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

Abstract

What is the central question of this study? Water drinking increases muscle sympathetic nerve activity (MSNA), and it increases arterial blood pressure (ABP) in older populations but not in young healthy subjects. Does an increase in gain of arterial baroreflex control of MSNA contribute to maintenance of ABP after water drinking in healthy young subjects? What is the main finding and its importance? The gain of arterial baroreflex control of MSNA was increased and remained elevated 60min after water drinking (500ml) but remained unchanged after saline intake. An enhancement in gain of arterial baroreflex control of MSNA contributes to the maintenance of ABP after water drinking in young healthy subjects, probably via osmosensitive mechanisms. Water drinking increases muscle sympathetic nerve activity (MSNA), which is accompanied by a profound pressor response in patients with impaired arterial baroreflex function and in older populations, but not in healthy young subjects. We tested the hypothesis that an enhancement in the gain of arterial baroreflex control of MSNA contributes to the maintenance of arterial blood pressure after water drinking in healthy young subjects. The MSNA, arterial blood pressure and heart rate were measured in 10 healthy men (24± 2 years old; mean ± SD) before and for 60min after ingestion of 500ml of bottled water or saline solution. Weighted linear regression analysis between MSNA and diastolic blood pressure was used to determine the gain (i.e. sensitivity) of arterial baroreflex control of MSNA. After water drinking, MSNA was significantly elevated within 15min and remained above baseline for up to 60min [e.g. 21± 10bursts (100heart beats)-1 mmHg-1 at baseline versus 35± 14 bursts (100heart beats)-1 mmHg-1 at 30min; P< 0.01], whereas mean arterial blood pressure (e.g. 87± 7mmHg at baseline versus 89± 7mmHg at 30min; P= 0.34) and heart rate were unchanged. The arterial baroreflex-MSNA gain for bursts incidence was increased and remained elevated throughout the protocol [e.g. -2.25± 0.99bursts (100heart beats)-1 mmHg-1 at baseline versus -4.32± 1.53 bursts (100heart beats)-1 mmHg-1 at 30min; P< 0.01]. Importantly, saline intake had no effect on arterial baroreflex-MSNA gain or any neurocardiovascular variables. These findings demonstrate that water drinking enhances the gain of arterial baroreflex control of MSNA in healthy young men, which may contribute to buffering the pressor response after water drinking, probably via osmosensitive mechanisms.