Effects of the perfusion of beta-, beta 2-, or beta 3-adrenergic agonists or epinephrine on in situ adipose tissue lipolysis measured by microdialysis in underfed ewes

The effects of isoproterenol (ISO, a non-selective beta -agonist), terbutal ine (TER, a selective beta2-agonist), CL316243 (CL, a selective beta3-agoni st), and epinephrine (EPI, beta- and alpha2-agonist) on in situ lipolytic r esponse of s.c. adipose tissue were investigated in vivo, using a microdial ysis method to measure glycerol release, in 12 adult nonlactating and ovari ectomized, underfed Lacaune ewes. All the adrenergic compounds were perfuse d for 120 min at 10(-6), 10(-5), and 10(-4) M. They had no lipolytic effect at 10(-6) M. Isoproterenol and EPI at 10(-5) and 10(-4) M enhanced, in the same way, maximal response and area under the concentration curve (AUC) of dialysate glycerol, thus suggesting that involvement of alpha2-adrenocepto rs in the control of in situ lipolysis is of minor importance in underfed e wes. Terbbutaline had only a slight lipolytic effect at 10(-5) M. This low effect could be due to a lower affinity of TER than of ISO for the beta2-ad renoceptors. The beta3-agonist, CL, had no lipolytic effect whatever the co ncentration perfused. Further studies are needed to prove the putative pres ence of beta3-adrenoceptors and their possible role in the ovine adipose ti ssue.