INTERLEUKIN-1-BETA INHIBITION OF INSULIN RELEASE IN RAT PANCREATIC-ISLETS - POSSIBLE INVOLVEMENT OF G-PROTEINS IN THE SIGNAL-TRANSDUCTION PATHWAY

In vitro exposure of rat pancreatic beta cells to interleukin-1 beta (IL-1 beta) inhibits glucose-stimulated insulin release (2140 +/- 239 and 323 +/- 80 pg . islet(-1) . h(-1) at glucose levels of 16.7 mmol/l in control and IL-1 beta-exposed islets, respectively, n = 7, p < 0.001). Cholera toxin (2 mu g/ml) or pertussis toxin (0.5 mu g/ml) potentiated, as expected, glucose-induced insulin release in control islets, but, in addition, when added together with IL-1 beta, were able to prevent the IL-1 beta mediated inhibition of glucose-stimulated insulin secretion (2087 +/- 301 and 1662 +/- 173 pg . islet(-1) . h(-1), respectively, p < 0.05 vs islets exposed to IL-1 beta alone). To investigate the mechanism by which the toxins prevent the IL-1 beta effect, we then measured nitrite levels, glucose oxidation and Ca2+ uptake. Nitrite levels in the culture medium were 4.2 +/- 1.4 and 24.0 +/- 5 pmol . islet(-1) . 24 h(-1) in control islets and in IL-1 beta-exposed islets, respectively (n = 6, p = 0.05). In islets exposed to IL-1 beta and cholera or pertussis toxins, nitrite levels were 9.1 +/- 3 and 12.4 +/- 6 pmol . islet(-1) . 24 h(-1), respectively (n = 6, NS vs control islets). Glucose oxidation at 16.7 mmol/l glucose was 31.1 +/- 2.9 pmol . islet(-1) . 120 min(-1) in control islets and 16.8 +/- 2.7 pmol . islet(-1) . 120 min(-1) in IL-1 beta-treated islets (p < 0.05). The addition of cholera or pertussis toxins simultaneously to IL-1 beta prevented the inhibition of glucose oxidation at 16.7 mmol/l glucose (32.9 +/- 3.8 and 31.7 +/- 3.3 pmol . islet(-1) . 120 min(-1) in the presence of cholera or pertussis toxins, respectively). Glucose-stimulated Ca-45(2+) uptake was also significantly inhibited in IL-1 beta-treated islets when compared to control islets (7.1 +/- 0.9 and 16.8 +/- 3.2 pmol . islet(-1) . 20 min(-1), respectively, p < 0.05). This inhibition was prevented the presence of cholera or pertussis toxins (14.0 +/- 3.8 and 11.2 +/- 2.7 pmol . islet(-1) . 20 min(-1), respectively). In conclusion, our data show that cholera and, to a lesser extent, pertussis toxins are able to partially prevent the IL-1 beta-induced increase in nitrite levels and block the inhibitory effects of IL-1 beta on different steps leading to glucose-induced insulin secretion. These findings support the possibility that in pancreatic beta cells, G-proteins may be involved or interfere with the cytokine signal transduction.