Modulation of aquaporin 2 expression in the kidney of young goats by changes in nitrogen intake

In ruminants, a decrease of dietary nitrogen (N) is an appropriate feeding concept to reduce environmental pollution and costs. In our previous study, when goats were kept on an N-reduced diet, a decrease of plasma urea concentration and an increase of renal urea transporters were demonstrated. Renal urea absorption plays a crucial role for renal water absorption and urine concentration. Renal collecting duct water absorption is mainly mediated by the water channel aquaporin 1 and 2 (AQP1 and AQP2). Therefore, the aim of the present study was to investigate the effects of a dietary N reduction on expression of renal AQP1 and AQP2 in young goats. Twenty male White Saanen goats, 3 months old, were divided equally into two feeding groups, receiving either a diet with an adequate or a reduced-N supply. Goats fed a reduced-N diet showed significantly higher amounts of AQP1 mRNA in cortical tissue, and the expression of AQP2 mRNA and protein were highly elevated in renal outer medulla. An increase of vasopressin concentrations in plasma were detected for the N-reduced fed goats. Therefore, a stimulation of renal water absorption can be assumed. This might be an advantage for ruminants in times of N reduction due to higher urea concentrations in the tubular fluid and which might result in higher absorption of urea by renal urea transporters. Therefore, interplay of aquaporin water channels and urea transporters in the kidney may occur to maintain urea metabolism in times of N scarcity in young goats.