Aquaporin-2 (AQP-2) is a vasopressin-regulated water channel in the kidney collecting duct. AQP-2 transcript has been identified by transcriptional profiling of rat kidneys as being regulated by dietary salt. We compared renal AQP-2 transcript expression in Sprague-Dawley and Dahl salt-sensitive (SS/Jr) rats using real-time RT-PCR. Expression of AQP-2 transcript is 5-fold less (P < 0.01) in the Sprague-Dawley and 3-fold greater in Dahl SS/Jr rats (P < 0.01) on high versus basal NaCl diets. The AQP-2 coded sequence was identical in Sprague-Dawley and Dahl SS/Jr rats. The present results provide evidence that: (1) AQP-2 plays a role in salt adaptation and (2) regulation of aquaporin transcript expression by salt is altered in the Dahl SS/Jr rat. (C) 2002 Elsevier Science (USA). All rights reserved.