Effects of normolipidemic high-density lipoproteins on proliferation of monkey aortic smooth muscle cells induced by hyperlipidemic low-density lipoproteins.

The primary outgrowth of medial explants of thoracic aorta from rhesus monkeys was used to study the influence of normolipidemic (N) high-density lipoproteins (HDL) on cell proliferation induced by hyperlipidemic (H) low-density lipoprotein (LDL). The experiments were initiated about 6 weeks after explantation when the cellular outgrowth had almost reached the stationary phase of growth. After being added to the culture media, 5% H-LDL induced another proliferative phase in the cultures, as measured by increase in culture area and [3H]thymidine incorporation. The cell proliferation stimulation by 5% H-LDL was prevented by adding 15% N-HDL along with the 5% H-LDL, so that the increment of colony size and incorporation rate of [3H]thymidine into nuclei were similar to those of a group maintained in a medium containing 5% N-HDL. In a second experiment the addition of 5% to 20% of N-HDL to the culture medium containing 5% H-LDL reduced the percentage of nuclei labeled by [3H]thymidine to control levels at all concentrations of N-HDL. In both experiments, the addition of N-HDL by itself at any concentration, from 5 to 20%, did not stimulate cell proliferation.