title: Sympathetic activation and nitric oxide function in early hypertension.
abstract: The purpose of this study was to determine if tonic restrain of blood pressure by nitric oxide (NO) is impaired early in the development of hypertension. Impaired NO function is thought to contribute to hypertension, but it is not clear if this is explained by direct effects of NO on vascular tone or indirect modulation of sympathetic activity. We determined the blood pressure effect of NO synthase inhibition with N(ω)-monomethyl-l-arginine (L-NMMA) during autonomic blockade with trimethaphan to eliminate baroreflex buffering and NO modulation of autonomic tone. In this setting, impaired NO modulation of vascular tone would be reflected as a blunted pressor response to L-NMMA. We enrolled a total of 66 subjects (39 ± 1.3 yr old, 30 females), 20 normotensives, 20 prehypertensives (blood pressure between 120/80 and 140/90 mmHg), 17 hypertensives, and 9 smokers (included as "positive" controls of impaired NO function). Trimethaphan normalized blood pressure in hypertensives, suggesting increased sympathetic tone contributing to hypertension. In contrast, L-NMMA produced similar increases in systolic blood pressure in normal, prehypertensive, and hypertensive subjects (31 ± 2, 32 ± 2, and 30 ± 3 mmHg, respectively), whereas the response of smokers was blunted (16 ± 5 mmHg, P = 0.012). Our results suggest that sympathetic activity plays a role in hypertension. NO tonically restrains blood pressure by ∼30 mmHg, but we found no evidence of impaired modulation by NO of vascular tone contributing to the early development of hypertension. If NO deficiency contributes to hypertension, it is likely to be through its modulation of the autonomic nervous system, which was excluded in this study.
authors.affiliation: Department of Medicine, Division of Clinical Pharmacology, Vanderbilt University, Nashville, Tennessee, USA. alfredo.gamboa@vanderbilt.edu
authors.forename: Alfredo
authors.initials: A
authors.lastname: Gamboa
authors.forename: Luis E
authors.initials: LE
authors.lastname: Okamoto
authors.forename: André
authors.initials: A
authors.lastname: Diedrich
authors.forename: Leena
authors.initials: L
authors.lastname: Choi
authors.forename: David
authors.initials: D
authors.lastname: Robertson
authors.forename: Ginnie
authors.initials: G
authors.lastname: Farley
authors.forename: Sachin
authors.initials: S
authors.lastname: Paranjape
authors.forename: Italo
authors.initials: I
authors.lastname: Biaggioni
mesh_terms: D000293:Adolescent; D000328:Adult; D000375:Aging / Q000502:physiology; D017704:Baroreflex / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009129:Muscle Tonus / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors; D011978:Receptors, Nicotinic / Q000187:drug effects; D012907:Smoking / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000503:physiopathology*; D014294:Trimethaphan / Q000494:pharmacology; D055815:Young Adult; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D014294:Trimethaphan; D052250:Nitric Oxide Synthase Type III