title: Oxidative stress exaggerates skeletal muscle contraction-evoked reflex sympathoexcitation in rats with hypertension induced by angiotensin II.
abstract: Muscle contraction stimulates thin fiber muscle afferents and evokes reflex sympathoexcitation. In hypertension, this reflex is exaggerated. ANG II, which is elevated in hypertension, has been reported to trigger the production of superoxide and other reactive oxygen species. In the present study, we tested the hypothesis that increased ANG II in hypertension exaggerates skeletal muscle contraction-evoked reflex sympathoexcitation by inducing oxidative stress in the muscle. In rats, subcutaneous infusion of ANG II at 450 ng·kg(-1)·min(-1) for 14 days significantly (P < 0.05) elevated blood pressure compared with sham-operated (sham) rats. Electrically induced 30-s hindlimb muscle contraction in decerebrate rats with hypertension evoked larger renal sympathoexcitatory and pressor responses [+1,173 ± 212 arbitrary units (AU) and +35 ± 5 mmHg, n = 10] compared with sham normotensive rats (+419 ± 103 AU and +13 ± 2 mmHg, n = 11). Tempol, a SOD mimetic, injected intra-arterially into the hindlimb circulation significantly reduced responses in hypertensive rats, whereas this compound had no effect on responses in sham rats. Tiron, another SOD mimetic, also significantly reduced reflex renal sympathetic and pressor responses in a subset of hypertensive rats (n = 10). Generation of muscle superoxide, as evaluated by dihydroethidium staining, was increased in hypertensive rats. RT-PCR and immunoblot experiments showed that mRNA and protein for gp91(phox), a NADPH oxidase subunit, in skeletal muscle tissue were upregulated in hypertensive rats. Taken together, hese results suggest that increased ANG II in hypertension induces oxidative stress in skeletal muscle, thereby exaggerating the muscle reflex.
authors.affiliation: Division of Integrative Physiology, Tottori University Faculty of Medicine, 86 Nishi-cho, Yonago, Tottori, Japan. skoba@med.tottori-u.ac.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Koba
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Watanabe
authors.forename: Naoko
authors.initials: N
authors.lastname: Kano
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Watanabe
mesh_terms: D014013:1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt / Q000008:administration & dosage; D000344:Afferent Pathways / Q000503:physiopathology; D000804:Angiotensin II; D047228:Angiotensin II Type 1 Receptor Blockers / Q000008:administration & dosage; D000818:Animals; D000975:Antioxidants / Q000008:administration & dosage; D001794:Blood Pressure; D015153:Blotting, Western; D002319:Cardiovascular System / Q000294:innervation*; D003497:Cyclic N-Oxides / Q000008:administration & dosage; D003655:Decerebrate State; D004195:Disease Models, Animal; D004558:Electric Stimulation; D006339:Heart Rate; D006614:Hindlimb; D006973:Hypertension / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology*; D007270:Injections, Intra-Articular; D007668:Kidney / Q000294:innervation*; D019808:Losartan / Q000008:administration & dosage; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013113:Spin Labels; D013481:Superoxides / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000503:physiopathology*; D013997:Time Factors
chemical_list: D047228:Angiotensin II Type 1 Receptor Blockers; D000975:Antioxidants; D003497:Cyclic N-Oxides; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D013113:Spin Labels; D013481:Superoxides; D000804:Angiotensin II; D014013:1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt; C500593:Cybb protein, rat; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D019808:Losartan; C001803:tempol