ABSTRACT
Somatostatin is an inhibitor of hormone secretion through specific receptors (sst1-5). The aim of this study was to investigate the putative regulatory role of somatostatin analogues on the secretion of insulin and glucagon by rat pancreatic islets. After 48 h exposure only the non-selective agonists (somatostatin, octreotide and SOM-230) inhibited insulin accumulation. The inhibition of insulin secretion was accompanied by increased islet insulin contents. None of the analogues showed a consistent effect on the glucagon accumulation in the medium after 48 h. Since we observed a difference in the regulatory effect between the non-selective and selective analogues, combinations of selective analogues were studied. Combination of sst2+sst5 agonists inhibited the medium insulin accumulation, while combination of sst1+sst2 analogues caused a decrease in glucagon accumulation. After removal of somatostatin a rebound effect with increased insulin secretion were observed. This effect was reversed after 6 h. For SOM-230 insulin secretion continued to be suppressed even after the analogue was removed and returned to control values after 3 h. As for glucagon secretion there was an initial decline after culture with octreotide, while the other substances failed to induce any changes. In summary, non-selective somatostatin analogues or combinations of receptor selective analogues may cause inhibition of hormone secretion from rat pancreatic islets. For insulin and glucagon, combinations of sst2+sst5 and sst1+sst2, respectively may exert this effects. Thus, our data suggest that more than one sst must be involved to down-regulate islet glucagon and insulin secretion.
Subject(s)
Gastrointestinal Agents/pharmacology , Glucagon/metabolism , Insulin/metabolism , Islets of Langerhans/metabolism , Somatostatin/analogs & derivatives , Somatostatin/pharmacology , Animals , Dose-Response Relationship, Drug , Drug Interactions , Gastrointestinal Agents/chemistry , Insulin Secretion , Islets of Langerhans/drug effects , Male , Octreotide/pharmacology , Rats , Rats, Sprague-DawleyABSTRACT
OBJECTIVE: Somatostatin acts on five specific receptors (sst1-5) to elicit different biological functions. The non-obese diabetic (NOD) mouse is an experimental model of type 1 diabetes. The aim of this study was to investigate whether the islet expression of sst1-5 is affected during the development of diabetes in NOD mice, with insulitis accompanied by spontaneous hyperglycaemia. METHODS: By immunostaining for sst1-5 the expression and co-expression together with the four major islet hormones in pancreatic islets were investigated in female and male NOD mice at different stages of disease. The NOD related non-diabetic ICR mouse was also examined. RESULTS: The islet cells of diabetic NOD mice showed an increased islet cell expression of sst2-5 compared with normoglycaemic female NOD mice. This correlated to increasing age and extent of insulitis. Major findings from the co-expression investigations were that sst2 was expressed in a majority of beta-cells in the normoglycaemic NOD mice, but absent in the beta-cells in the diabetic NOD mice. A majority of the alpha-cells expressed sst2 and 5 in normoglycaemic and diabetic NOD mice. About 60% of delta-cells showed co-expression of sst4 and 5 in both normoglycaemic and diabetic NOD mice. 60% of pancreatic polypeptide (PP)-cells expressed sst4 in both groups. Insulitis was found to be accompanied by a down-regulation of sst in normoglycaemic animals. CONCLUSIONS: The difference in sst expression in the islets cells of diabetic mice may suggest either a contributing factor in the process leading to diabetes, or a defence response against ongoing beta-cell destruction.
Subject(s)
Diabetes Mellitus, Type 1/metabolism , Islets of Langerhans/metabolism , Receptors, Somatostatin/biosynthesis , Age Factors , Animals , Cell Count , Diabetes Mellitus, Type 1/immunology , Diabetes Mellitus, Type 1/pathology , Disease Models, Animal , Female , Immunohistochemistry , Islets of Langerhans/immunology , Islets of Langerhans/pathology , Male , Mice , Mice, Inbred ICR , Mice, Inbred NOD , Microscopy, Fluorescence , Pancreatic Polypeptide/immunology , Receptors, Somatostatin/classification , Receptors, Somatostatin/genetics , Receptors, Somatostatin/immunology , Sex Factors , Time FactorsABSTRACT
Two unrelated families are presented with repeated occurrences of a congenital syndrome of which the main stigmata were polycystic kidneys and occipital encephalocele (Meckel syndrome). Prenatal diagnosis, followed by interruption of pregnancy, was performed in one case. The diagnosis was based on an increase of amniotic alpha-fetoprotein (AFP), and on the mode of growth and cell types of cultured amniotic cells. In another similarly examined case the diagnosis was suspected, but the parents did not wish the pregnancy to be interrupted. The child was stillborn and malformed. AFP values are presented and discussed in relation to the observed malformations. Neural tube defects are associated with an increase of AFP in amniotic fluid, but, as in normal pregnancies, the values decrease with increasing gestational age. On the other hand, kidney malformations seem to be associated with AFP values which remain high or even increase with increasing gestational age.
