Factors influencing the diuretic response of seated subjects to the ingestion of isotonic saline solution.

The ingestion of isotonic saline solution, long considered to have little or no immediate effect on urine flow (1), has recently been shown by Blomhert (2) to be followed by brisk water diuresis. Further, several investigators have demonstrated that similar diuresis may result from intravenous infusion of isotonic saline solution (2, 3, 4). Examination of the latter experiments reveals at least three factors which appear to be of importance in determining whether water diuresis ensues: hydration, posture and time of day. Thus Ladd (3) found that diuresis following saline infusion occurred only if the subjects had been prehydrated eight to thirteen hours before the infusion was given. A previous study from this laboratory (4) showed that diuresis occurred in recumbent subjects but not in those quietly seated in a chair. Blomhert (2) did not observe diuresis when infusion was accomplished at night, although it occurred regularly under the same conditions during the day. Since Blomhert's studies were made only on recumbent subjects and no mention of posture is to be found in other reports concerning the response to ingested saline, it was deemed worthwhile to ascertain whether diuresis might be induced, and if so, under what circumstances, following saline ingestion by seated subjects.