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Am J Physiol Regul Integr Comp Physiol 272: R1740-R1746, 1997;
0363-6119/97 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 6 1740-R1746, Copyright © 1997 by American Physiological Society

ARTICLES

Regulation of fluid intake in dehydrated humans: role of oropharyngeal stimulation

M. K. Figaro and G. W. Mack
John B. Pierce Laboratory, Yale University School of Medicine, New Haven, Connecticut 06519, USA.

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.


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