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Rapid modulation of adipocyte phosphofructokinase activity by noradrenaline and insulin.

ABSTRACT: 1. Alterations in phosphofructokinase properties can be reproducibly seen in tissue extracts prepared and rapidly assayed after exposure of rat adipocytes to hormones. 2. Noradrenaline, corticotropin or isoprenaline (isoproterenol; beta-adrenergic agonist) decreased the activity measured with high fructose 6-phosphate concentrations (3--6 mM), but increased activity measured with lower concentrations of this substrate (0.3--0.9 mM). Noradrenaline decreased the Vmax. and the concentration of fructose 6-phosphate that gave half the Vmax.. 3. Insulin opposed the actions of noradrenaline and itself increased phosphofructokinase activity. 4. The effect of noradrenaline appeared to be exerted through a beta- rather than an alpha-type of adrenoceptor. 5. The effects of noradrenaline to decrease phosphofructokinase activity at high [fructose 6-phosphate] and to increase activity at low [fructose 6-phosphate] could be rapidly reversed in cells by addition of the beta-blocker propranolol. 6. The effect of noradrenaline seen at low [fructose 6-phosphate] could be abolished by homogenization of cells in buffer containing albumin or reversed by brief incubation of tissue extracts with albumin, suggesting that this effect of the hormone is due to the association of some ligand with the enzyme.

SUBMITTER: Sooranna SR

PROVIDER: S-EPMC1158172 | biostudies-other | 1982 Mar

REPOSITORIES: biostudies-other

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Project description:Adipose harbors a large depot of free cholesterol. However, a role for adipose in cholesterol lipidation of high-density lipoprotein (HDL) in vivo is not established. We present the first evidence that adipocytes support transfer of cholesterol to HDL in vivo as well as in vitro and implicate ATP-binding cassette subfamily A member 1 (ABCA1) and scavenger receptor class B type I (SR-BI), but not ATP-binding cassette subfamily G member 1 (ABCG1), cholesterol transporters in this process.Cholesterol efflux from wild-type, ABCA1(-/-), SR-BI(-/-), and ABCG1(-/-) adipocytes to apolipoprotein A-I (apoA-I) and HDL3 were measured in vitro. 3T3L1 adipocytes, labeled with (3)H-cholesterol, were injected intraperitoneally into wild-type, apoA-I transgenic, and apoA-I(-/-) mice, and tracer movement onto plasma HDL was monitored. Identical studies were performed with labeled wild-type, ABCA1(-/-), or SR-BI(-/-) mouse embryonic fibroblast adipocytes. The effect of tumor necrosis factor-alpha on transporter expression and cholesterol efflux was monitored during adipocyte differentiation. Cholesterol efflux to apoA-I and HDL3 was impaired in ABCA1(-/-) and SR-BI(-/-) adipocytes, respectively, with no effect observed in ABCG1(-/-) adipocytes. Intraperitoneal injection of labeled 3T3L1 adipocytes resulted in increased HDL-associated (3)H-cholesterol in apoA-I transgenic mice but reduced levels in apoA-I(-/-) animals. Intraperitoneal injection of labeled ABCA1(-/-) or SR-BI(-/-) adipocytes reduced plasma counts relative to their respective controls. Tumor necrosis factor-alpha reduced both ABCA1 and SR-BI expression and impaired cholesterol efflux from partially differentiated adipocytes.These data suggest a novel metabolic function of adipocytes in promoting cholesterol transfer to HDL in vivo and implicate adipocyte SR-BI and ABCA1, but not ABCG1, in this process. Furthermore, adipocyte modulation of HDL may be impaired in adipose inflammatory disease states such as type 2 diabetes mellitus.

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Rapid modulation of adipocyte phosphofructokinase activity by noradrenaline and insulin.

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