Abstract
Summary
Water immersion to the neck has been demonstrated to produce a profound natriuresis in seated and standing subjects. Since an immersion–induced hydrostatic pressure gradient with a resultant redistribution of blood volume has been postulated to produce this natriuresis, it was of interest to examine this postulate by assessing renal sodium handling during immersion in supine subjects. Renal sodium, potassium and water handling was assessed in seven normal subjects during a control period and during water immersion under identical conditions of diet, supine posture and time of day. Although assumption of the recumbent position during immersion was associated with a gradual increase in U Na V, the resultant increase did not differ from the increase in U Na V following the assumption of recumbency during control. These data support the hypothesis that the natriuresis of water immersion is mediated by an immersion–induced hydrostatic pressure gradient acting on the vascular beds of the lower extremities and body trunk.
We thank Drs. Carlos A. Vaamonde and Lawrence M. Fishman for their constructive criticism and Robert Sackstein for invaluable technical assistance. We are also grateful to Peggy D. Cumby and Ronald J. Conroy for expert secretarial assistance. These investigations were supported from grants from the National Aeronautics and Space Administration (NGR 10–007–097), and by a VA Training Grant in Nephrology (TR–139). The clinical studies were carried out in the Clinical Research Unit of the University of Miami School of Medicine, supported by the General Clinical Research Centers Program of the Division of Research Resources, National Institutes of Health (RR–261).
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