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Résumé

During its seasonal cycle, alpine marmot (Marmota marmota) shows a great management of its fat stores. Fat accumulated by marmot during the summer period constitutes the only energy supply for winter season. Hormonal regulation of lipolysis in this hibernant is not much understood yet. The aim of this work is to study the seasonal hormonal sensitivity and response of white adipocyte from two differents sites: intraperitoneal and subcutaneous white adipose tissues. Lipolytic hormones used are norepinephrine and corticotrope hormone (ACTH) wich are largely responsible for the hormonal control of adipocytes lipolytic activity in mammals. By the use of Adenosine Deaminase (ADA), we also studied the effects of Adenosine (ADO) as local inhibiting factor of lipolysis. Simultaneous study of lipolytic effect of these hormones in the two adipose sites shows that the lipolytic rate of subcutaneous adipose tissue is higher than the one of peritoneal tissue during hibernation season and the two months following the spring arousal. Results obtained with ADA show the existence of an important control of basal lipolysis by ADO and that the stimulation of lipolysis is higher during hibernation and spring in subcutaneous than in intraperitoneal fat cells. Marmots are able to use selectively these two adipose sites, according to the season. Subcutaneus fat appears as the main energy supplier during medium and late hibernation and early spring. This phenomenon disappears when marmots regain a daily food rythm and subcutaneous fat shows a decrease in this lipolytic rate during the summer period. By this way, marmots can reconstitute their subcutaneus fat stores before the next hibernation season. These results point to a surprising and important contribution of subcutaneus fat in the mobilization of energetic substrats during the process of hibernation.