Synthesis and characterization of a high affinity radioiodinated probe for the alpha 2-adrenergic receptor

Journal Article · Sat Mar 01 04:00:00 EST 1986 · Mol. Pharmacol.; (United States)

OSTI ID:5741462

Lanier, S M; Hess, H J; Grodski, A; Graham, R M; Homcy, C J

The availability of radioiodinated probes has facilitated the localization and molecular characterization of cell membrane receptors for hormones and neurotransmitters. However, such probes are not available for the study of the alpha 2-adrenergic receptor. This report describes the synthesis and characterization of functionalized derivatives of the selective alpha 2-adrenergic antagonists, rauwolscine and yohimbine, which can be radiolabeled to high specific activity with 125I. Following demethylation of rauwolscine or yohimbine, the resultant carboxylic acid derivatives were reacted with 4-aminophenethylamine to yield the respective 4-aminophenethyl carboxamides, 17 alpha-hydroxy-20 alpha-yohimban-16 beta-(N-4-amino-phenethyl)carboxamide (rau-pAPC) and 17 alpha-hydroxy-20 beta-yohimban-16 alpha-(N-4-aminophenethyl)carboxamide. In competitive inhibition studies using rat renal membranes and the radioligand (3H)rauwolscine, rau-pAPC (Ki = 11 +/- 1 nM) exhibited a 14-fold greater affinity than the corresponding yohimbine derivative (Ki = 136 +/- 45 nM). The higher affinity compound, rau-pAPC, was radioiodinated by the chloramine T method, and the product, 125I-rau-pAPC (17 alpha-hydroxy-20 alpha-yohimban-16 beta-(N-4-amino-3 -(125I)iodophenethyl)carboxamide), was purified by reverse phase HPLC to high specific activity (2175 Ci/mmol) and its binding characteristics were investigated in rat kidney membranes. Specific binding of 125I-rau-pAPC was saturable and of high affinity as determined by Scatchard analysis (KD = 1.8 +/- 0.3 nM) or from kinetic studies (KD = k2/k1 = 0.056 +/- 0.013 min-1)/4.3 +/- 0.2 X 10(7) M-1 min-1 = 1.3 +/- 0.3 nM).

• Research Organization: Massachusetts General Hospital, Boston
• OSTI ID: 5741462
• Journal Information: Mol. Pharmacol.; (United States), Journal Name: Mol. Pharmacol.; (United States) Vol. 3; ISSN MOPMA
• Country of Publication: United States
• Language: English

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38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
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62 RADIOLOGY AND NUCLEAR MEDICINE
ADRENAL HORMONES
ADRENALINE
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BLOOD PLATELETS
BODY
BODY FLUIDS
CARDIOTONICS
CARDIOVASCULAR AGENTS
CELL CONSTITUENTS
CELL MEMBRANES
CHEMICAL PREPARATION
DAYS LIVING RADIOISOTOPES
DIGESTIVE SYSTEM
DRUGS
ELECTRON CAPTURE RADIOISOTOPES
GLANDS
HORMONES
IN VITRO
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LIGANDS
LIVER
MAMMALS
MATERIALS
MEMBRANE PROTEINS
MEMBRANES
NEUROREGULATORS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANS
PROTEINS
RADIOISOTOPES
RATS
REACTION KINETICS
RECEPTORS
RODENTS
SPECIFICITY
STEROID HORMONES
SYMPATHOMIMETICS
SYNTHESIS
VERTEBRATES