Assessment of beta 2- and beta 3-adrenoceptors in rat white adipose tissues by radioligand binding assay.
We investigated the characteristics of beta-adrenoceptors (beta-ARs) in rat white adipose tissues (WAT) with a radioligand receptor binding assay using (-)-[3H]-CGP12177. Scatchard analysis revealed that there are high- and low-affinity sites for (-)-[3H]-CGP12177 in WAT. The (-)-[3H]-CGP12177 bound to a high-affinity site was displaced by 1 microM propranolol. The rank of pKi values of catecholamines for the site was isoproterenol > epinephrine > norepinephrine. By contrast, BRL37344A, BRL35135A and SR59230A, beta 3-selective agonists had high affinity for the low-affinity site of (-)-[3H]-CGP12177, whereas (-)-[3H]-CGP12177 bound to a low-affinity site was completely displaced by 100 microM bupranolol but not 1 microM propranolol. The pKi values of the catecholamines (isoproterenol, norepinephrine, epinephrine) for this site were very low. In addition, the correlation between the pKi values of various beta-agonists for the low-affinity site of rat WAT and those obtained from rat cloned beta 3-ARs was significant, but those of human cloned beta 3-ARs were not. Consequently, the results suggested that the high- and low-affinity sites were beta 2-ARs and beta 3-ARs in rat WAT, respectively.
Kubo
S
S
Department of Pharmacology, Niigata College of Pharmacy, Japan.
Matsuda
A
A
Ohnuki
T
T
Hattori
K
K
Suzuki
J
J
Nagatomo
T
T
D000273:Adipose Tissue / Q000378:metabolism*; D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D066298:In Vitro Techniques; D008297:Male; D011412:Propanolamines / Q000378:metabolism / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D022702:Receptors, Adrenergic, beta-3; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism
D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D018343:Receptors, Adrenergic, beta-2; D022702:Receptors, Adrenergic, beta-3; D011994:Recombinant Proteins; C033394:CGP 12177