Kinetic analysis of 3-quinuclidinyl 4-( sup 125 I)iodobenzilate transport and specific binding to muscarinic acetylcholine receptor in rat brain in vivo: Implications for human studies

Journal Article · Thu Nov 01 00:00:00 EST 1990 · Journal of Cerebral Blood Flow and Metabolism; (USA)

DOI:https://doi.org/10.1038/jcbfm.1990.136· OSTI ID:6217656

Sawada, Y; Hiraga, S; Francis, B; Patlak, C; Pettigrew, K; Ito, K; Owens, E; Gibson, R; Reba, R; Eckelman, W ^[1]

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1. National Institutes of Health, Bethesda, MD (USA)

Radioiodinated R- and S-Quinuclidinyl derivatives of RS-benzilate (R- and S-125IQNB) have been synthesized for quantitative evaluation of muscarinic acetylcholine receptor binding in vivo. Two sets of experiments were performed in rats. The first involved determining the metabolite-corrected blood concentration and tissue distribution of tracer R-IQNB (active enantiomer) and S-IQNB (inactive enantiomer) in brain 1 min to 26 h after intravenous injection. The second involved the measurement of brain tissue washout over a 2-min period after loading the brain by an intracarotid artery injection of the ligands. Various pharmacokinetic models were tested, which included transport across the blood-brain barrier (BBB), nonspecific binding, low-affinity binding, and high-affinity binding. Our analysis demonstrated that the assumptions of rapid equilibrium across the BBB and rapid nonspecific binding are incorrect and result in erroneous estimates of the forward rate constant for binding at the high-affinity receptor sites (k3). The estimated values for influx across the BBB (K1), the steady-state accumulation rate in cerebrum (K), and the dissociation rate constant at the high-affinity site (k4) of R-IQNB were independent of the specific compartmental model used to analyze these data (K1 approximately 0.23 ml/min/g, K approximately 0.13 ml/min/g, and k4 approximately 0.0019 min-1 for caudate). In contrast, the estimated values of k3 and the efflux rate constant (k2) varied over a 10-fold range between different compartmental models (k3 approximately 2.3-22 min-1 and k2 approximately 1.6-16 min-1 in caudate), but their ratios were constant (k3/k2 approximately 1.4).

• OSTI ID: 6217656
• Journal Information: Journal of Cerebral Blood Flow and Metabolism; (USA), Vol. 10:6; ISSN 0271-678X
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ACETYLCHOLINE
RECEPTORS
BENZILIC ACID
MEMBRANE TRANSPORT
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL MODELS
BLOOD-BRAIN BARRIER
IODINE 125
LIGANDS
RATS
TRACER TECHNIQUES
AMINES
AMMONIUM COMPOUNDS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BETA DECAY RADIOISOTOPES
CARBOXYLIC ACIDS
DAYS LIVING RADIOISOTOPES
DRUGS
ELECTRON CAPTURE RADIOISOTOPES
ESTERS
HYDROXY ACIDS
INTERMEDIATE MASS NUCLEI
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
MAMMALS
MEMBRANE PROTEINS
NEUROREGULATORS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
PARASYMPATHOMIMETICS
PROTEINS
QUATERNARY COMPOUNDS
RADIOISOTOPES
REACTION KINETICS
RODENTS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques