Endometrial and pituitary responses to the steroidal antiprogestin RU 486 in postmenopausal women

The effects of the antiprogestin RU 486 on the human endometrium were investigated. Seventeen postmenopausal women were injected with estradiol (E2) benzoate (0.625 mg/day) for 15 days. Progesterone (P) (25 mg/day) and/or RU 486 (100 or 200 mg/day) were given to groups of 2-3 women during the last 6 days of E2 benzoate treatment. Serial blood samples were drawn for the measurement of plasma E2, P, and LH and FSH. An endometrial biopsy was performed on the last day of treatment, and processed for histology or for assays of DNA polymerase alpha, E2-dehydrogenase (E2DH), and P receptor (PR). Treatment with E2 benzoate alone resulted in a marked decrease of plasma gonadotropins; in those patients who received either P, RU 486, or both, in addition to E2 benzoate, the concentrations of plasma LH and FSH were further decreased to premenopausal levels. In absence of glycerol, the affinity of RU 486 for the endometrial PR (Kd = 0.8 nM) was higher than that of P (Kd = 1.2 nM). Glycerol decreased markedly the affinity of RU 486, whereas the affinity of P for the PR was unchanged. RU 486 had negligible affinity for plasma transcortin. Either P or RU 486, but not both together, induced secretory changes in the endometrium as determined from histologic sections of tissue biopsies. Either P or RU 486 decreased DNA polymerase alpha and increased E2-DH activities in the endometrium. Unexpectedly, when P and RU 486 were given together. E2-DH activity remained at the level found in E2-treated women. In vitro cultures of proliferative endometrium treated with the synthetic progestagen R 5020 or with RU 486 also had increased E2-DH activity; RU 486 counteracted R 5020 effects. We conclude that, contrary to previous results with experimental animals, the anti-P RU 486 has some progestomimetic activity in humans under specific conditions. Paradoxically, when given together with P, RU 486 lost most of its progestomimetic activity in the endometrium and behaved as a pure antagonist.     

Biologic activities of growth hormone secretagogues in humans

Growth hormone secretagogues (GHSs) are synthetic peptidyl and nonpeptidyl molecules with strong, dose-dependent, and reproducible growth hormone (GH)-releasing activity even after oral administration. GHSs release GH via actions on specific receptors (GHS-R) at the pituitary and, mainly, at the hypothalamic levels. GHSs likely act as functional somatostatin antagonists and meantime enhance the activity of GH-releasing hormone (GHRH)-secreting neurons. The GH-releasing effect of GHSs is independent of gender but undergoes marked age-related variations. Estrogens play a major role in enhancing the GH response to GHSs at puberty, which GHRH hypoactivity, somatostatinergic hyperactivity and impaired activity of the putative GHS-like ligand and receptors probably explain the reduced GH-releasing effect of GHSs in aging. The activity of GHSs is not fully specific for GH. Their slight prolactin-releasing activity probably comes from direct pituitary action. In physiological conditions, the ACTH-releasing activity of GHSs is dependent on central actions; a direct action on GHS-R in pituitary ACTH-secreting tumors likely explains the peculiar ACTH and cortisol hyperresponsiveness to GHSs in Cushing disease. GHSs have specific receptor subtypes in other central and peripheral endocrine and nonendocrine tissues mediating GH-independent biologic activities. GHSs influence sleep pattern, stimulated food intake, and have cardiovascular activities. GHs have specific binding in normal and neoplastic follicular derived human thyroid tissue and inhibit the proliferation of follicular-derived neoplastic cell lines. The discovery of ghrelin, a 28 amino acid peptide synthesized in the stomach but also in other tissues, has opened new fascinating perspectives of research in this field.     

Presence of cortistatin in the human pancreas

Cortistatin (CST), a 17-amino acid peptide partially homologous to somatostatin (SRIF), has been originally isolated from the cerebral cortex and recently found in monocytes and macrophages of the immune system. CST binds all 5 SRIF receptors, as well the GH secretagogue (GHS)/ghrelin receptors. CST exerts sleep promoting activities, acts on animal motility and behavior and inhibits GH and insulin secretion. To investigate the possible occurrence and activities in peripheral tissues, expression of CST at the mRNA and peptide level was analyzed in the human pancreas by means of RT-PCR, in situ hybridization and immunohistochemistry. The specific CST mRNA was found in 3 of 4 pancreatic RNA extracts and in the control cerebral cortex. By in situ hybridization, CST mRNA was localized in the pancreatic islets, but not in the exocrine pancreas. This finding was confirmed by immunostaining with a specific antibody to CST-17 which detected CST in single islet cells. These cells also expressed SRIF receptors types 2, 3 and 5, ghrelin and GHS receptors. Thus, our findings show the presence of CST in the human endocrine pancreas. Local autocrine or paracrine circuits, only in part overlapped with those of SRIF, may be active to modulate insulin and/or glucagon levels.     

The GH-releasing effect of ghrelin,a natural GH secretagogue,is only blunted by the infusion of exogenous somatostatin in humans

OBJECTIVE: Ghrelin, a 28-amino-acid peptide purified from the stomach and showing a unique structure with an n-octanoyl ester at the serine 3 residue, is a natural ligand of the GH secretagogue (GHS) receptor (GHS-R). Ghrelin strongly stimulates GH secretion in both animals and humans, showing a synergistic effect with GH-releasing hormone (GHRH) but no interaction with synthetic GHS. However, the activity of ghrelin as well as that of non-natural GHS is not fully specific for GH; ghrelin also induces a stimulatory effect on lactotroph and corticotroph secretion, at least in humans. DESIGN: To further clarify the mechanisms underlying the GH-releasing activity of this natural GHS, we studied the effects of somatostatin (SS, 2.0 microg/kg/h from -30 to +90 min) on the endocrine responses to ghrelin (1.0 microg/kg i.v. at 0 min) in seven normal young male volunteers [age (mean +/- SEM) 28.6 +/- 2.9 years; body mass index (BMI) 22.1 +/- 0.8 kg/m2]. In the same subjects, the effect of SS on the GH response to GHRH (1.0 microm/kg i.v. at 0 min) was also studied. MEASUREMENTS: Blood samples were taken every 15 min from -30 up to +120 min. GH levels were assayed at each time point in all sessions; PRL, ACTH and cortisol levels were assayed after ghrelin administration alone and during SS infusion. RESULTS: The GH response to ghrelin (hAUC0'-->120' 2695.0 +/- 492.6 microg min/l) was higher (P < 0.01) than that after GHRH (757.1 +/- 44.1 microg min/l). SS infusion almost abolished the GH response to GHRH (177.0 +/- 37.7 microg min/l, P < 0.01); the GH response to ghrelin was inhibited by SS (993.8 +/- 248.5 microg min/l, P < 0.01) but GH levels remained higher (P < 0.05) than with GHRH. Ghrelin induced significant increases in PRL, ACTH and cortisol levels and these responses were not modified by SS. CONCLUSIONS: Ghrelin, a natural GHS-R ligand, exerts a strong stimulatory effect on GH secretion in humans and this effect is only blunted by an exogenous somatostatin dose which almost abolishes the GH response to GHRH. The stimulatory effect of ghrelin on lactotroph and corticotroph secretion is refractory to exogenous somatostatin, indicating that these effects occur through pathways independent of somatostatinergic influence.     

Immunohistochemical detection of somatostatin receptor types 1-5 in medullary carcinoma of the thyroid

BACKGROUND: We have analysed the distribution of the five somatostatin receptors (sst1-5) by immunohistochemistry in a large retrospective series of 51 medullary carcinoma of the thyroid (MCT) specimens and correlated the pattern of sst expression with expression of somatostatin (SRIF) peptide, tumour pathology and clinical outcome. MEASUREMENTS: Immunohistochemistry was performed with rabbit polyclonal antipeptide antibodies directed against the extracellular domains or cytoplasmic tail of human (h) sst1-5. SRIF immunoreactivity was investigated in parallel paraffin sections. RESULTS: Eighty-five percent of the tumours were positive for one or more sst, localized to both tumour cells as well as surrounding peritumoural structures, especially blood vessels. Forty-nine percent of the tumours were positive for sst1, 43% for sst2, 47% for sst3, 4% for sst4, and 57% for sst5. Fifty-one percent of tumours expressed one or two sst subtypes; 33% were positive for three or more sst isoforms. All five sst receptors were detected in only two cases. Tumours expressing octreotide sensitive subtypes (sst2,3,5) accounted for 75% of the series. 50% of the tumours co-expressed SRIF suggesting tumour cell regulation by endogenous SRIF via paracrine/autocrine circuits. There was no correlation between sst1-5 expression and age, sex, tumour size or stage, histological type or clinical outcome. Simultaneous analysis of primary tumour and lymph node metastases revealed a similar pattern of sst immunoreactivity indicating that sst expression is not modified in the course of disease progression. CONCLUSIONS: With the exception of sst4, medullary carcinoma of the thyroid display a rich but heterogeneous expression of sst subtypes. Immunohistochemical typing of sst receptor expression using specific antireceptor antibodies represents an ideal approach for characterizing sst subtype expression in medullary carcinoma of the thyroid for optimizing receptor targeted diagnosis and therapy with somatostatin analogs.     

The Cholesterol Side-Chain Cleavage Complex in Human Brain White Matter

Specific antibodies obtained in rabbits after injection of bovine cholesterol side-chain cleavage enzymes cytochrome P-450scc, adrenodoxin and adrenodoxin-reductase were used for immunohistochemical studies in human brain. The three enzymes were co-localized in the white matter of the cerebellum. This observation strongly suggests the existence of steroidogenic activity in human oligodendrocytes, as previously reported in the rat, and suggests that the concept of 'neurosteroids' can be applied to Δ5–3ß-hydroxysteroid metabolites of cholesterol that accumulate in human brain.     

Brain-gut communication: cortistatin, somatostatin and ghrelin.

Although cortistatin (CST) shares great structural homology with somatostatin (SST) and binds to all SST receptor subtypes with similar affinity, these neurohormones have divergent biological roles, as evidenced by their different patterns of tissue expression and biological actions. Moreover, CST, but not SST, can bind to the proadrenomedullin N-terminal peptide (PAMP) receptor MrgX2 and type 1a growth hormone secretagogue (GHS) receptor (GHSR-1a), also known as the 'ghrelin' receptor. These findings suggest that CST-specific actions could be mediated by the GHSR-1a and CST might represent a link between the ghrelin and the SST systems. Here, we review the data leading to this working hypothesis and discuss the in vitro, in vivo and clinical implications of potential SST-receptor-independent, GHSR-1a-mediated neuroendocrine and metabolic effects of CST.     

Gastric carcinoids and their precursor lesions. A histologic and immunohistochemical study of 23 cases.

A histologic and immunohistochemical study was carried out in 23 unselected nonantral gastric carcinoids and their precursor lesions classified according to Solcia et al. None of the patients showed Zollinger-Ellison syndrome. Two variants of carcinoids showing distinctive pathologic and pathogenetic characteristics were identified on the basis of presence or absence of associated chronic atrophic gastritis type A (A-CAG). Chronic atrophic gastritis type A was found in 19 cases showing either single or multiple neoplasms, tumor extension limited to the mucosa or submucosa, consistent endocrine cell precursor changes in extratumoral mucosa, and consistent hypergastrinemia and/or G cell hyperplasia. Associated precursor lesions were only hyperplastic in all but two cases with single carcinoids whereas they were also dysplastic in all but one case with multiple carcinoids. The four tumors arising in nonatrophic mucosa were all single, more aggressive, and not associated with extratumoral endocrine cell proliferations or with signs of gastrin hypersecretion. Tumor cells were diffusely immunoreactive for chromogranin A and synaptophysin but usually negative for chromogranin B or HISL-19. Scattered serotonin cells were found in ten carcinoids. They were more frequent in infiltrating than in intramucosal tumors as were the less represented pancreatic polypeptide cells whereas the reverse was found for alpha-subunit-containing cells. These results are of relevance for tumor pathogenesis and may provide the rationale for a less aggressive therapeutic approach in the patients.