In vitro regulation of human monocyte insulin receptors by insulin and 1-methyl-3-isobutylxanthine.
Monocytes separated from human blood by Ficoll-Hypaque and adherence to polystyrene flasks were maintained successfully in culture for 7 days. The cultured cells showed normal morphology and good viability. The insulin binding properties of the cultured monocytes were also identical to those of fresh monocytes. In vitro pretreatment of the monocytes with insulin decreased both the number and affinity of insulin receptors, resulting in a 72% reduction in the binding of tracer quantities of 125I-insulin. Insulin-induced receptor down regulation was dose-dependent and specific to the insulin receptor. Monocytes pretreated with insulin in the presence of the cyclic nucleotide phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine (MIX) lost significantly fewer insulin receptors than monocytes treated with insulin alone. Tracer binding to these cells was 62% of control levels. MIX had no effect on basal insulin binding. The cAMP analogues N6,O2'-dibutyryl cAMP and 8-bromo-cAMP did not counteract insulin-induced receptor downregulation by themselves and did not significantly enhance the effects of MIX. These results indicate that MIX may counteract insulin receptor downregulation by a cAMP-independent process.
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000097:blood; D003994:Bucladesine / Q000494:pharmacology; D000242:Cyclic AMP / Q000097:blood; D005934:Glucagon / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D011972:Receptor, Insulin / Q000187:drug effects / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism; D018027:Receptors, Glucagon; D013806:Theophylline / Q000031:analogs & derivatives*
D007328:Insulin; D011956:Receptors, Cell Surface; D018027:Receptors, Glucagon; D003994:Bucladesine; D005934:Glucagon; D013806:Theophylline; D000242:Cyclic AMP; D011972:Receptor, Insulin; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D015056:1-Methyl-3-isobutylxanthine