http://repub.eur.nl/res/aut/3944/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/8652/ 1997-01-01T00:00:00Z 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 microM) 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 microM) significantly inhibited PRL release and the intracellular PRL concentration of 7315b cells that were cultured in medium supplemented with FCS or with HS + 10 nM E2 but not in HS alone. This indicates that the sst present on these cells are biologically active. RT-PCR analysis revealed that none of the five currently known sst subtypes were present in freshly dispersed 7315b pituitary tumor cells. The expression of sst2- and sst3-messenger RNA (mRNA) was unequivocally correlated to the presence of E2 because these sst subtypes were detected only in cells that were cultured for 7 and 14 days in medium supplemented with FCS or with HS + 10 nM E2. sst1, sst4 and sst5 messenger RNA could not be detected. The 7315b tumor itself synthesizes and secretes huge amounts of PRL. The high PRL levels in tumor-bearing rats inhibit the ovarian E2-production. No detectable E2 levels could be measured in the serum of 7315b tumor-bearing rats. The sc administration of 20 micrograms/day E2-benzoate normalized the circulating E2 levels in 7315b tumor-bearing rats. Moreover, E2-treatment indeed induced sst expression in vivo as shown by ligand binding studies using membrane homogenates and [125I-Tyr3]-octreotide as radioligand and by autoradiography on tissue sections. In agreement with the in vitro studies, the expression of the sst2 subtype was established by RT-PCR analysis in 7315b tumors of E2-treated rats. However, in contrast to the in vitro studies, E2-treatment did not effectuate the expression of the sst3 subtype, suggesting that the in vitro stimulus of E2 is stronger. In conclusion: 1) sst2 and sst3 expression in the 7315b rat prolactinoma model is primarily dependent upon the presence of estrogens; 2) the antihormonal action of octreotide in 7315b tumor cells in vitro is mediated via the sst2 and/or sst3 subtypes; 3) the absence of sst expression in vivo can be explained by the hormonal environment of the 7315b tumor cells. The 7315b tumor cells in vivo may down regulate their own receptor status via their host, because of the ensuring hyperprolactinemia results in a hypo-estrogenic state. http://repub.eur.nl/res/pub/8716/ 1997-01-01T00:00:00Z The effects of somatostatin (SS-14 and/or SS-28) and of the three octapeptide SS-analogs that are available for clinical use (octreotide, BIM-23014 and RC-160) on hormone release by primary cultures of 15 clinically nonfunctioning pituitary adenomas (NFA), 7 prolactinomas, and 2 insulinomas were investigated. In the pituitary adenoma cultures, a comparison was made with the effects of the dopamine (DA) agonists bromocriptine and/or quinagolide. In 5 NFAs, 2 prolactinomas and 1 insulinoma somatostatin receptor (subtype) expression was determined by ligand binding studies and by in situ hybridization to detect sst1, sst2, and sst3 messenger RNAs (mRNAs). Four NFA cultures did not secrete detectable amounts of alpha-subunit, FSH, and/or LH. In the other cultures, hormone and/or subunit release was inhibited by DA-agonists (10 nM) in 9 of 11, by SS (10 nM) in 7 of 11, and by octapeptide SS-analogs (10 nM) in 3 of 10 cultures. In three NFA cultures, hormone release was sensitive to SS but not to SS-analogs. In all cultures, except for one, DA-agonists were the most effective in inhibiting hormone release. In the prolactinoma cultures, PRL release was inhibited by DA-agonists (10 nM) in 7 of 7, by SS in 4 of 4, and by octapeptide SS-analogs in 3 of 7 cultures. A dissociation between the effects of SS and SS-analogs was found in 3 cases. In the cultures sensitive to both bromocriptine and SS-28, bromocriptine was the most potent compound in 2 out of 4 cultures. In the 2 other cultures, both compounds were equally effective. In 2 insulinoma cultures, insulin release was inhibited by SS, and by octapeptide SS-analogs in only one. The presence or absence of an inhibitory effect by octreotide was in all cases in parallel with the presence or absence of the inhibitory effect by BIM-23014 and RC-160. Autoradiographic studies using [125I-Tyr0]SS28 showed specific binding in 4 of 5 NFAs, 1 of 2 prolactinomas, and 1 of 1 insulinoma. Specific [125I-Tyr3]octreotide binding was found in 2 of 5 NFAs, in 1 of 2 prolactinomas, and in the insulinoma. Two NFAs showed binding of SS28, but not of the sst2.5 specific ligand octreotide. The tumors showed variable sst1 and/or sst3 mRNA expression, whereas no sst2 expression was found. In conclusion, a dissociation between the inhibitory effects of SS on the one hand and of the octapeptide SS-analogs octreotide, BIM-23014 and RC-160 on the other hand, is observed in a small subgroup of NFAs, prolactinomas, and insulinomas, suggesting that novel sst subtype specific SS-analogs might be of benefit in the treatment of selected patients with somatostatin receptor positive secreting tumors not responding to octapeptide SS-analogs. However, in the majority of NFAs and prolactinomas, DA-agonists were equally or more effective than SS in the suppression of tumoral secretion products. http://repub.eur.nl/res/pub/17271/ 1993-03-10T00:00:00Z