Influence of development and reduction of fat stores on the antilipolytic alpha 2-adrenoceptor in hamster adipocytes: comparison with adenosine and beta-adrenergic lipolytic responses.
The response of the hamster adipocyte to various lipolytic (beta-adrenergic) and antilipolytic (alpha(2)-adrenergic and adenosine-dependent) stimuli was studied during the development and after cold-induced regression of fat stores. Alpha(2)-adrenergic binding ([(3)H]clonidine binding sites) was also investigated. Adipocytes came from young animals (4-5 weeks), adults (20-25 weeks), and adults submitted to a 6-week cold exposure (6 degrees C) that promoted a large decrease in fat stores and in fat cell size. The lipolytic response induced by isoproterenol (beta-agonist) was equivalent in the different groups. Adenosine and alpha(2)-adrenergic antilipolytic effects were estimated through the inhibition of theophylline-induced lipolysis by phenylisopropyladenosine and clonidine, respectively. The adenosine effect was unchanged in all the groups. In contrast, the alpha(2)-adrenergic effect, which was not present in young hamsters, increased simultaneously with fat cell size, was fully effective in adult hamsters, and had completely disappeared in small adipocytes from cold-exposed hamsters. In fat cell ghosts, alpha(2)-adrenoceptors ([(3)H]clonidine binding sites), followed similar modifications: they increased with fat cell enlargement and disappeared after cell size reduction following cold exposure. These results suggest that: 1) the increased alpha(2)-adrenergic antilipolytic response which is concomitant with fat cell enlargement could partly explain the growth-related decrease in the previously reported lipolytic effect of epinephrine; 2) the alpha(2)-receptivity of the adipocyte seems to be strictly fat cell size-dependent while the beta-adrenergic and adenosine responses are unaffected; and 3) the regulation in the adipocytes of the adenosine, alpha(2)- and beta-receptors seems to be unrelated.-Carpene, C., M. Berlan, and M. Lafontan. Influence of development and reduction of fat stores on the antilipolytic alpha(2)-adrenoceptor in hamster adipocytes: comparison with adenosine and beta-adrenergic lipolytic responses.
D000241:Adenosine / Q000031:analogs & derivatives*; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D003000:Clonidine / Q000378:metabolism / Q000494:pharmacology*; D006224:Cricetinae; D054755:Imidazoline Receptors; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D008066:Lipolysis / Q000187:drug effects*; D008297:Male; D008647:Mesocricetus; D010660:Phenylisopropyladenosine / Q000494:pharmacology*; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D018341:Receptors, Adrenergic, alpha-2; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013806:Theophylline / Q000494:pharmacology
D054755:Imidazoline Receptors; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D018341:Receptors, Adrenergic, alpha-2; D011943:Receptors, Adrenergic, beta; D010660:Phenylisopropyladenosine; D013806:Theophylline; D000241:Adenosine; D007545:Isoproterenol; D003000:Clonidine