title: Biphasic effects of the beta-adrenoceptor agonist, BRL 37344, on glucose utilization in rat isolated skeletal muscle.
abstract: 1. The effects of the selective beta 3-adrenoceptor agonist, BRL 37344 (BRL) on glucose uptake and phosphorylation (i.e. glucose utilization; GU) and glycogen synthesis in rat isolated soleus and extensor digitorium longus (EDL) muscle preparations in vitro were investigated by use of 2-deoxy-[3H]-glucose (GU) and [U-14C]-glucose (glycogen synthesis). 2. Low concentrations of BRL (10(-11)-10(-9) M) significantly increased GU, with maximal increases of 30% in soleus and 24% in EDL at 10(-11) M. Neither the selective beta 1-adrenoceptor antagonist, atenolol (10(-8)-10(-6) M), nor the selective beta 2-adrenoceptor antagonist, ICI 118551 (10(-8)-10(-6) M) had any effect on the stimulation of GU induced by 10(-11) M BRL. 3. High concentrations of BRL (10(-6)-10(-5) M) caused significant inhibition (up to 30%) of GU in both soleus and EDL muscles. The inhibition of 10(-6) M BRL was blocked completely by 10(-6) and 10(-7) M ICI 118551 in soleus, and by 10(-6)-10(-8) M ICI 118551 in EDL; atenolol (10(-8)-10(6) M) had no effect. 4. Another selective beta 3-adrenoceptor agonist, CL 316,243, also caused a significant stimulation of muscle GU, with maximal increases of 43% at 10(-9) M in soleus and 45% at 10(-10) M in EDL. The stimulation of GU declined with further increases in the concentration of CL 316,243, but no inhibition of GU was seen, even at the highest concentration (10(-5) M) tested. 5. BRL at 10(-5) M inhibited completely insulin-stimulated glycogen synthesis in both soleus and EDL, but this inhibitory effect of BRL was abolished by 10(-6) M ICI 118551. BRL at 10(-11) M (with or without 10(-6) M ICI 118551) had no effect on insulin-stimulated glycogen synthesis. 6. It is concluded that: (i) low (< nM) concentrations of BRL stimulate GU via an atypical beta-adrenoceptor that is resistant to conventional beta 1-adrenoceptor and beta 2-adrenoceptor antagonists; (ii) the stimulation of GU is negated by the activation of beta 2-adrenoceptors that occurs at higher (> nM) concentrations of BRL; (iii) inhibition of GU via beta 2-adrenoceptor activation is associated with inhibition of glycogen synthesis, possibly due to activation of glycogenolysis; (iv) the opposing effects of beta 2-adrenoceptor and atypical beta-adrenoceptor activation on GU suggest that in skeletal muscle these adrenoceptors are linked to different post-receptor pathways.
authors.affiliation: Department of Physiology, St George's Hospital Medical School, Tooting, London.
authors.forename: Y L
authors.initials: YL
authors.lastname: Liu
authors.forename: M A
authors.initials: MA
authors.lastname: Cawthorne
authors.forename: M J
authors.initials: MJ
authors.lastname: Stock
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001262:Atenolol / Q000494:pharmacology; D004149:Dioxoles / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004983:Ethanolamines / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013237:Stereoisomerism
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004149:Dioxoles; D004983:Ethanolamines; D011412:Propanolamines; C076126:disodium (R,R)-5-(2-((2-(3-chlorophenyl)-2-hydroxyethyl)-amino)propyl)-1,3-benzodioxole-2,3-dicarboxylate; C026777:ICI 118551; D001262:Atenolol; C057368:BRL 37344; D005947:Glucose