[3H]Rilmenidine-labelled imidazoline-receptor binding sites co-localize with [3H]2-(benzofuranyl)-2-imidazoline-labelled imidazoline-receptor binding sites and monoamine oxidase-B in rabbit, but not rat, kidney.
The distribution and relative densities of imidazoline-receptor binding sites (I-RBS) and monoamine oxidase (MAO)-A and -B enzyme(s) in rat and rabbit kidney were compared autoradiographically using fixed nanomolar concentrations of [3H]rilmenidine and [3H]2-(benzofuranyl)-2-imidazoline ([3H]2-BFI) to label I-RBS, and [3H]RO41-1049 and [3H]RO19-6327 to label MAO-A and -B isoenzymes, respectively. In rat kidney, high densities of I-RBS labelled by [3H]rilmenidine were observed in the cortex and outer stripe (120-280 fmol/mg tissue), in contrast to low I-RBS densities labelled by [3H]2-BFI (<4 fmol/mg). A relatively high density of [3H]RO41-1049 binding to MAO-A enzyme was present in all regions of the rat kidney (160-210 fmol/mg) compared with a low density of [3H]RO19-6327 binding to MAO-B (< 25 fmol/mg). Comparison of MAO-A and -B distributions with that of [3H]rilmenidine-labelled I-RBS strongly suggests a lack of association in rat kidney. Similarly, the extremely low densities of [3H]2-BFI-labelled I2-RBS in rat kidney contrasts with the density of MAO-A, but is consistent with the low density of MAO-B. Rabbit kidney cortex and outer stripe contained high relative densities of [3H]rilmenidine-labelled I-RBS (200-215 fmol/mg) and [3H]2-BFI-labelled I2-RBS (45-60 fmol/mg) with lower densities in the inner stripe and inner medulla (< or = 100 and 30 fmol/mg respectively). A high density of MAO-A binding was observed in the inner stripe (515 fmol/mg) with lower levels in the cortex and outer stripe (100-240 fmol/mg), while high densities of MAO-B binding were observed in the cortex and outer stripe (290-450 fmol/mg) with lower levels in the inner stripe (65 fmol/mg). The correlation between the localization of [3H]rilmenidine-labelled I-RBS and [3H]RO19-6327-labelled MAO-B in rabbit kidney (r = 0.87, P = 0.057) suggest that [3H]rilmenidine may label a binding site co-existent with MAO-B, but not MAO-A (n.s.), in this tissue, but rilmenidine did not inhibit [3H]RO41-1049 or [3H]RO19-6327 binding. The distribution of [3H]2-BFI-labelled I2-RBS overlapped the combined distributions of both MAO-A and -B isoenzymes, suggesting that [3H]2-BFI may label sites on both enzymes in the rabbit, but [3H]2-BFI binding only correlated with [3H]RO19-6327 (r = 0.84, P = 0.07), not [3H]RO41-1049 binding (n.s.). Moreover, 2-BFI only inhibited [3H]RO19-6327, not [3H]RO41-1049 binding. These data are consistent with reports that I2-RBS are located on MAO-B and allosterically influence the catalytic site. The relationship of [3H]rilmenidine- and [3H]2-BFI-labelled I-RBS and the identity of non-MAO-associated [3H]rilmenidine-labelled I-RBS requires further investigation.
King
P R
PR
The University of Melbourne, Department of Medicine, Austin and Repatriation Medical Centre, Heidelberg, Victoria, Australia. paulk@austin.unimelb.edu.au
Suzuki
S
S
Hosseini
A R
AR
Iakovidis
D
D
Nero
T L
TL
Jackman
G P
GP
Louis
W J
WJ
Gundlach
A L
AL
D000316:Adrenergic alpha-Agonists / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D001572:Benzofurans / Q000378:metabolism; D007093:Imidazoles / Q000378:metabolism*; D054755:Imidazoline Receptors; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D007668:Kidney / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D008995:Monoamine Oxidase / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors / Q000378:metabolism; D010080:Oxazoles / Q000378:metabolism*; D010848:Picolinic Acids / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D011921:Rats, Inbred WKY; D011955:Receptors, Drug / Q000378:metabolism*; D000077769:Rilmenidine; D013045:Species Specificity; D013844:Thiazoles / Q000378:metabolism
D000316:Adrenergic alpha-Agonists; D001572:Benzofurans; D007093:Imidazoles; D054755:Imidazoline Receptors; D007527:Isoenzymes; D008996:Monoamine Oxidase Inhibitors; D010080:Oxazoles; D010848:Picolinic Acids; D011955:Receptors, Drug; D013844:Thiazoles; C063456:Ro 41-1049; C059303:lazabemide; C103723:2-(2-benzofuranyl)-2-imidazoline; D008995:Monoamine Oxidase; D000077769:Rilmenidine