Introduction: Central administration of angiotensin II (Ang II) is known to reduce urinary volume and to increase sodium and potassium excretion. Recently, a novel signalling mechanism for Ang II in the periphery has been shown to involve reduced nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase-derived reactive oxygen species (ROS).Although ROS are now known to be involved in numerous Ang II-regulated processes in peripheral tissues, and are increasingly implicated in CNS neurodegenerative diseases, the role of ROS in central regulation of Ang II-induced hydromineral metabolism remains unexplored.The hypothesis that ROS are involved in central Ang II signalling and in Ang II-dependent antidiuresis, natriuresis and kaliuresis was tested by the use of selective antagonists of the NAD(P)H oxidase cascade.
Materials and methods: In intracerebroventricular (ICV)-cannulated rats,Ang II was injected ICV and urinary sodium and potassium excretion was assessed at 1-, 3-, and 6-hour periods of urine collection. Urine sample was analysed for sodium and potassium concentration using a flame photometer. The role of NAD(P)H oxidase-dependent signalling cascade was evaluated using the selective NAD(P)H oxidase inhibitor, apocynin; the superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol); and the protein kinase C inhibitor, chelerythrine.
Results: ICV administration of Ang II to conscious hydrated rats resulted in a significant decrease in urinary volume in the first hour, and an increased sodium and potassium excretion during the 6-hour period of urine collection, which was most effective during the 3 and 6 h. Interference with the NAD(P)H oxidase signalling by central administration of apocynin, tempol or chelerythrine, blunted the natriuretic and kaliuretic effect induced by central administration of Ang II, without affecting its antidiuretic action.
Conclusion: This study demonstrates that increases of urinary sodium and potassium excretion elicited by central administration of Ang II are mediated by NAD(P)H oxidase- dependent production of superoxide and protein kinase C activation in conscious hydrated rats.