Homologous up-regulation of the prolactin receptor in rat prostatic explants

Exposure of explants of rat ventral prostates and a rat Leydig cell tumour to ovine prolactin for 20 h caused alterations of the subsequent membrane binding of 125I-human prolactin to an extent and in a direction dependent on the dose of hormone used. Low prolactin concentrations (1-10 micrograms/2 ml) were associated with an increase in binding (up-regulation) which was 75% in the case of the prostatic tissue and 500% in the case of the tumour tissue above control levels. Higher concentrations caused a dose-dependent decrease in binding to below control levels (down-regulation), alterations which could not be explained by receptor occupancy. Time studies with an up-regulatory dose of hormone (3 micrograms/2 ml) indicated that the effects of prolactin on its receptor did not begin to become manifest until after 6-12 h of culture. The results suggest that homologous up-regulation of prolactin binding may be a general feature of prolactin target organs and that explant cultures of prostatic tissue may provide a convenient model for exploring its mechanisms.