Conway Review Lecture 1989

11/09/1989 in University College Galway

The Role of the Gut in the Regulation of Water Balance

Dr. Elizabeth M. Gebruers, Department of Physiology, U.C.C.

I would like to begin by thanking the President and the Selection Committee of the Academy for honouring me with the invitation to give the 1989 Conway Review Lecture. My choice of subject is the role of the gut in water balance. As animals migrated from sea to land the mechanisms developed to control excretion of body water became vitally important. It is not surprising therefore that the homeostatic mechanisms which regulate body water are both complex and subtle. Humans are approximately 60% water and the regulation of total body water is achieved by balancing water¬†intake with water output. Intake is regulated by drinking and controlled water output is brought about by regulation of water excretion through the kidneys. The development of our modem understanding of this balance mechanism could be said to begin with the realisation that water balance depended to a greater or lesser degree on water absorption. The earliest recorded evidence supporting this position, if evidence it could be called, is the fairytale observation of the 18th century Baron von Munchausen that his thirsty horse failed to stop drinking following bisection by a portcullis. The conclusion drawn is, “no absorption, no satiation”. More substantial evidence is recorded in the entry in RuUier’s medical dictionary of 18211 which cites an observation of Dupuytren that dogs who ran about in the sun failed to drink if they were given water intravenously.

This evidence is supported by the clinical observations of Magendie in 1823 and Latta of Leith in 1832, that the thirst of rabies and cholera victims was relieved by i.v. administration of fluids.

In 1856 Claude Bernard did experiments on dogs and horses which showed that the presence of an open gastrointestinal fistula, which prevented absorption of fluids drunk, caused these animals to drink larger quantities of water compared to when the fistula was closed. These experiments support the idea that proper water balance depends on the absorption of the water drunk.

The role of the gut in water balance