Urine concentration is dependent on the shuttling of aquaporin2 (AQP2) between intracellular vesicles (ICV) and the plasma membrane (PM) of the collecting duct principal cells, a process normally under the control of vasopressin (VP). However, many local and systemic factors modulate this response, and an understanding of these mechanisms may prove beneficial in the development of treatments for diseases such as nephrogenic diabetes insipidus (NDI). Angiotensin II (Ang II) is an important regulator of systemic and renal blood pressure, can modulate collecting duct urea transport via AT1 receptors (Kato et al., 2000) and upregulates expression of the V2 receptor and AQP2 mRNA (Wong & Tsui, 2003). Male Wistar rats were sacrificed by lethal overdose of pentobarbitone sodium (240mg/Kg I.P.) confirmed by cervical dislocation. The kidneys were removed and inner medulla tubules prepared as previously described (Shaw & Marples, 2002). The tubule suspension was divided into four aliquots: control, VP (1nM), Ang II (0.1nM), VP + Ang II, and incubated for 20 minutes. The tubules were then either separated into plasma membrane and intracellular vesicle fractions to determine the cellular AQP2 distribution by Western blotting (expressed as a PM:ICV ratio normalised to the control, n=9), or lysed in 0.1M HCl to release intracellular cAMP (n=11), which was then quantified using a standard kit (Sigma). Data are presented as means ± s.e.m. and compared using Student’s paired t-tests. As expected, VP (1nM) stimulation caused a shift of AQP2 from ICV to PM (238 ± 30% of control, p<0.01). Ang II (0.1nM) also increased the PM:ICV ratio (165 ± 16% of control, p<0.01), although the effect was smaller than that of VP. VP + Ang II caused a shift of AQP2 to the same extent as VP alone (235 ± 32% of control, p<0.01). Vasopressin acts via the adenylate cyclase/PKA pathway, and as expected, VP (1nM) caused an increase in cAMP in the tubules (from 12 ± 3pmol/ml to 54 ± 6pmol/ml, p<0.01). Ang II (0.1nM) also caused a rise in cAMP (from 12 ± 3pmol/ml to 25 ± 5pmol/ml, p<0.01) although the effect was smaller than that of VP. VP + Ang II caused an increase in cAMP (from 12 ± 3pmol/ml to 42 ± 6pmol/ml, p< 0.01) although it was not as large as VP alone. In summary, Ang II can cause a rise in cAMP and translocation of AQP2 to the plasma membrane of rat collecting ducts, as can VP. The effects are not additive, indicating that they are acting through at least partially common pathways. These data suggest drugs affecting the renal Ang II pathways may be useful in the management of NDI.