Microsoft Word - NEF369BF.rtf

Richard G. Appel, MD, Department of Internal Medicine/Nephrology, Bowman Gray School of Medicine, Medical Center Boulevard, Winston-Salem NC 27157-1053 (USA) Dear Sir, A number of studies indicate that atrial natriuretic factor (ANF) acts to impair argi-nine vasopressin (AVP)-induced water transport. In the perfused rabbit cortical collecting tubule, ANF inhibited the hydraulic conductivity response to AVP, but not to forskolin or cyclic AMP (cAMP) [1]. It was concluded that ANF acted proximally to the cAMP generation step. In perfused rat inner medullary collecting ducts, ANF inhibited AVP-induced osmotic water permeability, and also exogenous cAMP-stimulated osmotic water permeability [2]. It was felt that ANF acted distally to cAMP generation. In another study in perfused rat inner medullary collecting ducts, ANF inhibited AVP-stimulated hydraulic conductivity, but had no effect on the exogenous cAMP-induced hydroosmotic effect, suggesting that the effect occurs before cAMP formation [3]. Finally, in toad bladder, ANF inhibited vaso-tocininduced water reabsorption [4]. These studies indicate that ANF does appear to impair AVP-induced water transport. However, there is some disagreement as to the exact mechanism. We therefore chose to study the effect of ANF on cAMP metabolism. Renal papillary collecting tubule (RPCT) cells were isolated from the papillae of 125to 150-gram male Sprague-Dawley rats [5]. Intact RPCT cells were suspended in serum-free, fully defined medium which favors epithelial cell growth. Medium was changed daily until the cells approached confluence at 3-4 days. Experiments were performed on the primary cultures. Triplicate determinations of cAMP were made under each experimental condition in each of 6