Patients with arterial hypertension excrete a sodium load more rapidly than do individuals with normal blood pressure. The relationship of this abnormal sodium excretory response to blood pressure and such extrarenal factors as the central nervous system, dietary salt intake, body fluid volume and sodium content, and the adrenal glands has been studied. On the basis of this and other evidence, it is suggested that the exaggerated natriuresis is the result of a renal tubular defect which occurs after the development of hypertension.IT HAS been recognized since the studies of Farnsworth and Barker' that there is an abnormally high renal excretion of chloride in hypertensive individuals. Most subsequent research has been concerned with sodium rather than chloride. There have been several reports2-7 in which subjects with essential hypertension were observed to excrete an intravenous sodium load more rapidly than individuals with normal blood pressure. The explanation has been offered that this excretory derangement is related to alterations in renal function and that the high salt excretors were those hypertensive subjects whose renal plasma flow was reduced and filtration fraction elevated.8 Others,5' 6 however, have failed to observe such a relationship between increased sodium output and renal hemodynainics. The parallelism of the sodium clearance with both the level of the blood pressure2 4-6 9, 10 and renal vascular resistance6 suggested to The present study was undertaken to characterize further the hypertensive pattern of sodium excretion and the factors contributing to it. Consideration was given to the followinig: (1) the relationship of sodium excretion to blood pressure in subjects with labile, essential, and secondary hypertension; (2) the influence of extrarenal factors, such as the central nervous system, dietary salt intake, body fluid volume and sodium content, and the adrenal glands. MATERIALS AND METHODSThe studies were performed on the following subjects: 16 with essential hypertension of varying severity, 4 with labile hypertension, 4 with secondary hypertension, and 11 with normal blood pressure. In the presentation of the data, the subjects with essential hypertension have been grouped in order of increasing blood pressure as follows: for 2 patients with severe essential hypertension and diminished glomerular filtration there was no evidence of renal functional impairment. Cardiac decompensation was absent in all patients. The degree of retinopathy in the subjects with elevated blood pressure was grade II or less. There was no dietary restriction except when the effect of salt intake was being studied. No patient was receiving antihypertensive drugs.Procedures, except when noted, were carried out at approximately the same time in the morning. Water and food were withheld from the preceding midnight until the completion of the study. The subjects were in the supine position. Whenever possible urines were collected through a soft rubber, nmultiholed, indwelling urethral catheter. In the remai...

obtained at 30 and 60 minutes after the start of the infusion. Blood samples were drawn during the control period and at the midpoint of all subsequent urine collections. Hydration Studies Food and fluids were withheld from midnight preceding the study. In the morning the patients received 1,000 ml. of water orally over a 15-minute period. This positive balanee of a liter was nmaintained tlhroughout the procedure bv replacing u'iimarv losses witlh watter bv moutlh. Whieni urinie 867 by guest on May 31, 2015 http://circ.ahajournals.org/ Downloaded from

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