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.
Angiotensin II (ANGII) acting on ANGII type 1 (AT1) receptors in the solitary tract nucleus (NTS) depresses the baroreflex. Since ANGII stimulates the release of nitric oxide (NO), we tested whether the ANGII-mediated depression of the baroreflex in the NTS depended on NO release. In a working heart-brainstem preparation (WHBP) of rat NTS microinjection 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 donor was without effect. NTS microinjection of non-selective NO synthase (NOS) inhibitors (L-NAME; 50 pmol) or (L-NMMA; 200 pmol) prevented the ANGII-induced baroreflex attenuation (P > 0.1). In contrast, a neurone-specific NOS inhibitor, TRIM (50 pmol), was without effect. Using an adenoviral vector, a dominant negative mutant of endothelial NOS (TeNOS) was expressed bilaterally in the NTS. Expression of TeNOS affected neither baseline cardiovascular parameters nor baroreflex sensitivity. However, ANGII microinjected into the transfected region failed to affect the baroreflex.Immunostaining revealed that eNOS-positive neurones were more numerous than those labelled for AT1 receptors. Neurones double labelled for both AT1 receptors and eNOS comprised 23 +/- 5.4 % of the eNOS-positive cells and 57 +/- 9.2 % of the AT1 receptor-positive cells. Endothelial cells were also double labelled for eNOS and AT1 receptors. We suggest that ANGII activates eNOS located in either neurones and/or endothelial cells to release NO, which acts selectively to depress the baroreflex.
Department of Physiology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK. julian.f.r.paton@bris.ac.uk
J F
JF
Paton
J
J
Deuchars
Z
Z
Ahmad
L F
LF
Wong
D
D
Murphy
S
S
Kasparov
D000256:Adenoviridae / Q000235:genetics; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D003331:Coronary Vessels / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005799:Genes, Dominant; D005822:Genetic Vectors; D006321:Heart / Q000502:physiology; D007150:Immunohistochemistry; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D052250:Nitric Oxide Synthase Type III; D011355:Prodrugs / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012143:Respiratory Physiological Phenomena; D017552:Solitary Nucleus / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D014162:Transfection
D004791:Enzyme Inhibitors; D020030:Nitric Oxide Donors; D011355:Prodrugs; D000804:Angiotensin II; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat