Effect of increased plasma osmolality on cold-induced thirst attenuation

Abstract

The eVects of elevating plasma osmolality (P osm ) on thirst ratings was studied in eight dehydrated males during exposure to 4°C. On two occasions, subjects were dehydrated (DH; 3-4% body mass) via 90 min exercise-heat exposure and overnight Xuid restriction (day 1). On a third occasion, subjects were exposed to heat but were given Xuid (EU). On day 2, subjects consumed NaCl (NaCl; 0.1 g NaCl kg ¡1 body mass in 500 ml H 2 O; DH only) or Placebo (P; 500 ml H 2 O; DH and EU). Subjects stood for 30 min at 24°C and for 45 min at 4°C (75 min post-dose). P osm was elevated (P < 0.05) 30 and 75 min after NaCl administration in DH + NaCl versus DH + P and EU + P treatments. Thirst ratings remained elevated (P < 0.05) in the DH + NaCl treatment 30 min after dosing and 45 min at 4°C versus DH + P and EU + P. Attenuation of thirst when dehydrated in the cold can be over-ridden by increasing P osm .

Voluntary Water Intake during and Following Moderate Exercise in the Cold

“…Above this threshold value, it has been reported that the first sensation of thirst occurs, ultimately resulting in a desire to drink. In the cold it has also been suggested that there is a blunted thirst response which may affect water intake volumes (Kenefick et al, 2008). Following 30-min exposure to the cold, Kenefick and colleagues reported that the sensation of thirst was attenuated to a serum osmolality threshold of approximately 304 mOsmol·kg -1 .…”

“…Previous studies have examined the response to cold exposure without periods of exercise (Kenefick et al, 2008: O'Brien et al, 1998 and have not combined this with a recovery period allowing ad libitum water rehydration to be monitored. Although in this study, the recovery period was at a temperature of approximately 22.2 °C; therefore not causing continual exposure to the cold environment, this situation was felt to occur more readily in a sporting situation.…”

“…In the cold, water losses can occur through sweating, cold induced diuresis and respiratory losses and in addition to this there is a reduction in voluntary water intake . Cold environments, in relation to exercise studies, are often described as less than 10 °C with many studies using temperatures of 0-7 °C (Cheuvront et al, 2005;Kenefick et al, 2004aKenefick et al, , 2004bKenefick, et al, 2008;O'Brien et al, 1998).…”

High-sweat Na+ in cystic fibrosis and healthy individuals does not diminish thirst during exercise in the heat

“…Association of sweat [Na ϩ ] with serum osmolality, serum [Na ϩ ], %⌬PV, hormone responses, and ad libitum drinking and association of serum [electrolytes] with ad libitum drinking were analyzed with Pearson product-moment correlation. The number of subjects in each group (minimum of 6) provided sufficient statistical power (␤ ϭ 0.20) to detect a thirst rating difference equal to two times (1.0) the typical within-subject SD of 0.5, based on intrasubject variablility in thirst ratings determined in a previous study (18). Statistical testing was conducted using SPSS (version 17.0; Chicago, IL).…”