Dibutyryl cyclic AMP inhibits LDL binding in cultured fibroblasts and arterial smooth muscle cells.

The interaction of low density lipoproteins (LDL) with cell membrane receptors is regulated by certain hormones. To test whether LDL receptor activity is influenced by cyclic AMP, the effect of dibutyryl cyclic AMP on LDL binding uptake and degradation was studied in cultured human skin fibroblasts and in rat and human arterial smooth muscle cells. Dibutyryl cyclic AMP in concentrations of 10(-3) to 10(-7)M inhibited LDL binding and degradation in fibroblasts and rat arterial smooth muscle cells, and degradation in human arterial smooth muscle cells. Inhibition of LDL receptor activity by dibutyryl cyclic AMP did not appear to be due to a non-specific toxic effect of the nucleotide. It appeared to be mediated on the affinity of the receptor for LDL rather than receptor number.