The effect of estrogens and progestins on monkey prolactin synthesis

Dispersed monkey pituitary cells were cultured on extracellular matrix and in serum-free medium for up to 1 month, with medium changes every other day. The cells were treated with ethanol vehicle or 10 nM 17β-estradiol (E₂β), 17α-estradiol (E₂α), progesterone (P₄), pregnenalone (P₅), 17α-hydroxyprogesterone (17OH P₄), and E₂β plus P₄. Immunoreactive PRL (IR-PRL) levels in 48 h medium samples were first determined with a homologous human PRL RIA and then with a heterologous monkey PRL RIA. On the last day of culture, the cells were incubated with [³⁵S]methionine for 4 h, and ³⁵S-labeled PRL in the medium and cells was determined and compared to 4 h IR-PRL. Differences between control and treated groups in 48 h IRPRL were greater with the heterologous monkey RIA. E₂β, E₂α, and E₂β plus P₄ significantly elevated IR-PRL in 48 h medium samples an average of 73%, as determined with the monkey RIA. P₄, P₅, or 17OH P₄ had no effect on IR-PRL in 48 h medium samples. Secreted and intracellular [³⁵S]PRL were consistently elevated by E₂β and E₂β plus P₄, but less consistently elevated by E₂α. P₄, P₅, or 17OH P₄ had little effect on [³⁵S]PRL in medium or cells. IR-PRL in the 4 h medium sample and cells generally paralleled [³⁵S]PRL, although E₂α caused a more consistent elevation in IR-PRL than in [³⁵S]PRL. In summary, E₂β and E₂α directly stimulate PRL synthesis by monkey pituitary cells on extracellular matrix in long term serum-free culture. Nanomolar levels of progestins have little direct effect on PRL synthesis, nor does 10 nM P₄ block the stimulatory effect of E₂β.