17-BETA -ESTRADIOL-DEPENDENT REGULATION OF SOMATOSTATIN RECEPTOR SUBTYPE EXPRESSION IN THE 7315B PROLACTIN SECRETING RAT PITUITARY TUMOR IN VITRO AND IN VIVO

In the present study, we have investigated the role of estrogens in the regulation of somatostatin receptor subtype (sst) expression in 7315b PRL-secreting rat pituitary tumor cells in vitro and in vivo. sst were undetectable in freshly dispersed cells of the transplantable 7315b tumor. When 7315b cells were cultured in medium containing 10% FCS, the number of high affinity sst increased with prolonged culture time. However, when the medium was supplemented with 10% horse serum (HS) instead of FCS, no sst were detectable on 7315b cells even after three weeks of culturing. In contrast to HS, FCS contains high E2-levels (HS, 8 pm; FCS, 134 pm). The antiestrogen tamoxifen (0.5 μm) significantly inhibited the sst number to 50.5% of the value of untreated FCS-grown cells, suggesting that E2 stimulates sst expression in 7315b rat pituitary tumor cells. E2 (10 nm) induced a rapid increase in sst number in HS-grown 7315b cells. Octreotide (1 μm) significantly inhibited PRL release and the intracellular PRL concen...