Journal of Lipid Research, Vol. 24, 766-774, June 1983
Copyright © 1983 by Lipid Research, Inc.

Influence of development and reduction of fat stores on the antilipolytic ₂-adrenoceptor in hamster adipocytes: comparison with adenosine and ßbeta;-adrenergic lipolytic responses

Christian Carpene , Michel Berlan , and Max Lafontan

Institut de Physiologie, Université Paul Sabatier, ERA 412 CNRS, rue F. Magendie, 31400 Toulouse, France, and Laboratoire de Pharmacologie Médicale, Faculté de Médicine, allées Jules Guesde, 31100 Toulouse, France

The response of the hamster adipocyte to various lipolytic (ßbeta;-adrenergic) and antilipolytic (₂-adrenergic and adenosine-dependent) stimuli was studied during the development and after cold-induced regression of fat stores. Alpha₂-adrenergic binding ([³H]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°C) that promoted a large decrease in fat stores and in fat cell size. The lipolytic response induced by isoproterenol (ßbeta;-agonist) was equivalent in the different groups. Adenosine and 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 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, ₂-adrenoceptors ([³H]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 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 ₂-receptivity of the adipocyte seems to be strictly fat cell size-dependent while the ßbeta;-adrenergic and adenosine responses are unaffected; and 3) the regulation in the adipocytes of the adenosine, ₂- and ßbeta;-receptors seems to be unrelated.—Carpene, C., M. Berlan, and M. Lafontan. Influence of development and reduction of fat stores on the antilipolytic ₂-adrenoceptor in hamster adipocytes: comparison with adenosine and ßbeta;-adrenergic lipolytic responses.

Supplementary key words fat cell size • ₂-receptor sites • ßbeta;-receptor sites • adenosine receptor sites • [³H]clonidine • isoproterenol • phenylisopropyladenosine • clonidine

Submitted on July 27, 1982
Revised on January 31, 1983

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