Smooth-muscle cell cultures were grown from thoracic aortas of normal and diabetic rabbits. The effect of diabetic rabbit serum on the growth of these cultures was studied both in the first, rapid-growth phase and the following, more “stationary” phase of growth. Control experiments were carried out on normal sera to which glucose had been added. The concentrations of cholesterol, phospholipid, and triglyceride were same in both normal and diabetic sera.

Media containing diabetic serum stimulated the growth of cultures significantly in both phases (2p < 0.01). This occurred in experiments utilizing cells from normal as well as from diabetic rabbits. Control media containing normal serum with added glucose had no such effect. The growth-promoting effects of diabetic serum and of hyperlipemic serum from nondiabetic rabbits were of the same order of magnitude.

Autoradiographic studies showed that the number of 3H-thymidine-labeled cells increased significantly after culture in diabetic serum (2p < 0.005).

Cells cultured from the very beginning in diabetic serum or normal serum with added glucose were significantly larger than cells grown in control serum (2p < 0.05 and 2p < 0.01, respectively). Cells grown in hyperlipemic serum were significantly smaller than those grown in normal serum (2p < 0.01).

These results indicate that diabetic serum contains a factor or factors that stimulate the arterial medial cell to excessive growth. This factor is not glucose, insulin, or lipid. The results may be of relevance for the understanding of human diabetic macroangiopathy.

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