Cyclosporin A, rapamycin and FK506 decrease prolactin release from rat pituitary cells in primary culture

It is at present well established that prolactin exerts a non-specific immunoactivating function. In this work we tested whether the immunosuppressant drugs cyclosporin A, FK506 and rapamycin influence prolactin release from rat pituitary cells in primary culture. The tested drugs had no effect on the prolactin release measured during a 2h incubation period, indicating that they do not influence the secretion of prolactin from intracellular stores into the culture medium. During longer incubation times (48h), however, prolactin release was diminished to 56% +/- 18 (10 microM cyclosporin A), 64% +/- 14 (1 microM rapamycin) or 64% +/- 7 (1 microM FK506), suggesting an effect on prolactin production. At these drug concentrations no toxic effects were observed. The data indicate that inhibition of pituitary prolactin synthesis might contribute to the immunosuppressant action of cyclosporin A, rapamycin and FK506.