8-bromocyclic-gmp and Pancreatic-Neoplasms

5-hydroxytryptamine (5-HT) is a mitogen for fibroblasts, vascular smooth muscle cells, renal mesangial cells, and jejunal crypt cells. The human carcinoid cell line (termed BON) that we established in our laboratory from a pancreatic carcinoid tumor produces and secretes 5-HT. In this study, therefore, we examined the effect of 5-HT on growth of BON cells. Furthermore, by use of selective 5-HT receptor antagonists, we examined receptor and post-receptor mechanisms by which 5-HT-induced responses were produced. 5-HT stimulated growth of BON cells. 5-HT stimulated phosphatidylinositol (PI) hydrolysis in a dose-dependent fashion and inhibited cyclic AMP production in a dose-dependent fashion. The 5-HT1A/1B receptor antagonist, SDZ 21-009, prevented the reduction of cyclic AMP production evoked by 5-HT and inhibited the mitogenic action of 5-HT. The 5-HT1C/2 receptor antagonist, mesulergine, competitively inhibited PI hydrolysis, but did not affect the mitogenic action of 5-HT. The mitogenic action of 5-HT and the reduction of cyclic AMP production evoked by 5-HT were also inhibited by pertussis toxin. These results suggest that 5-HT is an autocrine growth factor for BON cells and that mitogenic mechanism of 5-HT involves receptor-mediated inhibition of the production of cyclic AMP which may be linked to pertussis toxin-sensitive GTP binding protein. 8-bromo-cyclic AMP inhibited growth of BON cells whereas 8-bromo-cyclic GMP had no effect on cell growth. Involvement of protein kinase A in BON cell growth regulation was confirmed by the observation that a cAMP-dependent protein kinase antagonist (Rp-cAMPS) could stimulate BON cell growth.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Cell Division; Cyclic AMP; Cyclic GMP; Ergolines; Humans; Pancreatic Neoplasms; Pertussis Toxin; Phosphatidylinositols; Pindolol; Receptors, Serotonin; Second Messenger Systems; Serotonin; Serotonin Antagonists; Tumor Cells, Cultured; Virulence Factors, Bordetella

L-Arginine (L-Arg) is metabolized by nitric oxide synthase to the reactive intermediate nitric oxide. Since nitric oxide stimulates guanylyl cyclase and cGMP synthesis, L-Arg effects on cGMP accumulation in isolated pancreatic islets of the rat and RINm5F insulinoma cells were determined. Both L-Arg and glucose stimulation increased islet cGMP levels, and glucose potentiated the response to L-Arg alone. A competitive inhibitor of L-Arg metabolism to nitric oxide, NG-monomethyl-L-arginine, reduced glucose- and L-Arg-stimulated insulin release and glucose-induced increases in cGMP; however, basal insulin release was slightly increased. D-Arg and L-ornithine did not affect islet cGMP levels, although insulin release was stimulated. RINm5F cell cGMP levels and insulin release increased in response to L-Arg in a concentration- and time-related manner, whereas glucose and L-histidine were without effect. 8-Bromo-cGMP also slightly increased RINm5F cell insulin release. Sodium nitroprusside as a source of nitric oxide increased RINm5F cell cGMP production. Methylene blue and LY83583, inhibitors of soluble guanylyl cyclase activation, reduced RINm5F cell cGMP levels in the presence and absence of L-Arg; LY83583 also reduced glucose-stimulated cGMP levels in islets. Insulin release by glucose and L-Arg was also inhibited by methylene blue and LY83583 in islets. We conclude that glucose and L-Arg stimulate guanylyl cyclase activity and cGMP formation in beta-cells at least in part through metabolism to the reactive intermediate nitric oxide. However, neither nitric oxide nor cGMP synthesis is obligatory for insulin secretion.

Topics: Aminoquinolines; Animals; Arginine; Cyclic GMP; Glucose; Guanylate Cyclase; Insulin; Insulin Secretion; Insulinoma; Islets of Langerhans; Male; Methylene Blue; Nitroprusside; Pancreatic Neoplasms; Rats; Rats, Inbred Strains; Tumor Cells, Cultured