Developmental expression of aquaporin 1 in the rat renal vasculature

Aquaporin 1 (AQP-1) is a water channel protein that is constitutively expre ssed in renal proximal tubule and descending thin limb cells as well as in endothelial cells of the descending vasa recta. Studies in the developing r at kidney have demonstrated that AQP-1 is expressed in renal tubules before birth. However, nothing is known about the expression of AQP-1 in the rena l vasculature during kidney development. The purpose of this study was to e stablish the distribution of AQP-1 in the renal vasculature of the developi ng rat kidney and follow the differentiation of the vascular system during kidney development. Kidneys from 16-, 17-, 18-, and 20-day-old fetuses and 1-, 4-, 7-, 14-, 21-, and 28-day-old pups were preserved and processed for immunohistochemical studies using a preembedding immunoperoxidase procedure . AQP-1 immunoreactivity was detected using affinity-purified rabbit polycl onal antibodies to AQP-1. AQP-1 was expressed throughout the arterial porti on of the renal vasculature of the fetal and neonatal kidney from gestation al age 17 days to 1 wk after birth. AQP-1 immunoreactivity gradually disapp eared from the renal vasculature between 1 and 2 wk of age and remained onl y in the descending vasa recta. In contrast, AQP-1 immunoreactivity was not observed in lymphatic vessels until 3 wk of age and persisted in the adult kidney. AQP-1 was also expressed in a population of interstitial cells in the terminal part of the renal papilla at 3 wk of age as well as in the adu lt kidney. The transient expression of AQP-1 in the arterial portion of the renal vasculature in the developing rat kidney suggests that AQP-1 is impo rtant for fluid equilibrium and/or drainage in the developing kidney or, al ternatively, plays a role in the regulation of growth and/or branching of t he vascular tree during kidney development.