The outgrowths of medial explants of thoracic aorta from New Zealand rabbits were used to study the influence of estrogen on cell proliferation. After 5-6 weeks of rapid growth in Basal Eagle Medium (BME) supplemented with 10% normal rabbit serum, such cultures reached a stationary phase during which they showed little mitotic activity and little further increase in surface area. Replacement of 5% of the normal serum with hyperlipemic rabbit serum resulted in a stimulation of these stationary cultures into a phase of renewed proliferation, which was measured directly as increase in cell culture size and by [3H]thymidine incorporation visualized by autoradiography. The addition of estrogen (estradiol, Progynon, Schering Corp.) in a concentration of 0.02 microgram/ml to the culture medium inhibited the proliferative effect induced by the hyperlipemic serum. On the other hand it had no effect on the growth rate of such explant cultures during their rapid growth phase if added at the time of explantation for 6 weeks. This would indicate that the inhibition of the hyperlipemic serum-induced proliferation by estrogen is not due to a toxic effect on mitosis in general. Cells exposed to estrogen tended to have larger amounts of intracellular lipid as visualized by oil red O staining. Moreover, prolonged exposure to estrogen resulted in a significant decrease in stainable collagen and elastin in these cultures.
Animals Aorta, Thoracic