title: Metabolic fate of [13N]ammonia in human and canine blood.
abstract: Nitrogen-13- ([13N]) ammonia is a widely used tracer for PET myocardial blood flow studies. Quantification of blood flow using tracer kinetic principles requires accurate determination of [13N]ammonia activity in blood. Since [13N] ammonia is rapidly metabolized, the arterial input function may be contaminated by labeled metabolites. We, therefore, characterized the 13N-labeled metabolites in blood after intravenous (i.v.) injection of 20 mCi [13N]ammonia in nine healthy volunteers. Utilizing a series of ion exchange resins, 13N-labeled compounds were separated into four groups: ammonia, neutral amino acids, acidic amino acids, and urea. Analysis of the metabolic fate of [13N]ammonia indicates that over 90% of the blood activity within the first two minutes after injection is present as [13N]ammonia. However, there is considerable contamination of the blood activity at 3-5 min by [13N]glutamine (amide) and urea, which collectively represent 18%-50% of the blood activity. Thus, correction of the arterial input function for 13N-metabolites is required to accurately quantify the arterial input function of [13N]ammonia in myocardial blood flow studies.
authors.affiliation: University of Michigan Medical Center, Department of Internal Medicine, Ann Arbor.
authors.forename: K C
authors.initials: KC
authors.lastname: Rosenspire
authors.forename: M
authors.initials: M
authors.lastname: Schwaiger
authors.forename: T J
authors.initials: TJ
authors.lastname: Mangner
authors.forename: G D
authors.initials: GD
authors.lastname: Hutchins
authors.forename: A
authors.initials: A
authors.lastname: Sutorik
authors.forename: D E
authors.initials: DE
authors.lastname: Kuhl
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000097:blood; D000641:Ammonia / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D000818:Animals; D004285:Dogs; D006801:Humans; D007275:Injections, Intravenous; D007474:Ion Exchange; D008297:Male; D009590:Nitrogen Radioisotopes; D014508:Urea / Q000097:blood
chemical_list: D000596:Amino Acids; D009590:Nitrogen Radioisotopes; D000641:Ammonia; D014508:Urea