IMMUNOREACTIVE PROLACTINS OF THE NEUROHYPOPHYSEAL SYSTEM DISPLAY ACTIONS CHARACTERISTIC OF PROLACTIN AND 16K PROLACTIN

We have described the expression of the prolactin (PRL) gene and the o ccurrence of PRL-like immunoreactive proteins in the hypothalamic-neur ohypophyseal system of the rat. Here, we investigated the nature of ne urohypophyseal PRL-like antigens, by studying the biological activity of medium conditioned by incubated neurohypophyses in specific bioassa ys for PRL and for the 16 kDa N-terminal fragment of PRL (16K PRL). Ne urohypophyseal conditioned medium (NHCM) obtained after incubating neu rohypophyseal robes (1 h at 37 degrees C) was enriched with proteins o f 14 kDa and 23 kDa, that crossreacted with PRL- and 16K PRL-directed antisera. The NHCM stimulated in a dose-dependent fashion the prolifer ation of Nb2-lymphoma PRL-dependent cells. This effect paralleled that of PRL and 16K PRL standards and was neutralized by different dilutio ns of both PRL- and 16K PRL-antisera. Also, the NHCM inhibited the pro liferation of endothelial cells in culture, an antiangiogenic-effect e xerted by 16K PRL. The antiangiogenic effect of the NHCM was parallel to that of 16K PRL standard and neutralized by 16K PRL antiserum in a dose-dependent fashion. These results indicate that NHCM contains prot eins that share receptor activation properties as well as antigenic de terminants with both PRL and 16K PRL.