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In fourteen hypertensive and fourteen normotensive renal transplant recipients, and in a group of thirteen healthy controls, changes in natriuresis, glomerular filtration rate (GFR), and tubular reabsorption of sodium were determined in relation to intravenous infusion of 2 mmol isotonic sodium chloride per kg body weight. An exaggerated natriuresis was demonstrated in the hypertensive renal transplant recipients. This new finding indicates that the augmented natriuresis following plasma volume expansion, which is a characteristic finding in subjects with arterial hypertension, is not mediated by the renal nerves. Investigation of the tubular reabsorption rates of sodium by simultaneous determination of the renal clearance of 51Cr-EDTA and lithium showed that in the hypertensives the changes in tubular handling of sodium were different from those registered in the normotensive subjects. The increased sodium excretion in the hypertensive renal transplant recipients was caused by an increased output of sodium from the proximal tubules which was not fully compensated for by an increased distal reabsorption. Whether this increased delivery of sodium to the distal segments was caused by changes in GFR or in the proximal tubular reabsorption of sodium could not be clarified in the present study and warrants further investigations.

A method by which 51Cr-EDTA plasma clearance is determined from a single capillary blood sample (Clsc) was studied in 52 children less than 1 year old. The Clsc is calculated as the ratio between the injected dose and the total area under a transformed monoexponential function. The monoexponential curve is determined from the plasma activity 120 min after i.v. single injection of 51Cr-EDTA and a hypothetical initial activity calculated as the injected dose divided by the distribution space of 51Cr-EDTA. The distribution space was estimated from the body surface area. The rate constant of the monoexponential function is transformed by an empirically determined factor to make the area under the curve identical to the area under the true plasma disappearance curve. The Clsc was compared with 51Cr-EDTA plasma clearance (range 18-146 ml/min/1.73 m2) determined by a standard method from five capillary blood samples (Cl). The regression of Cl on Clsc did not differ from the line of identity, the SD being 5.9 ml/min/1.73 m2. In advanced renal failure the one-sample method is very sensitive to inaccuracies in the distribution space estimate and, accordingly, this method should be used only when the clearance value is predicted higher than 30 ml/min/1.73 m2.