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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 (CI). The regression of CI 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.

The effect of propranolol on renal haemodynamics was studied in nine patients with arterial hypertension and moderate to severe chronic renal failure. A reduction of the renal function in this type of patient might have clinical consequence. The patients, whose glomerular filtration rate (GFR) ranged between 17 ml/min/1.73 m2 and 71 ml/min/1.73 m2, were studied during three 4-week periods with alternately placebo, propranolol (40 mg b.i.d.) and placebo treatment. The GFR and the effective renal plasma flow (ERPF) were determined as the plasma clearance of 51Cr-EDTA and 125I-hippurane. The GFR fell on the average 7% (95% confidence limits: 1-12%) during propranolol treatment, and the fall was reversible. No changes were found in ERPF. In conclusion, propranolol treatment in this type of patient causes a modest and reversible fall of GFR.

Renal haemodynamics and extracellular homeostasis during the menstrual cycle were studied in 14 healthy women (age 21–41 years) who were not taking oral contraceptives in the follicular (Period I) and luteal phase (Period II). The glomerular filtration rate ([51Cr] EDTA clearance) and the effective renal plasma flow ([125I] hippuran clearance) increased from Period I to II by a median of 6.3 (95 confidence interval (CI): 0.6–9.2) and 7.3 (95 CI: -0.4–22) respectively. Serum sodium decreased from period I to II (p<0.01) by a median of 1 mmoll (95 CI: -2.0 to -0.5 mmoll) and the urinary excretion rate of potassium increased (p<0.02) from a median value of 35 μmolmin in Period I to 45 μmolmin in Period II. The extracellular fluid volume did not change between the two periods but the concentration of water in serum increased (p<0.05) from a median value of 91.7–92.0 g100 g in Period II. Serum total protein and serum albumin both showed a borderline statistically significant decrease from Period I to II. The investigation demonstrated a number of physiological and biochemical changes from the follicular to the luteal phase, most of which in a lower scale mimic well known changes that occur during pregnancy.