P117	Angiotensin mediated contraction of vasa recta in young SHR is enhanced and hydrogen peroxide dependent.
M.Baumann, A.Topdag, J.Smits, H.Struijker Boudier
Dept. of Pharmacology and Toxicology, CARIM, University Maastricht, Maastricht, NL.

The renal medulla is involved in long-term blood pressure regulation. Angiotensin II (AngII) is known to act as a key regulator of renal medullary blood flow through effects on reactive oxygen species. The aim of the study was to determine whether angiotensin differentially affects vasa recta in young SHR and how far hydrogen peroxide is involved in this process. We used male 6-8 week old WKY (n=17) and SHR (n=18) and performed experiments on kidney slices (800μm) after kidneys were perfused and washed using standard buffer. The following incubations (10min) were performed; one on each slice: AngII 10-10-10-7M, AngII 10-10-10-7M plus 550IU/ml catalase, hydrogen peroxide 100μM, hydrogen peroxide 100μM plus 550IU/ml catalase. Kidneys were fixated, cut, stained for α-actin and thereafter diameter of 20 vasa recta per kidney slide were measured. Hydrogen peroxide of medullary tissue was photometrically determined under basal conditions and after AngII stimulation. Results show small inner-group and intra-rat standard deviations. Secondly, AngII dose-dependently enhanced contraction of vasa recta in young SHR (AngII 10-7M: -23±2%), but not WKY (AngII 10-7M: -3±2%). These results in young SHR can be neutralized by catalase (-6±3%), and contractility can be mimicked by hydrogen peroxide (-16±3%), although neither basal medullary content nor AngII stimulated hydrogen peroxide production differ between young SHR and WKY. We conclude that (1) this method is a useful tool to investigate medullary action independent of tubuloglomerular feedback but including an intact tubulovascular crosstalk and (2) angiotensin differentially contracts vasa recta via hydrogen peroxide mediated pathway in young SHR.

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