The Aquaporin 2 (AQP2) water channel is a small-molecule transmembrane protein expressed in mammalian kidneys that plays a crucial role in the renal water retention and production of concentrated urine. AQP2 is a vasopressin-regulated water channel and is excreted into urine. When AQP2 was discovered in rat renal tubules, intensive research began, which was soon reflected in the literature by numerous articles, both research reports and reviews, which provided more details on the localization of AQP2 and its expression regulation factors. Most of the research in this field, however, has been carried out on humans and laboratory animals, with very few reports concerning livestock animals. This is the first review that summarizes our current knowledge on renal AQP2 in such groups of animals as cattle, small ruminants, horses and pigs. This article presents the recent findings concerning the structure and function of AQP2 in the renal water reabsorption. This review will mainly focus on: (1) the distribution of AQP2 in the renal tubule cells in cattle and horses; (2) changes in urinary AQP2 excretion during osmotic diarrhea in calves; (3) the effect of dietary supplementation on the renal expression of AQP2 by growing piglets and young goats; (4) AQP2 expression changes during the fetal and neonatal life in sheep. The information and prospects in the research on renal AQP2 in farm animals presented in this article will hopefully be a contribution to further studies in both basic and clinical research.  

23.3.2018