Weak estrogenic activity of phenol red in the culture medium: its role in the study of the regulation of prolactin release in vitro.

Phenol red, which is commonly used in culture media as a pH indicator, has recently been shown to possess estrogenic properties. In this study we investigated the effects of phenol red on prolactin release and synthesis by cultured female and male rat anterior pituitary cells and on the sensitivity of these cells of dopamine, TRH and somatostatin (SRIF). It was shown that phenol red stimulated rat prolactin release and cell content in a dose-dependent manner. The effects of 30 microM phenol red, which is the medium concentration in our regular culture medium, and a submaximally active concentration of 17 beta-estradiol (E2) were additive. Male rat pituitary cells were far more responsive to phenol red and also to E2 than female pituitary cells. The antiestrogen tamoxifen (100 nM) significantly inhibited the phenol red-stimulated prolactin release by male rat pituitary cells but caused a 2-fold increase of prolactin release in the absence of phenol red. 30 microM phenol red did not modulate the responsiveness of female and male rat lactotrophs to dopamine, TRH or SRIF. We propose from our results that the estrogenic effect of 30 microM phenol red is too weak in order to alter the responsiveness of rat lactotrophs to dopamine, TRH and SRIF but the presence of phenol red in culture media should be considered when the effects of estrogens and antiestrogens on rat prolactin release and synthesis in vitro are studied.