ATRIAL NATRIURETIC PEPTIDE RELAXS ARTERIAL BASAL TONE OF SPONTANEOUS HYPERTENSIVE RATS. ROLE OF ENDOTHELIUM.

PERAL DE BRUNO M; RISSO PATRÓN F; JOO TURONI C; COVIELLO A

São Paulo – SP – Brazil

Congreso; 20th Scientific Meeting of the International Society of Hypertension; 2004

International Society of Hypertension

Objective: Atrial natriuretic peptide (ANP) relaxes precontracted vessels, however in previous work we demonstrated that in non contracted angiotensin II (Ang II) sensitized rabbit aortic rings ANP was able to relax the basal tone (BT) . The purpose of present waork was to determine if the basal tone of spontaneous hypertensive rats (SHR) could be relaxed by ANP Design and Methods:  Rings with (E+) or without endothelium (E-) of thoracic aorta of SHR and Wystar Kyoto (WKY) were mounted in  an organ chamber  to measure contractility. After a 2 h    equilibration period a treatment with ANP or calcium-free Krebs+EGTA 2.10-3M +sodium nitroprussiate 10-5M (0Ca+EGTA +SNP) was performed in  non stimulated vessels. Results:In SHR  ANP (10-6 M) in E+ lowered BT (-86±35, ANP versus +21.8±17.2 mg, control N=6, p<0.02). This effect was potentiated in E- (-380±83 mg, ANP N=6, p<0.01). Similar results were obtained with  0Ca+EGTA+SNP  in SHR  E+ (-97.7±27.7 mg, N=7,p<0.02) and a higher BT decrease in E- (809.6±231.2, N=5,p<0.05).. In unrubbed SHR aorta L-NAME (10-4M)  as well as E- potentiated in a similar magnitud the relaxant effect of ANP. No effect could be obtained with ANP or 0Ca+EGTA+SNP in E+ or E- of WKY. Conclusion: These results demonstrate by the first time that the aorta basal tone of SHR  turns responsive to a vasorelaxant effect of ANP dependent in a calcium increased active tone. Potentiation of this effect by removal of endothelium suggests a contraregulatory role of  NO in the increased SHR basal tone.