The activities of purine-metabolizing enzymes, 5'-nucleotidase, adenosine deaminase, and purine nucleoside phosphorylase in microdissected rat nephron segments were measured. The specific activity of 5'-nucleotidase was highest in the proximal tubules and the cortical collecting duct, but low in the glomerulus. In contrast, the highest activity of adenosine deaminase was found in the glomerulus. The distribution pattern of purine nucleoside phosphorylase was similar to that of adenosine deaminase. These results suggest that various nephron segments can form adenosine and that the glomerulus exhibits highest capacities to metabolize this nucleoside.

5'-Nucleotidase↗

PubMedDate not supplied

Cellular adenosine triphosphate production and consumption in the descending thin limb of Henle's loop in the rat.

To characterize the properties of cellular adenosine triphosphate (ATP) production and consumption in the descending thin limb of Henle's loop (DTL) in rats, we measured the cellular ATP content by applying the microchemiluminescence method. For ATP production, isolated DTL from the short- and long-loop nephron (SDL and LDL, respectively) was incubated with several substrates such as alanine, glucose, glutamine, beta-hydroxybutyrate (beta-HBA), lactate, and pyruvate; for ATP production from each substrate indicated that glucose and pyruvate were the preferred substrates to maintain cellular ATP in both SDL and LDL. ATP production from glutamine, beta-HBA, and lactate was substantial in LDL. In SDL, glutamine was the preferred substrate, and beta-HBA and lactate were minimal. The utilization of alanine was minimal in both LDL and SDL. The cellular ATP was significantly restored by ouabain at concentrations of 1.5 x 10(-5) and 1.5 x 10(-3) M in LDL, but in SDL only at 1.5 x 10(-3) M. In both segments, the cellular ATP level was significantly decreased by monensin above the concentrations of 1 micrograms/ml in LDL and 5 micrograms/ml in SDL. From these observations, we conclude that there exist clear differences between LDL and SDL in ATP-supplying substrate specificities and ATP-consuming properties.

Adenosine Triphosphate↗

PubMedDate not supplied

Intranephron distribution of glycine-amidinotransferase activity in rats.

Guanidinoacetic acid (GAA), a precursor of creatine, is an essential substrate for muscle energy metabolism, and synthesized by glycine-amidinotransferase (transamidinase) mainly in the kidney. Since the intranephron distribution of transamidinase activity has never been quantified yet, the purpose of this study is to provide evidence about the localization of transamidinase activity using microdissected individual nephron segments. Synthesized GAA was separated by HPLC and detected fluorometrically after reacting with 9,10-phenanthrenequinone. Results obtained were as follows. (1) Transamidinase activity was distributed only in the first (S1) and the second (S2) portion of the proximal tubule, S1 being significantly higher than S2. (2) In S2, arginine and glycine were better substrates for GAA synthesis than canavanine and glycine. These results clearly indicate that GAA is synthesized in definite portions of the proximal tubule, and would be transported to the liver for further creatine production.

Amidinotransferases↗

PubMedDate not supplied

Pseudocoarctation of the aorta--a case report.

We report a case of a 43-year-old woman with pseudocoarctation of the aorta manifested by a superior mediastinal mass on the chest roentgenogram. Evaluation was made using computed tomography (CT), magnetic resonance imaging (MRI) and digital subtraction angiography (DSA). No other congenital anomalies or aneurysms below the kinked area of the aorta could be found. The characteristic "kink" of the aorta and the absence of true coarctation were evident in the sagittal plane by MRI. MRI is of great value for examining disorders of the aorta.

Adult↗