Regulation of fluid intake in dehydrated humans: role of oropharyngeal stimulation.
We examined the effect of oropharyngeal stimulation on thirst, secretion of arginine vasopressin ([AVP]p), and fluid intake in six healthy adults after dehydration (28.6 +/- 1.4 ml/kg water loss) induced by mild exercise in the heat (2 h, 38 degrees C, relative humidity < 30%). Subjects performed three identical dehydration protocols followed by 75 min of rehydration at 27 degrees C consisting of 1) ad libitum drinking (Con), 2) infusion of a similar volume of water directly into the stomach via a nasogastric tube (Inf) during the first 25 min followed by combined Inf and ad libitum drinking during the remaining 50 min of rehydration; or 3) ad libitum drinking with simultaneous extraction of ingested fluid via a nasogastric tube (Ext). Plasma osmolality (Posm), [AVP]p, fluid intake, and thirst perceptions were measured throughout. On average, for all three protocols, Posm increased 7.8 +/- 0.6 mosmol/kgH2O and plasma volume decreased 4.7 +/- 1.3%, whereas thirst ratings and [AVP]p increased 7.6 +/- 1.3 cm and 3.1 +/- 0.4 pg/ml, respectively. Reflex inhibition of [AVP]p and thirst occurred within 5 min of rehydration in Con and Ext (P < 0.05) but not during Inf, supporting the hypothesis that oropharyngeal reflexes modulate osmotically stimulated thirst and [AVP]p. However, the reduction in [AVP]p during the first 5 min of Ext (-1.1 +/- 0.3 pg/ml) was less than that seen during Con (-2.1 +/- 0.4 pg/ml), suggesting that oropharyngeal stimulation is not the only factor contributing to the rapid reduction in [AVP]p during the first 5 min of drinking. During Con, subjects ingested 20.0 +/- 2.0 ml/kg of water but only drank 15% more (31.3 +/- 7.1 ml/kg) during Ext, demonstrating a clear role of oropharyngeal metering in limiting total fluid intake in humans in the presence of a persistently high dipsogenic drive.
Figaro
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John B. Pierce Laboratory, Yale University School of Medicine, New Haven, Connecticut 06519, USA.
Mack
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GW
D000328:Adult; D001127:Arginine Vasopressin / Q000378:metabolism; D003681:Dehydration / Q000503:physiopathology* / Q000628:therapy; D004326:Drinking / Q000502:physiology*; D005260:Female; D005440:Fluid Therapy; D006801:Humans; D007441:Intubation, Gastrointestinal; D008297:Male; D009960:Oropharynx / Q000503:physiopathology*; D010812:Physical Stimulation; D013894:Thirst
D001127:Arginine Vasopressin