Effect of adenohypophyseal pars tuberalis secretions on pars distalis prolactin liberation

Evidences presented indicating that factors produced by the pars tuberalis (PT) affect the prolactin the pars distalis (PD). The effect of the secretion products of bovine PT cells in culture medium was checked on dispersed PD cells of rats. PD cells were assayed in incubations of 30 minutes and superfusion experiments. When medium was obtained from total PT cells, the addition of 9 mu g of protein was needed to reach the major stimulation of prolactin liberation. However, when the medium from 50-60% Percoll gradient fractions was used, only 4 mu g of total protein were required. The partial purification of such medium by Sephadex G50 produced the same effect on the liberation of prolactin by PD cells with 80 ng of total protein. The active factor/s should have a molecular weight higher than 30 kDal. The results obtained suggest, at least for the prolactotrophic cells, that PD could be the effector organ for some of the secretory product(s) of PT.