Cerebral extraction of N-13 ammonia: its dependence on cerebral blood flow and capillary permeability -- surface area product.
- 1 September 1981
- journal article
- research article
- Published by Wolters Kluwer Health in Stroke
- Vol. 12 (5), 607-619
- https://doi.org/10.1161/01.str.12.5.607
Abstract
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.This publication has 31 references indexed in Scilit:
- QUANTITATIVE ANATOMY OF THE CEREBRAL VASCULAR BED WITH ESPECIAL EMPHASIS ON HOMOGENEITY AND INHOMOGENEITY IN SMALL PARTS OF THE GRAY AND WHITE MATTERActa Neurologica Scandinavica, 2009
- Barrier mechanisms for neurotransmitter monoamines and their precursors at the blood‐brain interfaceAnnals of Neurology, 1980
- Tomographic measurement of local cerebral glucose metabolic rate in humans with (F‐18)2‐fluoro‐2‐deoxy‐D‐glucose: Validation of methodAnnals of Neurology, 1979
- Regional myocardial perfusion assessed with N-13 labeled ammonia and positron emission computerized axial tomographyThe American Journal of Cardiology, 1979
- FACTORS AFFECTING UPTAKE OF 13N-AMMONIA BY THE BRAINJournal of Computer Assisted Tomography, 1978
- Blood flow measurements with radionuclide-labeled particlesProgress in Cardiovascular Diseases, 1977
- An improved method for the cyclotron production of 13N-labelled ammoniaThe International Journal of Applied Radiation and Isotopes, 1975
- The Partition of Trace Amounts of Xenon Between Human Blood and Brain Tissues at 37°CPhysics in Medicine & Biology, 1965
- The Permeability of Capillaries in Various Organs as Determined by Use of the ‘Indicator Diffusion’ MethodActa Physiologica Scandinavica, 1963
- Ammonia Toxicity and pHNature, 1962