The presser response to water drinking in humans - A sympathetic reflex?

Background-Water drinking increases blood pressure profoundly in patients w ith autonomic failure and substantially in older control subjects. The mech anism that mediates this response is not known. Methods ana Results-We studied the effect of drinking tap water on seated b lood pressure in 47 patients with severe autonomic failure (28 multiple sys tem atrophy [MSA], 19 pure autonomic failure patients [PAF]). Eleven older controls and 8 young controls served as control group. We also studied the mechanisms Chat could increase blood pressure with water drinking. Systolic blood pressure increased profoundly with water drinking, reaching a maximu m of 33+/-5 mm Hg in MSA and 37+/-7 in PAF mm Hg after 30 to 35 minutes. Th e presser response was greater in patients with more retained sympathetic f unction and was almost completely abolished by trimethaphan infusion. Systo lic blood pressure increased by 11+/-2.4 mm Hg in elderly but not in young controls. Plasma norepinephrine increased in both groups. Plasma renin acti vity, vasopressin, and blood volume did not change in any group. Conclusions-Water drinking significantly and rapidly raises sympathetic act ivity. Indeed, it raises plasma norepinephrine as much as such classic symp athetic stimuli as caffeine and nicotine. This effect profoundly increases blood pressure in autonomic failure patients, and this effect can be exploi ted to improve symptoms due to orthostatic hypotension. Water drinking also acutely raises blood pressure in older normal subjects. The presser effect of oral water is an important yet unrecognized confounding factor in clini cal studies of presser agents and antihypertensive medications. (Circulatio n. 2000;101:504-509.).