β 3-adrenergic receptors are responsible for the adrenergic inhibition of insulin-stimulated glucose transport in rat adipocytes

Abstract

The inhibition of insulin-stimulated glucose transport by isoprenaline, a mixed beta-adrenergic-receptor (AR) agonist, is well documented in rat adipocytes. Since it has been described that rat adipocytes possess not only beta 1- and beta 2- but also beta 3-ARs, the influence of various subtype-selective beta-AR agonists and antagonists on 2-deoxyglucose (2-DG) transport was assessed in order to characterize the beta-AR subtype involved in the adrenergic counter-regulation of the insulin effect. The stimulation of 2-DG transport by insulin was counteracted, in a dose-dependent manner, by all the beta-AR agonists tested, and the magnitude of the inhibition followed the rank order: BRL 37344 > isoprenaline = noradrenaline >> dobutamine = procaterol. The same rank order of potency was obtained for lipolysis activation. This is not in accordance with the pharmacological definition of a beta 1- or a beta 2-adrenergic effect, but agrees with the pharmacological pattern of a beta 3-adrenergic effect. The inhibitory effect of the beta 3-agonist BRL 37344 on insulin-stimulated 2-DG transport was not reversed by either the selective beta 1-antagonist ICI 89406 or the beta 2-antagonist ICI 118551. In addition, neither of these beta-antagonists was able to block the isoprenaline and noradrenaline effects, supporting major beta 3-adrenoceptor-subtype involvement in the adrenergic inhibition of insulin-stimulated 2-DG transport. Like isoprenaline, BRL 37344 inhibited (60% inhibition) insulin-stimulated glucose transport only when adenosine deaminase was present in the assay. Furthermore, the maximal inhibitory effects of isoprenaline and BRL 37344 were not additive, and were both dependent on albumin concentration in the incubation medium: they increased when the albumin concentration decreased in the medium from 3.5 to 1%. To conclude, the similarities between isoprenaline and BRL 37344 action on insulin-stimulated 2-DG transport, the poor efficacy of the beta 1-/beta 2-agonists and the lack of effect of selective beta 1- and beta 2-antagonists are compelling arguments to support the important role of beta 3-adrenoceptors in the adrenergic inhibition of glucose transport in rat adipocytes.

Role of Semicarbazide-sensitive Amine Oxidase on Glucose Transport and GLUT4 Recruitment to the Cell Surface in Adipose Cells

“…After centrifugation, the cells (upper part of the tubes) were placed in scintillation vials, and the incorporated radioactivity was counted. The extracellular 2-deoxyglucose present in the cell fraction was determined with adipocytes previously stopped with cytochalasin B; it did not exceed 1% of the maximum 2-deoxyglucose transport in the presence of insulin, as previously reported (35).…”

Alterations of lipid metabolism and gene expression in rat adipocytes during chronic olanzapine treatment

“…The radioactivity incorporated into the fat cells was counted as described by Olefsky,26 using dinonyl phthalate to separate intact fat cells from medium by a pulse spin as reported previously. 27 RNA preparation and real-time RT-PCR Total RNA was extracted using RNA easy minikit (Qiagen, Courtaboeuf, France). cDNA was synthesized from 1 mg of total RNA using random hexamers.…”

Suppression of insulin‐stimulated phosphatidylinositol 3‐kinase activity by the β3‐adrenoceptor agonist CL316243 in rat adipocytes

“…Therefore, insulin receptor activation caused the rapid delivery of IRS-l/PI 3-kinase complexes to intracellular membranes where 3'-phosphoinositides had accumulated and functioned in the membrane-associated events which accompanied the translocation of GLUT 4 to the plasma membrane. On the other hand, adrenoceptors (ARs) of the rat adipocytes are mainly ßi and ß 3 types according to pharmacological analysis [18,19]. Hence, it is possible that ß3-AR agonists affect insulin-stimulated glucose transport via PI 3-kinase activity.…”