17-β-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 (l0 nM) induced a rapid increase in sst number in HS-grown 7315b cells. Octreotide (1μM) significantly inhibited PRL release and the intracellular PRL concentration of 7315b cells that were cultured in medium supplemented with FCS or with HS + l0 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 for7 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 μg/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 ensuing hyperprolactinemia results in a hypo-estrogenic state.</p

IGF-I Bioactivity in an Elderly Population: Relation to Insulin Sensitivity, Insulin Levels, and the Metabolic Syndrome

OBJECTIVE - There is a complex relationship between IGF-I, IGF binding proteins, growth hormone, and insulin. The IGF-I kinase receptor activation assay (KIRA) is a novel method for measuring IGF-I bioactivity in human serum. We speculated that determination of IGF-I bioactivity might broaden our understanding of the IGF-I system in subjects with the metabolic syndrome. The purpose of our study was to investigate whether IGF-I bioactivity was related to insulin sensitivity and the metabolic syndrome. RESEARCH DESIGN AND METHODS - We conducted a cross-sectional study embedded in a random sample (1,036 elderly subjects) of a prospective population-based cohort study. IGF-I bioactivity was determined by the IGF-I KIRA. Categories of glucose (in)tolerance were defined by the 2003 American Diabetes Association criteria. Insulin sensitivity was assessed by homeostasis model assessment. The Adult Treatment Panel III definition of the metabolic syndrome was used. RESULTS - In subjects with normal fasting glucose and impaired fasting glucose, IGF-I bioactivity progressively increased with increasing insulin resistance, peaked at fasting glucose levels just below 7.0 mmol/l, and dropped at higher glucose levels. Mean IGF-I bioactivity peaked when three criteria of the metabolic syndrome were present and then declined significantly when five criteria of the metabolic syndrome were present. CONCLUSIONS - We observed that IGF-I bioactivity was related to insulin sensitivity, insulin levels, and the metabolic syndrome. Our study suggests that there exists an inverse U-shaped relationship between IGF-I bioactivity and number of components of the metabolic syndrome. This observation contrasts with previous results reporting an inverse relationship between total IGF-I and components of the metabolic syndrome

A CLOSE CORRELATION BETWEEN THE INHIBITORY EFFECTS OF INSULIN‐LIKE GROWTH FACTOR‐I AND SMS 201‐995 ON GROWTH HORMONE RELEASE BY ACROMEGALIC PITUITARY TUMOURS IN VITRO AND IN VIVO

In the present study we compared the in‐vitro effects of IGF‐I and SMS 201–995 on GH release by cultured tumour cells obtained from seven acromegalic patients with the preoperative in‐vivo GH dynamics, including the acute response to 50μg SMS 201–995 subcutaneously. IGF‐I and SMS 201–995 inhibited GH release during a 24 h incubation in four and five of the seven tumour cell preparations, respectively. The inhibitory effect of SMS 201–995 was greater than that exerted by IGF‐I (P &lt; 0.01). There was a close correlation between the in‐vitro inhibitory effects of IGF‐I and SMS 201–995 (P &lt; 0.01). In addition, the acute inhibitory effect of 50 μg SMS 201–995 on circulating GH levels in vivo correlated with the inhibitory effects in vitro of both SMS 201–995 (P &lt; 0.01) and IGF‐I (P &lt; 0.05). The inhibitory effects of IGF‐I and SMS 201–995 on GH release in vitro were shown to be additive in two of four tumours. There was no relation between the in‐vitro effects of IGF‐I and/or SMS 201–995 and several in‐vivo parameters, including fluctuations in GH levels, sleep‐induced GH release, a paradoxical increase of GH in response to TRH, and the circulating IGF‐I and PRL levels. In conclusion: (1) there is a close correlation between the sensitivity of GH release by cultured human adenoma cells to IGF‐I and SMS 201–995. (2) There is also a close correlation between the in‐vivo inhibitory effect on GH release of SMS 201–995 and the in‐vitro inhibitory effects of both SMS 201–995 and IGF‐I. (3) A subgroup of acromegalic patients harbour pituitary tumours in which the qualitative regulation of hormone secretion is similar to that of normal GH secretion.</p

GLYCOPROTEIN HORMONE ALPHA‐SUBUNIT AND PROLACTIN RELEASE BY CULTURED PITUITARY ADENOMA CELLS FROM ACROMEGALIC PATIENTS:CORRELATION WITH GH RELEASE

In‐vitro data of pituitary adenoma cells from 28 acromegalic patients were evaluated. In addition to GH, PRL was produced by 16 adenomas (57%) and alpha‐subunit by 15 adenomas (54%) while there was a significantly higher incidence of tumours producing PRL and alpha‐subunit simultaneously. From 26 pituitary adenomas enough cells were obtained in order to perform secretion studies. Percentage basal hormone release (medium: (medium + intra‐cellular hormone)) ± 100% of GH and alpha‐subunit by 11 adenomas showed a close correlation while such a correlation for GH and PRL was present only in a subgroup of 10 of 13 adenomas. The responses of GH and alpha‐subunit release to 10nM SMS201–995, 10nM bromocriptine, 100nM TRH and 10nM GHRH were closely related in that a response or an absent response of GH release to the four secretagogues was virtually always attended with a response or an absent response respectively of alpha‐subunit release. Such a relationship was less evident with respect to the effects of SMS201–995, bromocriptine, TRH and GHRH on GH and PRL release. We conclude that basal and secretagogue‐induced alpha‐subunit release by cultured pituitary adenoma cells from acromegalic patients closely follows the pattern of GH release while such a relationship for GH and PRL is present only in a subgroup of the adenomas secreting GH and PRL simultaneously.</p

De invloed van immunoscintigrafie met monoklonale antilichamen op bepalingen van hormonen en tumormerkstoffen: Een muis met een staartje.

The use of monoclonal antibodies in medicine for in-vivo diagnostic methods and for therapeutic purposes will increase in the future. Although monoclonal antibodies possess a high specificity, the animal origin of these antibodies remains a problem. Repeated administration of animal monoclonal antibodies (in vivo) may induce the formation of human antibodies against these monoclonal antibodies. Because animal monoclonal antibodies are also used in laboratory assays (in vitro), the presence of human antibodies against these animal monoclonal antibodies may cause spuriously elevated or depressed results of these assays. The clinician should be alert to this possibility. A case history is presented to demonstrate the problem