Differential effects of cytokines on long-term mitogenic and secretory responses of fetal rat pancreatic beta-cells

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Abstract
It has been proposed that certain cytokines secreted by islet-infiltrating leukocytes may be involved in the pathogenesis of insulin-dependent diabetes mellitus by participation in beta-cell destruction. In the present study, the impact of various cytokines on replication and long-term insulin secretion by pancreatic beta-cells was investigated. To this end, fetal rat pancreatic islets containing a high fraction of beta-cells were exposed in culture for 1-3 days to interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), interferon-alpha (IFN-alpha), and interleukin-6 (IL-6) at different concentrations. It was found that IL-1 beta markedly decreased beta-cell DNA synthesis during the first day of exposure, an effect that vanished after 2 days and was turned into a potent and dose-dependent stimulation by 3 days of exposure. At this latter time point, IL-1 beta also amplified the mitogenicity of growth hormone (GH) and 16.7 mM glucose. In contrast, basal as well as glucose- and GH-stimulated insulin secretion was consistently suppressed by IL-1 beta from days 1-3. IL-1 beta also lowered the islet adenosine 3',5'-cyclic monophosphate (cAMP) content at all time points studied. However, addition of the stimulatory cAMP analogue Sp-diastereomer of adenosine 3',5'-cyclic monophosphothioate or pertussis toxin, which themselves enhanced DNA synthesis and insulin secretion, failed to prevent the inhibitory actions of IL-1 beta on these parameters, making it unlikely that a decrease in cAMP is an important event in transduction of the inhibitory effects of the cytokine.(ABSTRACT TRUNCATED AT 250 WORDS)