PROLACTIN-RELEASE FROM SUBPOPULATIONS OF RAT LACTOTROPHS IN RESPONSE TO THYROTROPIN-RELEASING-HORMONE

This experiment was designed to examine the responsiveness of lactotro ph subpopulations from different zones of rat pituitaries to TRH. Pitu itaries, obtained from ovariectomized (OVX) rats either untreated or t reated with estradiol, progesterone or a combination of estradiol and progesterone, were cut into an inner zone and an outer zone, Each of t hese regions was enzymatically dispersed and the resulting cells subje cted to density sedimentation through a discontinuous Percoll gradient to separate cells into fight and heavy subpopulations. These cells an d unseparated controls were perifused sequentially over a 3.5 h period in the presence of PRL secretagogues (Dopamine, TRH, All). PRL releas e into the perifusion medium was measured by radioimmunoassay. In this paper only the data obtained during TRH treatment are given. Prolacti n release from unseparated cells of both outer and inner zone was incr eased significantly by TRH in the steroid treated groups but not in th e OVX group. However, when lactotrophs of OVX rats were separated on P ercoll, light cells of both zones did respond significantly to TRH as did heavy cells from the outer but not the inner zone. Pretreatment of rats with estradiol significantly increased the response to TRH above OVX controls in the heavy but not light cell fractions of both zones. Finally, combined estradiol and progesterone pretreatment enhanced th e stimulatory effect of estradiol on TRH-induced PRL release in unsepa rated cells of both inner and outer zones. The results suggest that la ctotrophs of the inner and outer zones of OVX and OVX, steroid treated rats respond similarly to TRH, but that within each of these zones, e stradiol and estradiol plus progesterone pretreatment makes heavy cell s more responsive than light cells.