Signals from the oropharynx may contribute to the diuresis which occurs in man to drinking isotonic fluids.

The drinking of a variety of isotonic salt solutions provoked a short load-dependent diuretic response in man, similar in latency to that of a water diuresis and reaching its maximum 40-60 min from the start of drinking. Subjects differed in the threshold load at which the response became evident, and also in the magnitude of their responses. Changes in free water clearance matched the increases in urinary minute volume, with no significant change in either urinary sodium or potassium excretion. Changes in urinary pH and in ammonium excretion were similar to those described for a water diuresis. Drinking an isotonic solution of mannitol provoked a diuresis similar to that of the salt solutions. All subjects had diarrhoea after drinking the mannitol. Signals arising from the oropharynx might be partly responsible for eliciting the diuresis. The significantly smaller urinary responses to infusions of isotonic salt solutions directly into the stomach support this view. The absence of a significant response to 'sham drinking' appears inconsistent with this, but oropharyngeal signals may only have a priming role in man and interact with other signals to give the full response.