Effects of posture on renal excretion of sodium and chloride in orthostatic hypotension.

Large decreases in the rates of sodium excretion, chloride excretion, and glomerular filtration were observed in patients with orthostatic hypotension when they assumed the upright posture following a period of recumbency. When they returned to the recumbent position, sodium excretion typically was not restored immediately in spite of immediate restoration of filtered sodium load. The decreased sodium excretion found to occur in patients with orthostatic hypotension when they are in the upright posture is considered to be due in part to the decreased filtered sodium load and in part to changes in tubular reabsorption that are independent of filtered sodium load.