Abstract
The effect of insulin on the LDL pathway was studied in cultured human fibroblasts in relation to the cell proliferative and glucoregulatory effects of insulin. The number of LDL receptors increased within 2 hr, and half the maximal stimulation by insulin was observed below an insulin concentration of 2.5 ng/ml, which is similar to that for the half maximal effect on glucose incorporation.
The effect of insulin on the LDL pathway was also studied in relation to the MI cycle, by using synchronized cells. A stimulatory effect of insulin on the LDL pathway was observed in the G1 phase (phase of preparation for DNA synthesis), but not in the S phase (DNA synthetic phase). A stimulatory effect of insulin on glucose metabolism was also observed in the G, phase, but not in the S phase.
These results suggest that insulin plays a physiologically important role in LDL metabolism by increasing the number of LDL receptors. Furthermore, the lack of an insulin effect in the S phase without changing insulin receptor binding provides an interesting finding for the elucidation of cellular insulin action.
