Effect of cyclic AMP on low density lipoprotein binding and internalization by cultured human fibroblasts.

Pretreatment of cultured human fibroblasts by cyclic AMP resulted in a marked decrease in the binding and internalization of the low density lipoproteins (about 55% of controls for cyclic AMP 2.10(-3) M). This effect was dose dependent and increased by theophyllin. DL propranolol, an inhibitor of adenylcyclase, had an opposite effect. Isoproterenol, which stimulates adenylcyclase, reproduced the effect of cyclic AMP. The cholesterol synthesis from [2-14C] acetate was decreased by cyclic AMP, theophyllin and isoproterenol, and increased by propranolol. The incorporation of [1-14C] oleate into cholesteryl esters was reduced by cyclic AMP, theophyllin, isoproterenol and propranolol.