8-bromocyclic-gmp and Diabetes-Mellitus--Type-2

Recent investigations have demonstrated an influence of melatonin on insulin secretion in pancreatic beta-cells. The effects are receptor-mediated via two parallel signaling pathways. The aim of this study was to examine the relevance of a second melatonin receptor (MT2) as well as the involvement of a third signaling cascade in mediating melatonin effects, i.e. the cyclic guanosine monophosphate (cGMP) pathway. Our results demonstrate that the insulin-inhibiting effect of melatonin could be partly reversed by preincubation with the unspecific melatonin receptor antagonist luzindole as well as by the MT2-receptor-specific antagonist 4P-PDOT (4-phenyl-2-propionamidotetraline). As melatonin is known to modulate cGMP concentration via the MT2 receptor, these data indicate transmission of the melatonin effects via the cGMP transduction cascade. Molecular investigations established the presence of different types of guanylate cyclases, cGMP-specific phosphodiesterases and cyclic nucleotide-gated channels in rat insulinoma beta-cells (INS1). Moreover, variations in mRNA expression were found when comparing day and night values as well as different states of glucose metabolism. Incubation experiments provided evidence that 3-isobutyl-1-methylxanthine (IBMX)-stimulated cGMP concentrations were significantly decreased in INS1 cells exposed to melatonin for 1 hr in a dose- and time-dependent manner. This effect could also be reversed by application of luzindole and 4P-PDOT. Stimulation with 8-Br-cGMP resulted in significantly increased insulin production. In conclusion, it could be demonstrated that the melatonin receptor subtype MT2 as well as the cGMP signaling pathway are involved in mediating the insulin-inhibiting effect of melatonin.

Topics: 1-Methyl-3-isobutylxanthine; Animals; Brain; Cell Line, Tumor; Colforsin; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 2; Cyclic Nucleotide-Gated Cation Channels; Diabetes Mellitus, Type 2; Dose-Response Relationship, Drug; Glucose; Guanylate Cyclase; Insulin; Insulin Secretion; Insulin-Secreting Cells; Insulinoma; Melatonin; Pineal Gland; Rats; Rats, Wistar; Receptor, Melatonin, MT2; Signal Transduction; Tetrahydronaphthalenes; Tryptamines

The present study was designed to investigate the hypothesis that cells from ill patients and from healthy subjects may have different reactivities under metabolic stimulation.. The study was performed with granulocytes from non-diabetic subjects and from type II -Non Insulin Dependent Diabetes mellitus (NIDDM) patients. The nitric oxide (NO) generation was comparatively determined by the nitrite concentration (micromolar of nitrite) after cell incubation in the presence of cyclic nucleotide-elevating agents.. Our results showed an inverse reactivity for granulocytes from diabetic patients when compared to non-diabetic subjects. Granulocytes were incubated in the presence of drugs that elevate the intracellular level of cyclic AMP aminophylline (AMF), dibutyryl cyclic AMP (dbcAMP)], cyclic GMP [8.Br. cyclic GMP(8.Br.cGMP) or levamisole (LEV)]. The cyclic AMP-elevating agents (AMF and d bcAMP) inhibited NO production by granulocytes from non-diabetic subjects and activated cells from diabetic patients. By contrast, cyclic GMP-elevating agents (8.Br.cGMP and LEV) activated cells from non-diabetic subjects and inhibited granulocytes from diabetic patients. The activation of NO generation by cyclic nucleotides was blocked by pretreatment of granulocytes with L-NAME.. The authors describe for the first time that both cyclic AMP and cyclic GMP were able to modulate nitric oxide production in human granulocytes and that cell reactivity in ill patients (diabetic) showed altered and inverse response in comparison to granulocytes from healthy subjects. This inverse reactivity possibly reflects a disease-induced adapted metabolic response. The consequences of this altered metabolic response on host defense and inflammation may be speculated, but further experiments are needed to confirm this hypothesis.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Aged; Cyclic AMP; Cyclic GMP; Diabetes Mellitus, Type 2; Female; Granulocytes; Humans; Male; Middle Aged; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitrites; Reference Values