Temperature and benzyl alcohol as probes of the antilipolytic mechanism of insulin action in adipocytes.
The temperature dependence of cAMP accumulation and glycerol release in response to epinephrine and insulin in adipocytes is examined. (1) Glycerol release in the presence of epinephrine demonstrated linear Arrhenius kinetics to 41 degrees C, and above 45 degrees C glycerol release was progressively inhibited. (2) In contrast, incubation of the cells with both epinephrine and insulin resulted in glycerol release rates that were relatively temperature insensitive. (3) Calculation of the efficacy of insulin to inhibit epinephrine-stimulated glycerol release as a function of temperature yielded a biphasic response, with a distinct optimum around 41 degrees C, in a similar manner to the effects of insulin on hexose transport activation determined previously. (4) A saturating dose of insulin (40 ng/ml) was found to have no significant effect on epinephrine-stimulated intracellular cAMP over the temperature range studied. (5) Addition of benzyl alcohol (to 40 mM) resulted in substantial inhibition of basal, epinephrine stimulated, and insulin inhibited glycerol release, without affecting the magnitude of insulin inhibition. We conclude from these studies that (a) insulin inhibition of glycerol release can not be mediated directly by intracellular cAMP modulation, (b) as in the case of hexose transport activation, the signalling mechanism by the occupied insulin receptor appears to be relatively independent of the membrane lipid environment.
Hyslop
P A
PA
Department CNS Pharmacology, Lilly Research Laboratories, Indianapolis, IN 46285.
Kuhn
C E
CE
Sauerheber
R D
RD
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D019905:Benzyl Alcohol; D001592:Benzyl Alcohols; D003994:Bucladesine / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism / Q000502:physiology; D004837:Epinephrine / Q000502:physiology; D005990:Glycerol / Q000378:metabolism*; D007328:Insulin / Q000502:physiology*; D008066:Lipolysis; D008297:Male; D015335:Molecular Probes; D051381:Rats; D011919:Rats, Inbred Strains; D013696:Temperature
D001592:Benzyl Alcohols; D007328:Insulin; D015335:Molecular Probes; D003994:Bucladesine; D000242:Cyclic AMP; D019905:Benzyl Alcohol; D005990:Glycerol; D015056:1-Methyl-3-isobutylxanthine; D004837:Epinephrine