Evaluation of myocardial metabolism, with /sup 13/N- and /sup 11/C-labeled amino acids and positron computed tomography
To evaluate the utility of labeled L-amino acids (AA) for imaging regional myocardial AA metabolism by positron computed tomography (PCT), the myocardial uptake and clearance of Ala,* Glu, Gln, Asp, Leu tagged with /sup 13/N, and of /sup 11/C-tagged Asp, and oxaloacetate (Oxal), were examined in 44 experiments at control, during ischemia, and after transaminase inhibition. The myocardial time-activity curves recorded after intracoronary tracer injection had two clearance phases (an early and a late) for all /sup 13/N AA, and three (early, intermediate, late) for the two /sup 11/C compounds, with significantly different clearance half-times of 18.7 +/- 8.0 (s.d.) sec for the early phase, 141.7 +/- 56.5 sec for the intermediate, and 61.2 +/- 43.5 min for the late phase. The residual fractions ranged from 0.07 to 0.23 in normal myocardium, and consistently increased with ischemia by 0.01-0.07 for /sup 13/N-labeled Ala, Glu, Asp, and Leu, but not for /sup 13/N Gln and /sup 11/C compounds. Transaminase inhibition shortened the half-times of the late phases of /sup 13/N-labeled Ala, Glu, Asp, and Leu; had no effect on t1/2 of /sup 13/N Gln and /sup 11/C Oxal; and resulted in a loss of /sup 11/C CO/sub 2/ production and of the intermediate phase for /sup 11/C Asp. On the PCT images, /sup 13/N activity from labeled Ala and Glu was not decreased in an ischemic segment despite a significant flow reduction, as demonstrated by /sup 13/N NH/sub 3/ imaging and labeled microspheres. From the results, a three-compartment tracer kinetic model is proposed for the noninvasive quantification of Krebscycle activity, protein synthesis, and metabolic derangements related to ischemia.
- Research Organization:
- UCLA School of Medicine, University of California at Los Angeles, California
- OSTI ID:
- 6581362
- Journal Information:
- J. Nucl. Med.; (United States), Journal Name: J. Nucl. Med.; (United States) Vol. 23:8; ISSN JNMEA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
62 RADIOLOGY AND NUCLEAR MEDICINE
AMINO ACIDS
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BIOCHEMISTRY
BODY
CARBON 11
CARBON ISOTOPES
CARBOXYLIC ACIDS
CARDIOVASCULAR DISEASES
CARDIOVASCULAR SYSTEM
CHEMISTRY
COMPUTERIZED TOMOGRAPHY
COUNTING TECHNIQUES
DIAGNOSTIC TECHNIQUES
DIAGNOSTIC USES
DISEASES
ELECTRON CAPTURE RADIOISOTOPES
EMISSION COMPUTED TOMOGRAPHY
EVEN-ODD NUCLEI
HEART
ISCHEMIA
ISOTOPES
LIGHT NUCLEI
METABOLISM
MINUTES LIVING RADIOISOTOPES
MUSCLES
MYOCARDIUM
NITROGEN 13
NITROGEN ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANS
PATHOLOGY
POSITRON COMPUTED TOMOGRAPHY
RADIOISOTOPE SCANNING
RADIOISOTOPES
SCINTISCANNING
TOMOGRAPHY
USES
VASCULAR DISEASES