EXERCISE ATTENUATES THE ANTI-LIPOLYTIC EFFECT OF ADENOSINE IN ADIPOCYTES ISOLATED FROM MINIATURE SWINE

Four pairs of female and six pairs of male litter-mate Yucatan miniatu re swine (Sus scrofa) were used in this study which examined the possi bility that endurance exercise training reduces the sensitivity of adi pocytes to the anti-lipolytic effects of adenosine. One member of each pair was exercise-trained on a treadmill for three months while its l itter-mate remained sedentary, after which time over-the-shoulder fat and left brachialis muscle were biopsied. Despite a predominance of ty pe IIB fibres, biopsied muscle of exercised swine had 38% more citrate synthase activity than controls (P < 0.05). The average cell diameter s of adipocytes isolated from exercisers were 14% smaller (P < 0.05) t han those from controls. Rates of adrenaline-stimulated lipolysis expr essed as nmol glycerol released/90min incubation period per 10 000 cel ls failed to differ between the two groups; however, when expressed pe r cm(2) surface area, a significant 37% increase was observed. Incubat ion with 1 mu M adrenaline and increasing doses of phenylisopropyladen osine (PIA) caused a rightward shift in the dose-response curve of adi pocytes in five of the ten exercisers compared to litter-mate controls . The concentration of PIA causing one-half inhibition of lipolysis wa s 64% greater in adipocytes from exercisers than controls (4.03 nM vs. 2.49 nM, n = 10, P < 0.05). These data support the hypothesis that en durance exercise-training induces a reduction in adipocyte sensitivity to adenosine, thereby facilitating fatty acid mobilization.