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Ascorbic acid increases cardiovagal baroreflex sensitivity in healthy older men

¹Department of Integrative Physiology, University of Colorado at Boulder, Boulder 80309; and ²Divisions of Cardiology and Geriatric Medicine, Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262

Submitted 5 November 2003 ; accepted in final form 9 February 2004

Cardiovagal baroreflex sensitivity (BRS) declines with advancing age in healthy men. We tested the hypothesis that oxidative stress contributes mechanistically to this age-associated reduction. Eight young (23 ± 1 yrs, means ± SE) and seven older (63 ± 3) healthy men were studied. Cardiovagal BRS was assessed using the modified Oxford technique (bolus infusion of 50–100 µg sodium nitroprusside, followed 60 s later by a 100- to 150-µg bolus of phenylephrine hydrochloride) in triplicate at baseline and during acute intravenous ascorbic acid infusion. At baseline, cardiovagal BRS (slope of the linear portion of the R-R interval-systolic blood pressure relation during pharmacological changes in arterial blood pressure) was 56% lower (P < 0.01) in older (8.3 ± 1.6 ms/mmHg) compared with young (19.0 ± 3.1 ms/mmHg) men. Ascorbic acid infusion increased plasma concentrations similarly in young (62 ± 9 vs. 1,249 ± 72 µmol/l for baseline and during ascorbic acid; P < 0.05) and older men (62 ± 4 vs. 1,022 ± 55 µmol/l; P < 0.05) without affecting baseline blood pressure, heart rate, carotid artery compliance, or the magnitude of change in systolic blood pressure in response to bolus sodium nitroprusside and phenylephrine hydrochloride infusion. Ascorbic acid (vitamin C) infusion increased cardiovagal BRS in older (58 ± 16%; P < 0.01), but not younger ( – 4 ± 4%) men. These data provide experimental support for the concept that oxidative stress contributes mechanistically to age-associated reductions in cardiovagal BRS in healthy men.

baroreceptors; blood pressure; antioxidants

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