Figure 5.

Phenolsulfonphthalein (phenol red), the pH indicator in cell culture media, is structurally similar to the natural estrogen estradiol (Figure 1) and synthetic estrogens. Unlike normal chemical titration analyses that use a pH indicator at very low concentrations, phenol red is incorporated at µM levels in culture media. The estrogenicity was found to vary from batch to batch [176]. However, a potent estrogenic contaminant (right) exerts growth stimulatory effects on breast cancer cells [38].