Water drinking enhances the gain of arterial baroreflex control of muscle sympathetic nerve activity in healthy humans

Abstract

Water drinking increases efferent sympathetic outflow in young healthy subjects in the absence of a pressor response, whereas in autonomic failure patients and healthy older adults water‐induced sympatho‐excitation is accompanied by a large pressor response. The extent to which the arterial baroreflex (ABR) buffers the blood pressure (BP) response to water intake is unclear. We tested the hypothesis that water drinking increases ABR control of muscle sympathetic nerve activity (MSNA) in young healthy subjects. MSNA (microneurography) and arterial BP (Finometer) were measured in 8 men (24 ± 1 yrs) before, and for 60 min after drinking 500 mL of room‐temperature (22°C) tap water or saline. Weighted linear regression analysis between MSNA and diastolic BP was used to assess spontaneous ABR MSNA gain. As expected, MSNA was elevated after water intake (22 ± 4 baseline to 36 ± 5 bursts/100 heart beats at 30 min, P<0.05) and BP was unchanged. ABR MSNA gain for burst incidence (−2.4 ± 0.3 baseline vs. −4.4 ± 0.6 bursts/100 heart beats/mmHg at 30 min; P<0.05) and total MSNA (−3.6 ± 0.8 baseline vs. −5.6 ± 0.8 au/beat/mmHg at 30 min; P<0.05) were increased and tended to return to baseline at 60 min. ABR‐MSNA gain remained unchanged following saline intake. These data indicate that ABR MSNA gain is enhanced following water intake in healthy young subjects, which likely contributes to the maintenance of BP.Supported by CAPES, CNPq & FAPERJ