Coexistence of three beta-adrenoceptor subtypes in white fat cells of various mammalian species.
The nature of the beta-adrenoceptors (beta-ARs) of the white fat cells of five mammalian species (rat, hamster, rabbit, dog and humans) was reassessed. The coexistence of at least three beta-ARs on the fat cell (except human) was demonstrated. Comparative binding and lipolysis studies were performed, using recently synthesized compounds selective for the atypical beta-AR of the rat brown fat cell and of the rat colon. beta 1- and beta 2-ARs have previously been identified in all the mammalian white fat cells using [125I]cyanopindolol ([125]CYP) or [3H]dihydroalprenolol. In addition to these receptors, we now demonstrated the existence of a third beta-AR directly involved in adrenergic-mediated lipolysis, and identified it in the white fat cells of the most commonly studied animal species, except humans. This receptor is not detected by the classically used beta-antagonist radioligands, explaining the discrepancies in reports on the nature of the beta-ARs of the adipose tissue. Pharmacological delineation of the third type of beta-AR-induced lipolysis showed this receptor to be rather similar to the previously proposed atypical beta-AR of brown and white rat fat cells. Its pharmacological properties were clarified, using new selective full agonists and partial agonists also acting as non-selective beta 1/beta 2-antagonists. The limits of [125]CYP as a radioligand were reported and the usefulness of BRL 37344, (+/-)-CGP 12177 and phenylethanolaminotralines derivatives (having an atypical beta-activity on intestinal motility) as major tools usable for atypical beta-AR activation was demonstrated. Moreover, confirming our previous results about the nature of the beta-ARs (beta 1- and beta 2-ARs) located in the fat cells of women (Mauriège et al., J. Lipid Res., 1987, 17, 156), no atypical beta-AR-mediated lipolysis was identified in abdominal adipose tissue from healthy women. The possible differences and similarities between this receptor and the recently cloned beta 3-AR are discussed.
INSERM Unité 317, Institut de Physiologie, Université Paul Sabatier, Toulouse, France.
D
D
Langin
M P
MP
Portillo
J S
JS
Saulnier-Blache
M
M
Lafontan
D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D002001:Adipose Tissue, Brown / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D004285:Dogs; D004983:Ethanolamines / Q000494:pharmacology; D006801:Humans; D007457:Iodine Radioisotopes; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008066:Lipolysis / Q000187:drug effects / Q000502:physiology; D008297:Male; D008647:Mesocricetus; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011412:Propanolamines / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000145:classification* / Q000187:drug effects / Q000378:metabolism
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004983:Ethanolamines; D007457:Iodine Radioisotopes; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; C047975:cyanopindolol; C057368:BRL 37344; D010869:Pindolol; D007545:Isoproterenol; C033394:CGP 12177