Cerebral extraction of N-13 ammonia: its dependence on cerebral blood flow and capillary permeability -- surface area product

Journal Article · · Stroke; (United States)

DOI:https://doi.org/10.1161/01.STR.12.5.607· OSTI ID:5387253

Phelps, M E; Huang, S C; Hoffman, E J; Selin, C; Kuhl, D E

13N-labeled ammonia was used to investigate 1) the cerebral extraction and clearance of ammonia, 2) the mechanism by which capillaries accommodate changes in cerebral blood flow (CBF) and 3) its use for the measurement of CBF. The unidirectional extraction of 13NH3 in rhesus monkeys was measured during PaCO2 induced changes in CBF and dog studies were performed using in vitro tissue counting techniques to examine 13NH3 extraction in gray and white matter, mixed tissue and cerebellum during variations in CBF produced by combinations of embolization, local brain compression, and changes in PaCO2. The single pass extraction fraction of 13NH3 varied from about 70 to 20% over a CBF range of 12 to 140 cc/min/100 g. Capillary permeability-surface area product (PS) estimates with a Renkin/Crone model show PS increasing with CBF. The magnitude and rate of increase in PS with CBF was highest in gray matter greater than mixed tissue greater than white matter. Tissue extraction of 13NH3 vs CBF relationship was best described by a unidirectional transport model in which CBF increases by both recruitment of capillaries and by increases of blood velocity in open capillaries. This saturable-recruitment model provides a possible explanation for the mechanism of flow changes at the capillary level. The net 13NH3 extraction subsequent to an i.v. injection increases non-linearly with CBF. Doubling or halving basal CBF produced from 35 to 50% changes in the 13N tissue concentrations with further increases in CBF associated with progressively smaller changes in 13N concentrations.

• Research Organization: Department of Radiological Sciences, UCLA School of Medicine, Los Angeles, CA
• OSTI ID: 5387253
• Journal Information: Stroke; (United States), Journal Name: Stroke; (United States) Vol. 12:5; ISSN SJCCA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMMONIA
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BIOLOGICAL PATHWAYS
BLOOD FLOW
BLOOD VESSELS
BODY
BRAIN
CAPILLARIES
CARDIOVASCULAR SYSTEM
CENTRAL NERVOUS SYSTEM
CEREBRUM
DISTRIBUTION
DOGS
ELECTRON CAPTURE RADIOISOTOPES
HYDRIDES
HYDROGEN COMPOUNDS
ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
MACACUS
MAMMALS
METABOLISM
MINUTES LIVING RADIOISOTOPES
MONKEYS
NERVOUS SYSTEM
NITROGEN 13
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ORGANS
PERMEABILITY
PRIMATES
RADIOISOTOPES
TISSUE DISTRIBUTION
VERTEBRATES