C. Westenfelder

The Critical Importance of Urinary Concentrating Ability in the Generation of Urinary Carbon Dioxide Tension

Measurement of urine to blood (U-B) carbon dioxide tension (P(CO2)) gradient during alkalinization of the urine has been suggested to assess distal H(+) secretion. A fact that has not been considered in previous studies dealing with urinary P(CO2) is that dissolution of HCO(3) in water results in elevation of P(CO2) which is directly proportional to the HCO(3) concentration. To investigate the interrelationship of urinary HCO(3) and urinary acidification, we measured U-B P(CO2) in (a) the presence of enhanced H(+) secretion and decreased concentrating ability i.e., chronic renal failure (CRF), (b) animals with normal H(+) secretion and decreased concentrating ability, Brattleboro (BB) rats, and (c) the presence of both impaired H(+) secretion and concentrating ability (LiCl treatment and after release of unilateral ureteral obstruction). At moderately elevated plasma HCO(3) levels (30-40 meq/liter), normal rats achieved a highly alkaline urine (urine pH > 7.8) and raised urine HCO(3) concentration and U-B P(CO2). At similar plasma HCO(3) levels, BB rats had a much higher fractional water excretion and failed to raise urine pH, urine HCO(3) concentration, and U-B P(CO2) normally. At a very high plasma HCO(3) (>50 meq/liter), BB rats raised urine pH, urine HCO(3) concentration, and U-B P(CO2) to the same levels seen in normals. CRF rats failed to raise urine pH, urine HCO(3), and U-B P(CO2) normally at moderately elevated plasma HCO(3) levels; at very high plasma HCO(3) levels, CRF rats achieved a highly alkaline urine but failed to raise U-B P(CO2). Dogs and patients with CRF were also unable to raise urine pH, urine HCO(3) concentration, and U-B P(CO2) normally at moderately elevated plasma HCO(3) levels. In rats, dogs, and man, U-B P(CO2) was directly related to urine HCO(3) concentration and inversely related to fractional water excretion. At moderately elevated plasma HCO(3) levels, animals with a distal acidification defect failed to raise U-B P(CO2); increasing the plasma HCO(3) to very high levels resulted in a significant increase in urine HCO(3) concentration and U-B P(CO2). The observed urinary P(CO2) was very close to the P(CO2) which would be expected by simple dissolution of a comparable amount of HCO(3) in water. These data demonstrate that, in highly alkaline urine, urinary P(CO2) is largely determined by concentration of urinary HCO(3) and cannot be used as solely indicating distal H(+) secretion.

Measurement of renal blood flow with radioactive microspheres

Various methods have been used to measure total renal blood flow. Of these the most commonly employed are the clearance of paraamino-hippurate (PAH) and techniques that make use of the electromagnetic flowmeter. PAH clearance (corrected for extraction ratio) is a cumbersome method requiring catheterization of the renal vein. It would be desirable to have a method which is simple and less traumatic but equally reliable. Neutze et al. (1) have shown that total renal blood flow can be determined using a radioactive microsphere (MS) technique, and that values so obtained correlate well with renal blood flow as determined by using the electromagnetic flowmeter. Neutze and co-workers measured renal blood flow by multiplying cardiac output by the ratio of counts in the kidney to total body counts. Thus, their technique involved determination of cardiac output and total body counting and is obviously no less cumbersome than any of the other commonly used techniques. Using the Fick principle we reasoned that total renal blood flow could be obtained by the ratio of radioactivity in the kidney to that in arterial blood sampled immediately after the injection of microspheres. This report describes this technique and the results obtained using it as compared to PAH clearance. Methods. Twelve female dogs were anesthetized with sodium pentobarbital and catheters were placed in the left ventricle (for microsphere injection), the femoral artery (for blood sampling), and the femoral vein (for PAH infusion). The left kidney was exposed through a flank incision and the renal vein catheterized via the ovarian vein. The ureters were cannulated by a suprapubic approach. Renal plasma flow was measured by the clearance of PAH using Wolfs equation (2): RPF = (U – R) × V/(A – R)(A, R and U represent PAH concentration in arterial, renal venous and urine samples, respectively; V is the urine flow expressed in ml/min).

Marked Improvement of Erythropoiesis in an Anephric Patient

The hemoglobin concentration of an anephric patient rose steadily from 4.7 to 12.5 g/dl over a period of 20 months. This marked improvement in erythropoiesis was observed following subtotal parathyroidectomy and at a time when the patient had an episode of hepatitis B.