Short-term metabolic fate of L-[13N]glutamate in the Walker 256 carcinosarcoma in vivo.

In vivo studies with L-[13N]glutamate in the Walker 256 carcinosarcoma implanted under the renal capsule of female Sprague-Dawley rats demonstrate that uptake of glutamate and the rate of incorporation of the nitrogen label from this amino acid into metabolites is slower in the tumor than in nontumorous kidney tissue. Glutamate dehydrogenase, glutaminase, and alanine aminotransferase activities are significantly lower within the tumor than within the adjoining kidney. However, the tumor expresses high levels of aspartate aminotransferase, attesting to the importance of this enzyme in the metabolism of glutamate.

Methods for the enzymatic synthesis of tyrosine and phenylalanine labeled with nitrogen-13.

L-[13N]Tyrosine and L-[13N]phenylalanine were synthesized using immobilized enzymes by two methods. In method 1, [13N]ammonia is converted to L-[13N]glutamate; transamination with p-hydroxyphenylpyruvate yields L-[13N]tyrosine. [13N]Tyrosine is separated from other labeled intermediates on a Poropak Q column.

Short-term metabolic fate of 13N-labeled glutamate, alanine, and glutamine(amide) in rat liver.

Tracer quantities (in 0.2 ml) of 13N-labeled glutamate, alanine, or glutamine(amide) were administered rapidly (less than or equal to 2 s) via the portal vein of anesthetized adult male rats. Liver content of tracer at 5 s was 57 +/- 6 (n = 6), 24 +/- 1 (n = 3), and 69 +/- 7 (n = 3)% of the injected dose, respectively.

Short-term metabolic fate of [13N]ammonia in rat liver in vivo.

The short-term metabolic fate of [13N]ammonia in the livers of adult male, anesthetized rats was determined. Following a bolus injection of tracer quantities of [13N]ammonia into the portal vein, the single pass extraction was approximately 93%, in good agreement with the portal-hepatic vein difference of approximately 90%. High performance liquid chromatographic analysis of deproteinized liver samples indicated that labeled nitrogen is exchanged rapidly among components of: mitochondrial aspartate aminotransferase and glutamate dehydrogenase reactions and cytoplasmic aspartate aminotransferase and alanine aminotransferase reactions (t1/2 for the exchange of label toward equilibrium is on the order of seconds).

High-performance liquid chromatographic on-line flow-through radioactivity detector system for analyzing amino acids and metabolites labeled with nitrogen-13.

A flow-through radioactivity detector was used for the high-performance liquid chromatographic determination of amino acids and other nitrogenous substances labeled with 13N, a short-lived (t1/2 9.96 min) positron-emitting radionuclide. 13N-Labeled compounds were analyzed using cation, anion and amino columns, or as the o-phthaldialdehyde derivative on an ODS column.