Alpha 1-adrenoceptor subtype affinities of drugs for the treatment of prostatic hypertrophy. Evidence for heterogeneity of chloroethylclonidine-resistant rat renal alpha 1-adrenoceptor.
We have used radioligand binding and inositol phosphate accumulation studies to determine the affinity at mixed alpha 1A- and alpha 1B-adrenoceptors (rat cerebral cortex and kidney), alpha 1A-adrenoceptors (rat cerebral cortex and kidney following inactivation of alpha 1B-adrenoceptors by chloroethylclonidine treatment) and alpha 1B-adrenoceptors (rat spleen) for drugs currently under investigation for the treatment of benign prostatic hypertrophy, alfuzosin, naftopidil and (-)- and (+)-tamsulosin. Alfuzosin and naftopidil had similar affinities in all model systems (approximately 10 nM and 130 nM, respectively) and lacked relevant selectivity for alpha 1-adrenoceptor subtypes. Their potency to inhibit noradrenaline-stimulated inositol phosphate formation in cerebral cortex matched their affinities as determined in the binding studies. Tamsulosin had higher affinity at alpha 1A- than at alpha 1B-adrenoceptors, and was slightly more potent than alfuzosin and naftopidil at alpha 1B- and considerably more potent at alpha 1A-adrenoceptors. However, the interaction of the tamsulosin isomers with chloroethylclonidine-insensitive (alpha 1A-like) adrenoceptors was complex. A detailed analysis of the tamsulosin data and those obtained with other drugs, most notably noradrenaline and oxymetazoline, suggested that chloroethylclonidine-insensitive alpha 1-adrenoceptors may be heterogeneous and that this heterogeneity may differ between cerebral cortex and kidney of the rat.
Michel
M C
MC
Department of Medicine, University of Essen, Germany.
Büscher
R
R
Kerker
J
J
Kraneis
H
H
Erdbrügger
W
W
Brodde
O E
OE
D000477:Alkylating Agents / Q000494:pharmacology*; D000818:Animals; D002499:Centrifugation, Density Gradient; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D003000:Clonidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004351:Drug Resistance; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D011470:Prostatic Hyperplasia / Q000188:drug therapy*; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000378:metabolism*
D000477:Alkylating Agents; D007295:Inositol Phosphates; D018340:Receptors, Adrenergic, alpha-1; C051731:chlorethylclonidine; D003000:Clonidine