EFFECT OF A BETA(3)-ADRENERGIC AGONIST, BRL35135A, ON GLUCOSE-UPTAKE IN RAT SKELETAL-MUSCLE IN-VIVO AND IN-VITRO

The effects of the beta(3)-agonist, BRL35135A, on glucose uptake in th e peripheral tissues of the rat, including skeletal muscle, were studi ed using the 2-[H-3]deoxyglucose method in anaesthetized adult animals . Intravenous infusion of the beta(3)-agonist dose-dependently increas ed the rate constant of glucose uptake in three types of skeletal musc le, brown adipose tissue, white adipose tissue, heart and diaphragm, b ut not in the brain, spleen or lung. Although infusion of the beta(3)- agonist did not change the plasma concentration of glucose appreciably , it caused an increase in the plasma concentration of insulin when gi ven at more than 25 mu g/kg per h. To ascertain whether the effect of the beta(3)-agonist on glucose uptake in skeletal muscle is mediated b y insulin, glucose uptake into soleus muscle isolated from young rats was also measured in vitro using different concentrations of the beta( 3)-agonist. The beta(3)-agonist BRL37344 (an active metabolite of BRL3 5135A) significantly increased glucose transport in a dose-dependent m anner, with maximum stimulation at 100 pmol/l. These results demonstra te that glucose uptake in skeletal muscle can be enhanced through the mediation of beta(3)-adrenoceptors present in the tissue.