM
authors: O'Carroll
mesh_terms: D054392:Adipokines; D000818:Animals; D050034:Antidiuretic Agents / Q000494:pharmacology; D000073861:Apelin; D000075244:Apelin Receptors; D001127:Arginine Vasopressin / Q000097:blood / Q000235:genetics; D001826:Body Fluids / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism*; D003894:Deamino Arginine Vasopressin / Q000494:pharmacology; D004326:Drinking / Q000502:physiology; D005260:Female; D005838:Genotype; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology*; D007031:Hypothalamus / Q000502:physiology*; D036341:Intercellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009994:Osmolar Concentration; D011247:Pregnancy; D043562:Receptors, G-Protein-Coupled / Q000235:genetics* / Q000378:metabolism*; D014556:Urine; D014868:Water Deprivation / Q000502:physiology; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology*
chemical_list: D054392:Adipokines; D050034:Antidiuretic Agents; D000073861:Apelin; D000075244:Apelin Receptors; C402826:Apln protein, mouse; C491285:Aplnr protein, mouse; D002352:Carrier Proteins; D036341:Intercellular Signaling Peptides and Proteins; D043562:Receptors, G-Protein-Coupled; D001127:Arginine Vasopressin; D003894:Deamino Arginine Vasopressin