Vasopressin, along with oxytocin, is synthesized primarily within these neurones, which project their axons from hypothalamic learn more cell bodies to terminals on the capillaries of the posterior pituitary neural lobe to release the peptides into the systemic circulation. Hormone release studies from isolated rat SON and neural lobes in vitro show significantly decreased basal vasopressin release from SON but not from neural lobe preparations after apelin administration, indicating a possible role for apelin in dendritic rather than axonal vasopressin

release [51]. The species difference in APJ distribution seems likely to reflect a more extensive role for apelin in mouse pituitary function to regulate neurohypophysial hormone release. In the mouse adrenal gland APJ mRNA and I125[Pyr1]apelin-13

binding sites were expressed throughout the cortex, with little to no presence in the medulla. This is the first reported detailed distribution of APJ expression within the rodent adrenal gland, with no described BTK inhibitor chemical structure function to date. The localization however, points to a possible role of APJ and its cognate ligand in corticosteroid release. In contrast to the mouse distribution, in human adrenals APJ-ir is confined to endothelial cells of the surrounding arteries, small resistance arteries within the capsular plexus and the central vein while APJ-ir was not detectable in secretory cells of either the adrenal cortex or medulla [23]. APJ mRNA and I125[Pyr1]apelin-13 binding sites were present throughout mouse renal cortex and medulla, however before APJ expression was not integral to the glomeruli as previously reported in the rat [34], a localization that was suggestive of a role for this receptor in the regulation of blood flow or glomerular filtration. Expression in the mouse was associated with the renal corpuscle, similarly signal was observed in sporadic cells along proximal and distal tubules although a specific association with blood vessels or collecting ducts, as has been seen previously in the rat

[18], was not observed. The low resolution of APJ mRNA on autoradiographic films of the kidney does not allow us to clarify morphologically the exact cell types in the kidney within which mouse APJ expression is localized. APJ mRNA has also been identified in mouse kidney using RT-PCR [30]. The role of apelin in the kidney is unclear however strong expression of APJ mRNA and high levels of I125[Pyr1]apelin-13 binding suggests an involvement of peripheral aspects of the apelinergic system in the regulation of fluid homeostasis as has been suggested by studies in the APJ KO mouse [42] and [43], while APJ expression in the highly vascularized inner stripe of the outer medulla suggests a possible renal medullary microcirculatory role for the mouse receptor.