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O Paulmyer-Lacroix, G Anglade, and M Grino


The regulation of ACTH secretion during stress is a multifactorial process that mainly involves two hypothalamic neurohormones: corticotrophinreleasing factor (CRF) and arginine vasopressin (AVP). In this report we measured, using semiquantitative in situ hybridization, the concentrations of CRF and AVP mRNA in hypophyseotrophic paraventricular parvocellular cell bodies of male rats after an acute (3-h) exposure to insulin-induced hypoglycaemia.

Insulin injection (2·5 IU/kg) induced a significant decrease in blood glucose levels and a strong increase in plasma ACTH concentrations. The concentration of CRF mRNA in the paraventricular nucleus (PVN) was significantly increased after insulin-induced hypoglycaemia (150% of control levels), while the number of CRF mRNA-containing cell bodies was not changed. Double-labelling experiments demonstrated that the number of CRF mRNA-containing cell bodies that also contained AVP mRNA was doubled after insulin injection. These data demonstrate that the established increased colocalization of AVP immunoreactivity in nerve terminals immunoreactive for CRF after exposure to stress follows a pretranslational activation of AVP synthesis.

Cell-by-cell analysis indicated that the mean CRF hybridization signal was increased in doublelabelled cells (about 150% of control levels), suggesting that the increase in CRF gene expression occurs equally in the AVP-synthesizing and in the AVP-deficient CRF mRNA-containing cell bodies. The mean AVP hybridization signal in the double-labelled cells was decreased, suggesting that the amount of AVP mRNA was unchanged in the cell bodies that expressed both CRF and AVP in the basal state and that AVP mRNA levels in the cell bodies recruited after insulin-induced hypoglycaemia were below control values.

Taken together, these observations suggest that the hypophyseotrophic neurones of the PVN adapt to an acute stress situation by increasing CRF gene transcription in the whole population of CRF-synthesizing cells and by increasing AVP gene transcription in a silent population of CRF-synthesizing cells. Such changes may lead to increased peptide synthesis in response to increased functional demand.

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V Vuaroqueaux, A Dutour, N Bourhim, L Ouafik, G Monges, N Briard, N Sauze, C Oliver, and M Grino

Numerous studies have suggested that the antiproliferative potency of somatostatin (SS) analogues may be an efficient tool to improve the prognosis of colorectal cancer. In order to facilitate current efforts to design potent antitumour SS analogues, we studied the distribution of human SS receptors (hsst1-5) mRNAs in a large set of tumoural and normal colonic tissues. Localisation of hsst1-5 mRNAs in normal and tumoural tissues was performed by in situ hybridisation using radioactive antisense or sense riboprobes. Semi-quantitative analysis of hsst5 mRNA was performed using a computerised image analysis system. Hsst binding sites were characterised by studying the relative potency of SS14, SS28 or SS analogues in displacing [(125)I]Tyr degrees -d-Trp(8)-SS14 bound to HT29-D4 cells. Hsst5 mRNA was by far the most expressed subtype in both normal and transformed epithelial cells as well as in the HT29-D4 cell line. An increased expression of hsst5 mRNA was found in tumours. Hsst1 mRNA was expressed preferentially as clusters in immune cells in lamina propria and in stroma close to the tumour. A low expression of hsst4, hsst3 and hsst2 was seen in normal and tumoural tissue. In HT29-D4, binding experiments with SS14 demonstrated the existence of one SS binding class (K(d)=524 nM, B(max)=1fmol/10(6 )cells). In competition binding studies, SS28 and BIM23268 (an analogue that shows preferential specificity towards hsst5) effectively inhibited binding of [(125)I]Tyr degrees -d-Trp(8)-SS14 (IC(50)=15 and 157 nM respectively), while BIM23197 (an analogue that shows preferential affinity for hsst2) was ineffective. Our results show a high expression of hsst5 mRNA in human tumoural colonic tissue, while hsst5 protein is the predominant hsst protein subtype in a tumoural colonic cell line.