Comparison of alpha 1-adrenoceptors between rat brain and spleen.
Scatchard analyses of 3H-prazosin binding in rat brain membranes showed biphasic curves, which identified the presence of alpha 1High- and alpha 1Low-affinity sites. The alpha 1High-affinity site was completely inhibited by 0.1 microM phenoxybenzamine. On the other hand, 3H-prazosin binding in rat spleen membranes resulted in linear curves that were identical to the binding curve for the alpha 1High-affinity site in the brain. The displacement potencies of alpha 1-adrenergic antagonists were characterized by 3H-prazosin binding to alpha 1High-affinity sites in the rat spleen and brain and alpha 1Low-affinity sites in the brain in the presence of 0.1 microM of phenoxybenzamine. The affinities of WB-4101, phenoxybenzamine, phentolamine, chlorpromazine, labetalol and nifedipine for brain alpha 1High-affinity sites were significantly higher than those in the spleen. The affinities of most ligands for alpha 1Low-affinity sites were significantly lower than those for both alpha 1High-affinity sites in the brain and spleen, but chlorethylclonidine was significantly selective for alpha 1Low-affinity sites, and bunazosin, dibenamine and 5HT had the same affinities for the alpha 1Low- and both alpha 1High-affinity sites. These results show that two alpha 1-adrenoceptor subtypes, alpha 1High- and alpha 1Low-affinity, are present in the rat brain and that a different alpha 1High-subtype, exists in the rat spleen.
Tsuchihashi
H
H
Department of Pharmacology, Niigata College of Pharmacy, Japan.
Maruyama
K
K
Baba
S
S
Mano
F
F
Kinami
J
J
Nagatomo
T
T
D000317:Adrenergic alpha-Antagonists / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D003983:Dibenzylchlorethamine / Q000378:metabolism; D007700:Kinetics; D008297:Male; D010643:Phenoxybenzamine / Q000378:metabolism / Q000494:pharmacology; D011224:Prazosin / Q000378:metabolism; D011799:Quinazolines / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000737:chemistry / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism; D013154:Spleen / Q000378:metabolism*
D000317:Adrenergic alpha-Antagonists; D011799:Quinazolines; D011942:Receptors, Adrenergic, alpha; D010643:Phenoxybenzamine; D012701:Serotonin; D003983:Dibenzylchlorethamine; C018176:bunazosin; D011224:Prazosin