title: Influence of age on arterial baroreflex inhibition of sympathetic nerve activity in healthy adult humans.
abstract: Resting levels of muscle sympathetic nerve activity (MSNA) increase markedly with age in healthy adult humans. An age-related reduction in arterial baroreflex inhibition of MSNA could contribute to these elevations. To test this hypothesis, we measured MSNA using peroneal microneurography in young (age, 25 +/- 1 yr; n = 8) and older (69 +/- 1 yr; n = 7) healthy normotensive men before (baseline control) and during graded constant infusion of phenylephrine hydrochloride (0.5-2.0 microgram . kg-1. min-1) that produced a sustained approximately 10-mmHg increase in arterial blood pressure. Central venous pressure was controlled at baseline levels (+/-1 mmHg) using lower body negative pressure. Resting MSNA was approximately 95% higher in the older compared with the young subjects (43 +/- 5 vs. 22 +/- 3 bursts/min; P < 0.05). However, arterial baroreflex MSNA inhibitory responsiveness was similar in the older compared with the young subjects (254 +/- 112 vs. 259 +/- 40 arbitrary integration units/mmHg, respectively), although the percent reduction in MSNA was smaller in the older men (8.9 +/- 0.7 vs. 5.2 +/- 1.1%/mmHg), due to their elevated baseline levels. The reflex increase in the R-R interval was not different in the two groups (13 +/- 10 vs. 16 +/- 7 ms/mmHg). In summary, our findings suggest that arterial baroreflex inhibition of MSNA is preserved with age in healthy normotensive adult humans. As such, this mechanism does not appear to contribute to the age-related rise in tonic MSNA.
authors.affiliation: Human Cardiovascular Research Laboratory, Center for Physical Activity, Disease Prevention, and Aging, Department of Kinesiology and Applied Physiology, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
authors.forename: K P
authors.initials: KP
authors.lastname: Davy
authors.forename: H
authors.initials: H
authors.lastname: Tanaka
authors.forename: E A
authors.initials: EA
authors.lastname: Andros
authors.forename: J G
authors.initials: JG
authors.lastname: Gerber
authors.forename: D R
authors.initials: DR
authors.lastname: Seals
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001158:Arteries / Q000294:innervation* / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D013564:Sympathetic Nervous System / Q000502:physiology*