Effects of Sex Steroids on Prolactin Secreting Rat Pituitary Cells in Culture

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Abstract
A clonal strain of rat pituitary tumor cells (GH3) was used to study the effects of different sex steroids on the production of prolactin (PRL). Hormone production was measured by radioimmunoassay and expressed as the amount of hormone which accumulated in the medium of monolayer cultures during 24 h. The stimulatory effect of 17.beta.-estradiol (10-11 M-10-6 M) on PRL production was significant after 4 days, and the maximum effect (300% of control cultures) was observed at 10-8 M after 10 days of treatment. After removal of added 17.beta.-estradiol, the production of PRL returned to control levels in 5 days. Progesterone (10-11 M-10-6 M) caused a dose-related decrease in PRL production reaching 60% of control values at 10-6 M. Testosterone (10-6 M) stimulated the production of PRL (130% of controls), whereas 5.alpha.-dihydrotestosterone (10-6 M) had a small effect (107% of controls) which was not always reproducible. None of the sex steroids affected cell growth. Progesterone (10-6 M) inhibited the stimulatory effect of 17.beta.-estradiol (10-8 M) on PRL production. The effect of 17.beta.-estradiol (10-8 M) and thyrotropin releasing hormone (TRH) (3 .times. 10-7 M) was additive, while no additional stimulatory effect was observed when 17.beta.-estradiol (10-8 M) was combined with testosterone (10-6 M). If the properties of the GH3 cells are analogous to those of normal lactotropes, the sex steroids may alter PRL production at the pituitary level, an influence that may be further modulated by TRH.

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