AJP - Endocrinology and Metabolism, Vol 245, Issue 5 494-E501, Copyright © 1983 by American Physiological Society
In vitro regulation of human monocyte insulin receptors by insulin and 1-methyl-3-isobutylxanthine
R. H. Whitson and S. A. Kaplan
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.
