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Relevance of the use of [ 3 H]‐clonidine to identify imidazoline receptors in the rabbit brainstem
Author(s) -
Bricca G.,
Zhang J.,
Greney H.,
Dontenwill M.,
Stutzmann J.,
Belcourt A.,
Bousquet P.
Publication year - 1993
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1993.tb13998.x
Subject(s) - clonidine , imidazoline receptor , medulla oblongata , chemistry , endocrinology , medicine , brainstem , receptor , alpha (finance) , agonist , adrenergic receptor , biology , biochemistry , central nervous system , construct validity , nursing , patient satisfaction
1 [ 3 H]‐clonidine binding was investigated in membranes isolated from the ventral medulla oblongata of the rabbit where clonidine produced a hypotensive effect which was not mediated by adrenoceptors. [ 3 H]‐clonidine specific binding, as defined by the difference between the binding of [ 3 H]‐clonidine in the presence and in the absence of 10 μ m cirazoline, occurred at two sites: a high affinity site with a K D = 2.9 ± 0.7 n m and a B max of 40 ± 8 fmol mg −1 protein and a low affinity site with a K D = 18.2 ± 0.4 n m and a B max of 66 ± 14 fmol mg −1 protein. 2 The high affinity sites being catecholamine‐sensitive were identified as α 2 ‐adrenoceptors. The low affinity binding of [ 3 H]‐clonidine was insensitive to catecholamines, as well as to other α 2 ‐adrenoceptor specific probes, and could be inhibited with high affinity only by compounds which lowered blood pressure when directly injected in the nucleus reticularis lateralis of the ventral brainstem, or by antagonists. 3 It was concluded that in the ventral medulla of the rabbit, [ 3 H]‐clonidine labelled α 2 ‐adrenoceptors and imidazoline receptors (IRs). Only the latter were related to the hypotensive effects of clonidine and rilmenidine directly injected into the rostroventrolateral medulla oblongata (RVLM) of the rabbit. The methodological problems regarding the study of IRs with [ 3 H]‐clonidine are discussed.