Adenoviral vector demonstrates that angiotensin II-induced depression of the cardiac baroreflex is mediated by endothelial nitric oxide synthase in the nucleus tractus solitarii of the rat

1. Angiotensin II (ANGII) acting on ANGII type 1 (AT(1)) receptors in the s olitary tract nucleus (NTS) depresses the baroreflex. Since ANGII stimulate s the release of nitric oxide (NO), we tested whether the ANGII-mediated de pression of the baroreflex in the NTS depended on NO release. 2. In a working heart-brainstem preparation (WHBP) of rat NTS microinjectio n of either ANGII (500 fmol) or a NO donor (diethylamine nonoate, 500 pmol) both depressed baroreflex gain by -56 and -67 %, respectively (P < 0.01). In contrast, whilst ANGII potentiated the peripheral chemoreflex, the NO do nor was without effect. 3. NTS microinjection of non-selective NO synthase (NOS) inhibitors (L-NAME ; 50 pmol) or (L-NMMA; 200 pmol) prevented the ANGII-induced baroreflex att enuation (P>0.1). In contrast, a neurone-specific NOS inhibitor, TRIM (50 p mol), was without effect. 4. Using an adenoviral vector, a dominant negative mutant of endothelial NO S (TeNOS) was expressed bilaterally in the NTS. Expression of TeNOS affecte d neither baseline cardiovascular parameters nor baroreflex sensitivity. Ho wever, ANGII microinjected into the transfected region failed to affect the baroreflex. 5. Immunostaining revealed that eNOS-positive neurones were more numerous t han those labelled for AT, receptors. Neurones double labelled for both AT( 1) receptors and eNOS comprised 23 +/- 5.4% of the eNOX-positive cells and 57 +/- 9.2% of the AT, receptor-positive cells. Endothelial cells were also double labelled for eNOS and AT, receptors. 6. We suggest that ANGII activates eNOS located in either neurones and/or e ndothelial cells to release NO, which acts selectively to depress the baror eflex.